JP2003106804A - Balance cable length measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a balance cable length measuring apparatus capable of measuring the cable length of various balance cable length. SOLUTION: The balance cable length measuring device 1 comprises a pulse generator 2 generating a pulse SP0 for inspection, a transmitter/receiver 3 injecting the generated pulse for inspection SP1 in the balance cable CB as an inspection object and detecting the reflection wave signal SR1 of the injected pulse for inspection SP1, a measuring part 4 measuring the time from the injection of the pulse for inspection SP1 to the detection of the reflection wave signal SR1, and a controller 5 producing the pulse generator 2, producing the pulse SP0 for inspection and calculating the cable length of the balance cable CB based on the measured time by the measuring part 4. The pulse generator 2 is constituted in making the pulse width of the pulse SP0 extendable and contractable for inspection.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a UTP (Unshield)
ed Twisted-Pair Cable) A balanced cable length measuring device for measuring the cable length of a balanced cable such as a cable.

[0002]

2. Description of the Related Art TDR (Time-Domain Reflectometry)
As a measuring device for measuring the cable length of the balanced cable according to the measuring method, the balanced cable length measuring device 5 shown in FIGS.
1,61 are known.

The balanced cable length measuring device 51, as shown in FIG. 7, includes a pulse generating section 52, a transmitting / receiving section 53, a measuring section 4,
The control unit 55 and the display unit 6 are provided. In this case, the pulse generator 52 receives the signal SA and receives the inspection pulse SP0 having a predetermined voltage value with a predetermined time width determined in advance.
To generate. The transmitter / receiver 53 includes an amplifier 3a and an output resistor 3
b, a balun 53c, a differential comparator 53d and a connector 3e. This transceiver 53
Converts the inspection pulse SP0 generated by the pulse generation unit 52 into an inspection pulse SP1 having a predetermined voltage value by the amplifier 3a and outputs the inspection pulse SP1 via the balun 53c into a balanced pulse, which is converted into the inspection pulse SP1. The pulse SP1 is injected between the ends of the pair of signal lines in the balanced cable CB to be inspected, which is connected to the connector 3e. Further, the transmission / reception unit 53 has a voltage waveform (inspection pulse SP1 and a reflected wave signal generated by injecting the inspection pulse SP1) generated between the respective ends (between the input ends) of the pair of signal lines via the balun 53c. The waveform of SR1) is shaped by the comparator 53d and output. Specifically, as shown in FIGS. 4A and 4B, the comparator 53d has a high level when a voltage equal to or higher than a predetermined threshold voltage VTH is input between the input side end portions of the balun 53c. Of the inspection pulse SP1 by outputting the low level signal when the voltage is less than the threshold voltage VTH.
And the pulse S for inspection by waveform shaping of the reflected wave signal SR1
It outputs as P2 and reflected wave signal SR2, respectively.

The measuring unit 4 measures the time difference T (see FIG. 4) between the inspection pulse SP2 and the reflected wave signal SR2 output from the comparator 53d of the transmitting / receiving unit 53, and the measured time difference T is the time data. Output as DT. The controller 55 outputs the signal SA to cause the pulse generator 52 to generate the inspection pulse SP0. Further, the control unit 55 calculates the cable length (electrical length) L of the balanced cable CB based on the time data DT output from the measuring unit 4, and displays the calculated cable length L on the display unit 6. In this case, the control unit 55 calculates the cable length L using the following equation (1). L = NVP × (T / 2) × Vc ... (1) where NVP (Nominal Velocity of Propagation:
1>NVP> 0) is a propagation coefficient and means a value specific to the balanced cable CB to be measured. For example, in a UTP cable, the NVP value is about 0.6. Also,
Vc means the speed of light. Further, the cable length L means the entire length of the balanced cable CB if it is normal, as will be described later, and the inspection pulse SP when the balanced cable CB has a failure location such as a disconnection failure or a short circuit failure. Means the length from one end where is input to this fault location.

In the balanced cable length measuring device 51, first, the connector 3e of the transmitter / receiver 53 is connected to the connector attached to one end of the balanced cable CB. In this case, the other end of the balanced cable CB is set so as to be in a mismatched state with the characteristic impedance of the balanced cable CB (for example, in an open state or a shorted state).
Next, the controller 55 generates the signal SA to generate the pulse generator 5
The pulse generator 52 generates and outputs the inspection pulse SP0 by outputting the inspection pulse SP0.

