DE2327497C3 - Detector for changes in resistance with a downstream alarm device - Google Patents

Description

The main reason for this is that the detector constantly monitors itself as a whole and in the event of failure and / or change of a circuit part or circuit element issues a message. So can can not be differentiated when known, if the vibrations are fanned or stop, whether this change of state is actually due to a change in the (to be monitored) physical Size or can be traced back to the detector or its components. To check the operational readiness at most a measure comparable to the fire test described in connection with CH-PS 4 68 683 would come into consideration, im Case of DE-AS 14 66 554 thus creating an "artificial" level by immersing the Sensor in a material sample or switching on an impedance between the terminals of the encoder.

In the drawings shows

F i g. 1 a prior art 7ählfinilp. Circuit arrangement of a fire alarm device,

Fig. 2 shows a first embodiment of a detector according to the invention,

F i g. 3 shows a second exemplary embodiment of a detector using an integrated circuit,

F i g. 4 shows a third exemplary embodiment of a MeI- as alternatively according to the invention as a variant of the arrangements shown in FIGS. 2 and 3,

F i g. 5 an interconnection of several parallel-connected, mutually and automatically monitoring single detectors,

6 shows an interconnection of several in series, mutually and automatically monitoring single detectors,

F i g. 7 an embodiment of an evaluation device,

F i g. 8 an embodiment of a detector according to the invention for monitoring fill levels,

FIG. 9 shows a modification of that shown in FIG Detector arrangement,

Fig. IG a further modification of a detector according to the invention for monitoring temperatures.

In Fig. 1 shows a conventional detector for changes in resistance, a so-called ionization detector, for example. It consists of a transmitter 1 converting changes in physical quantities into resistance changes between its terminals, a threshold amplifier V _s and an alarm device A. The transmitter is, for example, an ionization chamber. This consists of a radioactive source 2, z. B. an americium-241 or a cesium-137 oil. low dose rate. This source is arranged on a carrier plate which simultaneously serves as electrode 3. An electrode 4 is provided opposite the radiator. Both electrodes form the terminals of the transmitter 1.

The threshold amplifier V _s is constructed in two stages. It has a metal oxide field effect transistor 5, referred to below as a MOSFET, with a gate bleeder resistor 6, a drain resistor 7 and a source resistor 8, connected as a source stage. The base of the following transistor 9 is galvanically connected to the drain connection of the MOSFET 5. In the collector circuit of the transistor 9 there is a relay iö. whose coil is bridged by a free diode 11. The relay 10 has a transfer contact 12. An alarm device A, in this case a pair of incandescent lamps 13, 14, can be switched on by means of this contact.

How the ionization shield described above works emerges from the following:

After the operating voltage U _{n has been applied} , electrons migrate to electrode 4 and the ions to electrode 3 due to the ionization. A current flows which results in a voltage drop across gate resistor 6. If the voltage drop across this resistor 6 is sufficiently large, the MOSFET is turned on, whereby the transistor 9 is again turned on. As a result, relay 10 picks up and actuates the changeover contact 12. Lamp 13 lights up.

If the ionization in the ionization chamber changes, for example due to combustion gases or smoke particles, the current flow through the Innisntionskammpr l or through the gate resistor 6. Below a certain voltage across the gate resistor, the MOSFET S blocks, the relay 10 drops and applies the lamp 14 to the operating voltage U ₁₁ .

A deterioration in the insulation resistance in the transmitter 1, the ionization chamber, or a defect in the transistors S and / or 9 does not occur during normal operation of such an ionization detector ^; hung and can usually only be determined during the fire test. On the other hand, changing the electrical parameters of the circuit can trigger a false alarm.

To remedy this deficiency, the in F i g. 1 circuit shown by means of automatic Monitoring in the form of a feedback circuit expanded. This is in the circuitry of the F i g. 2 shown for example. In the F i g. 1 and 2, the same parts are provided with the same reference numerals.

Compared to the arrangement of FIG. 1, the one in FIG. The detector arrangement shown in FIG. 2 by means of a feedback system consisting of a /? C element, resistor 15 and capacitor 16 from the output of the threshold amplifier to the input of the same. This feedback is brought about by the relay 10, the switching contacts of which, when energized, connect the resistor 15 of the AC element to ground potential or to a voltage U_ which is even more negative than the operating voltage. In the non-excited state, said resistor is connected to U ₁₁ via switching contact 12.

The mode of operation of the circuit arrangement. j according to F i g. 2 follows from the following:

When the operating voltage U _{n is applied} , the voltage on the capacitor 16 and thus also on the terminals of the encoder 1 increases according to the exponential law. The rate of rise is defined by the RC element 15, 16. This increase in voltage continues until the gate voltage at the MOSFET is sufficient to control it. As a result, transistor 9 also turns on, relay 10 picks up.

The switching contact 12 of the relay 10 connects the switch-side end of the resistor 15 to ground or to the aforementioned negative voltage U_, whereby the capacitor 16 is discharged via this resistor, if the voltage on the plates of this capacitor falls below a certain value, the relay 10 drops again from, the charging process of the

densators starts all over again. An approximately square-wave voltage with an amplitude of approximately U _n arises at the collector of transistor 9. The frequency of this voltage is essentially determined by the Zeilkonlanle of the resistor 15 and capacitor 16 /? C element. This voltage U ₉ , which can be tapped off between the collector of the transistor 9 and the occupant or U _H, provides unambiguous information about the functionality of the indicator and about changes in the ionization capacity within de. Ionization chamber 1.

