US3115622A

US3115622A - Panoramic scanning counter

Info

Publication number: US3115622A
Application number: US767444A
Authority: US
Inventors: Jaffe David Lawrence
Original assignee: POLARD ELECTRONICS CORP
Current assignee: POLARD ELECTRONICS Corp
Priority date: 1958-10-15
Filing date: 1958-10-15
Publication date: 1963-12-24
Anticipated expiration: 1980-12-24

Description

Dec. 24, 1963 D. L. JAFFE PANORAMIC scANNING COUNTER 3 sheets-sheet 1 Filed Oct. 15. 1958 Dec. 24, 1963 D. L. JAFFE PANORAMIC scANNING COUNTER 3 Sheets-Sheet 2 Filed Oct. 15, 1958 IN VEN TOR. EA/CE @FFE United States Patent 3,ll5,622 FANRAMEC EQANNENG CUNTER David Lawrence laffe, Great Neck, NX., assignor to Polarad Electronics Corporation, Long siand City, NX., a corporation of New York Filed (het. 15, 1953, Ser. No. 767,444 l@ Claims. (Cl. 34e- 224) This invention relates to a system for counting objects, and more particularly to an all electronic system which continuously counts and tallies the number of authorized objects within a specified area and which system also has the added facility of automatically indicating when the total tally of objects is in error with a preset number.

The present invention provides an all-electronic system for continuously counting and tallying moving or stationary objects within a given area. In accordance with the operation of the system, each of the objects authorized to be within the given area is provided with a miniature radio transmitter, and each of the transmitters continuously broadcasts a radio frequency signal of a different frequency. The radio frequency signals are received by the antenna of a panoramic receiver within the area covered by the radiation pattern of the antenna. The received signals are then displayed on a cathode ray tube connected to the receiver along a time axis on which the time is proportional to the frequency of the signal received from the transmitter. In this manner, each of the objects is identifiable by means of the position on the time axis of the display means that its associated transmitter occupies. A tally, or count, of the number of the different radio frequency signals received by the panoramic receiver is effected by a computer type device. An alarm is actuated when the tally of the received signals is in error with a certain preset number. By viewing the panoramic receiver display device, after the alarm has been actuated, the frequency and hence the identity of the object or objects causing the error may be ascertained.

Such a counter system has many applications. Among these are for use in a restricted security area, where it would function to keep a constant tally on the number and identity of authorized persons present within the area, and would also provide an indication of the identity of an authorized person who has left or entered the area. The system also has utility in banks and other high security areas to determine the presence of unauthorized personnel. Other uses of the scanning counter are in keeping track of the number of persons boating on a lake or in the vicinity of a ship, or in determining the number of personnel or livestock within a given area. The system also has utility in a storage area to provide continuous surveillance over normally stationary objects.

It is therefore an object of this invention to provide an electronic system for continuously counting and tallying the number of objects, either moving or stationary, within a specified area.

Another object of this invention is to provide a scanning counter system wherein an indication is provided when the number of objects within a predetermined area falls below a preset number.

Yet another object of this invention is to provide a counter system wherein the identities of authorized objects within a given area are readily ascertainable.

Other objects and advantages of this invention will become more apparent upon consideration of the following specification and annexed drawings in which:

FIGURE l is aschematic block diagram of the system;

FIGURE 2 is a schematic circuit diagram of a portion of the system of FIGURE 1;

FIGURE 3 is a chart showing the outputs of the respective counter stages after counting a certain number rice i of pulses and the switching arrangement of the count comparator used to set up the preset count number;

FIGURE 4 is a partially broken away, perspective view of the oscillator capsule which comprises a radio transmitter useful in the invention;

FIGURE 5 is a schematic diagram of a typical transistor oscillator circuit which may be used in the oscillator capsule of FIGURE 4, and

FIGURE 6 is a schematic block diagram of a modication of the counter system.

In accordance with the objects of this invention, the radiation pattern of a receiving antenna is used to define the area within which the counting and identifying of the objects is to be accomplished. Each of the objects authorized to be within this area is provided with a radio transmitter, such as one housed in an oscillator capsule, which continuously transmits a radio frequency signal. The signals from the respective transmitters are of different frequencies normally spaced from each other by an equal amount. These signals are picked up by the receiving antenna within its radiation pattern and are conveyed to a panoramic receiver such as n superheterodyne type receiver with a local oscillator which is cyclically swept through a range of frequencies.

The signals picked up by the antenna are continuously heterodyned with the swept local oscillator and produce, at successive instants of time, a heterodyne signal at the intermediate frequency of the receiver. The intermediate frequency signal is then detected and supplied to the vertical deflection elements of a cathode ray tube monitor where it is used to vertically deflect the electron beam of the cathode ray tube. In the meantime, the electron beam of the cathode ray tube is swept horizontally in synchronism with the cyclical scanning of the local oscillator of the panoramic receiver. This arrangement presents a display along the time (horizontal) axis of the cathode ray tube monitor which is an indication of the transmitters, and therefore the objects, within the predetermined area, since the signal from each transmitter occurs at a certain respective time along the horizontal axis of the display device. If any one of the transmitters is missing from within the area, its absence is indicated on the display device by the absence of an indication for that particular transmitter.

Also in accordance with the invention, the input signals to the monitor of the panoramic receiver are applied to a counter circuit. The counter circuit automatically counts the number of signals received during each cycle of the sweeping of the panoramic receiver and cathode ray tube monitor. The count output from the counter circuit is fed to a count comparator circuit whose function .it is to determine whether the count compares correctly with -a num-ber set into the comparator, usually the number of authorized transmitters. If the count falls below the preset number, a signal is generated by the count comparator which actuates an alarm. After the alarm is actuated, which signifies that one, or a number of the objects `are missing from or have entered the area, the indication appearing on the cathode ray montor dis-` closes the identity of this object or objects.

For a more specific description of an example of the present invention, reference is rnade to FIGURE 1 where the specified area is illustratively shown, as dened by -a receiving antenna 1. The antenna 1 may be of any suitable design so long as its radiation pattern is sufficiently directive to establish the specified area within which signals of a given signal strength from radio frequency transmitters can be received. In the preferred form of ythe invention shown, a loop antenna is used. The loop antenna may be constructed of a number of turns of wire or of a solid piece of conducting material which may be placed above or below the surface of the earth. The particular type or construction of the antenna used forms no part of the present invention, since any suitable antenna which has the necessary frequency and directional characteristics may be used.