Next, the transmitter / receiver 53 amplifies the generated inspection pulse SP0, converts it into a balanced pulse, and injects it into one end of the balanced cable CB. In this case, the inspection pulse SP1 injected into the balanced cable CB is reflected at the characteristic impedance mismatched portion of the balanced cable CB and returns to the one end (input end) side. For example, in a normal state in which there is no faulty part in each signal line, the inspection pulse SP1 reaches the other end of the balanced cable CB (where the characteristic impedance does not match), is reflected at this other end, and is input. Return to the edge. On the other hand, when any one of the signal lines has a failure part in the middle of the signal line, the failure part becomes a mismatched part of the characteristic impedance. Therefore, the injected inspection pulse SP1 is reflected and returns to the input end when it reaches the failure point. In particular, since the transmitter / receiver 53 injects the inspection pulse SP1 as a balanced pulse, even if there is a failure point in any of the pair of signal lines, this failure point is a mismatch point of the characteristic impedance. Then, reflection occurs. Therefore, as shown in FIG. 4A, the inspection pulse SP1 first appears on one end side of the balanced cable CB, that is, the input end side of the balun 53c, and the reflected wave signal SR1 is delayed after the inspection pulse SP1. appear. in this case,
When a failure occurs in the balanced cable CB, the time from the injection of the inspection pulse SP1 to the appearance of the reflected wave signal SR1 is shorter than that of the normal balanced cable CB, and this time is the input of the balanced cable CB. The shorter the length from the end to the characteristic impedance mismatching point (breaking point, short-circuiting point or other failure point), the faster the speed.

Next, the transmitter / receiver 53 generates a voltage waveform generated between the input-side ends of the balun 53c (the inspection pulse SP1 injected between the input-side ends of the balun 53c and the input-side ends thereof). Pulsed reflected wave signal SR1)
Waveform is shaped by the comparator 53d, as shown in FIG.
Inspection pulse SP2 and reflected wave signal SR as shown in FIG.
2 is output to the measuring unit 4. The measuring unit 4 measures a time difference T between the inspection pulse SP2 and the reflected wave signal SR2, and outputs the measured time difference T as time data DT.
In this case, when the balanced cable CB has a failure point, the time difference T is shorter than that of the normal balanced cable CB, and the time difference T is from the input end of the balanced cable CB to the characteristic impedance mismatching point (failure). The shorter the length up to the point), the shorter it becomes. Then, the control unit 55
Calculates the cable length L of the balanced cable CB based on the time data DT and the equation (1), and displays the calculated cable length L on the display unit 6.

By adopting the above structure, the balanced cable length measuring device 51 can automatically measure the cable length (electrical length) of the balanced cable CB and display the measurement result. Therefore, for example, a laying operator or an inspecting operator of the balanced cable CB can use the balanced cable length measuring device 51 to inspect the balanced cable CB for a failure after laying the balanced cable CB or at the time of inspection. Specifically, the balanced cable length measuring device 5
The cable length measured by performing the work of measuring the cable length of the balanced cable CB using 1 and the work of comparing the cable length displayed on the display unit 6 with the actual cable length (known) laid When L is different from the laid cable length, it is possible to detect that the balanced cable CB has a failure point. Further, at that time, it can be specified that a failure location has occurred at a portion separated from the one end side of the balanced cable CB by the cable length L.

Next, the balanced cable length measuring device 61 will be described with reference to FIG. Balanced cable length measuring device 6
1 is different from the balanced cable length measuring device 51 in that it has a balun 5
3c and the differential comparator 53d
It was developed in order to avoid the cost increase of products due to the configuration of the balanced circuit. Therefore, the balanced cable length measuring device 61 has the same configuration as the corresponding components of the balanced cable length measuring device 51 except for the balun 53c and the comparator 53d in the transmitting / receiving section 53 of the balanced cable length measuring device 51. Has been done. Therefore, the same components as those of the balanced cable length measuring device 51 are designated by the same reference numerals, and duplicated description will be omitted.

