DE2039718A1 - Method and apparatus for supplementing a photographic developer - Google Patents

Description

"Method and device for replenishing a photographic developer"

The invention relates to the photographic complement Developer) to maintain its activity in a bath, i.e. in a container in which development takes place and in which activity of the developer material is weakened.

Various methods are known to supplement a bath of photographic developer "so that the activity of the Entwicklere is maintained. However, methods of this type are based on imprecise assumptions, such as a constant ratio of time to loss of activity regardless of changes in the average exposure and regardless of changes in the amount of treated per unit of time

109809 / U?

BATH ORIGINAL

Materials. You known processes also work incompletely, as far as the sampling or evaluation of the developer is concerned.

On this basis, the object of the present invention is to evaluate the sample photographic To monitor and control the activity of this developer.

It is intended to provide an improved display or monitoring of the activity of photographic material taken in the form of a sample Developers are enabled to identify changes and to allow additional developers to work can. It is intended to supplement the developer with the photographic developer as indicated in the activity and admitted according to the changes. A device is to be used to carry out the procedure to be able to perform automatically.

The invention is embodied in a method and apparatus for adding supplemental developer to a bath of photographic developer in which photographic material is being developed as indicated on a test strip of photographic material. The test strip of photographic material is developed using developer samples from the developer bath. In this way one obtains a compensation for losses in the activity of the developer, which occur through use, aging or other reasons . The addition of the components used to supplement Entwiokler s depends on the acceptance of the monitored, optical density rule successive, developed parts of the test strips * from. There is no xur supplement serving

10Ö90Ö / U7S

BATH ORIGINAL

Developer added as long as the monitored optical density a certain measure for the activity of the developer, which corresponds to a predetermined value, indicates. The amount of the replenishing developer actually added is intentionally larger than to compensate for the actual decrease in the amount of developer activity required when the acceptance is displayed in accordance with the monitored, optical Density.

Embodiments of the present invention are explained with reference to the accompanying drawings.

Fig. 1 is a schematic side view of the device according to the present invention in their position to a test strip photographic Materials;

Fig. 2 is another embodiment of components a device in position with respect to a test strip;

3 is an enlarged side sectional view of one of the device components of the previous views; showing a block body having an exposure chamber;

FIG. 4 is a perspective view of components of the FIG Fig. 3 shown device;

Fig. 5 is a top plan view of one using the device of the foregoing views;

10Ö809 / U78

U 3 9 7 1

Fig. 6 is a view of a slightly modified developed film;

7 is an enlarged side sectional view of a further component of that in FIGS. 1 and 2 illustrated devices showing a block body having a development chamber and a display chamber;

Fig. 8 is an enlarged, schematic view

a device containing the developer and associated components; and

Figure 9 is a schematic view of the electrical circuit of the present invention.

The object of the present invention is achieved by a controlled development of a photographic material containing a photographic object in a developer bath, in which the developer activity decreases or is exhausted when the developer is used. An improved method for supplementing or adding the developer is used, which is characterized in that a test strip of photographic material is exposed, that successive samples of the developer are removed from the bath within which the photographic material is developed, that Successive areas of the exposed test strip are developed with the successive samples of the developer, that the optical density of successive areas of the developed strip is flattened, and that the developer bath is added in accordance with the decrease in the sensed optical density to supplement the developer.

109809 / U78 " ⁵ "

The invention is carried out with the aid of a developer supplementing device which is constructed so that it comprises a device for exposing and developing a test strip of a photographic material, the developer being taken from a bath in which photographic material is developed. The device has an arrangement in order to be able to add developer serving to replenish the bath in order to compensate for a decrease in developer activity. Successive samples of the developer can be taken from the bath with a device. With the help of another device, successive areas of the test strip are developed using successive samples of the developer; the optical density of successive developed areas of the test strip is sensed. A successive to the decrease in optical density ranges responsive control device is used to the Ent wicklerbad serving for replenishing amount shall be included.