There are essentially four different detector states that can occur:

a) The output voltage U ₉ has an amplitude of approximately U _n , its frequency corresponds to the "nominal value" determined by the C-element,

b) the frequency of the output voltage LZ ₉ deviates from this »setpoint«,

c) the output voltage U ₉ is no longer an alternating voltage, its amplitude is approximately U ₁₁ ,

d) the amplitude of the output voltage U ₉ has dropped to approximately the residual voltage of the transistor 9, and vibrations can no longer be detected.

In case a) the detector that has ionization capacity in ionization chamber 1 is ready for operation practically does not change.

In. Case b) the detector is no longer 100 percent operational. Active or passive components of the indicator, its supply voltage U ₁ , or other variables have changed that make a check necessary.

In case c) the detector is defective.

In case d) the transistor 9 is turned on: Fire gases or smoke particles in the ionization chamber caused the detector to respond.

In addition to the collector voltage of the transistor 9, the voltage IZ ₁₆ between the plates of the capacitor 16 can also be used to differentiate between the four operating states of the detector. This voltage IZ ₁₆ is also an alternating voltage with a frequency defined by the RC-GYicd 15, 16, but with a smaller amplitude than the alternating voltage that can be tapped off at the collector of the transistor 9.

In addition, the mentioned voltage ί / _1β provides additional information that is characteristic of the functionality and responsiveness of the detector.

As mentioned above, this voltage is an approximately square-wave alternating voltage with a frequency defined by the AC element 15, 16. In contrast to the voltage at the collector of transistor 9, this voltage U _le fluctuates between the following two DC voltage levels IZ ₁ and U ₂ :

U _t : If the resistor 15 is connected to the supply voltage U _R , then the capacitor f ö is charged via the mentioned resistor until the voltage across the gate resistor 6 controls the MOSFET 5. This voltage at the gate corresponds to a certain voltage across the capacitor, since the resistor 5, the ionization chamber 1 and the gate resistor form a voltage divider chain between U _B and ground.

l / _ä : After the MOSFET 5 has been turned on, the relay 10 picks up, and the resistor 15 is connected to U_ by means of switch 12. The discharge of the capacitor 16 via the resistor 15 continues until the voltage at the gate of the MOSFET 5 is no longer sufficient to control it. At the time this MOSFET is blocked, there is a certain voltage between the plates of the capacitor 16. This differs from the voltage level IZ ₁ defined above, due to the hysteresis of the

ίο Threshold amplifier, in a very specific way. In the exemplary embodiment shown, this level U _{2 is} lower than the level U ₁ .

The two levels U ₁ and U ₂ are a measure of the functionality and responsiveness of the detector. This can be seen from the following:

If for any reason the value of the resistor 6, the operating voltage, the response threshold changes of the threshold amplifier or the like, so acts

SiCii uiCS ünrnittCiuär äüi uic called level äüS, ClU

to then also the voltage divider ratio of the voltage divider chain 15, 1, 6 changes. Thus, in addition to the voltage at the collector of the transistor 9, the voltage (Z can be further processed ₁₉ between the plates of the capacitor 16 to the manner to be described. In the latter case, however, it is expedient, not directly the voltage U _1n a generally spatially by the indicator separate evaluation device, but to connect an impedance converter in between.

From the above, another major advantage of the proposed indicator becomes clear: The working point of the indicator "oscillates", so to speak, always around its area of greatest sensitivity. Changes in the dose rate of the radiation source or other, adversely affecting the Environmental influences affecting the response threshold of the detector are regulated.

Due to the mentioned oscillations, one also comes with lower dose rates of the Radiation source. This in turn makes it possible to reduce the effort involved in shielding the radiation source to drift.

A possible embodiment of a circuit arrangement for evaluating a measure of the operational readiness of the detector according to FIG. 2 representing output voltages U ₉ and t / ₁₆ is shown in FIG. 7 shown.

This evaluation circuit consists of a Schmitt trigger 17, which is followed by a monostable multivibrator 18. The Q output of the multivibrator 18 is followed by a low-pass filter, best made up of the resistor 19 and the capacitor 20. The voltage U, _B applied to the plates of the capacitor 20 can be applied to a voltage

knife 21 can be read. A voltmeter is preferably used with switch contacts actuated by the pointer and displaceable on the reading scale. Above or below the voltage V _<0 defined values, then the contacts are closed and, for example, alarm lamps A od. Like. Turned on. Schmitt triggers, monostable multivibrators and voltmeters constructed in this way are known and will not be explained in more detail.

The mode of operation of this circuit arrangement can be seen from the following:

Corresponds to the voltage at the collector of transistor 9 (Fig. 2) in terms of amplitude and frequency the setpoint (case a), the Schmitt trigger switches

17 each time a certain voltage value is exceeded, which should be greater than the residual voltage of the transistor 9, through. An L signal is generated at its output, which sets the monostable multivibrator 18. The proper time of the monostable multivibrator 18 should be smaller than the period of U ₉ . The low-pass filter 20, 19 integrates this output pairing U ₁₆ . To the plates of the capacitor 20, a voltage U is ₂₀ made of, which is the time average of U _ls proportional. The display on the instrument 21 is a measure of the frequency of this voltage U _le and thus also a measure of the frequency of the voltage at the collector of the transistor 9.

If the frequency of this voltage falls below or exceeds an adjustable value, one of the two contacts on the instrument 21 closed.

If the amplitude of the voltage U ₉ does not reach the value required to switch the Schmitt-Trießer 17 through, the monostable multivibrator 18 remains in the idle state. The voltage across the capacitor 20 then also remains below a certain value. Then, too, an alarm is triggered by means of the contacts of the instrument 21.