The balanced cable length measuring device 61 comprises a pulse generating section 52, a transmitting / receiving section 63, a measuring section 4, a control section 55 and a display section 6. In this case, the transmission / reception unit 63 includes an amplifier 3a, a resistor 3b, a non-differential comparator 3d and a connector 3e, converts the input inspection pulse SP0 into an inspection pulse SP1 as an unbalanced pulse, and then a balanced cable. The inspection pulse SP1 is injected between one end side (input end) of one of the pair of signal lines in CB and the ground as the reference potential. In addition, the transmitting / receiving unit 63
Then, the comparator 3d waveforms the inspection pulse SP1 and the reflected wave signal SR1 respectively when the voltage generated between the input terminal of this one signal line and the ground potential is equal to or higher than a predetermined threshold voltage VTH. It is shaped and output as the inspection pulse SP2 and the reflected wave signal SR2.

The balanced cable length measuring device 61 is also similar to the balanced cable length measuring device 51, and the inspection pulse SP1.
Is injected into one signal line of the balanced cable CB, and the cable length of one signal line of the balanced cable CB is measured based on the time difference T between the waveform-shaped inspection pulse SP2 and the reflected wave signal SR2. By adopting this configuration, the balanced cable length measuring device 61 does not use the expensive balun 53c, so that the product cost can be reduced.

[0012]

However, these balanced cable length measuring instruments 51 and 61 have the following problems. That is, in the balanced cable length measuring devices 51 and 61,
Inspection pulse SP generated by the pulse generator 52
0 is a fixed predetermined time width and generates one kind of pulse that is defined in advance to a fixed predetermined voltage value. Therefore, when the pulse width of the inspection pulse SP0 is defined in advance to be narrow so that the cable length L of the short balanced cable CB can be measured, as shown in FIG. 5A, the reflected wave signal increases as the cable length increases. As a result of the amplitude of SR1 gradually decreasing,
When measuring a long balanced cable CB, there is a problem that the amplitude of the reflected wave signal SR1 becomes equal to or lower than the threshold voltage VTH of the comparators 53d and 3d, and the reflected wave signal SR1 cannot be detected. vice versa,
When the pulse width of the inspection pulse SP0 is specified to be wide in advance so that the cable length L of the long balanced cable CB can be measured,
When measuring the short balanced cable CB, the time from the injection of the inspection pulse SP1 to the generation of the reflected wave signal SR1 becomes short, and as a result, as shown in FIG. 6A, during the injection period of the inspection pulse SP1. Since the reflected wave signal SR1 appears on the both sides and both of them overlap each other, the appearance of the reflected wave signal SR1 cannot be detected.

The present invention has been made in view of the above problems, and a main object of the present invention is to provide a balanced cable length measuring device capable of measuring the cable lengths of balanced cables of various lengths. .

[0014]

In order to achieve the above object, a balanced cable length measuring device according to a first aspect of the present invention comprises a pulse generating section for generating an inspection pulse and a balance of an inspection object with the generated inspection pulse. A transmission / reception unit that injects into the cable and detects the reflected wave signal of the injected inspection pulse, a measurement unit that measures the time from the injection of the inspection pulse to the detection of the reflected wave signal, and the pulse generation unit. A balanced cable length measuring device comprising: a control unit that controls the generation of the inspection pulse and calculates a cable length of the balanced cable based on a measurement time by the measuring unit, wherein the pulse generation unit includes: The pulse width of the inspection pulse can be expanded and contracted.

The balanced cable length measuring device according to claim 2 is
The balanced cable length measuring instrument according to claim 1, wherein the control unit controls the pulse generation unit to detect the reflected wave signal by the measuring unit when the reflected wave signal is not detected by the measuring unit. Until then, the pulse width of the inspection pulse is expanded / contracted.

The balanced cable length measuring device according to claim 3 is
The balanced cable length measuring device according to claim 1 or 2, wherein one of a pair of signal lines in the balanced cable is connected to an output section of the transmitting / receiving section and the other of the pair of signal lines is connected to a reference potential. A switching unit for switching is provided, and the transmission / reception unit transmits the inspection pulse to the one of the signal lines and receives the inspection pulse from the one of the signal lines via the switching unit. It is configured to be possible.

The balanced cable length measuring device according to claim 4 is
The balanced cable length measuring device according to claim 3, wherein the control unit controls the switching unit to inject the inspection pulse between each of the pair of signal lines and the reference potential, and each of the control pulses. The cable length of each signal line is calculated based on each measurement time corresponding to the signal line, and the shorter cable length of the calculated both cable lengths is determined as the cable length of the balanced cable.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a balanced cable length measuring device 1 according to the present invention will be described below with reference to the accompanying drawings.