Shown within the area defined by the antenna 1 are a number of fixed or moving objects, here illustrative-ly represented by the stick figures 3. It should be understood that the system is designed for operation with any moving objects, for example vehicles, boats, aircraft, live stock, etc., or with any stationary objects for example, stored crates, explosives, etc.

Each of the objects 3 has attached to it, in any desired manner, as by means of a ribbon or cord 4, a radio transmitter 5 `which is housed in an oscillator capsule 6, (FiG. 4).

Each of the transmitters 5, which is an oscillator circuit housed within oscillator capsule 6, produces a radio frequency signal of an individual frequency, representative of f1, f2, f3 fn. The transmitters are continuously operable in order to provide for continuous counting and surveillance. The signals transmitted from all the transmitters 5 are simultaneously picked up by the antenna 1 and are coupled by means of input transformer 8 tto the input of arradio frequency amplifier 9. The radio frequency amplifier 9 is any well known radio frequency amplifier which is capable of equally amplifying all of the different frequencies which are received by the -antenna 1.

The output signal from the radio frequency amplifier 9, which contains all of the individual frequencies of the individual transmitters 5, is then supplied to a one input of a mixer 1li, which may comprise any of the well known types of mixer circuits. The other input of the mixer 1f) receives a signal from a scanning local oscillator 11. The function of the scanning local oscillator 11 is to provide a signal which periodically sweeps thro-ugh a predetermined range of frequencies `as wide as the range of the transmitted frequencies. Such oscillators are well known in the `art and for example could comprise an oscillator that has a capacitor in the frequency determining circuit, to determine the frequency of the oscillator, whose capacitance is cyclically varied (for example, mechanically) or other types of similar arrangements. In a preferred form of the present invention, a ferrite type scanning oscillator is used. This type of oscillator utilizes a ferrite element which is placed in the frequencydetermining circuit of the oscillator and which is supplied with a periodic sawtooth voltage of a predetermined frequency. The ferrite element of the scan oscillator `11 receives a sawtooth voltage from a sawtooth generator 17. Sawtoothvgenerator 17 may be of any well known type, such as for example a multivibrator which discharges into an integrating network, a relaxation oscillator etc. The sawtooth generator 17 is periodically triggered by means of a trigger generator 18. Trigger generator 18 is preferably of the multivibrator type which is synchronized to operate at a constant frequency. The sawtooth voltage wave produced by sawtooth generator 17 is of a predetermined duration and is periodic. The trigger generator 18 is preferably arranged so as to `allow a time interval between the production of the successive sawtooth waves.

Theiferrite element of the oscillator is a voltage-sensitive component whose impedance varies substantially linearly in response to the applied sawtooth voltage from sawtooth generator 17. Since the impedance of the ferrite element varies linearly, and this element is located in the frequency-determining circuit of the oscillator 11, the output frequency of the oscillator 11 also varies linearly in accordance with the variation of the impedance of the feurite ele-ment. The oscillator 11 therefore sweeps 'through a range of frequencies which may be set by a suitable choice of the components of the oscillator. The ferrite type oscillator therefore eliminates the need for any moving parts and is also compact in size.

As the oscillator l11 cyclically sweeps through its predetermined ran-ge of frequencies, heterodyne signals are produced in the mixer circuit 1@ as a result of the beating of the individual frequencies from the transmitters, and the output of the swept oscillator 11. Since the oscillator 11 is continuously vsweeping through `a range of frequencies, each of the heterodyne signals produced in the mixer stage 10 also continuously varies. For example, the `heterodyne signal produced by the beating of the signal from one of the transmitters 5, of a frequency f1, with the signal from the scan oscillator 11, increases as the frequency of the signal from the scan .oscillator 11 increases. The same result follows for signals from the other transmitters 5 of frequencies f2, f3 fn. If there are, illustratively, seven objects 3 within the predetermined area 1, each having a transmitter 5 of different frequency f1, f2, f3 f7, seven continuously sweeping heterodyne signals are simultaneously produced in the mixer 1t?. It should be recognized that any suitable number of transmitters 5 having frequencies of transmission f1 fn may be used.

The output of the mixer .14B is connected to an intermediate frequency amplifier 12. The intermediate frequency amplifier 12 is of a suitable conventional type which comprises a number of Stages of amplifiers each having a selective band pass circuit. The band pass circuits are all narrowly tuned to one frequency, which is the intermediate frequency ff, of the receiver. In this manner, the only signals from the output of mixer 10 which are amplified by the intermediate frequency amplifier 12 are those having the frequency f.

The frequency fif is produced at the output of the mixer stage 16, as a result of the heterodyning of the signais from the various transmitters 5 vand the signal of lthe scanning oscillator 11, at intervals dependent upon the frequency separation between the frequencies f1, f2 f7. Preferably this separation is chosen to 'be uniform between the frequencies f1, f2 f7. The band 0f frequencies through which the oscillator 11 sweeps is chosen in relation to the transmitted signal frequencies so that all of the frequencies f1 f7 produce the intermediate frequency f at some instant of time during each cycle of sweep when mixed with the swept frequency of the mix-er 1?. For example, assu-ming that one of the transmitters 5 is radiating a signal of a frequency f1, at one instant of time, the output of the mixer 1t) produces a signal of frequency fit, as a consequence .of the beating of the signal f1 from the transmitter 5 and the scanning signal from the scanning oscillator 11. Similarly, for a higher transmitter frequency f2 the frequency fu is produced at the output of the mixer 19 only at a later instant when the frequency of oscillator 11 has increased suffrciently to differ from f2 by fig. Thus, such instants occur w en the heterodyning `of the frequencies f2, f3 f7 with the scanning oscillator signal of the oscillator 11 produces the frequency fif. By separating the frequencies f1 to f7 of the transmitters 5, by equal amounts and by scanning the oscillator 1.1 linearly, the output of the mixer circuit 1@ consists of signals of frequency f equal- Aly spaced in time.

After suitable amplification in an intermediate frequency amplifier 12, the intermediate frequency signals of frequency if are detected in a detector 13. The detector 13 serves to demodulate the intermediate frequency and only the envelopes of the signals, which have the corresponding amplitudes of the signals received from the transmitters 5, appear `at the output of the detector 13.