Likewise, if the monostable multivibrator 18 is set continuously, it triggers an alarm if the voltage U ₉ constantly remains above the threshold voltage at the input of the Schmitt trigger 17.

In order to be able to differentiate between the two states of the detector described under b) and d), d. H. To be able to differentiate between the disturbance of the detector and the actual outbreak of fire becomes the following suggested:

A resistor is connected to the first input of an AND element 23 with the interposition of a resistor 24 and a capacitor 25 existing low pass the "Ö output of the Schmitt trigger 17 connected, while the second input of the AND gate with the interposition of another Low-pass filter 26, 27 and an inverter 28 are connected to the Q output of the monostable multivibrator 18 is. In another variant, the Q output of the monostable multivibrator 18 with the interposition of the low-pass filter 26 ', 27' to the mentioned second input of the AND element 23 be switched on. The output of the AND element 23 can activate a further alarm device 29. The two low-pass filters 24, 25 and 26, 27 are to be designed in such a way that the output signals of the Schmitt trigger 17 and of the monostable multivibrator 18, the voltages at the inputs of the AND gate 23 not enough to let this change its initial state. Further variants can be between a Schmitt trigger 29 and 30, respectively, can be connected to said low-pass filters 24, 25 and 26, 27.

The evaluation circuit described above is only to be regarded as an example. It's on that This field addressed expert using known building blocks of the analog and / or Leave digital technology, an optimal evaluation device suitable for the desired purpose to realize.

In Fig. 3 is a second embodiment of a detector according to the invention as a variant of that Circuit arrangement according to FIG. 2 shown

In this exemplary embodiment there is an integrated Circuit consisting of a metal oxide field effect transistor 31, a bipolar transistor 32 and one between the drain or base terminal of the MOSFET or bipolar transistor and its Emitter connection switched resistor 33 use. One such integrated circuit is available on the market under the designation TAA 320. The Structure of a detector according to FIG. 2 particularly easy, as its output current is so large, to a relay 34 to excite. This detector is also equipped with a device for automatic monitoring of its Provide functional readiness. However, this differs from that in connection with the in F i g. 2 by a different type of feedback.

The gate resistor 15 'is now connected to ground via a switching contact 35 which can be actuated by the relay 34. A capacitor 36 is located between the gate connection of the MOSFET 31 and ground. The ionization chamber 1 is located between the gate connection u.id of the operating voltage U ₁₁ .

The mode of operation of the circuit arrangement according to FIG. 3 results from the following:

Shortly after the application of the operating voltage U _{; l} , the MOSFET 31 is turned on, as is the transistor 32. The relay 34 is energized. The contact 35 designed as a normally closed contact separates the resistor 15 'from ground. Shortly after the operating voltage is switched on, practically zero voltage is applied to the capacitor. Due to the finite resistance between the electrodes 3, 4 of the ionization chamber 1, the voltage between the plates of the capacitor 36 increases slowly. If this voltage reaches a certain value, the MOSFET 31 is blocked, the relay 34 drops out and closes the contact 35, whereby the capacitor 36 is discharged. The relay picks up again and the processes described above are repeated. At the collector of transistor 32 there is an approximately rectangular shape; Voltage U ₃₂ , comparable to the voltage U ₉ arising at the collector of transistor 9 (FIG. 2). This voltage can now be adjusted in the same way as described above by means of a FIG. 7 corresponding evaluation circuit can be further processed.

Instead of the resistor 15 'between the gate connection of the MOSFET 31 and the switching contact 35 The relay 34 can expediently be joined by a further ionization chamber. This must be encapsulated in this way ensure that no fire gases or smoke particles can penetrate into them.

Of course, this measure can be used in the case of the FIG. 2 apply circuit arrangement described. There the resistor 6 would have to be replaced by a further ionization chamber.

The use of an encapsulated and an unencapsulated ionization chamber for deactivation of certain environmental influences is state of the art and, for example, in CH-PS 2 97 463 described in detail.

Another variant of the in FIG. The arrangement shown in Fig. 3 is to use instead of resistor 15 'and contact 35 one through the relay or a suitable electromagnet, which takes the place of the Relay coil can occur to provide actuated absorber between electrode 4 and radioactive radiation 2. The absorber is pushed in between when the relay or the coil is de-energized. The condenser

36 then discharges due to its insulation resistance by itself.

Such an absorber, albeit separately operable can also be used conveniently to control the responsiveness of the devices shown in FIGS shown indicators can be used. If you train the absorber in such a way that the Introducing the same the ionization capacity in the ionization chamber in the same way as in the presence of fire gases or smoke particles of a defined concentration changes, so it can be done in a simpler way Way the responsiveness of the indicator can be controlled.

Such absorbers can also be introduced automatically, controlled by a corresponding device take place at regular intervals. With the actuation of the absorber would have to avoid False alarms during such a test the actual alarm device can be neutralized. This can be done by switching the output of the indicator at the same time as activating the absorber take place.

4 shows a further exemplary embodiment of the invention. The resistor between the gate connection of the MOSFET 5 and ground is replaced by a capacitor 36, and the ionization chamber 1 is connected to the operating voltage U _n via a resistor 37. Instead of the output transistor 9, there is now a Schmitt trigger formed from the transistors 38 and 39 and the resistors 40, 40a ... 43. The output voltage t / ₃₀ can be tapped off at the collector of the transistor 39. This output voltage is fed to the base of a further transistor 45 via a Zener diode 44. This transistor is parallel to the series circuit consisting of ionization chamber 1 and capacitor 36.