First, the configuration of the balanced cable length measuring device 1 will be described with reference to FIG. The same components as those of the conventional balanced cable length measuring instruments 51 and 61 are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIG. 1, the balanced cable length measuring device 1 includes a pulse generating section 2, a transmitting / receiving section 3, a measuring section 4, a control section 5 and a display section 6. In this case, the pulse generation unit 2 generates and outputs the inspection pulse SP0 having a pulse width corresponding to the pulse width data DPL output from the control unit 5 and having a predetermined voltage value when the signal SA is input. To do. In this case, the voltage value of the inspection pulse SP0 is
The voltage level at the time of being input to the comparator 3d via an amplifier 3a and an output resistor 3b, which will be described later, is preset so as to sufficiently exceed the threshold voltage VTH in the comparator 3d. The transmission / reception unit 3 is configured to include an amplifier 3a, an output resistance 3b, a signal switch 3c as a switching unit, a non-differential comparator 3d and a connector 3e, and one of the later-described ones via the signal switch 3c. Transmission of the inspection pulse SP1 to the signal line and inspection pulse SR from one of the signal lines
1 is received. The amplifier 3a amplifies the inspection pulse SP0 generated by the pulse generator 2 to a predetermined voltage value and outputs it as an inspection pulse SP1. Output resistance 3
b matches the output impedance of the amplifier 3a with the characteristic impedance of the balanced cable CB. The signal switch 3c connects one of the pair of signal lines in the balanced cable CB to be tested to the output section of the transmitting / receiving section 3 through one terminal of the connector 3e, and the other of the pair of signal lines is the connector. The connection is switched to the ground potential as the reference potential via the other terminal of 3e. Specifically, the signal switching unit 3c uses the input selection signal SSE.
The internal circuit is selectively switched based on L, and the inspection pulse SP1 input via the output resistor 3b is supplied to either one of the pair of signal lines in the balanced cable CB connected to the connector 3e and the pair of signals. Injection to earth potential connected to either line. In this case, the ground potential is the device ground and is commonly connected to the ground potential of each part in the balanced cable length measuring instrument 1. As shown in FIG. 4, the comparator 3d has a voltage waveform (inspection pulse SP1 and this inspection pulse SP1) that appears at its input side (the input side end of the signal switch 3c).
Each voltage waveform of the reflected wave signal SR1 appearing by injection of
When the voltage exceeds the threshold voltage VTH, the waveform is shaped into a pulse and output as the inspection pulse SP2 and the reflected wave signal SR2.

The measuring unit 4 measures the time difference T (see FIG. 4) between the inspection pulse SP2 and the reflected wave signal SR2 output from the transmitting / receiving unit 3, and measures the measured time difference (measurement time) T as time data. It is output to the control unit 5 as DT.
In this case, the measuring unit 4 is configured to include, for example, a counter that counts in a predetermined cycle and a multiplication circuit inside. In the measuring unit 4, the counter has a reset signal RS.
When T is input, the count value is reset and then the state is changed to the count enable state. In addition, when the first pulse signal is output from the transmitting / receiving unit 3 in the countable state, the counter starts the counting operation by using the pulse signal as a start trigger. After that, the counter continues the counting operation at a predetermined count cycle until the next pulse signal as the stop signal is output from the transmitting / receiving unit 3. On the other hand, the multiplier multiplies the final count value of the counter by the count cycle. In this case, the multiplication value means the time difference T between the first pulse signal (inspection pulse SP2) and the next pulse signal (reflected wave signal SR2). In the measuring unit 4, a maximum value is defined in advance for the count value of the counter, and when the next pulse signal (stop signal) is not input before the count value reaches this maximum value, the reflected wave signal SR2 Is output to the controller 5 to the effect that the data DN has not been detected.

The control unit 5 has an internal memory, in which a plurality of types of pulse width data DPL are stored in advance as a pulse width data table. For example,
The pulse width data table stores the pulse width data DPL in ascending order of pulse width (or in ascending order).
The control unit 5 sequentially extracts one pulse width data DPL from this pulse width data table (sequentially from the narrowest pulse width or sequentially from the widest pulse width) and outputs the pulse width data DPL to the pulse generation unit 2 as well as the signal SA. To the pulse generator 2. The control unit 5 also outputs the selection signal SSEL to the signal switch 3c. Further, the control unit 5 outputs the reset signal RST to the measuring unit 4 and, when the measuring unit 4 outputs the time data DT, based on the time data DT and the above formula (1). The cable length (electrical length) L of the balanced cable CB is calculated, and the calculated cable length L is displayed on the display unit 6. Further, when the data DN is output from the measurement unit 4, the next pulse width data DPL is taken out from the pulse width data table and output to the pulse generation unit 2. In addition, the control unit 5
Every time the pulse width data DPL is output to the pulse generation unit 2, the reset signal RST is output to the measurement unit 4.