The signals from detector 13 are conveyed to one part .of an amplifier 14 where they are inverted and amplified. From one of the outputs of the amplier 14, the amplified and inverted signal is then conveyed to the input of a vertical deflection amplifier 26. The vertical deflection amplifier 26 again inverts and amplies the signals supplied to its input and the amplified signals are applied to one vertical deflection element `27 of a cathode ray tube 31 land is used to vertically `deflect the electron beam of the cathode ray tube. The other vertical deflection element 29 of the cathode ray tube 31 is connected to a suitable source of reference potential such as ground 33. A horizontal deflection element 34 receives a horizontal deection-voltage from the sawtooth :generator 17 after suitable amplication in a sawtooth amplifier 36. The other horizontal deflection element 35 is connected to the source of reference potential 33. This arrangement enables the cathode ray tube 31 to scan horizontally in synchronism with the scanning oscillator 11 as the detected intermediate frequency signal from the amplifier 26 is being applied to the vertical deflection plate 27.

Therefore, it is seen that, as the oscillator 11 is scanned, a series of pulses are produced in the receiver along a time axis in accordance with the frequencies of the signals broadcast by the transmitters 5. As the electron beam of the cathode ray tube 31 is swept across the face of the tube, the detected intermediate frequency signals from the amplifier 14- and vertical deflection amplilier 26 are presented in lcorrect time sequence in accordance with the frequencies of the transmitters 5. This is shown on the display of the cathode Iray tube 31 of FIG- URE 1 which is a representation of a display for a sevenobject system. If the oscillator 11 sweeps from a low frequency to a higher frequency and the difference heterodyne frequency is selected in mixer 10, the representation of FIG. 1 shows the lower frequency transmitters 5 beginning at the left end of the cathode ray tube trace and the higher frequency transmitters at the right hand end of the trace. The duration of the trace of the cathode -ray tube 31 is equal to ,the period of the sawtooth wave produced yby sawtooth generator 17 and therefore equal to the period in which the scan oscillator y11 completes one cycle of scanning from its lowest frequency to its highest frequency. The variation in amplitudes of the signals on the face of the cathode ray tube 31 is due to rthe physical disposition of the objects 3 within the antenna radiation pattern 1. In the display shown, the object 3 having a transmitter 5 of frequency f4 is missing from the area `1, as indicated by the absence of a sisnal at the position for the f4 transmitter. a

The signals from the detector `13 are also conveyed to another section of amplier 14 where they are processed into binary type unidirectional pulses which are capable of operating a binary counter circuit. In a preferred form of the invention, these pulses are of negative polarity, but

it should be realized that positive pulses may be desired and utilized if so desired. The derivation of the negative pulses is accomplished by suitably amplifying, peaking and clipping the signals present at the output of the detector 13. Amplifier 14 is understood to comprise the proper amplifying stages, peaking circuits and clipping c1rcu1ts necessary to form the unidirectional pulses. All of these circuits are well known in the art and require no further description or explanation.

Starting at the beginning and lasting through the entire interval that the sawtooth generator 17 produces the sawtooth wave which causes both the oscillator 11 and the electron beam of the cathode ray tube 31 to scan, the trigger generator 18 produces a negative pulse which is supplied to the input of a count gate lit-t?. The processed, negative binary pulses from amplifier 14, which are indicative of `the number of transmitters `5 within the predetermined area 1, are applied to a second input of the count gate 40. As has been previously stated, these binary pulses occur only during the interval when the oscillator 111 is scanning. The count gate '40 is a suitable and circuit and at the simultaneous occurrence of the negative pulse from trigger generator 18 and the negative binary pulses from the amplifier 14, the binary pulses are passed by the count gate i0 to a counter 41. At all other f3 times, i.e., in the absence of a pulse from trigger generator 18, no pulses are passed to the counter 41.

The negative binary pulses received by the counter 41 are counted by means of a plurality of binary counter stages lwhich are connected in a ring type or some other suitable type of counting arrangement. The count, or tally, of the counter i1 is then compared in a count comparator 42 which is preset to a desired count total. if the number of pulses received by the counter 41 from the amplifier 11 compares with the preset count, an alarm trigger inhibit pulse is generated which is fed to one input of an alarm gate 43. The alanm gate i3 is also an and circuit which passes pulses only upon the coincidence of two pulses at the gate 43.

The end of the sawtooth wave produced by sawtooth generator 17, which coincides with the end of the trace on cathode ray tube 31 and the end of the scan of oscillator 11, is used to generate a pulse. This is accomplished by connecting the sawtooth generator 17 to a differentiator circuit dei which produces pulses in response to the portion of the sawtooth wave which changes rapidly during the time from the end of one sawtooth wave cycle to the start of the next. This pulse is conveyed to the other input of the alarm gate 43 and also to a reset means 45 which rests the counter d1 to an original condition in respouse to the pulse which is formed in the differentiating cincuit ifi at the beginning of the sawtooth Wave produced by sawtooth generator 17. The counter 41 therefore arts counting from zero at the beginning of each scan of the cathode ray tube 31 and the oscillator 11.

lf there is no trigger inhibit pulse generated by count comparator d2, which indicates that the tally of the number of objects within the defined area 1 is in error with the preset count, the pulse from dierentiator circuit 44 is not inhibited in the alarm gate 43 but passes to an alarm driver de. The alarm driver 46 in turn actuates any suitable alarm 47 which may be of the aural or visual type or a combination of both. Therefore, unless the count from counter i1 tallies with the preset count of the count comparator 4Z, no alarm inhibit pulse is produced by the count comparator i2 and the alarm driver 46 operates and actuates an alarm 47. When the alarm 47 is actuated, indicating that the tally is in error, a look at the face of the cathode ray tube display 311 indicates the identity of the object causing the enroneous count.

131C: 2 shows the circuit for the various blocks 411-47 of FTG. l. ln describing YFIG. 2 binary terminology is utilized wherein the number 1 indicates a pulse of relative negative polarity, such as the pulse appearing at the output of amplifier 14, and a 0 indicates a pulse of positive polarity. While the circuit about to be described illustratively utilizes a negative binary 1 pulse for operation, it should be recognized that the various and gates and counter circuits may be made to operate in response to binary pulses which are of positive polarity. This may be accomplished by suitable modification of amplifier 14 and the circuit shown in FIG. 2. Both systems are well known in the art and it is therefore deemed necessary to describe only one.

Referring to FIGURE 2, the trigger generator l18 produces a negative pulse during the entire int-erval that the electron beam is swept across the face of the cathode ray Itube 31 and the oscillator 111 is being scanned. This negative pulse is applied to a diode Sfl, which is one input of the and circuit comprising count gate 4t). The other input of the and circuit, diode 51, receives negative (1) pulses lfrom amplifier 14 which are indicative of the transmitters 5. The diodes Si and 51 are connected together at the output of the and circuit to a suitable source of negative potential 52 by a resistor 53. Upon simultaneous occurrence of negative pulses at the diodes Sil and 51 a negati-ve pulse is passed to the junction of cathodes of two

diodes

54 and 55. Another diode S6 is connected between the output of the and circuit formed. by diodes 5@ and 51 and the point of reference potential 33 and is so poled as to clip ofi any positive polarity overshoots present at the output of the and circuit.