The mode of operation of the in F i g. 4 is shown in the following:

After the operating voltage U _{n has been applied} , the voltage zero is initially between the plates of the capacitor 36. The MOSFET S is blocked. The collector of the transistor 39 of the Schmitt trigger is at low potential, which is practically determined by the voltage divider ratio of the resistors 40 and 42. Due to the potential at the collector of transistor 39, transistor 45 is blocked. Its collector is approximately at t / _ß potential. Under normal conditions, the capacitor 36 is now charged by the charge generated in the ionization chamber 1 during the ionization. The voltage at the gate connection of the MOSFET 5 increases until it is sufficient to control the MOSFET 5. As a result, the Schmitt trigger switches over, the potential at the collector of transistor 39 rises, which in turn activates transistor 45. Due to the inherent losses of the capacitor 36, it discharges again until the voltage between its plates is so low that the MOSFET changes from the conductive to the blocked state. Then the process just described is repeated. At the collector of the transistor 39 or between the collector and emitter of the transistor 45, an approximately square-wave alternating voltage arises with the voltage in connection with the one shown in FIG. 2 shown and described embodiment mentioned properties. This voltage can be processed in the same way as described there.

In Fig.4 there is another variant of a detector illustrated with Schmitt trigger for example. If you replace the ones shown on the left with the dash-dotted lines Line consisting of transistor 45 and Zener diode 44 through a circuit arrangement at between the Zener diode 44 and the base of the transistor 45, a further resistor 46 and between If a further capacitor 47 is connected to the base and ground, the arrangement thus modified acts in a manner similar to that described above. A change in the switching state of the Schmitt trigger then causes the capacitor 47 to be charged until the transistor 45 turns on.

is Another (not shown) modification the in F i g. 4 shown circuit arrangement 'admits between the electrodes 4 and the radioactive emitter 2 one at ground potential Ue-

"""" --- ··· ■ »■» ■■ ·· "" · ', * "« »« *'"'·»!<Wl WWWI WIIIW 1.WW aperture , to be provided. In this way, the discharge process of the capacitor 36 is accelerated.

The following principle is common to all of the exemplary embodiments described above:

The input of the threshold amplifier is via an input variable is fed to a type of feedback circuit which determines the switching state in changes a state corresponding to an alarm time without primarily triggering an alarm. By time-defining Limbs, e.g. B. ÄC-member, the resistor or resistors of this J? C-member by the Donors can be formed themselves, this state is canceled again. So it is about an oscillatable arrangement of the most general kind. The parameters of these oscillations are through affects active, passive or other components, or the arrangement listens under certain conditions on to swing. These vibrations, e.g. B. Frequency or amplitude, or just the determination, whether an oscillation takes place at all is used according to the invention to determine the operational readiness or to automatically monitor the functionality of the indicator.

While in the examples described so far, so-called ionization detectors in The focus should now be on the basis of an exemplary embodiment of a detector according to a further development the invention its application for the independent monitoring of fill levels or as Overflow securing will be explained. In doing so, I should which, however, only show minor differences to ionization detectors.

The same parts are shown in FIG. 8, which shows an exemplary embodiment of a level indicator, with the same Reference numerals are provided as in FIG. 2 and 4, respectively.

In Fig. 8, a resistor 48 takes the place of the ionization chamber. The gate resistor 6 is replaced by a pair of electrodes 49, the transmitter. The pair of electrodes are insulated from each other in attached to a support plate 50 and arranged in a container 51, the level of which is to be monitored. If the liquid touches both electrodes, the electrical resistance at the terminals changes.

The operation of the shown in FIG Arrangement is explained below.

After applying the operating voltage U _B , the relay 10 is initially the one break contact 12 '

13 14

has fallen off. The capacitor charges through this amplifier then becomes an Alann device

the resistor 15 on. This also increases the triggered.

Voltage at the gate connection of the MOSFET 5 until the incandescent lamp 63 turns on at a constant level instead. The normally closed contact 12 'opens to supply current, it is closed by the switch and connects the resistor 15 to ground or a negative current U_ which is dependent on the threshold amplifier. The capacitor 16 discharges pulses controlled. For this purpose, the glow lamp, which causes the voltage at the gate connection to drop, is connected to a resistor 15 with one of the MOSFET 5 actuated by the Rewo, and the switch 10 actuated, which closes in AbKontakt 12 'via relay 10. Then the dependency on the switching status of the threshold value process begins again. io strengthen this resistance with either one

If the resistance between the elec- trical or with the other pole of the supply voltage decreases

Troden 49 in that it connects with the liquid in U _B.

The MOSFET cannot come into contact. The mode of operation of the arrangement according to FIG. 9

pass more into the conductive state. The con- is evident from the following:

bar 12 'remains closed. The arrangement oscillates 15 after applying the operating voltage U ₀ switches

no longer. When dimensioning this switch the threshold amplifier V _s immediately through and puts

It is important to note that at the gate connection, the resistor 15 is connected to U _B by means of relay 10. As a result

When the MOSFET 5 is closed and the resistance thereof becomes low, the incandescent lamp 63 lights up. this in turn

Encoder, a small one to control the MOSFET has the consequence that the voltage drop at the photo

there is insufficient voltage. This can be 20 resistance 64 becomes smaller. Below a loading

by selecting the resistors 15 and the correct voltage, the threshold amplifier blocks

48 accomplish. It is advisable to use the resistance V _s . The relay 10 drops out. The lamp goes out. as

form as a trimming resistor to different result, the Schwellwertverstärker V _s is ER-

