DE2528764A1 - Electrically operated fire alarm circuit - with several series fire detectors connected in one arm of bridge circuit - Google Patents

Abstract

The fire alarm circuit has a number of fire detectors (F) connected in series, each detector (F) having a contact (K) which opens when an abnormal current is detected. The contacts (K) of the detectors (F), are each connected in series with a resistor (r is not =) and the contact (K) and resistor (r is not =) are connected in paralle with a further resistor (R). The series of detectors (F) are conencted in one arm of a bridge circuit, the olto arm of which has a series of resisters (R1, R5) of selected values, so that predetermined voltages (Uk, Unull, UA, Uu) are obtained across them.

Description

Circuit arrangement for monitoring fire alarms The invention relates to a circuit arrangement for monitoring n series-connected fire alarms, which work according to the current weakening principle, so that in the event of an alarm the flowing through Current is reduced, in which arrangement each fire alarm has a detection and contains evaluation device, the end member of which opens in the event of an alarm Contact is formed and the contacts of all fire alarms are connected in series and are each bridged by a parallel resistor.

Commercially available fire alarms work either - like the ones described above - According to the current weakening principle (abbreviated S., P; in the event of an alarm, the Current reduced) or on the current amplification principle (magnification of the current flowing through in the event of an alarm ?, whereby the SSP variant is more widespread and has found more general use.

The disadvantage of the previous circuits for evaluating the alarm message is that some circuit defects either go undetected or that they can lead to false positives; so, for example, stick to the one already proposed Circuit according to FIG. 1, a line short circuit via a fire alarm F (through a dashed connection indicated) undetected, although this is the corresponding one Fire alarm becomes ineffective. In Fig. 1, F are the individual fire alarms with the contacts a; three fire alarms are drawn. Every common detection and evaluation principle - e.g. ionization chambers for smoke detection - can be used here. In series with the fire alarms have test facilities with pushbuttons and contacts; E.g. the contact TK causes a short circuit when the associated pushbutton is pressed the entire range of fire alarms, TA simulates an alarm and TU a line interruption. The scheme according to FIG. 1 corresponds to the current state of the art. For current measurement a device S is provided.

However, there is a selective display of faults for safety reasons must be requested without false positives an improved Strive for solution.

The invention is based on the disadvantages of the known To fix circuits and for the SSP encoder the desired selective display of To enable faults without false alarms.

This is done according to the invention in a circuit of the type described at the outset achieved by the fact that each fire alarm in series with the contact still has a resistance so that this series connection is bridged by the parallel resistor, and also by classifying the series of fire alarms in a branch of a bridge circuit, in the other branch series resistances of selected size lie between them Well-defined tensions develop.

2 shows the basic circuit diagram of the circuit arrangement according to the invention. Two fire alarms F are drawn, others in a row by dots indicated. Usually 4-8 such transmitters are connected in series to an evaluation unit switched. The resistance of the leads can vary within wide limits (typically between almost zero and 500 ohms).

As a major change compared to today's technology (so.) In the fire alarm F in series with the contact a * a resistor is established according to the invention r switched, in such a way * that the series connection of a and r of the already in Fig. 1 shown parallel resistor R is bridged. In the idle state is the Contact a closed, so that the total resistance r of the fire alarm F of the parallel combination * of r and R corresponds to: * r = r * R r + R In the event of an alarm, the contact opens and the Resistance of the detector increases to R.

* The proposed introduction of the series resistance r enables a new kind of evaluation of the disturbances. The circuit in Fig. 2 represents a bridge In series with the fire alarms F there is a test circuit with pushbuttons, a simulation of alarm (TA), short circuit via a single encoder (TK) and enable line interruption (TU).

To be independent of the number of sensors and line resistances used To always have defined resistance ratios, two adjustments are provided. A switch S is used to add the total resistance of the encoder part to the eight times an encoder resistance r (see above) (setting value (8-n) -r, where n is the number of encoders used).

With a potentiometer P, the line resistance R L is reduced to one The nominal value is added, which is roughly the maximum possible line resistance is equivalent to. The number "8" is of course only chosen as an example.

The voltage UM between node M and ground is used as a measured variable evaluated by comparing it to a series of voltages obtained by the same Power supply are derived.

During normal operation (no malfunction, no alarm) UM = UNull, which is achieved by adjusting the potentiometer P during installation. At the Alarm (when one or more contacts are opened) drops UM without doing so to fall below a lower limit, which is due to the simultaneous opening of all 8 contacts is intended.

In the event of a line break, UM sinks to zero.

In the event of a short circuit across the external terminals of one (or more) detectors, on the other hand, UM increases as the total resistance is reduced of these changes the alarm selectively trigger as well as the individual The selective detection of malfunctions can be demonstrated using a numerical example will.

If, for example, the parallel resistance R r .R = 10 r (r =), r * + R der maximum line resistance rLmax = r and the measuring resistance rS = r so is normal Operating status U UM = 11 In the event of a short circuit across a single detector, increases UM to U UM =, 10 so by 10%.