Diodes

54 and 55 Iare poled so lthat the negative pulses. passed by lthe and circuit 50, 51 are allowed to appear on the control electrodes of Aboth sections of a binary counter stage v57. A second counter stage 59 is connected to the output of counter 57 and other counter stages, such as those represented by the block 6l, may be added `as desired by connecting them to the preceding counter stage output. rlhe counter stages S7, 59 and 61 are identical in construction and are preferably of the multivibrator type. lt should be recognized that either tubes or transistors may be used for the counter stages and that yother types of counters may be utilized. The output pulses `from each of the counter stages 57, S9 and 61, which lappear on

lines

63, 65 and 67 are used to trigger the next succeeding counter stage in a well-known, ringtype counter arrangement. Any suitable number of counter stages may be cascaded in accordance with the number of authorized objects, 3, supplied with radio transmitters being counted.

Before the counting operation begins, a reset pulse in the -form of a negative pulse is applied to the control electrodes of the

counters

57, 59 and 61 via the

respective diodes

76, 72 and 74. The reset pulse serves to set the counter stages 57, 59 and 6-1 into an original condition which is indicative of a Zero count. The negative reset pulse is genenated by means of ydifferentiator circuit 44 at the beginning of the cathode ray tube 31 sweep and oscillator l1 scan. Diodes 70, '72, and 74 are so poled as to pass the negative reset pulse. In this manner, the counter stages 57, d@ `and 61 are reset to a Zero count condition awaiting :the arrival of the binary pulses from amplifier `1-43. This reset pulse occurs at the beginning of each sawtooth Wave so that the counter stages are therefore cleared lof the count accumulated during .the period of the preceding cathode ray tube trace.

Each of the

output lines

63, 65 4and 67 of the respective counter stages 57, 59 `and 6i terminates at the s1 contact of a respective one of a series of switches 75a, 75h and '7"5c located in the count comparator ft2. Each off the switches 75a, 75h and 75C `also has `an s1 contact which is connected to a suitable source of B+ potential 77 by means of Ia voltage divider formed by resistors 78 and 79. Connected to the center arm of each of the switches 75a, 75h `and 75C is the cathode `of a respective one of

diodes

81, 82. and 83. Each of these diodes is so poled as to pass a negative pulse from the center arm of its switches 75a, 7Sb or 75C. FDhe anodes of the diodes opposite switches 75a, '7'5b and '75C are connected to 4a common line 8'5. yLine S5 is connected tothe control electrode 86 of an inhibit-pulse-producing .tube 87 and a positive bias voltage is supplied to Iline 85 and the grid S6 of the tube $7 from the B+ voltage source 77 by means of a resistor 88. A ldiode @t3 is connected between line 85 and fthe point of reference potential 33. Diode 90 is so poled that ya negative pulse applied on line 85 causes `diode 9) to conduct and thereby to short the B+ potential on line S5 to ground. This causes line 85 and the grid S6 of the tube S7 to have a zero potential.

When there is no negative pulse present on line 8S, to cause the diode 90 to conduct, the control electrode S6 of the inhibit-pulse-producing tube 87 is supplied with the positive bias potential from the source 77. The tube `87 is consequently conducting heavily and a negative pulse is produced at its anode. It is this negative pulse which is used to inhibit the `alarm 47 from being actuated by the alarm driver 46. If the count comparator 42 does not allow this negative inhibit pulse to be produced by the tube S7, the alarm 47 is actuated. The latter circumstance occurs when the count from the counter stages does not equal the count preset in the count comparator 42.

The openation of the count comparator circuit 42 is as follows: Each successive negative (l) pulse applied to the input of counter stage 57 causes the counter ring to successively advance. The output of cach `of the counter stages, as has been previously described, is connected to the s1 contact of a respective one of switches 75a, 75h and 75e in the count comparator 42. The object of the count comparator 4Z is tto produce fa negative pulse when the count produced by the counter stages 57, 59 and 6l is in error with the preset count of the count comparator 4.2. This negative pulse makes diode 90 conduct and shorts out the positive potential from source 77, thereby causing a zero potential to appear on line d5.

This operation is illustrated as follows. For example, assume that the original condition of the counter stages 57, 59 and 61, after receipt of the reset pulse from the 'diiiierentiator circuit 44, is such that each of the outputs `63, yand 67 of the counter stages 57, 59 and 61 is producing a negative pulse. 1f the input of counter stage 57 receives four binary l pulses from the amplifier 14, indicative of four radio transmitters 5 within the specied area `1l, the ring counter advances so that the counter stages 57 and 59 have a 1 pulse at their outputs, and counter stage 61 has la 0 (positive) pulse at its output. To set the count comparator t2 .to detect 'a preset count of four, switches a and 75b are set to the s2 contacts (las shown), which are in turn connected to tJhe positive voltage from ythe source 77. Switch 75C is connected to the output line 67 of the counter 61. Since the

output lines

63 and 65 of the respective counters -57 `and 59 are not connected tto the center arms of switches 75a and 7517, no l (negative) pulses can pass through the respective diodes 81 and 62 to line S5. This follows since the anodes of diodes Si and 32 are connected to the source of positive potential connected to line and as poled keep the potential of the B+ source 77 on line 85. Since switch 75e receives a 0 (positive) pulse from counter stage 6l over output line 76, diode 83 also does not conduct and therefore line S5 still has the positive bias voltage supplied by the source 77 through resistor 88. In this instance, a correct comparison in the comparator 42 keeps the positive bias on line S5. The positive bias in turn keeps iuhibit-pulseproducing tube 87 conducting to supply the inhibit pulse to the alarm gate To illustrate how the count comparator operates to detect an error in the total ytally again consider the case where the count comparator `42 fis preset to count to the number four but where only three pulses are received by the counter 41 from amplifier 14. Switches 75a, 75b and 75C are again connected as discussed above to compare a count of four. When three binary pulses are received at the input of counter stage 57, indicative of three objects 3 within the area 1, a 'O (positive) pulse appears on

lines

63 and 65 and a l (negative) pulse appears on lfine 67. The 0 pulses on lines 63 and `65' cannot under any circumstances make diode 99 conduct. iowever, the negative pulse from counter stage 61 on output line 67 passes through diode 83 since switch 75u is connected to the s1 position. This negative pulse from diode 83 is received on line 85 and causes diode 9th to conduct. Upon conduction tof diode 99, line S5 is shorted to ground 33 and a negative voltage, with respect to the positive bias voltage normally present on line 85' from B+ source 7-7 is placed `on the grid 86 of tube S7. The appearance of this negative voltage on the control electrode 86 of tube S7 causes the tube to change its state from conducting to non-conducting, with a resultant positive pulse appearing at its anode. In this state of operation, there is no alarm inhibit pulse supplied to the alarm gate 43.