Next, the cable length measuring process of the balanced cable CB when measuring the cable length L of the balanced cable CB to be inspected will be described with reference to FIGS. Prior to the measurement, a connector attached to one end of the balanced cable CB to be inspected is connected to the connector 3e of the transmission / reception unit 3, and the other end of the balanced cable CB is set to be in a mismatched state with its characteristic impedance. It is set in advance so that (for example, it is set to either the open state or the short-circuited state).

In this state, in the balanced cable length measuring device 1, first, the control unit 5 outputs the selection signal SSEL to the signal switching device 3c, so that the pair of signals in the balanced cable CB is as shown in FIG. One of the lines (first
Signal line: Specifically, the signal switch 3c is set to a state in which the inspection pulse SP1 can be injected between the first signal line and the ground as the reference potential (step 10).
1).

Next, the control section 5 carries out a cable length measuring process for the first signal line (step 10).
2). Specifically, as shown in FIG. 3, the control unit 5 determines the first pulse width data DPL from the pulse width data table.
Is taken out and output to the pulse generation unit 2 to set the time width (pulse width) of the inspection pulse SP0 generated by the pulse generation unit 2. Then, the control unit 5
By outputting the signal SA to the pulse generator 2, the inspection pulse SP0 having the set pulse width is generated. The inspection pulse SP0 is input (amplified) to the amplifier 3a of the transmission / reception unit 3 and amplified (voltage), and then is output as the inspection pulse SP1 via the output resistor 3b and the signal switch 3c.
Injected between signal line and ground (step 20)
1). At this time, the inspection pulse SP1 is also input to the comparator 3d via the output resistor 3b. Therefore, the comparator 3d outputs the waveform-shaped inspection pulse SP2 as a start trigger to the measuring unit 4, and as a result, the measuring unit 4 starts the counting operation.

Further, the inspection pulse SP1 injected to the one end side of the first signal line propagates in the first signal line while being attenuated toward the other end side, and reaches the mismatched portion in the first signal line. It will be reflected when you do. Further, the reflected wave signal SR1 reflected at the mismatched portion propagates in the first signal line while being attenuated toward the one end side and reaches the one end side. Therefore, on one end side of the first signal line, that is, on the input side of the comparator 3d, as shown in FIG.
The inspection pulse SP1 and the reflected wave signal SR1 appear after a delay of a predetermined time from the inspection pulse SP1. In this case, this predetermined time is a time proportional to the length from one end of the first signal line to this mismatched portion. On the other hand, when the input voltage exceeds the threshold voltage VTH, the comparator 3d, as shown in FIG.
2 is output as a stop signal. At this time, the measuring unit 4
When the reflected wave signal SR2 is input (step 2
02), the counting operation is stopped normally, and then the time difference T between the inspection pulse SP2 and the reflected wave signal SR2 is calculated and output as time data DT.

The control unit 5 receives the time data DT from the measuring unit 4.
Is output, the cable length L1 of the first signal line in the balanced cable CB is calculated based on this time data DT and the above equation (1) (step 203). Next, the control unit 5 stores the calculated cable length L1 in the internal memory, then ends this processing, and proceeds to step 103 in the cable length measurement processing of the balanced cable.

On the other hand, when the length from the one end side of the first signal line to the mismatched portion becomes long, the attenuation of the inspection pulse SP1 and the reflected wave signal SR1 propagating in the first signal line becomes large. As shown in (a), the voltage level of the reflected wave signal SR1 appearing on the input side of the comparator 3d gradually decreases in proportion to this length. Therefore, when the length from the one end side of the first signal line to the mismatched portion becomes a predetermined length or more, the voltage level of the reflected wave signal SR1 reaching the one end side of the first signal line becomes the threshold voltage of the comparator 3d. Since it becomes VTH or less, the comparator 3d cannot shape the waveform of the reflected wave signal SR. Therefore, in step 202 described above, the reflected wave signal SR2 as the stop signal is not input to the measurement unit 4. Therefore, since the count value reaches the maximum value, the measuring unit 4 outputs the data DN indicating that the reflected wave signal SR2 could not be detected.

