DE1773227B2 - Photometric measuring method and device, especially for determining the absorption of a blood sample - Google Patents

Description

The invention relates to a photometric measuring method, in particular for determination the absorption of a blood sample in which proportional Separate measured values for the light transmission of a reference body and a test body are generated photoelectrically, which are stored and compared and the comparison of the measured values supplies the measurement result, as well as to a device for carrying out this method.

Such a photometric measuring method is already known from FR-PS 1 199 483. Disadvantageous is in this known method that both the measured value for the reference body and for the Specimen is stored. Two storage capacitors are used for storage. The separate control this memory and the need to use two memories require one unnecessarily high construction costs. The measurement result from the two measured values to be compared becomes formed by comparing potentials on both storage capacitors. The two storage potentials are fed to a differential amplifier. As long as there is a potential difference, from This amplifier is driven by a servomotor for the wiper of a potentiometer. These storage capacitors must be connected to discharge resistors. Even if the time constant of this formed /? C-circle is chosen to be very high, a discharge of the Storage capacitors take place, at least when a relatively long time is necessary Move the wiper of the potentiometer into the adjustment position. It will thus be necessary from that The comparison body or the test body should not only take one measurement, but several times in a row to carry out such measurements, so that new measured values are always stored in the storage capacitors can be entered. In this known measuring method, this formation of measurement results is unnecessary large expenditure of time. Especially when serial examinations of test specimens are carried out should be, but the shortest possible measurement times for each individual specimen are desired.

From Kortüm, colorimetry, photometry and Spectrometry, Springer Verlag, 1962, it is known in so-called single-beam photometry for the reference body and to generate only one measured value for the sample and to generate the larger measured value to save. For this purpose, the measuring instrument is set to 100.degree. I) when measuring the reference body performed. However, this known method can be applied to that described at the beginning Do not use the measuring method.

The invention is based on the object of the above-described measuring method improve that the measurement result can be obtained more quickly and easily. In addition, this should Process executing device be cheaper to manufacture.

The invention solves this problem in that only a single memory for storing the larger Measured value is used so that the memory is emptied when the smaller measured value is generated until the stored value equals the smaller measured value

ίο is, and that from the duration of the emptying of the memory the measurement result is determined.

The measuring method according to the invention offers the advantage that the measurement can be carried out relatively quickly is, the measurement result from a time measurement for the discharge of the memory from the stored larger measured value is obtained for the smaller measured value.

The device for carrying out the method according to the invention with a photoelectric transducer, a measured value storage device, a measured value comparison device, an output device for the measurement result and a control device for the device stages is characterized in that only a memory in the form of a capacitor for charging to the larger measured value potential is available is that a discharge circuit can be connected to the memory, that a control device is present that the discharge circuit switches on and off time-dependent, that a circuit is available, connected to the memory changes its switching states depending on the discharge time of the memory.

Such a device, which works according to the method according to the invention, can be relatively cheap can be set up, since only a single memory for both the sample measured value and the comparative measured value necessary is. Processing by comparing these measured values can also be carried out without any structural effort.

The method and apparatus according to the invention is particularly advantageous in the determination the hemoglobin content of a blood sample can be used, but not for this application limited. As is well known, hemoglobin is an iron-containing protein pigment that is found in red blood cells found in humans and in many other forms of animal life. The relative amount of hemoglobin in a blood sample is one of the most important parameters that determine the diagnosis and used to treat various diseases and conditions, such as anemia. Known methods for determining the hemoglobin content consist of hemolyzing the blood, to break down the red blood cells and release the hemoglobin from inside them, and then treating the suspension obtained with a suitable reagent. An international one Hematology Committee has established standard values. The standard for measuring hemoglobin using a particular wavelength of light is defined by the formula

HGB = 36.77 D = 36.77 log ₁₀ 100 / Γ (I) in which

HGB is the hemoglobin in grams per 100 ml, D is the optical density or absorbance a :;

540 nanometer light in a length of 1.00 cm and
T is the percentage of light transmission

is. D above is equal to the logarithm of the following blood samples. In the following BeBasis 10 of 100, divided by the percentage notation of the invention, the reference measurement of the transmittance of light is given. The selected medium representing signal as of the higher voltage wavelength can be described by using more specific than that of the sample and first obtained the filter, the length of the beam can be supplied to 5 memory circuit. This is the case when a factor in the results sets the reference medium to have a higher light transmission, and the function is logarithmic. than the sample medium has. However, the invention is

Advantageous embodiments of the invention are also capable of working if the relative optical seals

ben from the subclaims. tegrade are reversed and first the measured value of the

The invention is converted into io Probe below with reference to FIG.