FIGURE 3 shows a chart of the outputs of the counter stages 57, 59 and 61 [in response to different numbers of input pulses. The chart also shows the settings of the switches 75a, 7511 and 75C for the proper comparison of the various numbers. It should be recognized that additional counters and a corresponding suitable number of switches may be added as desired. While in the present illustration, the count comparator i2 is shown as set up to cause the alarm 47 -to be actuated upon receipt of a number of pulses which is less than the preset count, it should be recognized that a suitable count comparator may be used in which both missing or excess pulses would cause the alarm i7 to be actuated. In some instances, even with the type count comparator shown in FIGURE 2 the receipt of a number of pulses in excess of the counter preset in the comparator 42, causes the alarm 47 to be actuated.

The anode of inhibit pulse producing tube 87 is connected to the cathode of a diode 92, which is one input of an and circuit which is connected to be responsive to and pass positive pulses. The other input of the and circuit, diode 93, is connected to the differentiating circuit 441. The anodes of diodes '92 and 93 are connected to the source of B+ potential 77 through a resistor 94. The diode 93 receives a negative pulse from the differentiating circuit 44 at the beginning of the sweep of the cathode ray tube, i.e. when trigger generator 1S begins to produce its negative pulse. Diode 93 also receives a positive pulse from the diiferentiator circuit 44 at the end of the sweep of a cathode ray tube 3/1, i.e. when the pulse produced by the trigger generator 18 goes positive. As has been previously explained, the negative pulse from the diferentiator circuit 44 which occurs at the Ibeginning of the sweep is utilized to reset the counter stages 57, 59 and 61 to their original condition. When this negative pulse is present at diode 93 of the and circuit 92, 93, no positive pulse can be produced at the output of the and circuit. However, when the positive pulse from differentiator circuit 44, which appears at the end of the sweep of the cathode ray tube is present at the diode 93 the and circuit can produce a positive pulse if there is a simultaneous occurrence of a positive pulse at diode '92 from the inhibit-pulse-producing tube 87. This `does not occur as long as the number of binary pulses from amplifier 14 equals the preset count in count comparator 42. If a positive pulse is passed by the and circuit 92, 93, which is the alarm gate 43, the alarm 47 is actuated. As can be seen from the arrangement of the and circuit, this can occur only at the end of the trace of the cathode ray tubes, i.e., after a complete count of all the radio transmitters 5 present with-in the area 1 during a complete scan of the oscillator 11.

When -a negative pulse is produced at the output of count comparator 42, due to a diiference between the tally of the counter stages 57, 59 and 61 and the preset count of the count comparator 42, the diode 9i) conducts and places line `85 and the grid S6 of tube S7 at ground or zero potential. When the grid 86 of the inhibit-pulseproducing tube '87 is at zero potential, tube 87 is cut ol and a positive voltage at or near the value of the B-lpotential 77, appears at its anode. This positive pulse is conveyed to diode 92. When the diode 93 receives the positive pulse from the dilerentiator circuit 44 at the end of the cathode ray tube sweep, `a positive pulse is produced at `the anode of a diode 97 connected to the and circuit 92, 93. As can be seen, even though tube 87 may produce a positive pulse at other times during the counting interval, there is only one instant when the alarm gate 43 can produce a positive pulse. This instant occurs only at the end of a complete counting interval, after all the objects -within the area 1 have been counted.

The positive pulse from the `cathode of diode '97 is conveyed to the control electrode g8 of the lefth-and section of the alarm driver tube 11rd, which is illustratively show-n as consisting of a conventional multi-Vibrator. Upon receiving the positive pulse at control electrode 98, the leftband section of the tube 106 conducts and a current ows in a coil 101, which is in the plate circuit of the alarm driver tube 161). Coil 161 may be a coil of a relay, or some other suitable device, which is used to actuate the alarm represented by the block 47. The alarm i7 may be of any suitable type either aural or visual or a combination of both. Preferably, the coil l@ `101 is the coil of a latching type relay, and` once it ac tuates :the alarm 47 no subsequent pulse is needed to keep the alarm 47 energized.

As long as inhibit-pulSe-producing tube S7 keeps the negative pulse at its anode, which occurs as long as the tally is correct in the count comparator 412, a negative voltage appears at the cathode of diode 92;. This negative voltage at the cathode of diode 92 prevents the alarm gate from passing a positive pulse to the anode of diode 97 and consequently no positive pulse is received by the grid 9S of the alarm driver tube 16d. This prevents the lefthand section of tube 11i@ from becoming conductive, which in turn keeps the alarm 47 de-actuated. To reset the alarm driver tube 11i@ to a condition where the alarm 47 is not actuated, a positive voltage is applied to the control electrode 162 of the righthand section of the alarm driver tube 16d through resistor 135 and diode 106 when the single pole, single throw switch 1137 is closed. Upon receipt of this positive pulse the righthand section of the alarm driver tube 11)@ conducts, causing the lefthand section containing coil 1111 to become nonsconducting due to the multivibrator connection of the tube 194i. This removes the energizing current from coil 101, which in turn deenergizes the relay and causes the alarm 47 to be de-actuated.

Therefore it is seen that a counting circuit is provided which utilizes the unidirectional pulses produced by the amplifier 14. ln response to the number of these pulses, an alarm is either kept de-actuated or else is actuated in accordance with whether the number of pulses received by the counter either agrees or disagrees with a preset number.

FIG. 4 shows the details of a preferred. form of the oscillator capsule 6 which houses the transmitter 5. Transmitter S primarily comprises a transistor oscillator circuit and its associated components. The oscillator capsule 6 comprises two hollow

hemispherical sections

119 and 111 which are made of plastic or some other suitable non-conducting material. The top hemispherical section 110 has a support ring 113 through which the cord or ribbon 4 is passed. While a support ring 113 is shown in this embodiment, it should be realized that other means for fastening the oscillator capsule 6 to the object 3 may be utilized, for example, screws, brackets etc. The top hemispheroid 110 is threaded as at 115 and engages an internal threaded portion 116 of the bottom hemispheroid 111. When the two sections 11@ and 111 are screwed together, a hermetic seal is provided for the capsule 6.