When the data DN is output, the control unit 5
Outputs a reset signal RST to the measuring unit 4 and determines whether or not there is unused pulse width data DPL in the pulse width data table (step 20).
4). When there is unused pulse width data DPL, the pulse width data DPL having the next largest pulse width is determined as the pulse width data DPL to be output to the pulse generator 2 (step 205). After that, the control unit 5 returns to step 201, outputs the new pulse width data DPL to the pulse generation unit 2, and resets the time width (pulse width) of the inspection pulse SP0 generated by the pulse generation unit 2. At the same time, by outputting the signal SA to the pulse generator 2, the inspection pulse SP0 having a new pulse width is generated.

Further, the control unit 5 detects the reflected wave signal SR2 at one end of the first signal line as described above and normally stops the counting operation by the measuring unit 4 (step 202), or the pulse width data. When there is no unused pulse width data DPL in the table (step 20
The above step 201 is performed until one of the states of 4) is reached.
Repeat steps 205 to 205. In this case, step 2
In 04, when the control unit 5 determines that there is no unused pulse width data DPL in the pulse width data table, the control unit 5 determines that the cable length L of the first signal cable cannot be measured. Along with the determination (step 206), the fact is stored in the internal memory, and then the signal line cable length measuring process is terminated and the process proceeds to step 103 in the balanced cable cable length measuring process.

After finishing the measurement process of the cable length L for the first signal line, the control unit 5 returns to step 103 in FIG. 2 and outputs the selection signal SSEL to the signal switch 3c.
Then, the internal circuit of the signal switch 3c is set to a state in which the inspection pulse SP1 can be injected into the other (second signal line) of the pair of signal lines in the balanced cable CB (step 103).

Thereafter, the control section 5 measures the cable length of the second signal line in the same manner as the first signal line according to the above-mentioned cable length measuring process (step 104).
In this case, when the cable length L2 of the second signal line can be measured, the control unit 5 stores the cable length L2 in the internal memory, and when the cable length L2 of the second signal cable cannot be measured, that effect is notified. Is stored in the internal memory.

Next, the control unit 5 refers to the measurement result stored in the internal memory after the cable length measuring process for the second signal line is completed, and refers to either the first signal line or the second signal line. Cable lengths L1 and L2
Is not determined (step 10).
5). When it is determined that the cable length L of one of the first signal line and the second signal line cannot be measured as a result of this determination, the control unit 5 causes the display unit 6 to display “the cable length of the balanced cable is measured. A message indicating "impossible" is displayed (step 106), and the cable length measurement process for the balanced cable CB ends.

When the control section 5 determines in step 105 that both the cable lengths L1 and L2 of the first signal line and the second signal line can be measured,
The measured cable lengths L1 and L2 are compared (step 107). At this time, when it is determined that the cable lengths L1 and L2 are different from each other, the control unit 5 causes the signal line name (identification data) of the signal line having the shorter cable length.
At the same time, the cable length is displayed on the display unit 6 (step 108), and the cable length measuring process for the balanced cable CB is completed. On the other hand, when it is determined in step 107 that both cable lengths L1 and L2 are the same,
The control unit 5 displays the cable lengths L1 and L2 on the display unit 6 together with the display indicating that the cable lengths L1 and L2 are the same length (step 109), and ends the cable length measurement process for the balanced cable CB.