109809/147

^ 039718

ό -

1 of the drawings shows a test strip Io made of photographic material which is stored in unexposed form on a supply reel 11. The supply reel 11 is shown in Fig. 1 to the left in a partial view. From this supply reel the test strip Io runs over a roller 12, between an exposure block 13 and a pressure pad I ¹ I, between a development and display block 23 and a pressure pad 24, through the gap between a drive roller 27 and an idle roller 28 and onto the take-up roller 31, which is shown in partial view on the right side in Fig. 1 of the drawings. The corresponding pressure pads or pressure pads are elastically attached to leaf springs 15 and 25. The opposite end of the leaf springs is attached to a holding frame (only indicated schematically) with corresponding struts 15a and 25a. The idler roller 28 is rotatably mounted on a pivot arm 26; the other end of the swing arm is attached to the frame by means of bolts. The arm is tensioned in the direction of the drive roller 28 by a tension spring 29, which is attached to the central part of the arm. The drive roller is set in rotation by a synchronous motor 3o in order to convey the test strip in the direction of the take-up roller 31. The electrical feed is done with a pair of cables via external connection points χ and y, which are connected to the Mfcor. The electrical feed to the exposure block takes place via a constant voltage device 9 j while the development and display block is fed via a constant voltage device 19. The latter block has respective inlet and outlet lines 33 and 3 ¹ * for developer samples. Lines 33 and 3 ¹ * extend from the base of the block. The pressure pad 2Ί has a pair of electrical lines 37 and 38 which are connected to earth and an external point a. The effect of the

109809 / U78

20397 IS.

Components shown in Fig. 1 will be described in greater detail explained.

In Fig. 2 of the drawings, a structure substantially comparable to the device shown in Fig. 1 is shown; Some additional components are provided between the exposure block: 13 and the development, Si and display block 23. An additional Syndron motor 5o for the tape transport drives the drive roller 4? at. An idle roller 48 on a swivel arm 46 is resiliently in the direction of the drive roller 4? tense. In this way, a gap is formed for receiving and transporting the test strip Io made of photographic material. From there, the test strip is passed under an idle roller 52 which is located on a swivel arm 56. This pivot arm is biased by a tension spring 59 in such a way that the test strip is displaced from the straight path. From there the strip runs over an idle roller 58 which is arranged on a stationary shaft in the rectilinear path. A switching arm 61 of a limit switch 62 is also provided on the pivot arm 56. The limit switch 62 has a switch arm 63 on one side of the power line so that the switch is opened when there is enough slack in the test strip to allow extreme downward pivoting of the arm. The switch is closed when there is a minimum of slack in the test strip so that the arm can move to its extreme up position. The synchronous motor 3o for the strip transport in the vicinity of the take-up roller 31 is not connected to the external power connections in the present exemplary embodiment , but is connected to points i, e, as will be explained in more detail in detail.

The so-called exposure block 3 is shown in FIG. 3 of the drawings shown on an enlarged scale in sectional view. the

1 09809 / H78

^ 039718

Inner chimney of the block 13 has the shape of a cylindrical bore. At the lower end of the chamber there is a lamp 16, while a slit diaphragm 17 with a continuous slit and a slit diaphragm 18 with a central web (full-image and half-image diaphragms) are arranged between the lamp and the test strips above it. In Fig. 4 of the drawings, this assignment is shown in a perspective view without the exposure block. The pressure pad 1h is shown in broken lines in the raised position (with the leaf spring 15 tensioned), which makes it easier to insert the test strip over the open, upper end of the chamber.

5 and 6 of the drawings, developed test strips areas Io 'and Io "are shown which developed Have areas of variable density corresponding to varying exposure along the length of the strip. The one in the Wide variable track delimited by an opaque background, as can be seen from Figure 5 of the drawings is produced by applying a hard (high contrast) litho developer to a strip, which through the slot assignment shown in FIGS. 3 and 4 was exposed. A homogeneous area of variable density according to Figure 6 of the drawings is produced by exposure through a single, full slit corresponding to slit 17, which placed close to the lamp, after which the strip was developed with a soft (low contrast) developer. Both, the above methods or others can be used satisfactorily in the present invention.