Iichen conductivities of the fluids calculation, the just described pre-

to wear. 25 gear repeats itself. At the output of the threshold value

In contrast to the ion amplifiers described above, approximately square-wave sationsmeldem arise here primarily the cessation of alternating voltages, the frequency of which is caused by the Helder oscillations, which occur at practically any increase in the light intensity of the incandescent lamp and the inertia of the circuit arrangement in the form of alternate the nature of the photoresistor is determined.
Approximately square-wave alternating voltages from 30 which are accessible at the output of the amplifier or also at, an indication of the alarm status. The alternating voltage that can be tapped at the incandescent lamp is, on the one hand, changes in the frequency, these are a measure of the functionality and the operating AC voltage is a measure of the functionality of the device.

speed and can by an evaluation circuit of the circuit arrangement shown in FIG

described type can be detected. 35 of a detector for level monitoring can be

The circuit arrangement described above by varying the encoder in a simple manner as well

for the automatic monitoring of filling levels - they for monitoring other physical quantities

can also be used as an overflow protection - use.

shows the broad field of application of the invention. One of the many possibilities is shown in FIG

underlying idea. However, it is shown as an example. It's about

indicated that with the in F i g. 8 shown filling a temperature monitoring device.

Level monitoring device of the sensors 49, 50 The photoresistor 64 takes the place of the photo resistor 64

not completely in the automatic monitoring NTC thermistor 65. In the immediate vicinity of the NTC thermistor

is involved. Although a short circuit in is a heat source 66, z. B. an incandescent lamp,

reliably detect the supply lines, but not an orderly one. In place of the incandescent lamp can also

Interruption. a heating coil that partially surrounds the thermistor

The way in which a level is monitored, step.

The giver is also responsible for determining the effectiveness of this device

Functionality and responsiveness is based on the above, in connection with mil

can be detected, reference is made below with reference to the statements made in FIG. 9. As

In the exemplary embodiment illustrated in FIG. 9, the output voltage is also described above.

tert. voltage of the threshold amplifier V _s a measure of the

To simplify the representation, the functionality of the entire detector is

The indicator shown there is largely schematic. Finally he of the giver.

consists of a transmitter 61, a threshold value controller 55. According to the invention, such detectors are toi stronger V _s and the threshold amplifier monitoring of physical variables, the downstream evaluation device, z. B. one in the form of resistance changes to the Klem-Fig. 7 arrangement shown. The encoder 61 is based on an input that is more responsive to the named variables, the one used in CH-PS 5 12 060 known from CH-PS 5 12 060. Under the direction. If the liquid level in the term "changes in resistance" is used here, such containers 51 are a certain adjustable level, so changes between the clamps change the intensity of the changes between the clamps at which the ratio of voltage between the truncated 62 is reflected by one Incandescent lamp 63 see the terminals and the light generated from the transmitter. This change in intensity is flowing or flowing into this current in a light-sensitive element 64, z. B. a 65 changes.

Photoresistor, in a change in resistance in addition to the encoders already described, Ioni

set, which in turn controls the threshold amplifier sation chamber, photosensitive element, hot

makes you respond. By addressing the conductors, all types of givers are of the type defined above

is

can be used, depending on which physical variable is to be detected or monitored. For example for the monitoring of fire gases or smoke particles also a working on semiconductor basis Encoders are used. In the case of such known detectors, their conductivity changes to Dependence on certain gaseous or other substances in the immediate vicinity of the active Avenge of the detector.

The circuit arrangement shown in FIG. 5 shows a parallel connection of several individual detectors which mutually automatically monitor one another. The arrangement consists of individual modules, each framed by dashed lines, a control or reference indicator / _s and three parallel connected detectors / ,, I ₂ , / ₃ and a logic L, which links the output signals of the detectors 7 to I ₃ .

All detector / _s , I ₁ , I ₃ and I ₃ have the same structure and correspond roughly to that in FIG. 2 with the following differences. Instead of the relay 10 in the coil circuit of the output transistor 9 or 109, etc., there is a resistor 10 'azw. 110 ', and parallel to the gate resistor 6 or 106 etc. there is a capacitor 48 or 148 etc. The inputs of the indicators / _s , I ₁ , 1 ₂ and I ₃ are denoted by E _s , E ₁ , E ₂ and E ₃ , respectively, and the outputs are labeled A _s , A ₁ , A ₂ and A ₃ , respectively. These outputs are connected to the three equivalent inputs of a logic L consisting of a transistor 49, two resistors 50, 51, a capacitor 52 and three diodes 53, 54 and 55. This logic represents an AND element, the output A _{L of which is led} to the input E _{s of} the indicator / _s . The inputs E ₁ , E ₂ and E _{3 of} the indicators I ₁ , I ₂ are the output A _{s of} the indicator / _s and / "connected in parallel.

The mode of operation of a single detector has been described above. The interaction of the three parallel-connected individual detectors I ₁ to I ₉ together with the control and reference detector / _s and the logic L is explained in more detail below.

After the operating voltage U _n has been applied, the voltage between the plates of the capacitors 48 and 148 is zero. The MOSFETs 5 and 105 are blocked. About the voltage U _{n is applied} to the collectors of the transistors 9 and 109. The voltage at the output A _{L of} the AND element and thus also the voltage at the electrode 2 of the ionization chamber 1 is approximately zero. As a result of the charging of the capacitor 116, a current flows through the ionization chamber 101, the voltage at the gate of the MOSFET105 increases until it cliahet through. The MOSFETs of the remaining detectors I ₂ and / are also switched through in a corresponding manner. As a result, the output transistors 109 etc. turn on. When all inputs of the logic are at low potential, the transistor 49 of the logic blocks. The potential at the electrode 4 of the ionization chamber 1 increases. A current flows through the ionization chamber 1, which in turn results in an increase in the voltage at the gate of the MOSFET 5. As a result, the latter controls through, which in turn results in the transistor 9 being switched through. The potential at the electrodes 104 etc. of the ionization chambers 101 etc. of the individual detectors /, to Λ, falls to approximately zero potential. The current flow through this ionization chamber stops. The capacitors 148 etc. connected between gate and ground are discharged via the resistors 106 etc. lying parallel to them. The corresponding MOSFETs block, as do the corresponding output transistors 109 etc., whereby their collector potential rises. If all the inputs of the logic L are at high potential, the transistor 49 controls through, its collector potential drops to approximately zero potential. The processes described above are thus repeated.