Thus, this balanced cable length measuring device 1
Then, since the pulse width of the inspection pulse SP0 generated by the pulse generation unit 2 is configured to be expandable and contractable, for example, the balanced cable CB is long, and the injected inspection pulse S is
When the transmission / reception unit 3 cannot detect the reflected wave signal SR2 due to the large attenuation of P1 and the generated reflected wave signal SR1 (in the case of the waveform A in FIG. 5A).
However, as shown in FIG. 5B, the inspection pulse S
By sequentially extending the pulse width of P0, it becomes possible to maintain the waveform of the inspection pulse SP1 (see waveform B in the figure) at a voltage higher than the threshold voltage VTH,
The transmission / reception unit 3 can detect the reflected wave signal SR2. Therefore, the conventional balanced cable length measuring devices 51, 61
Even in the case of a long balanced cable CB that cannot be measured, the cable length can be reliably measured. On the other hand, for example, since the balance cable CB is short, the time required for the reflected wave signal SR1 generated from the injection of the inspection pulse SP1 to reach the input end is short, and as shown in FIG. Even when the reflected wave signal SR1 overlaps and the reflected wave signal SR2 cannot be detected by the transmitting / receiving unit 3, as shown in FIGS. 7B and 7C, the inspection pulse SP0 (in the drawing, the inspection pulse SP0) is detected. The reflected wave signal SR2 can be detected by the transmitter / receiver 3 by sequentially reducing the pulse width of SP1). Therefore, it is possible to reliably measure the cable length of a short balanced cable CB which cannot be measured by the conventional balanced cable length measuring devices 51 and 61.

Further, in this balanced cable length measuring device 1,
Using the signal switch 3c in the transmitter / receiver 3, the inspection pulse S is respectively applied to the pair of signal lines of the balanced cable CB.
By adopting the configuration of injecting P1, unlike the balanced cable length measuring instrument 51, it is possible to inspect for short-circuit failure or disconnection failure of each signal line without using the balun 53c, resulting in reduction of product cost. be able to.
In addition, the cable lengths L1 and L2 of the pair of signal lines in the balanced cable CB are configured to be individually measurable, and the signal line name with the short cable length and the cable length are displayed, so that one of the signal lines Only when there is a failure point and the other signal line is in a normal state, the signal line where the failure point exists can be reliably and accurately specified. Therefore, the balanced cable C
It becomes extremely easy to specify the faulty cable during the inspection at the time of laying B and at the time of the inspection at the time of occurrence of a failure.

The present invention is not limited to the configurations shown in the above-mentioned embodiments, and can be modified appropriately.
For example, in the balanced cable length measuring device 1, instead of the configuration in which the unbalanced pulse is injected into the balanced cable CB as the transmitting / receiving unit 3, the balanced pulse is injected like the transmitting / receiving unit 53 in the balanced cable length measuring device 51. It is also possible to adopt a configuration that does. When this configuration is adopted, the balun is used, so that the product cost is increased, but the pair of signal lines are inspected without selectively injecting the inspection pulse SP1 into each signal line by using the signal switch 3c. Since the application pulse SP1 can be injected at the same time, the measurement time can be shortened sufficiently. Further, as the control unit 5, when changing the pulse width of the inspection pulse SP0, instead of the configuration in which the pulse width data DPL stored in advance in the pulse width data table is sequentially extracted from the pulse width data table, It is also possible to adopt a configuration in which the pulse width of the inspection pulse SP0 is changed while sequentially obtaining the pulse width. Further, the signal switch 3c is connected to the transmitter / receiver 3
It can also be arranged outside.

In step 105 in the cable length measuring process of the balanced cable, the first signal line and the second signal line are measured.
When the cable lengths L1 and L2 of either one of the signal lines cannot be measured, the measurement impossible display is made in step 106, but the control unit 5 makes the first signal line and the second signal line in step 102 or step 104. When it is possible to measure at least one of the cable lengths L1 and L2 of the signal line, the control flow may be adopted in which the cable length is displayed on the display unit 6 and this process is terminated.

[0039]

As described above, according to the balanced cable length measuring device of the present invention, since the pulse generator is configured to expand / contract the pulse width of the inspection pulse, various balanced cables having different lengths can be used. The cable length can be measured reliably.

Further, according to the balanced cable length measuring instrument of the present invention, when the measuring section does not detect the reflected wave signal, the control section controls the pulse generating section so that the measuring section can detect the reflected wave signal. By controlling the expansion and contraction of the pulse width of the inspection pulse, it is possible to reliably and automatically measure the cable lengths of various balanced cables of different lengths.

Further, according to the balanced cable length measuring instrument of the present invention, one of the pair of signal lines in the balanced cable is connected to the output section of the transmitting / receiving section and the other of the pair of signal lines is set to the reference potential. By providing a switching unit for switching the connection and configuring the transmitting / receiving unit through the switching unit to enable transmission / reception of the unbalanced type pulse as the inspection pulse, since the balun is not used, the product cost is reduced. It is possible to reliably measure the cable length of both signal lines in the balanced cable.