Embodiments shown in the drawing As in FIG. 1 shows a memory circuit 12 with

described in more detail. In the drawing, the transducer 10 shows through a line 14

F i g. 1 shows a block diagram of the device according to which the two cells R and S are coupled

an embodiment of the invention. The memory circuit is provided so that

FIG. 2 shows a simplified electrical circuit diagram of FIG. 15, first the output from the reference cell R to genomin F i g. 1 shown embodiment, men and stored. Since the reference medium

F i g. 3 A and 3 B diagrams on the storage location- coloring density is relatively low, only finds

treatment according to Figure 2, operated after two slightly a slight absorption instead of so that a signal

different modes, converted from a relatively high value

F i g. 4 a block diagram of a device according to ao and the memory circuit 12 is supplied,

a second embodiment of the invention, with the memory circuit 12 is a receiving

F i g. 5 a simplified electrical circuit diagram of the circuit 16 coupled by an output line 18. Embodiment according to FIG. 4 and pelt. The receive circuit is during delivery

F i g. Fig. 6 is a diagram showing the voltage at the signal from the reference cell, R to the memory tray at various points in the device of Fig. 5 to device 12 ineffective, but is during the supply shows consecutive times. of the signal representing the sample in cell 5 the

It is first referred to FIG. Referred to 1, unlocked in the receiving circuit so that it can be used as a derivation

which in block form an electro-optical measured value for that stored in the memory circuit 12

converter 10 is shown. This measured value uni reference signal is effective. This control is through a

Converter can have various forms and converts control device 20 via its output line 22

process different types of inputs in order to be enabled, which can be used as control input via the

To achieve the goal, namely the delivery of two interception circuit 16 is used. The control device is in

successive electrical outputs, from reality an automatic programming center,

which one the translucence of a cover which the various functions in the full-

mediums while the other controls the automated lighting system. Through a switching line

represents permeability of the diluted blood sample. In device 24, the control device also regulates which

a simple form can be a photoelectric of the cells R or S through the converter circuit

Cell and an illumination source operated in opposite order within the transducer 10

set sides of a narrow channel is firmly arranged.

The output 22 of the control device is the one R and then a sample cell 5, which shares the input of a control circuit 26, so that a thin blood sample contains the reference line, both the receiving circuit 116 and the The control can also contain a volume of a diluent containing circuit 26 during the transducer conversion, which in turn can be the conventional saline hemoglobin reagent and 45 which is simultaneously triggered and preserves the contents of the sample cell S. The control circuit 26 has a content of hemolyzing material. A dilution 28 coupled to the venting input E of a means of such a composition is bistable device 30 Illumination passing through a line 32 is absorbed. 50 coupled. In this way, the bistable pre-through the use of a volume of the dilution direction is switched to the onward state if the signal from the sample cell of the storage circuit is fed to a common diluent source as a reference value and through the use of the signal from the sample cell, and after a period of time, which both the Bezugszeiie as would also the sample to the difference between the density of the Bezugsmezelle S changes the optical density of 55 diums and that of the sample medium proportiodes diluent due to its composition is nal switched into the blocking state, pollution, temperature, etc., no fundamental If desired, the output from the bistable precursor, direction 30 of an analog form of a registering device, which is continuously controlled with regard to its measurements in the comparative color monitoring

In a simple form of the transducer 60 measuring device 34 are supplied. Otherwise odei 10 can either simulate a dilution - even jointly the time-dependent output of the reference filter, air, clear water or an input from the bistable device can be superimposed on a pulse of the reference medium or another reference subgenerator 36 and then as a series of pulses instead of the fluid volume, stamp the diluent in a printer 38 or another digitally can be used by means of. A more complicated shape 65 oriented output device can be created, of the transducer works according to the principle The schematic representation of FIG