In Fig. 7 of the drawings, the development and display block 23 is shown in an enlarged sectional view. the inner chambers of the block are formed by left and right, vertical bores 71 and 8l, over which a Pressure pad 24 lies. This pressure pad is also in

1 09809 / U78

/0.39718

dashed lines shown in raised position, the leaf spring 25 being tensioned accordingly. On the underside of the left-hand hole 71, the inputs are watertight. laßleitung 33 and Äuslaßleitung 34 'attached for the bore. The inlet line ends at the bottom of the bore, while the outlet line extends upwards in the direction of the The upper side of the bore extends and in a central opening 73 ends in a spacer 7o. This forms the development space 74 at the top of the hole. On the left and right edges, the spacer has a pair of gaps 72 on which developer gets into the development room. From this the developer hits the one in the slide opening of the spacer, as through the Line is indicated.

The display or measuring chamber, through which the test strip then extends, consists of a bore 81 in the Block 23 and from a bore 82 in the pressure pad 24 .. A lamp 83 is detachable by means of a seat 87 in the upper part the bore 8l held and has electrical lines; these electrical leads extend from the lamp through the bottom of the block to a constant voltage device 19. A filter 85 at the upper end of the bore 81, between lamp 83 and test strip Io (now developed and coated with a developer) attached, makes the transmitted light non-actinic to another exposure (and prevent development) of the test strip «, over of bore 82 and near the opposite side of the A densitometer head 84 is provided for the test strip from the lamp 83, the electrical photoresistor (R4, not shown separately) changes according to the light intensity when the light passes through the test strip will. The electrical lines of the densitometer are connected to ground and to a funct a, as shown in Fig. 1 and 2 of the drawings.

109809/1478

2Ü3JJ718

ίο

Referring to Figure 8 of the drawings, a bath 92 of developer in a developer tank 91 is shown. In the developer, photographic material, carried by a belt.9o, is developed as it is passed over sets of rollers including a drive roller 93. Line 9 ¹ J leads from the bottom of the container along a junction to line 34 which is the outlet line for the sample from the development chamber in the display block. A pump P is located in the line between this branch point and a branch point at which the line 33 branches off. This line is the sample inlet line for the test development chamber, thereby providing the desired circuit (indicated by arrows). Before the line 9k is returned to the top of the development container, it is constricted into a Venturi body 95 to which the supplementary line 96 is connected. The other end of line 96 is connected to a supply of developer replenisher 97 in reservoir 98. The line is widened in a flow chamber 99 between its ends. The interior of the flow chamber is constructed in such a way that by opening the valve Io3 which is electrically operated via the solenoid Io4, developer can be supplied at a flow rate which is indicated by a flow meter loo and which is adjustable by manual operation of the button Io2. The button Io2 is intended for the valve lol. The flowing at a certain speed or developer these supplementary developer flows from the container 98 through the conduit 96 and into the conduit 9 ¹ * where it mixes, in order to raise its activity in the container 91 'with the bath 92 of the developer. The pump is driven by a motor M, which is connected to support power connections x, y and is provided with manually operated speed controls. These have an indicator Io5 which is used for control.

109809/1478

2Ü397T8

As shown by connecting dashed lines, the motor M also drives the drive roller 93 to drive the photographic material carried by the belt 9o to transport the developer bath 92 "Likewise, an electrical alternating current generator G is driven", which "with the points i, e, also shown in Pig »2 of the drawings, connected. These are with the lines for the synchronous motor 3o of the strip transport in connection to the To supply the motor with power. The solenoid coil is connected to the external power connection point y and to the control point c connected, which is explained below in the course of the description.