ίο The detector arrangement described above represents an oscillatory arrangement similar to the one previously described. The frequency of these oscillations can be taken in the form of electrical voltages at various points in the circuit arrangement, e.g. B. at the output A _{L of} the logic L or at the output / i _{s of} the control or reference detector 7 _S , but is no longer determined in the simple manner, as is the case, for example, with the circuit arrangement according to FIG

ao was. The switching of the logic L does not take place until the AND condition is fulfilled at its inputs. This means that the checking of the individual detectors Z ₁ to I ₃ initiated by the control or reference detector / s only takes place again when all these inputs

a5 detectors have indicated their functionality by emitting a corresponding signal. If one or more of the detectors / until I _{3 respond} later, the entire arrangement is not checked until later. This delayed onset results in a change in the frequency of the output voltages of the logic L or of the control or reference indicator / _s .

The output voltages mentioned can now be used in the above in connection with FIG. 2 described and the evaluation device shown in FIG. 7, for example, processed v / ground.

In one implementation of a detector arrangement according to FIG. 5 is expediently the taxor Reference detectors and the logic are installed in the alarm center, while the individual detectors are in the rooms to be monitored are housed in a suitable location. The low-resistance outputs of the transistor circuits used make it possible to use relatively long lines. Possibly the output of each individual detector can be equipped with an additional collector-base stage for the purpose of further Lower the output impedance. The other alternative, where to be monitored Space to install only an ionization chamber and the remaining parts of the circuit in to summarize the central unit, because of the large output impedance of ionization chambers. The latter applies in the same way to those shown in FIGS. 2 to 4 shown detectors.

For certain applications it can be useful to monitor the functionality of the detector directly (at least qualitatively) in the area it is monitoring. For this purpose, an indicator lamp K ₁ , K ₂ , K ₃ is assigned to each detector output.

arranges, which is connected, for example, between the collector of the respective output transistor and ground. These lamps are expediently gallium arsenide light-emitting diodes, which are characterized by extremely low power consumption and thus only insignificantly load the circuit. Such indicator lights can of course also be installed in the alarm center.
The use of indicator lights on the

17 18

The output of a detector is naturally limited. The output A ₁ ) drops to zero. This Absin-

not on the circuit arrangements shown in FIG. 5 causes the blocking of the input transistor of the

voltage, but can also be used with the circuit indicator / _ä , which in turn blocks the relevant

Regulations of the F i g. Realize 2 to 4. speaking input transistor in detector I ₃ for

Instead of the control or reference indicator in the 5 sequence. As a result, the counter electrode of the alarm center has to be installed, it can also _{serve as the ionization chamber of this detector Z 3} for the operational monitoring of a room. It recommends voltage. The parallel to the gate of the MOSFET read, however, the mentioned detector 7 _S , as above, the capacitor charges up and controls the written to be arranged in the control center, where it passes through with the MOSFET. At the output Z _{3 of} the detector I _{3 with the} exception of fire gases or smoke particles the io is now approximately I / ß potential, which in turn is exposed to the same environmental influences as the remaining transistor 56 of the input stage of the first detector I ₁ borrowed detector. blocks The capacitor 60 discharges via the Wi-

In Fig. 6 an embodiment of one from the standö, the MOSFET5 blocks, at the output A ₁

several connected in series and each other is again approximately [/ g potential. Repeat it

and self-monitoring individual detectors, the processes described above are triggered. The ones from the

built detector shown. The individual detectors are three detectors Z ₁ to Z ₃ existing circuit arrangements

denoted by Z ₁ , Z ₂ and Z _3. Their structure corresponds to voltage - similar to that in FIG. 5 shown

that of the detector according to F i g. 4. The same parts are arranged - a structure that can vibrate.

the F i g. 4 and 6 with the same reference numerals. In the case of FIG. 6 virtually switches a detector

see. 20 subsequent detector, which in turn has the

The ionization chamber 1 is an amplifier stage, which switches on following it. The output signal

formed from a transistor 56 with collector resistance- this chain is inverted and thus switches the

stood 57 and base resistor 58, upstream The first detector in the chain, which in turn had the

Base resistor 58 is switched off by a capacitor 59 when the next detector is switched off

bridged This is used to filter out even 25 of the last detector in this chain is the first again

tual interfering signals. The counter electrode 4 of the ionider is switched on, etc.

sationskammer is connected to the collector of the transistor Die at any Em- and output ab-56, the other end of the ionization chamber tangible voltage is a measure for the functional mer 1 is at the input of the transistors 5, readiness or efficiency of all Threshold amplifier connected in series - 38 and 39. Between 30 detectors and can be further processed in the manner described above, its input, the gate of the MOSFET 5,
and ground lies the resistor 6 and a capacitor. In the circuit arrangements of FIG. 5 and 6 sator 60. The threshold value ^{amplifier J} xer has two outputs A _t UHdZ ₁ for reasons of a clear representation. A _{1 shows} the parallel connection or series connection of one Zener diode 61 and one V resistor 62 with three individual detectors. The inventors collector of the transistor 38, Z ₁ is directly connected to the manure of course not limited to the collector of the transistor 39. this number.