Transducer 10, the ~,

the receiving circuit 16 and the 26 which members are marked by dashed lines, «,. u» »-« - are. In the reader context, daxauf is point out that this electrical circuit arrangement is greatly simplified, but sufficient should be an appropriate application to the skilled person to give after the an equivalent assembly that was put on the market can be easily built. The primary electrical components: - within

of the converter 10 are a photo cell 40

and a current-voltage converter

42. Only one photo cell is required

Reference and sample cell /?

Equivalents mechanically to the

be transferred or themselves

to an optical system *

via the control device 20 a

Stimulation of the photo cell 40 by d

causes. Of course two can

assigned

f £ _a rester Ano <ü

^15th

is Leet The capacitor 46 is therefore discharged via the Wisand 48 and the transistor 50 _to who. _Furthermore , the bistable device 30 is actuated in the same way as the control circuit 26

early, _{nter transistor is} 52.

a gee g ^ P ^^ ^ _M

Hemoglobin performing in the sample clamping ^ n ₈ leads, the transistor 44 the line status has not been driven to the second Ma Γη This is due ^^ ^ fact that, brought to the capacitor 46 charge due to the Umwandde s _elleninha i _th greater than the tension

is, which is now fed on line 14, so ^ _{transistor 4} 4 is blocked. However, since capacitor continues to _discharge through resistor 48, the difference ^ base voltage increases in the emitter _voltage of the transistor chip 44 as long s voltage on the emitter sufficiently low P ^ ^ _{hemoglobin verurS} eighth Ba ^ tung state _{the transistor in the Lei}

can bring. The duration of the capacitor discharge s proportional to the base voltage that is used for the The hemoglobin content of the blood sample is inversely proportional

^ & ^^^ SSSZ ₂₅ ^ Ve ^ the transistor 44 brought back into the control room meter changes between the two monitors * ₅ ^ _n J, he changed the level of the

1 « ^

, V mt

+ / and a conventional ^Ä J; ^G ^ _H ^d ground capacitor 46 undf stand 48, which allows access to the output. The initial on aden gate occurs when the photocell 40 lighting is excited, which passes through, and the line 14 sets a controlling. This has become conductive to ^ transistor 44 is coupled whereby capacitor ^ Because the ^ bistable devices vorderflanken- or j can be fiankenempfindlich, which means stood that the transistor 44 is now lertend ^ f ^ l that 32 em disable signal is gen übema_ from its output . The transducer 10 responds to every representation of the reference cell for a short period of time. Goodbye W ra

the capacitor on the relative. ^We £ ^ f £ J which is proportional to the permeability ^ IS ^ o

Absorption of the reference media. Although the word 48 indicates a discharge path, a tnt charge is prevented because the reception patterns, 16 * e of a square wave, are reversed from the device 30. _{This duration can} easily be regulated.

^^ ^ ₁ and / or digital _{outputs through her che Mittdj beispi} el _{S as} of the type shown in m Fig. 1, convert. Although m Fig. 1 ^ _{2 is not} shown, the locking of the bistable _{Vorrichtu 30 or} even the second Entspen-en ^ may _transistor 44 tnggern _n ^ _{control device by geeigri} ete jerk coupling to a _feminine he! To initiate the work cycle of the same in order _{to monitor and convert the contents} and a further blood sample as successively. Of course, during the generated Ar _{the capacitor m will have the} same discharge

_αια5 ^ _{ι & η (1} , which he initially owned

In Fig. 3 A and 3B typical capacitor ^^ are _{shown F} 3 ^ _represents ^ _€

_The method of operation _{already described shows which capacitor is} initially charged to a value ^ _{(S au {due to the} reference cell)

I ^ ^ ^ ^ _{a w F (due} to the

_{above A} voltage) discharged dD

Direction 20 your programming values ^ ^Q via the circuit 24 the response _{formulas can be} found that

14 laid tension

will the

Zugsmediums is a constant, while the function amplifier is coupled via a line 116