In Fig. 9 of the drawings, the electrical control or circuitry of the present invention is essentially schematic and shown in block form. The control point e shown in Fig. 8 of the drawings is located at the right, outer power connection point x. On the left side of this View is an electrical comparator with a resistance bridge. The bridge consists of fixed Resistances R1 and R2 in the upper left and right arms and an adjustable resistor R2 on the lower left Poor; a photo-variable resistor R4 (not shown) des Densitometer head 84 is located on the right lower arm, as through the line to point a (also in Figs. 1 and 2 of the Drawings shown) is indicated. Electric voltage is generated with the help of the battery Bl across the bridge from the base (positive) fed to the top (negative); An activity meter AM is across the bridge as an indicator of the bridge compensation switched in the middle position. ~

On the lower right part of FIG. 9, triggering and carrier circuits 1 and 2 are shown in block form. Both circuits are entirely of conventional design and are excepted

10S809 / U78

■ 2Ü39718

the input and output elements are not described in detail. The circuits have corresponding input transistors T1 and T2. The base of transistor T2 on the right side takes the bridge output from a clamp on the left side of the bridge (slider from R2). Every these circuits is also provided with an output relay: RLl for the trigger circuit 1 and RL2 for the Trigger circuit 2. The relay RLl actuates the changeover switch Sl, which has arms Al, A2 and A3, while the relay RL2 the Ehfachsehalter S2 operated, which only one Arm A has. Both switches are shown with their switching arms in the normal position, which they assume when they by the rdais are not operated.

The corresponding switch arms connect as follows: Al connects with the capacitor Cl, which in turn connects to the left side or output side of the bridge manufactures. A2 connects to C2 whose other side is grounded and to R6 which to the negative terminal of the Battery B2 is connected. The positive terminal of the battery is grounded. A3 is connected to the connection point c (Fig. 8 of the drawings), while A is connected to the outer network point χ. The contacts that are in the specified rest position of the switching name are closed itself connected as follows: Al to one side of the diode D, the other side of which is grounded. A2 is with that normally open contact for arm Al and connected to low stand R5. This establishes the connection to the cfes base Transistor Tl. A3 (and A) have no contact. The normally open contacts for the respective arms are themselves connected in the following way: Al with the normally closed Contact for arm A2 and with resistor R5; A 2 to the positive terminal of battery B3 (its

1 09809 / U78

negative terminal is grounded.) A3 and A are connected to each other.

The method of operation of the device according to the invention is as follows: The test strip Io made of a photographic material is unwound from the supply reel 11 and is attached to the reference block 13 in accordance with the embodiment shown in FIG. 1 and FIG led along. There the strip is exposed by the lamp 1β. The test strip is then guided along the test development chamber 71 of the development and display block. In this chamber, the strip is flooded with a developer taken as a sample from the bath 92 (in the container 91). The photographic material is developed in the _{bath 92 9} located in the container 21, from which samples are taken. The developed test strip is then passed between lamp 83 and the density or densitometer head. The head senses the intensity of the light which is transmitted through the strip. This serves as an indication of the optical density of the strip before the strip is wound onto take-up reel 31. The sampling of the developer for the development of the test strip occurs continuously, with the continuous flow of developer samples being returned from the developer chamber 71 into the bath 92.

If the test strip is designed with sufficient density, the electric resistance (R4) is so high the densitometer 84, (due to the decrease of the transmitted light), that the bridge is in balance or something is moved outside of the equilibrium to the right. This is shown in a corresponding form on the AM activity meter. In this case, the output voltage on the line from the left side of the bridge to the base of input transistor T2 is the

1C9809 / U78

^ J 3 9 7 7 8

Trigger circuit 2 either positive, 0 or insufficiently negative to make transistor T2 conductive, so that it the relay RL2 is activated. This closed gate circuit prevents the addition of supplementary material serving for the developer, as can be seen in detail from the description.