In the _{case of the parallel detector Z 1} shown in FIG. 5, the input E _{2 of} a further detector Z _{2 is} connected to the output A _{t of} the above-described circuit, at whose output A ₂ the single detector is connected practically only connected by the load path E _{3 of} a third detector Z ₃ , the availability of which is limited to the output stage of the detector Z ₅ . Output Z _{3 is} connected to input E _{1 of} the first detector AND element with almost any number of inputs Z _1. The two detectors Z ₂ and Z ₃ are either directly monolithically integrated and have the same structure as the previously described circuits on the market or from such easy-to-open detectors Z ₁ , but the detector Z _{3 is} built from 45.

Zener diode and the resistor formed in series. In the case of FIG. 6 will be the maximum in series

connection to the collector of the last transistor, interconnectable number of individual detectors

that is to say the transistor which, at I _{3, has} practically no upper limit set for transistor 39. However, it is

corresponds to detector Z ₁ , connected. to note that the serial switching so

The mode of operation of the circuit arrangement lasts longer, the more individual detectors together F i g. 6 is explained below. After they are switched on.

set the operating voltage U _B are initially all for the last-mentioned circuit arrangement applies

MOSFETs blocked, the counter electrodes of the ionic likewise for the one shown in FIG. Even

sation chambers are almost at zero potential. here each of the outputs can be provided with a display

The outputs Λ _t and A _t are connected to approximately U _B - 55 lamp (gallium arsenide light-emitting diode).

Potential. The transistors in the input stages enable the operational readiness directly on the spot.

the indicators Z ₂ and Z ₃ are controlled. To be able to check the quality of the shaft.

Transistor 56 is in the input stage of Z ₁ , the interconnection of several individual alarms

Due to the different coupling to the indicators, it is of course not limited to the

gate Z ₃ , locked. The counter electrode 4 of the ionization 60 described in detail here for fire gases

on chamber 1 is at approximately IV potential. There and / or rough participation. That of the design of the

by increasing the voltage at the gate of the MOSFET 5 principle underlying the invention, several individual

at. When a certain voltage value is reached, they combine to form an oscillating arrangement.

the MOSFET 5 switches through, whereupon the switch on can also be opened without further ado

the Schmitt trigger connected to him falls over. Use the 65 detectors for which a transmitter other than

Voltage at the collector of transistor 38 (= Span- an ionization chamber is used.

In addition 6 sheets of drawings

Claims (18)