Grams per 100 ml of the sample equate to pelt. Therefore, the inputs are both of the

15.95 / amplifier 112 and circuit 118 in

_RC V 'of a voltage sequence relationship. The starting page

, ^{5 of} the circuit is through a line 120 with a

Similarly, if a digitized first side of a controlled switch 122 is coupled

Output when using a pulse generator and through a line 124 with a receiving

of the in F ι g. 1 is used, the circuit 126. A memory circuit 128 is with

Hemoglobin content can be calculated as follows: a second side of the controlled switch 122

k-fp-t (4) ^{10 connected by a} line 130. The arrow heads

,,,. ,, for lines 120 and 130 represent the fact

in which /: is a precalculated constant representing that the memory circuit 128 via the switch

Depending on the standard values used, the fp charged the 122 and subsequently by the same

Frequency of the pulse generator is and; the off switches to the receiving circuit 126 are discharged

walking time. In this way, the pulse can

The frequency can be adjusted so that a simple relation- An output converter 132 is through a line

there is an increase in hemoglobin concentration. At- 134 coupled to the output of amplifier 112

for example, one hundred pulses can produce 1 g of hemoglobin. A control device 136 provides a

bin represent 100 ml of sample. Line 138 a control input to the output

FIG. 3 B differs from FIG. 3 A in that 20 converters. A switching line 140 optionally regulates, as a two-stage reference sample method, which of the cells R or S is changed by the measured value. Initially, the transducer 110 is monitored while it is being operated. The control device converts a completely clear or btenkes medium, also regulates the status of the controlled switch, such as air or water. This has the consequence, symbolized by a control line 142,
that the capacitor to the value yon some charged K, ₂₅ The operation of the g in Fi. 5 is the straight line shown, which is higher than the value V _R. It is then in a very short summary as follows: the reference cell is optically monitored and the receiver initially selects the control device 136 the peripheral circuit 16 toggled. Since Κ «lower than K ₈ reference medium converting /? and closes is, the capacitor begins at t _b zu.entladen switch 122 so that one of the light transmitting which is earlier than r ₀ The control circuit is, however, 30 of the reference medium voltage proportional getnggert on only after the voltage V _KC to the amplifier 112, the circuit 118 and the value V _{R has} fallen. Switch 122 of the memory circuit 128 is supplied

The only electrical changes that are needed. The control device opens while the switch is manoeuvrable to carry out the working I ₂₂ shown in FIG. 3B and selects the sample S for conversion of the measured values. ₃₅ The sample has a lower light transmittance Js common output 22 from the control device to the reference medium R, so that it is unlocked via the amplifier and a third monitor 112 and the biasable circuit 118 marked position (blank) for the circuit 24 shown voltage is lower than that seen in the memory. Assume that the gestn circuit 128 is stored. Then the before te rectangle Λ in Fig.l both mechanical 40 control device closes the switch 122 and allows parts of this modified reference cell to contain. Furthermore, a discharge from the storage circuit? It is assumed that the transducer 10 is the controlled switch to the receiving circuit 126. The necessary mechanical and optical discharge equipment remains of importance until that includes the necessary monitoring and rela- storage circuitry located on the same lower tive arrangement of the reference and sample media to 45 potential as that gives way to really enable. As mentioned, the Meßwertum- the sample may comprise 5 umwandeltwird ^hinsichthch transducer 10 monitors two (or even during the discharge period of the prestressing ^ l ^d "f ^ ^{n" for} - ^d e f ^delivery ™ S ™ y, so that the bare circuit 118 to be blocked before

tzssr ^{Line 14} «£ ^ s? ^ J ** £% ^

should be. Circuit is balanced again, the

In Fig. 4 is a second embodiment of the Eende Einoano for ΓΤπ Γ

finding shown. For the sake of simplicity, the UmS ^ l ₃₂ ^ iRt H " ^U ™ ^Setzer ^ taken, assumed that the transducer 110 was the 55 er Wegw iZ * ^dlC ? ™ ^eT > ^{while we ] che} \