If the developed test strip is not sufficiently dense, the transmission of more light reduces the photoresistor RH of the densitometer enough to shift the bridge to the left out of equilibrium. The resulting negative polarity makes transistor T2 conductive, so that it actuates relay RL2 and shifts its arm to the left. If the switch Sl is actuated or switched by the relay RLl while the trigger circuit 2 is in this open gate position, the circuit from the external network point χ to the solenoid 1ο4 is completed or closed when the arm A3 from the switch Sl and the arm A from switch S2 are in their normally open positions. Since the other side of the solenoid is always connected to the external network point y, the solenoid is thereby actuated in order to open the valve Io3, so that developer serving to replenish is added to the circuit located in the container or bath. Thus, the amount of supplementary compound added depends on the period of time during which both relays RL1 and RL2 are closed. If the bridge output to the base of the transistor T2 becomes positive and indicates that a predetermined level of activity has been reached, the transistor T2 terminates its conductive connection and the relay RL2 drops out. As a result, the feed of the valve solenoid is interrupted and the addition of the additional developer is ended regardless of the conductivity of the transistor T1. However, as long as the sensed activity of the

109809 / U78

Developer is lower than this so-called »plateau value, the addition of the supplementary material takes place at the same time as the conductive connection in the transistor ¹ Tl.

The switch Sl is periodically toggled by the relay RLl, whenever the base of the transistor Tl becomes negative, so that the transistor conducts. The speed of the Switching sequence or switching repetition is essentially determined by the time constant of capacitor C2 and resistor R6 controlled. Every time the switch S1 is thrown, the arm A2 connects the capacitor C2 directly across the battery B3s which positively charges its top plate. If so the relay drops out, arm A2 disconnects capacitor C2 and connects it through resistor R6 across the battery B2, which has opposite polarity o The positive charge runs off the capacitor until the base of the transistor Tl becomes somewhat negative again, after which the cycle bsw, the sequence repeated.

If the switch Sl by the response of the Seiais RLl is switched to the line in the transistor Tl and when the capacitor C2 by the movement of the arm A2 from the normally closed position in the normally open position removed from the transistor base or removed the arm Al replaces the capacitor Cl in the base master circuit. The capacitor Cl is in series with the bridge output line on the left side; if the sum of the potentials or voltages achieved in this way is negative, the transistor Tl is conductive until the charge on the capacitor Cl by the flow of the Ti base current runs off enough to essentially to reach the voltage of O, after which the The conductive connection is interrupted and the addition of supplementary material is stopped. The overall tension

109809 / U7

becomes essentially O and cannot become positive. if the switch is in the normally closed position, the capacitor Cl is connected directly to the diode D, whereby in the case of this polarity, but otherwise not the capacitor is short-circuited to ground.

The residual voltage on the capacitor Cl is maintained when the 0 voltage is reached when the switch Sl returns to its normal rest position, since the connection from this capacitor to the base line of the transistor Tl is interrupted and only replaced by a connection to the diode D. Wm If the bridge enausgan, g during the non-conducting period of the transistor is more negative, a negative voltage is achieved, and Total made the conduit. The conductive period of the transistor is essentially proportional to the magnitude of the total negative voltage and essentially as (in a conventional manner) as if the resistor R5 had been replaced by a constant voltage source. However, if the bridge output should become less negative than during the last time period, the total voltage becomes essentially zero and no conductive connection occurs.

Since the only variable in the bridge circuit of the photo- a resistance * (R ^) of the densitometer 84, which increases as it absorbs less light through the test strip and which decreases when it receives more light through the test strip, the change in the Bridge Cl output via a switching sequence proportional to the average rate of change in the density of the developed test strip and thus proportional to the average rate of change in developer activity taken from samples. The addition time (and thus the total time) of the developer added to each sample and used as a supplement is in the same way proportional to the rate of change in the

109809 / U78

Developing activity and not the extent to which the activity is changing. Whenever the rate of decrease in developer activity increases (or decreases), the system according to the invention responds immediately to this and triggers a corresponding compensation.