The bottom hemispheroid 111 houses a. battery 117 which powers the oscillator circuit of the transmitter S. Battery 117 is preferably of the mercury or other equivalent miniature type to conserve space within the capsule 6.

The top hemisphcroid 11@ houses an oscillator coil 119 of the transistor oscillator circuit. Coil 119 dsc serves as the antenna for the transmitter 5. The coil 11g is located within the top hemispheroid 11d in such a manner that when the oscillator capsule 6 is suspended from an object 3 by means of the cord or ribbon 4, the axis of the oscillator coil 119 is perpendicular to the plane of the pickup antenna 1. In this manner, maximum radiated energy is transferred from the oscillator capsule 6 to the pickup antenna 1.

The space between the battery 117 and the coil 119 is designed to accommodate the remaining components of the transistor oscillator circuit. A circuit of a preferred form of transistor oscillator, utilizable with the present invention, is illustratively shown in the FIGURE 5. In the circuit of FIG. 5 a PNP transistor 125 is shown having a base electrode 125, an emitter electrode 127 and a collector electrode 12S. The forward-biasing voltage for the emitter electrode 127 is supplied by the positive terminal of the battery 117 and the reverse bias for the collector electrode 128 is supplied from the negative terminal of battery 117. Suitable voltage dropping net- Works for the biasing voltages are provided if needed. The positive terminal of battery 117 is connected to the emitter electrode 127 through a coil i3d while a connection is established to the collector electrode 12S from the negative terminal of the battery M7' through the oscillator and antenna coil H9. A capacitor 132 is placed in parallel with the coil M9 and frequency of the oscillator is adjusted to the assigned frequency, f1, f2 fn by adjusting the inductance of the coil il@ or the capacity of capacitor 132. The regenerative feedback path for the oscillator circuit is provided by the mutual coupling between the coils 119 and 13d. The oscillator circuit shown in FIG. 5 is disclosed in FIGURE 14.2(b) on page 14-4 of the text titled Handbook of Semi-Conductor Electronics, by L. P. Hunter (McGraw-Hill, 1956). It should be recognized that other suitable transistor oscillator circuits may also be used and that these circuits could use an NPN instead of a PNP transistor.

In a preferred form of the invention, no switch is provided to turn the oscillator circuit in the capsule 6 on or off. This is to insure that the transmitters 5 continuously operate and thereby minimize any possible error in the system. However, if desired, a switch may be provided.

Many other modications of the panoramic scanning counter system of the present invention are envisioned. For example, a photoelectric cell counter may be placed at the entrance to a restricted area. This counter counts the number of objects passing into or leaving the area, and the tally of the photoelectric cell counter, of the total number of objects passing into the area, may be used to establish the preset count of the count comparator d2. Therefore, if an object Without a transmitter 5 is present Within the area, its presence is signalled by the sounding of the alarm t7 since the preset count will not agree with the count from the counter lll.

This modication is shown in FlGURE 6 where the phctoelectric counter is represented by the bloclr i140. The photoelectric counter is desirably placed at the only entrance of the restricted area and therefore counts all of the objects passing into the area. The count output of the photoelectric counter ld@ is then conveyed to a level setter 42. The function of the level setter 142 is `to change the preset number set into the count comparator 42 in response to the count of objects obtained by the photoelectric counter 14d. rEhe level setter 142 may illustratively be a suitable relay type device which is operative in response to the count of the photoelectric counter 142 and which in turn serves to operate switches 75a, 7517 and 75C of the count comparator 42 to set them to the positions corresponding to the number of objects which have passed into the area. As in the case of the embodiment of the invention shown in FIGURES l and 2, the count comparator 42 receives the count from the counter dll, which is a tally of the number of authorized objects within the restricted area. lf this tally does not agree with the preset count set into the count comparator 42 by the level setter 42, the alarm 47 is actuated.

Therefore it is seen that a novel arrangement is provided wherein the preset count of the count comparator 42 is changed in response to the number of objects passing into the restricted area. This arrangement provides for constant surveillance of an area into which objects are continually entering. If desired, the restricted area may be provided with a single exit. This exit may also be provided vvith a photoelectric counter, similar to photoelectric counter Mtl, which counts the number of objects leaving the restricted area. The count from the photoelectric counter positioned adjacent the exit may be subtracted from the count produced by the photoelectric counter 140 positioned adjacent the entrance and the level setter 142 will therefore receive a count which is the total of the number of objects actually within' the restricted area. This count may then be set into the count comparator i2 for comparison with the tally of the number of authorized objects.

Other modifications of the counter system may also be devised. For example, the transmitters 5 attached to the objects 3 may broadcast signals other than the radio frequency type. These signals may illustratively be sound signals of dilferent frequencies, visible light or invisible light of different wavelengths or of any other type of suitable signals. A suitable receiver may be designed to detect these signals Within the predetermined area and the counting and comparing function would then proceed as previously described.

While preferred embodiments of the invention have been described above, it will be understood that these are illustrative only, and the invention is limited solely by the appended claims.

What is claimed is:

l. A system for counting objects comprising a transmitter for each of said objects, each of said transmitters having means for transmitting at the same time a respectively different signal, means for receiving said respectively different signals from said transmitters, and means conected to said receiving means for counting the number of received respectively different signals.

2. An object counter system comprising a transmitter for each of said objects, each of said transmitters being yadapted to broadcast a respective signal, means for receiving said signals from said transmitters, means connected to said receiving means for counting the number of received signals, comparing means connected to said counting means, and means connected to said comparing means for producing a given number count, said comparing means producing a signal when the number of signals received and counted is different from said given number count.

3. An object counter system comprising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a respective signal, means for receiving said signals from said transmitters, means connected to said receiving means for counting the number of received signals, comparing means connected to said counting means, means connected to said comparing means for producing a given number count, said comparing means prcducing an alarm signal when the number 0f signals received and counted is different from said given number count, and alarm means connected to said comparing means, said alarm means being actuated upon receipt of said alarm signal.

4. An object counter system for counting the number of authorized objects within a predetermined area comprising a transmitter for each of said objects', each of said transmitters being adapted to broadcast a respective radio frequency signal, antenna means for receiving said radio frequency signals, the radiation pattern of said antenna denning said predetermined area, means connected to said antenna means for counting the number of re ceived radio frequency signals, and comparing means connected to said counting means, said comparing means including means for producing a preset number, said comparing means comparing the number of signals received and counted with said preset number.