! Same as the previously described measured value - the UnSsSed ü? * « ^E measurement, st proportional

converter 10 is Mi? the output of the measured value tZn ^ B ^ J ^ T

umwandle «110 is an arithmetic or function conversion of course a dirpVt" _{mmr (} ;

more strongly coupled 112 via a line 114. The “SowÄS _P ^? Γ
The arithmetic or function amplifier is in its 60 deals

construction designed in such a way that after a voltage sequence, the details of the device according to the invention

mode arbe, tet so that its output voltage can be determined by the schematisThe D ^ Sng m ^

the line 116 close to the entrance on the line in connection with the SZT W

114 follows. The arithmetic or function strength? Fig. 7 ^ s ^ L ^

^^^ X & s ^ ^{m 65} ^ iÄ ^k r ^b r ^tion T ⁱⁿ

A biasable circuit 118 is on its iHSS interface
The input side is only the output of the arithmetic or endeavor that they represent

12th

The primary electrical components inside indicate the voltage on the memory circuit 128 , the transducer 110 is a photocell which has a capacitor connected to ground. 144 and a current-to-voltage converter 146. As can be seen, the memory circuit and the output line 114 containing an isolating and stabilizing receiving circuit form a conventional RC-GYicd.
lization resistance 148 and a node / !. 5 Although the switch 122 is normally open. The node A and other nodes that are shown, it is at the time < ₀ by which are identified in more detail below, control device 136 are closed, so that the voltage comparison of different points in the + 10-V -Voltage at nodes A , B and are shown schematically with similar and with C also applied to the charging circuit and marked waveforms in F i g. 7 there is therefore also a voltage increase at node D in relation to this. For example, assume that there is a po- of + 10V. Environment for the purpose of Beschreisitives 10 V signal by the Meßwertumwandlung the typical voltage drop across the vordes reference medium R was generated and that the tensionable diode 118 for simplicity non-Meßwertumwandlung the sample S is a positive Si- taken into left, however, is as can be seen, results in a signal of only 5 V. Therefore, at t _t in FIG. 7 at 15 time f ₀ the voltage at node B is higher than the waveform at node A, a voltage than +10 and is, for example, + 10.6V.
of + 10 V, which shows that the light- First, the content of the output wall transmittance of the reference medium is then not described by the lers 132 and only mentioned that photocell 144 is measured. at its input a diode 152 normally

The node A is coupled to the positive (+) input ao by the positive voltage at the node in the input of the functional amplifier 112. This is operated in the reverse direction, which voltage amplifier is symbolically shown instead of near- higher than that which is symbolized by the circuit details, since numerous forms of positive voltage source, which can be used by circuit arrangements in the output converter. Therefore, as long as they are operated in a voltage _{follower mode at time ί 0} during the measured value conversion of the so that the voltage at the node reference medium R of the output converter is blocked, pointB in the amplifier output line 116 is very As can be seen from the following which exactly follows the voltage at node A. Span output converter 132 is only unlocked when there is a negative potential at the voltage follower functional amplifier corresponding to this node, ie between the two criteria in that they see an almost infinite time t _s and f ₄ .
Input impedance (of the order of magnitude of the time f, the control device 136 delivers 100 megohms) at the lowest load, a special signal on the line 142, so that the switch of the low output impedance (of the order of 122 opens and the memory circuit 128 of the voltage of 1 ohm) and a high level of reinforcement remaining circuitry is isolated. As in factor have. The illustrated amplifier 112 is a 35 FIG. 7, the voltages across each of the trim differential amplifiers remain constant and have a negative node. At time t, the input (-) is fed into negative feedback from a node sound line 140 of the control device in the position C. Even a change of a few milliliters is brought to the sample S and, furthermore, a blocking signal volt between the two inputs results in to the output transducer via line 138 that the output stably gives from the full negative to 40 to give switching surges in the event of an undesirable full positive saturation. In this form, to prevent triggering of the output converter,
the amplifier has negligible attenuation. Since the sample S allows a smaller amount of light to pass through and is well suited for its task, which allows it to pass upright, a lower voltage follows, while maintaining the voltage at nodes A, B at + 5V, than at Keep node A am and C on the same level. This is 45 node B so the diode of the circuit is shown at r ₀ on waveforms A, B and C. 118 is operated in the forward direction, whereby

Although other and simpler forms for the node C are also brought to + 5V

Voltage sequence circuit arrangement is used.