The manually operated control valve lol is set so that that the opening of the valve Io3 through the Solenoid Io4 occurring current is slightly higher than the total current the complementary mass sufficient to account for the actual decrease in activity since to activate the last, previous sample. This is essential because of the nature of the developer cycle and test development prevailing time lag. According to the invention, it should be avoided that wide oscillations or fluctuations occur in the development activity, in which the decrease in activity is promptly sensed and in which the addition of the supplementary material is proportionately proportioned according to the decrease in activity, while on the other hand the addition is avoided when the sensed activity reaches a predetermined so-called plateau value.

The test strip can be transported with the relatively simple structure shown in FIG. 1 or with the somewhat more complex system shown in FIG. 2, depending on the respective requirements. In any case, the entire web of the test strip is shielded from outside light until it is wound onto the take-up roll 31. The shielding is intended to avoid impairment of the individual test steps or examination steps. In the embodiment shown in Fig. 1 of the drawings, the test strip Io is substantially

109809 / 1UÖ

constant speed through the development chamber 71 transported (as well as through the exposure chamber in front of it and the following chamber with densitometer); the period of development thus has no special relationship for developing the photographic one carried by the belt 9o Materials. This development is usually a puncture of the Mfcors M's speed and attitude by a speed indicator Io5 (as well as a puncture of the entire path within the bath 92 from the entrance to the exit).

109009/1478

i039718

If there is a greater agreement or vote in the development times required or is not correct, can the För € shown in Fig. 2 eramordmmig for Use in which the test strip a through an additional synchronous motor 50 with a substantially constant Speed aa exposure day stoloek over- » - is run. Precautions have been taken that there is too much of the exposed film is saved, if the initial Transport speed the following tram speed, in the development and display chamber exceeds. It also ensures that the Exposure and the initially © transport of the tactile strip interrupted if the initial speed of the transport significantly exceeds the following speed. In this case the Swivel arm 56 to open the slack in the test strip, Ms the extent of the slack is sufficient to lower the swivel arm sufficiently to open the limit switch 63. This creates the electrical connection to the exposure lamp 16 and to the motor 50 interrupted. In this embodiment the exposed © test strip is exposed by the synchronous motor 50 on the development® and display block 23 moves along and becomes within the developing chamber 71 developed during a time proportional to the development time of the photographic material lies on the belt 90 in the developer bath 92, since the synchronous motor 30 does not have the same electrical, synchronous motor 50 supplied voltage is fed, but instead (see connection i, i in Fig. 8) via the alternating current generator G is fed. The alternating generator is in turn driven by the motor M, which also drives the drive roller 93 to

1098Q97H78.

BATH ORIGINAL

- 2o -

to transport the photographic material through the developer bath. To prevent the test strip from breaking Avoid, does not exceed the transport speed achieved by the synchronous motor 30 when the alternator G is running fastest, corresponding to the highest setting of the speed indicator 105 for the motor M, not the transport speed brought about by the synchronous motor 50. A system of this type in which the ™ Extent or the value of the indicated activity of the developer of the development time of the film to be treated is particularly useful in certain photographic work, such as those skilled in the art are common.

The present invention provides an improved apparatus and method for withdrawing photographic developer in sample form to determine the activity to monitor or display the same. The developer's activity is monitored for changes and for additional developer supplementation ^ to be able to admit in order to bring about a compensation. The supplementary mass compensates for the changes in the activity according to the level of the sensed decrease without exceeding an acceptable, predetermined value of the activity.

In Fig. 1 dargest & lte exposure block 13 can be united with the development and display block 23 in a single block body, with a corresponding reduction in the number of springs and Druckpoleter is achievable · single pressure pad or Druokauflagen, instead of the combined pressure Polstere 2k in

109809 / U78

used in each case ; a coil spring can be used instead of the leaf spring "Of course it can also other- 'elastic members -or other conditions have been applied.'