5. An object counter system for counting the number of authorized objects Within a predetermined area comprising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a respective radio frequency signal, antenna means for receiving said radio frequency signals, the radiation pattern of said antenna defining said predetermined area, means connected to said antenna means for counting the number of received radio frequency signals, comparing means connected to said counting means, means for producing a preset count, said comparing means being responsive to said preset count and the counted number of received radio frequency signals for producing a signal when the number of radio frequency signals received and counted is different from said preset count.

6. An object counter system for counting the number of authorized objects Within a predetermined area comaliases prising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a respective radio frequency signal, antenna means for receiving said radio frequency signals, the radiation pattern of said antenna defining said predetermined area, means connected to said antenna means for counting the number of received radio frequency signals, comparing means connected to said counting means, means for presetting said comparing means to a given number, said comparing means producing an alarm signal when the sumber of signals received and counted is different from said given number preset in said comparing means, and alarm means connected to said comparing means, said alarm means being actuated upon receipt of said alarm signal.

7. An object counter system for counting the number of authorized objectsv Within a predetermined area cornprising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a respective radio frequency signal, each of said signals broadcast by said ransmitters being of a different frequency, antenna means for receiving said radio frequency signals, the radiation pattern of said antenna means defining said predetermined area, means connected to said antenna means for displaying said received signals along a time axis, means connected to said antenna means for counting the number of received radio frequency signals, comparing means connected to said counting means, and means for presetting a given number into said comparing means, said comparing means comparing the number of signals received and counted with the given number which is preset in said comparing means.

8. Am object counter system comprising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a radio frequency signal of a respectively different frequency, means for receiving the radio frequency signals broadcast from said transmitters, said receiving means comprising means periodically operative for a predetermined interval of time to convert each of said received radio frequency signals into an intermediate frequency signal during said predetermined interval of time, means connected to said periodically operative means to process each of said converted intermediate frequency signals into a pulse, counter means connected to said processing means to count the number of pulses formed from said intermediate frequency signals by said processing means during said predetermined inerval of time, means for producing a preset number, and means connected to said counter means to compare the number of pulses received by said counter means during said predetermined interval of time with said preset number.

9. An object counter system for counting the number of objects within a predetermined area comprising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a respective radio frequency signal of a different frequency, an antenna for receiving the radio frequency signals broadcast from said transmitters, tbe radiation pattern of said antenna being used to define said predetermined area, a receiver connected to said antenna, said receiver comprising means periodically operative for a predetermined interval of time to convert eacn of said received radio frequency signals into an intermediate frequency signal during said predetermined interval of time, means connected to said periodically operative means to process each of said successively converted intermediate frequency signals into a pulse, counter means connected to said processing means to count the number of pulses formed from said intermediate frequency signals by said processing means during said predetermined interval of time, means for producing a given preset number, and means connected to said counter means to compare the number of pulses received by said counter means during said predetermined interval of time with said given preset number, said comparing means being adapted to produce a signal when the number of pulses lli l received by said counter means is different from said given preset number.

10. An object counter system for counting the number of authorized objects within a predetermined area comprising a transmitter for each of said objectsJ each of said transmitters being adapted to broadcast a respective radio frequency signal, each of said signals broadcast by said transmitter being of a different frequency, an antenna for receiving tbe radio frequency signals broadcast from said transmitters, the radiation pattern of said antenna being used to define said predetermined area, a panoramic receiver connected to said antenna, said panoramic receiver comprising means periodically operative for a predetermined interval of time, to convert each of said received radio frequency signals of different frequency into an intermediate frequency signal during said predetermined interval of time at successive instants of time dependent upon the frequency of said radio frequency signals, means for displaying said intermediate frequency signals along a time axis on which the time corresponds to the frequency of a respective transmitter signal thereby indicating the identity of a respective object by means of its associated transmitter, said display means being operative only during said predetermined interval, means connected to said periodically operative means to process each of said successively converted intermediate frequency signals into a binary pulse, counter means connected. to said processing means to count the number of binary pulses formed from said intermediate frequency signals by said processing means during said predetermined interval of time, means connected to said counter means for rendering said counter means operative to receive pulses from said processing means only during said predetermined interval of operation of said periodically operative means, and means connected to said counter means to compare the number of pulses received by said counter means during said predetermined interval with a preset number, said comparing means including means for producing an alarm signal only when the number of pulses received by said counter means is different from said preset number.

1l. An object counter system for counting the number of authorized objects within a predetermined area comprising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a respective radio frequency signal, each of said signals broadcast by said transmitter being of a different frequency, an antenna for receiving the radio frequency signals broad cast from said transmitters, the radiation pattern of said antenna being used to define said predetermined area, a panoramic receiver connected to said antenna, said panoramic receiver comprising means periodically operative for a predetermined interval of time to convert each of said received radio frequency signals of different frequency into an intermediate frequency signal during said predetermined interval of time at successive instants of time dependent upon the frequency of said radio fre1 quency signals, means for displaying said intermediate frequency signals alo-ng a time axis on which the time corresponds to the frequency of a respective transmitter n signal thereby indicating the identity of a respective object by means of its associated transmitter, said display means being operative only during said predetermined interval, means connected to said periodically operative means to process each of said successively converted intermediate frequency signals into a binary pulse, counter means connected to said processing means to count the number of binary pulses formed from said intermediate frequency signals by said processing means during said predetermined interval of time, means connected to said counter means for rendering said counter means operative to receive pulses from said processing means only during said predetermined interval of operation of said periodically operative means, means connected to said counter means to compare the number of pulses received by said counter means during said predetermined interval with a preset number, said comparing means including means for producing an alarm signal only when tbe number of pulse received by said counter means is different from said preset number, and alarm means connected to said comparing means, said alarm means being actuated upon receipt of said alarm signal, and further means connected to said comparing means to allow said alarm signal to reach said alarm means only at the end of said predetermined interval of time.

l2. An object counter system for counting the number of authorized objects within a predetermined area comprising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a respective radio frequency signal, each of said signals broadcast by said transmitter being of a different frequency and being spaced from each other in frequency by an equal amount, an antenna for receiving the radio frequency signals broadcast from said transmitters, the radiation pattern of said antenna being used to dene said predetermined area, a panoramic receiver connected to said antenna, said panoramic receiver comprising means periodically operative for a predetermined interval of time to successively convert each of said radio frequency signals of different frequency into an intermediate frequency signal during said predetermined interval of time at successive instants of time dependent upon the frequency of said radio frequency signals, means for displaying said intermediate frequency signals along a time axis on which the time corresponds to the frequency of a respective transmitter signal thereby indicating the identity of a respective object 'by means of its associated transmitter, said display means being operative only during said predetermined interval, means connected to said periodically operative means to process each of said successively converted intermediate frequency signals into a pulse, a counter means connected to said processing means to count the number of pulses formed said intermediate frequency signals by said processing means during said predetermined interval, means connected to said counter means rendering said counter means operative to receive pulses from said processing means only during said predetermined interval of 0peration of said periodically operative means, means connected to said counter means to compare the number of pulses received by said counter means during said predetermined interval with a given preset number, said comparing means producing an alarm signal only when the number of pulses received by said counter means is different from said given preset number, and alarm means connec ed to said comparing means, said alarm means being actuated upon receipt of the alarm signal.