It is recalled that the precision achieved by the switch invention would suffer. It is 50 122 opened at time t _x and even possible at time for nodes A and B to remain open immediately at t “. At time f _s , the bar is to be connected to one another or to be reunited with one another to switch 122 by the control device, but stability and accuracy would be closed, which would result in significant reactions. be less than desirable. The nodes C and D, at which different

The biasable circuit 118 has a 55 voltages are coupled together diode that is coupled so that it passes through the chipboard. The node C will continue to be the voltage at the node B in forward direction and + 5 V from the transducer as 110, Verdurch supplied to the voltage at node C in Sperrich- more 112 and the circuit 118 is operated austung. Feedback is taken from the Kno when circuit 118 is driven reverse bend point C to the negative input of amplifier 60, as will be described below. The 112 exists via a line 150. The line 124, node D can only draw off the voltage stored in the memory circuit coupling, both the node C and the line 128. At the time 120 with the receiving circuit 126, which discharges at a point r _s , the memory circuit therefore has a resistance connected to ground. via nodes D and C into the resistor

A node D and node C are 65 to the receiving circuit 126 and to ground. This has the consequence that the voltage at node C on switch 122 and are connected to switch 122 through the + 10 V line and then connected to clasps 130 and 120 at the same time. The node D voltage at node D drops to ground.

As soon as the voltage at the node jumps to a small discharge from the reference level to the sample level + 10 V, the biasable circuit is obtained, which operates in the reverse direction in an equivalent hemoglobin calculator, whereby a signal for the sample can be converted,
Teleable connection from the node to the node What the circuit arrangement of the output umtenpunkt C is prevented. At the same time, the converter and its mode of operation, the feedback line 150 brings a significantly different voltage when the diode 152 is operated in the forward direction than that which is applied to the line 114, current from the base of a transistor 154 is applied to Amplifier 112. The radio is distorted so that it is not conductive and its stronger is therefore driven to saturation, and its collector voltage goes positive. The positive output voltage at node B drops to generally the collector voltage becomes the basis of a unijunc- 5V. This has the consequence that the diode 152 in the tion transistor 156 is fed so that this conductive output converter 132 is operated in the forward direction and will love an output to an integrator 158, whereby the converter is unlocked. f ert. The integrator is for the duration of (r ₄ - 1 ₃ )

During the time between f ₃ and t _{t, they} are effective and deliver a at its output 160

Tensions as shown in Fig. 7 At the time f ₄ 15 analog value of the hemoglobin content to the further

has the voltage at node C down to + 5 V- processing by a suitable not shown

sounded, which value also aem negative one establishment. A transistor 162 is at its base

output to amplifier 112 via the feedback to the interlock signal line 138 connected to a

line 150 is fed, and the same voltage - unwanted switching on of the unijunction transi-

The flow rate is transmitted via the input line 114 to prevent the 20 stors during the time t _2,

positive input of the functional amplifier trains- So early after time r ₄ , as mechanical

leads. This makes the inputs of the radio feasible, can the reference medium /? again

tion amplifier adjusted so that this except by the control device for the beginning of a

When saturation comes, its output voltage can be selected from f ₀ to i ₄ at the Kno further duty cycle.

ten point B jumps back to + 5 V and the diode 25 It can be the same or different samples

152 in the output converter again in the lockout during each cycle or on a periodic basis

operation is operated, whereby the further operation of the or alternate basis depending on the programming

Converter is prevented. In this way, tion of the controller and the needs

a measurement of the exact point in time of the user's span can be analyzed.