10980071471

Claims (15)

2039/18 PATENT CLAIMS . A method of replenishing a developer with controlled development of a photographic material in a bath of developer in which the activity of the developer is attenuated in use, characterized in that a test strip of a photographic material is exposed to successive samples of the developer from the developer bath in which the photographic material is developed, that successive areas of the exposed test strip are developed, that successive samples of the developer are developed, that the optical density of the successive areas of the developed test strip is sensed, and that the developer replenishes and refreshes Mass is added in accordance with the decrease in the sensed optical density. 2. The method according to claim 1, characterized in that the test strip is continuous at a certain speed transported through an exposure area and exposed to this, and that the strip in a subsequent Development zone is developed. 3. The method according to claim 1, characterized in that the test strip is transported discontinuously, but has a fixed degree of transport smoothness during transport that he is at that speed for exposure is passed through an exposure area and subsequently passed through a development area, the transport speed in the developing area being inversely proportional to the developing time of the photographic Material is. BATH ORIGINAL 109809/1471 -23- 2639718 4. The method according to claim 1, characterized in that the amount of serving to supplement the developer mass proportional to the rate of decrease in the removed optical density of the test strip. 5. The method according to claim 4, characterized in that the sensed optical density of a previously developed area of the test strip with the withdrawn optical Density of a previously developed area of the test strip is compared. 6. The method according to claim 4, characterized in that the amount used to replenish the developer is added periodically in proportional amounts. 7. The method according to claim 6, characterized in that the amount serving to replenish the developer is added at time intervals, and that the doffing speed is determined according to the last time interval. 8. The method according to claim 1, characterized in that. the amount of supplemental material added proportional to the removal speed of the sensed, optical density is measured and is more than the amount required to compensate for the decrease. 9. The method according to claim 8 _S, characterized in that the addition of the developer replenishment is interrupted if and as long as the photo-sensed optical density indicates an acceptable, predetermined level of activity. 10. Device for adding photographic developer, characterized in that a test strip is photographic Material is developed with developer from a bath in which a photographic material is developed is that by means of a device to complement the 109809/1479 2Ü39718 Developer-serving mass is added to the bath to compensate for the decrease in developer activity that successive samples of the developer are taken from the bath that successive one by means of a device Areas of the test strip are developed using consecutive samples of the developer that the optical density of consecutive developed areas of the test strip was sensed by means of a device and that by means of a control device responsive to the decrease in the optical density of successive areas the addition of the developer supplement for the developer bath is brought about. 11. The device according to claim Io, characterized in that in that the control device comprises means for adjusting the sensed optical density of an immediately before developed test strip area with the optical density of the last developed area in front of it and to determine if the last optical density sensed is less than a set, more acceptable Value of the activity. 12. The device according to claim 11, characterized in that the comparison device is an electrical resistance bridge and means for generating and applying an electrical signal to the bridge, the signal indicates the sensed optical density of an immediately previously developed area of the test strip, while a Another electrical signal is the sensed optical density of the developed area of the test strip in front of it indicates, and that this device generate an electrical signal which is used to display the difference between the corresponding Signals is used to add the ent- 109009 / U78 21) 39718 ' to operate winder supplement serving device so that Complementary mass is added to the bath when the last sensed optical density is lower than that previously sensed optical density. 13. Apparatus according to claim 12, characterized in that an electrical gate with an electrical trigger attitude which is biased by an electrical signal that this signal is indicative of an acceptable level of activity of the developer serves that a relay responds to the output value of the trigger circuit and the actuation the device used to add the developer supplement prevented when that serves to indicate the sensed optical density of the immediately previously developed area Signal indicates that the prevailing activity is at an acceptable level. Ik. Device according to claim 12, characterized in that the control device also has an electrical trigger circuit which is optionally switched into conductive and non-conductive position, that the generated signal is applied to it by means of a device, that a relay responds to the output of the trigger circuit and the actuation the device used to add the developer to the bath is prevented when the signal used for the sensed optical density of the immediately previously developed area of the test strip indicates an optical density at least as great as it corresponds to the optical density of the previously developed area of the test strip . 15. The device according to claim 14, characterized in that that the change in the signal is proportional to a switching sequence is to the average speed in the change in optical density of consecutive areas of the developed 109809714 Test strip and thus proportional to the average rate of change in sample form withdrawn developer activity. 1098Ö9 / U7Ö