13. An object counter system for counting the number of authorized objects Within a predetermined area comprising a transmitter for each of said objects, each of said transmitters being adapted to broadcast a respective radio frequency signal, eacb of said signals broadcast by said transmitter being of a different frequency and being spaced from each other in frequency by an equal amount, an antenna for receiving the radio frequency signals broadcast from said transmitters, the radiation pattern of said antenna being used to define said predetermined area, a panoramic receiver connected to said antenna, said panoramic receiver comprising means periodically operative for a predetermined interval of time to successively convert each of said radio frequency signals of different frequency into an intermediate frequency signal during said predetermined interval of time at successive instants of time dependent upon the frequency of said radio frequency signals, means for displaying said intermediate frequency signals along a time axis on which the time corresponds to the frequency of a respective transmitter signal thereby indicating the identity of a respective object by mea-ns of its associated transmitter, said display means being operative only during said predetermined interval, means connected to said periodically operative means to process each of said successively converted intermediate I6 frequency signals into a pulse, counter means connected to said processing means to count the number of pulses formed from said intermediate frequency signals by said processing means during said predetermined interval, means connected to said counter means rendering said counter means operative to receive pulses from said processing means only during said predetermined interval of operation of said periodically operative means, means connected to said counter means to compare the number of pulses received by said counter means during said predetermined interval with a given preset number, said comparing means producing an alarm signal only when the number of pulses received by said counter means is different from said given preset number, alarm means connected to said comparing means, said alarm means being actuated upon receipt of the alarm signal, and further means connected to said comparing means to allow said alarm signal to reach said alarm means only at the end of said predetermined interval of time.

14. An object counter system for counting the number of authorized objects within a predetermined area comprising a transmitter for each of said authorized objects, each of said transmitters being adapted to broadcast a respective signal, rst counting means for counting the total number of objects within said predetermined area, means for receiving said signals from said transmitters, second counting means connected to said receiving means for counting the number of received signals, means including comparing means connected to said second counting means and presetable to a given number for producing a signal when the number of signals received and counted is different from said given number preset in said comparing means, and setting means connecting said rst counting means to said comparing means, said setting means being operative to set said given preset number into said comparing means in response to the number of objects counted by said rst counting means.

l5. An object counter system for counting the number of authorized objects within a predetermined area comd prising a transmitter for each of said authorized objects, each of said transmitters being adapted to broadcast a respective radio frequency signal, first counting means for counting the total number of objects Within said pre determined area, means for receiving said radio frequency signals, second counting means connected to said receiving means for counting the number of received radio frequency signals, comparing means connected to said second counting means and being presetable to a given number, said comparing means producing an alarm signal when the number of radio frequency signals received and counted is different from said given preset number, means connecting said rst counting means to said comparing means, said last named means being operative to set said given preset number into said cornparing means in response to the number of objects counted by said rst counting means, and alarm means connected to said comparing means, said alarm means being actuated upon receipt of said alarm signal.

i6. A system for counting objects comprising a transmitter for each of said objects, each of said transmitters producing at the same time a signal having respectively different frequency components, means for receiving the signals produced by said transmitters, means for converting the received signals from said transmitters into a plurality of sequentially occurring signals, and means for displaying the sequentially occurring signals in the order of occurrence.

17. A system for counting objects comprising a transmitter for each of said objects, each of said transmitters producing at the same time a signal having a respectively different frequency, means for receiving the signals produced by said transmitters, means for converting the received signals of diiferent frequencies from said transmitters into a plurality of sequentially occurring signals, and .mens connected to said converting means for count- 17 ing the number of said sequentially occurring signals.

18. A system for counting objects comprising a transmitter for each of said objects, each of said transmitters producing at the same time a signal having a respectively different frequency, means for receiving the signals produced by said transmitters, means for converting the received signals from said transmitters into a plurality of sequentially occurring signals, means connected to said converting means for counting the number of said se quentially occurring signals, and further means connected to said converting means for displaying said sequentially occurring signals on a time base.

19. An object counter for counting the number of authorized objects within a predetermined area comprising a transmitter for each of said objects, each of said transmitters having means for broadcasting a respective radio frequency signal of a different frequency, antenna means for receiving said different frequency radio frequency signals, the radiation pattern of said antenna dening said predetermined area, means connected to lsaid antenna means for displaying the received radio frequency signals along a time axis at times corresponding to the respective frequencies thereof, and means connected to said antenna for counting the number of received radio frequency signals.

References Cited in the le of this patent UNITED STATES PATENTS 1,406,996 Morrill Feb. 21, 1922 2,409,229 Smith et al Oct. 15, 1946 2,409,462 Zworykin et al Oct. l5, 1946 2,410,424 Brown Nov. 5, 1946 2,419,099 Wall Apr. 15, 1947 2,449,391 Kogane Sept. 14, 1948 2,465,976 Goldsmith Mar. 29, 1949 2,474,271 Meyer June 28, 1949 2,597,517 Noble May 20, 1952 2,602,853 Harrison July y8, 1952 2,764,634 Brooks et al Sept. 25, 1956 2,810,828 Gray et al. Oct. 22, 1957 2,870,435 De Graaf Jan. 20, 1959 2,877,416 Grisdale Mar. 10, 1959 2,895,128 Bryden July 14, 1959 FOREIGN PATENTS 627,081 Great Britain July 27, 1949

Claims

1. A SYSTEM FOR COUNTING OBJECTS COMPRISING A TRANSMITTER FOR EACH OF SAID OBJECTS, EACH OF SAID TRANSMITTERS HAVING MEANS FOR TRANSMITTING AT THE SAME TIME A RESPECTIVELY DIFFERENT SIGNAL, MEANS FOR RECEIVING SAID RESPECTIVELY DIFFERENT SIGNALS FROM SAID TRANSMITTERS, AND MEANS CON-