For this purpose 3 sheets of drawings

Claims (17)

Patent claims: 1. Photometric measuring method, especially for the determination of the absorption of a Blood sample which is proportional to the light transmittance of a reference body and a test body separate measured values are generated photoelectrically, which are stored and compared and the comparison of the measured values provides the measurement result, characterized in that that only a single memory is used to store the larger measured value, and that the memory is used when the smaller one is generated The measured value is emptied until the stored value is equal to the smaller measured value, and that the measurement result is determined from the duration of the emptying of the memory. 2. Device for performing the method according to spoke 1, with a photoelectric »o transducer, a measured value storage device, a measured value comparison device, an output device for the measurement result and a control device for the device stages, characterized in that only one memory (12, 128) in the form a capacitor for charging to the larger measured value potential is present, that a discharge circuit (16, 126) can be connected to the memory, that a control device (20, 136) is present that switches the discharge circuit on and off depending on time, and that a circuit ( 30, 118) is connected to the memory (12) which, depending on the discharge time of the memory, changes its switching states. 3. Apparatus according to claim 2, characterized in that the memory (12) with a comparison device (44) is connected for the comparison of the stored measured value with the non-stored measured value and this comparison device becomes effective when the compared Measured values are of the same size. 4. Apparatus according to claim 2, characterized in that the control circuit (20) with both the discharge circuit (16) as well as with the circuit (30) is coupled to this simultaneously with the formation of the measured value not to be saved. 5. Apparatus according to claim 4, characterized in that the circuit is a bistable device (30), the blocking input (D) of which is coupled to an output (32) of the memory (12) is (Fig. 1). 6. Apparatus according to claim 5, characterized by a pulse generator (36) and a therewith connected coincidence gate (AND), which is also connected to the bistable device (30), where, if the inputs of the coincidence gate coincide, the one output by the pulse generator Pulse series is allowed to pass, the number of pulses being a measure of the transparency of the Sample medium is. 7. Apparatus according to claims 2 to 6, characterized in that the discharge circuit (16) has a has an electronic switch (50) which has an output S3 connected to a reference potential possesses (Fig. 2). 8. Apparatus according to claims 2 to 7, characterized in that the memory (12) consists of a biasable, electronic switch (44), one input (14) with the transducer (10) and the other input with a fixed potential source (+ V) is connected to a C element, the capacitor (46) of which is connected to one output of the biasable switch and whose resistor (48) is connected at one end to the aforementioned one output of the biasable switch and thus to the capacitor ( 46), while the other end of the resistor is connected to the discharge circuit, while the other output (32) of the switch (44) is connected to the bistable device (30). 9. Apparatus according to claims, characterized in that that the switch is a normally non-conductive transistor (44) which is so switched is that it becomes conductive through one measurement signal and through the subsequent other measurement signal is blocked until the storage capacitor (46) via the resistor (48) to a Has discharged value which is below that of the smaller supplied measurement signal. 10. Apparatus according to claim 2, characterized in that the circuit is formed by a biasable circuit (118) which is arranged between the transducer (110) and the memory (128) , and that the control device (136) the discharge circuit (126 ) holds unlocked while the measured value not to be saved is being generated. 11. Apparatus according to claim 2 or 10, characterized by an output converter (132) which is connected to a node (B) which is located between the transducer (110) and an input to the circuit (118) , which output converter to a Can respond to change in the state of the circuit. 12. Apparatus according to claim 11, characterized in that the biasable circuit has a first diode (118) and the change in state depends on the bias state of this diode, that a second diode (152) forms an input stage for the output converter (132) and that the two diodes are polarized opposite to the node (B). 13. Apparatus according to claim 12, characterized in that the memory (128) and the discharge circuit (124) together form an A-C element and the output converter (132) has an analog structure which is actuated by the second diode during its response time. 14. Apparatus according to claims 2 or 10 to 13, characterized by a voltage amplifier (112) which is arranged between the transducer (110) and the input of the circuit (118) . 15. Apparatus according to claim 14, characterized by a Rückkopplungswcg (150) for the voltage amplifier (112) which is connected to the output of the circuit (118) and an input of the voltage amplifier. 16. Apparatus according to claim 15, characterized in that the voltage amplifier (112) is an operational amplifier constructed as a symmetrical differential amplifier and the feedback path (150) and the transducer (110) are connected to two separate inputs (+, -) of the amplifier mentioned. 17. Apparatus according to claims 2 or 10 to 16, characterized in that daf; the control device (36) actuates a controllable switch (122) which is arranged between the discharge circuit (126) and the memory (128) .