In the event of a short circuit across several detectors, the voltage increase is corresponding greater.

When an alarm is signaled by a detector, UM drops to UM = 20th with simultaneous signaling from all 8 detectors -UM decreases to UM 83 The decrease of UM below this level can only be done by a Line interruption.

If one then selects four comparison voltages in the multiple bridge arrangement according to FIG (UK, UNULL, UA, UU) is first used during commissioning.

TOGGLE = UNULL set.

In the normal state, UM S UA UM> UU UM <UK then applies in the alarm state, indicated by 1 to 8 detectors one has UM <UA UM U K UM> UU At the Short circuit across at least one detector is UM> UK UM> UA UM UU for one Line interruption results from UM <UK UM <UA UM <UU from these conditions the type of fault or an alarm can be identified selectively.

An example of a comparator circuit with a logical link, which carries out the selection of the message is shown in Fig. 3. The voltage UM is on Input from corresponding comparator units with the voltages UA, UK and Uu compared. L "signals or" O "signals appear at the outputs, namely appears an "L" signal at output "A" for "alarm", at output "K" for "short circuit" and at the "Ub" output in the event of "interruption". Another operational amplifier receives one hand half the voltage U and, on the other hand, a predetermined part of the output voltage via diodes of the respectively activated comparator. In the normal state, the delivers exit N this amplifier has an "L" signal.

Since the resistance of the line is only about 1/11 of the total value, is also the case with an Al line with a TC = 0.49% / ° C and a temperature fluctuation from t 40 ° C causes a total resistance error of + 1.8% of Zr.

* The absolute tolerances of r are irrelevant as they are at can be eliminated during commissioning by means of zero adjustment.

Even with a TC = 200 ppm / ° C, the worst case scenario is # 40 ° C an error of # 0.8% #r.

The largest possible error of i 2.68 for # 400C temperature fluctuations does not cause an error message.

It should also be noted that in a modification according to FIG. 4, the bridge principle also for monitoring the circuit of low-resistance switching elements (such as contactors, Signal lamps, sirens, etc.) can be used.

In a modification of the conventional technology, this is monitored Element a non-linear resistor (e.g. semiconductor diode) connected in series.

In the idle state (contact open) only a small current flows through it the diode and the low-resistance switching element (e.g.

Relay). The voltage UM is approx.

UM = UD, where UD is the forward voltage of the diode. The following applies: UM> UK UM <UU UM <US If the line is interrupted, UM increases to R2 UM = U R1 + R2 so that UM> UK UM UU UM <US In the case of a short circuit, UM <UK UM UM UM < US When the contact closes (operating status of the switching element or relay) is then UM> UK UM Uu UM> US With the help of three comparators and logical connection, all states can again be easily distinguished from one another.

Claims (5)

P a t e n t a n s p r ü c h e 1. Circuit arrangement for monitoring n series-connected Fire alarms that work according to the current weakening principle, so that in the event of an alarm the current flowing through is reduced, with which arrangement each fire alarm contains a detection and evaluation device, the end member of which in the event of an alarm opening contact is formed and the contacts of all fire alarms in Connected in series and each bridged by a parallel resistor, thereby marked that each fire alarm (F) in series with the contact (K) still has a resistor (r), so that this series connection is bridged by the parallel resistor (R) and also identified by the classification of the series fire alarms (F) in one branch of a bridge circuit, in the other branch of which series resistors are selected Size (R1 ... R5), between which precisely defined tensions develop (UK, ZERO, UA, UU). 2. Circuit arrangement according to claim 1, characterized in that means (S, P) are also provided in the bridge branch containing the fire alarms (F) are independent of the number of detectors and line resistances used to always have defined resistance ratios (Fig. 2). 3. Circuit arrangement according to claim 2, characterized in that the series connection between the fire alarms (F) and the ground connection of the bridge branch a switch (S), a potentiometer (P) and a resistor (rs) is that by means of S the total resistance of the detector bridge branch is increased by N of a detector counter *. R standes (r =) is added, where N is the total number of -r + R also not used - designates detectors, so that the setting value of S is the same (N-n) .r is, where n is the number of effectively deployed detectors, that further With the potentiometer (P) the line resistance (RL) is added to a nominal value which corresponds approximately to the maximum possible line resistance, that there is still a resistor (rs) between the potentiometer P and the ground, and that the voltage (UM) at node M between P and r5 is evaluated as a measured variable is compared, for which purpose it is compared with a series of specified voltages (UK, ZERO, UA, UU) in the other branch of the bridge from the same power supply unit by means of the series resistors (R1 ... R5) can be generated. 4. Circuit arrangement according to claim 3, characterized in that the comparison is carried out by means of a comparator circuit with a logical link (Fig. 3). 5. Circuit arrangement according to claims 2 to 4, characterized in that that in the bridge branch containing the detectors (F) between the detectors and the Supply voltage (+ U) and in series with the detectors a test circuit (T) with pushbuttons (TU, TA, TK) is provided, which simulates an alarm, short circuit via a enable individual detectors and line interruptions. L e r s e i t e