Patent claims: 1. Detector for changes in resistance, consisting of at least one sensor converting changes in physical quantities into changes in resistance, at least one threshold amplifier connected to the sensor, an alarm device connected downstream of the threshold amplifier and means for checking the operational readiness and functionality of the detector, which changes in resistance between the input terminals of the threshold amplifier simulate, characterized in that said means comprise a timing element (15, 16; 15 ', 36; 36, 37), which can be switched on by means of an electronic switch (9; 32; 38, 39) and which is fed from the output of the threshold amplifier (Vs) acts on its input that the feedback arrangement is designed and arranged in such a way that at the input of the threshold amplifier, depending on its switching state, changes in resistance that make it respond are generated, which in turn are> 5 cancel the feedback, and that the alarm device (A) comprises means (21) for detecting the amplitude and / or frequency of the threshold amplifier output voltage 2. Detector according to claim 1, characterized in that you; One terminal of the sensor (1) is connected to the input of the threshold amplifier (Vs), the other terminal of the sensor is connected via a capacitor (16) to one pole of the supply voltage (U _B ) of the threshold amplifier Sensor is connected via a resistor (15) depending on the switching state of the threshold amplifier either to the named pole or to the other pole of the supply voltage (LJb) of the threshold amplifier and that a resistor (6) is provided between the input and one pole of the supply voltage is. 3. Detector according to claim 1, characterized in that one terminal of the sensor (1) is connected to the input of the threshold amplifier (Vs), the other terminal of the sensor to one pole of the supply voltage (Ub) of the threshold amplifier, that between the Input of the threshold amplifier and the other pole of the supply voltage a capacitor (36) and that parallel to this capacitor a resistor (15 ') can be switched on by means of a switch (35) operated by the output of the threshold amplifier. 4. Detector according to claim 1, characterized in that between the input of the Schwellwertvei amplifier (Vs) and one pole of the supply voltage (Ub) of the threshold amplifier, a capacitor (36) and a series circuit between said input and the other pole of the supply voltage the sensor (1) and a resistor (37) and that a switch (45) actuated by the output of the threshold amplifier is provided between one pole of the supply voltage and the connecting line between the sensor (1) and said resistor. 5. Detector according to claim 1, characterized in that a flip-flop (38 ... 42) is provided between the output of the threshold amplifier (Vs) and the switch (45) 6. Detector according to claim 4 or 5, characterized in that the switch (45) via a Zener diode (44) is connected to the output of the trigger stage 7. Detector according to claim 1, characterized in that the sensor (1) is part of the feedback. 8. Detector according to claim 1 or 7, characterized in that the sensor is a photosensitive Element (64) is that depending on the to monitored physical variable is illuminated by means of a light source (63). 9. Detector according to claim 1 or 7, characterized in that the sensor is a temperature-sensitive Resistance element (65) and that a heat source (66) for generating changes in resistance is provided between the terminals of the resistance element (65) 10 detector according to claim 1, characterized in that several individual detectors (Iu h, h) are interconnected to form a chain of mutually monitoring detectors. 11. Detector according to claim 10, characterized in that a control indicator (l _s ) is provided, which is followed by at least one further individual detector (I \ ... ). 12. Detector according to claim 11, characterized in that the control indicator (l _s ) at least two parallel-connected individual detectors (U ... ) Are connected downstream. 13. Detector according to claim 12, characterized in that the interconnection of the individual detectors is designed and. it is arranged that, based on the response of an individual detector, this causes the remaining individual detectors to respond, and that a logic circuit (L) is provided, which serves to trigger the first detector (ls) \ n to move to its initial state (Fig. 5). 14. Detector according to claim 12, characterized in that the output of a first single detector (U) is connected to the input of the subsequent single detector (h) , the output of which is in turn connected to the input of a third single detector (h) and that the output of the The last detector in the chain is connected to the input of the first detector (U) with the interposition of a 180 ° phase rotation device (FIG. 6). 15. Detector according to one of the preceding claims 1 to 14, characterized in that Limit signaling devices for amplitude and / or frequency are provided. 16. Detector according to one of the preceding claims 1 to 15, characterized in that the Sensor an ionization chamber (1) or one that responds to smoke particles and / or combustion gases Semiconductor sensor is. 17. Detector according to one of the preceding claims 1 to 15, characterized in that in particular a light-sensitive element (64) is used to monitor fill levels of the sensor. 18. Detector according to one of the preceding claims I to 15. characterized in that in particular for monitoring temperatures Sensor is a temperature-sensitive resistance element (65) is assigned to a heat source (66) is. The invention relates to a detector for changes in resistance, consisting of at least a sensor that converts changes in physical quantities into changes in resistance, at least a threshold amplifier connected to the sensor, one to the threshold amplifier downstream alarm device and means for checking the operational readiness and functionality of the detector, what changes in resistance between the terminals of the threshold amplifier simulate. For monitoring physical quantities, e.g. B. level of a container, presence of Combustion gases or smoke, mist, etc., have become known to a number of devices. On the basis of one so-called fire warning device, as it is described for example in CH-PS 4 37 056, is described below the principle on which such detectors are based explains: An ionization chamber is connected to the input of a threshold amplifier the atmosphere to be monitored. The output of the threshold amplifier is with connected to an alarm device. Does the ionization capacity change due to presence, for example? of visible or invisible combustion products, this is expressed in a change in the electrical resistance between the terminals of the ionization chamber. This change in resistance in turn causes the threshold amplifier to respond, which then triggers the alarm triggers. The disadvantage of these devices is that they have a low sensitivity, see above that, for example, in the case of fire warning devices, smoldering fires are not always detected in good time can. Increasing the response sensitivity is usually not possible, since such measures the Significantly increase the risk of false alarms. Another disadvantage of the known devices is the fact that they - if at all - with very complex, mostly separately operable monitoring devices are provided. For example, in the case of the above-mentioned fire alarm device its functionality is checked by the fact that a Fire test is carried out. In another fire warning device known from CH-PS 4 68 683, which is provided with a device for checking its functionality, an S ₀ feedback process is initiated by means of a separate switch, which causes a resistance or current change between the input terminals of the threshold amplifier, which the Schwellwertverstärker by controlling, in turn, the downstream loading Alarmeinrichlung s ₅ actuated. The test alarm is ended again by a white switch and the fire alarm device is ready for operation again. While this known device for checking the operational readiness with relative can be realized by simple means, it has the serious disadvantage that only through a intentional external influence errors become recognizable. From DE-OS 21 07 862 is one of a resistor time-controlled pulse generator known whose pulse repetition frequency is determined by a resistor, the z. B. can be an ionization chamber, is determined after switching on the operating voltage loads this resistance increases the drain-gate capacitance of a field effect transistor. At a certain source voltage the circuit arrangement is disconnected from the operating voltage. This discharges the named capacity across the load resistance of the switching amplifier. Below a certain voltage the supply voltage is switched on again at the load resistor the ionization chamber, according to Setzer. the vibrations off. However, this exposure to the vibrations is not clear measure for the alarm, since other causes (changes in the sensor characteristics due to aging, Temperature influences, failure of other components · .; lead to the interruption of the vibrations which can then trigger a false positive. DE-OS 20 56 0.5 has a method and a device for alarm security to the object. The object to be secured is controlled by a vibration transmitter excited with a certain setpoint of frequency and / or amplitude. The vibrations are going through a vibration sensor tapped and deviations from the target value to trigger an alarm used. An automatic check of the operational readiness and functionality is here not intended and also not feasible, since there only permanent damage will trigger an alarm can. The invention is based on the object of creating a detector of the type mentioned at the outset, who does not have the disadvantages described, who constantly affects his or her without external influence Functionality and functionality checked and at the same time through simple structure and high responsiveness with the highest possible reliability. In the case of a detector of the type mentioned at the outset, this object is achieved according to the invention in that that said means consist of a timer and can be switched on by means of an electronic switch Include feedback arrangement from the output of the threshold amplifier to the Input acts that the feedback arrangement is designed and arranged such that at the input of the Threshold amplifier, depending on its switching state, these changes in resistance that make them respond are generated, which in turn cancel the feedback, and that the alarm device Means for detecting the amplitude and / or frequency of the threshold amplifier output voltage includes. Compared to known detector arrangements in which the physical quantity to be monitored, z. B. Presence orter Absence of a certain determining the resistance between the terminals of the sensor Material that stimulates or interrupts the oscillations of an oscillator (DE-AS 14 66 554 or DE-PS 16 16 280), the invention differs