Further, according to the balanced cable length measuring device of the present invention, the inspection pulse is injected into each of the pair of signal lines by controlling the switching unit, and based on each measurement time corresponding to each signal line. By calculating the cable length of each signal line by using the control unit so that the shorter cable length of the calculated cable lengths is determined as the cable length of the balanced cable, only one signal line of the balanced cable When there is a failure point and the other signal line is in a normal state, the signal line where the failure point exists can be identified reliably and accurately. Therefore, the faulty cable can be specified very easily during the inspection when the balanced cable is laid and when the fault occurs.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining a configuration of a balanced cable length measuring device 1 according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining a cable length measuring process of the balanced cable CB in the balanced cable length measuring device 1.

FIG. 3 is a flowchart for explaining a cable length measuring process of each signal line in FIG.

FIG. 4 is a voltage waveform diagram for explaining the detection operation of the inspection pulse SP2 and the reflected wave signal SR2 in the transmission / reception unit 3 of the balanced cable length measuring device 1, where (a) shows the input voltage waveform of the comparator 3d. The voltage waveform diagram shown in FIG. 1B is a voltage waveform diagram showing the output voltage waveform of the comparator 3d.

5A is a voltage waveform diagram showing the transition of the voltage waveform of the reflected wave signal SR1 when the balanced cable CB is long, and FIG. 5B is a reflected wave when the pulse width of the inspection pulse SP1 is widened. It is a voltage waveform diagram which shows the voltage waveform of signal SR1.

6A is a voltage waveform diagram showing a voltage waveform in a state where the balanced cable CB is short and the reflected wave signal SR1 overlaps the inspection pulse SP1, and FIG. 6B shows the inspection pulse SP1 in FIG. 6A. The voltage waveform diagram showing the voltage waveform in the state in which the inspection pulse SP1 and the reflected wave signal SR1 are separated by narrowing the pulse width of (1), (c) is a waveform diagram of the comparator 3d when the voltage waveform of (b) is input. It is a voltage waveform diagram which shows an output voltage waveform.

FIG. 7 is a block diagram for explaining a configuration of a conventional balanced cable length measuring device 51.

FIG. 8 is a block diagram for explaining a configuration of a conventional balanced cable length measuring device 61.

[Explanation of symbols]

1 Balanced cable length measuring instrument 2 pulse generator 3 transmitter / receiver 3c signal switch 4 measuring section 5 control unit 6 Display CB balanced cable SP0 to SP2 inspection pulse SR0 to SR2 reflected wave signal SSEL selection signal

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F063 AA17 BA30 BB02 BB05 BC08                       CA40 DA02 DA06 DD02 JA10                       KA02 LA09 LA15 LA23 LA29                       LA30                 2G033 AA07 AB01 AC01 AC04 AD10                       AE02 AF02 AG14

Claims (4)

[Claims] 1. A pulse generator for generating an inspection pulse, a transmitter / receiver for injecting the generated inspection pulse into a balanced cable to be inspected and for detecting a reflected wave signal of the injected inspection pulse, A measuring unit that measures the time from the injection of the inspection pulse to the detection of the reflected wave signal, and the pulse generation unit that controls the pulse generation unit to generate the inspection pulse and the balance based on the measurement time by the measuring unit. A balanced cable length measuring device comprising: a control unit that calculates a cable length of a cable, wherein the pulse generation unit is configured to expand and contract the pulse width of the inspection pulse. 2. The control unit controls the pulse generation unit to detect the inspection pulse until the reflected wave signal is detected by the measuring unit when the reflected wave signal is not detected by the measuring unit. The balanced cable length measuring device according to claim 1, wherein the pulse width is controlled to expand and contract. 3. A transmission / reception unit, comprising: a switching unit that connects one of a pair of signal lines in the balanced cable to an output unit of the transmission / reception unit and switches the other of the pair of signal lines to a reference potential. The unit is configured to be capable of transmitting the inspection pulse to the one of the signal lines and receiving the inspection pulse from the one of the signal lines via the switching unit. Or the balanced cable length measuring device described in 2. 4. The control unit injects the inspection pulse between each of the pair of signal lines and the reference potential by controlling the switching unit, and also controls each of the signal lines corresponding to each of the signal lines. The balanced cable length measuring device according to claim 3, wherein the cable length of each of the signal lines is calculated based on the measurement time, and the shorter cable length of the calculated both cable lengths is determined as the cable length of the balanced cable.