GB2097610A

GB2097610A - Monitoring lighting systems

Info

Publication number: GB2097610A
Application number: GB8208918A
Authority: GB
Original assignee: CEAG Licht und Stromversorgungstechnik GmbH
Current assignee: CEAG Licht und Stromversorgungstechnik GmbH
Priority date: 1981-03-28
Filing date: 1982-03-26
Publication date: 1982-11-03
Also published as: GB2097610B; ATA116782A; DE3112314C2; DE3112314A1; AT383934B; NL8201280A

Abstract

In an emergency lighting system comprising a plurality of lights (6) which are connected in parallel and supplied by a battery 4, the lights only being energised when the mains fails, a monitoring circuit continuously checks the state of each light whilst the system is not being energised from the battery. A constant voltage source (7) whose voltage is less than that of battery 4, is connected to the system via a current measuring resistor (8). The measured value of the current is evaluated by an amplifier (9) and comparator (10) and an indicating device (11, 12) is triggered if a predeterminable value is exceeded. At each light (Figure 2, not shown) a first threshold switch (26) monitors the voltage on supply conductors 20,21 and closes to energise the respective light only when the voltage corresponds to battery 4, rather than source 7. A resistor and indicator (27,28) bypassing this switch permit a small monitoring current to flow through the light from source 7 when the battery is disconnected. If the light fails, a second threshold switch (29) at the light switches in an extra load on to conductors 20,21, thus drawing increased current from source 7 to trigger comparator 10. <IMAGE>

Description

SPECIFICATION Safety lighting system The invention relates to a safety lighting system comprising a plurality of lights which are connected in parallel and supplied by a supply unit connected to the mains, the supply unit being provided with a battery, a charger and a mains monitoring circuit with a switch connected downstream for switching over from stand-by service to emergency service.

In safety lighting systems a plurality of parallelconnected lights with filament lamps are fed, inter alia, from a battery. The systems can be operated by permanent connection (the lamp is constantly illuminated) or by stand-by connection (the lamps are only illuminated in the case of a mains failure). If the lights are operated by stand-by connection, the operation can only be controlled by manually switching over to emergency light service and by a control step for each safety light.

Although the lamps can be constantly controlled if the lights are operated by permanent connection, a disadvantage in this case lies in the reduced operating time owing to the limited working life of the filament lamps.

Furthermore, central monitoring of the individual lights has not hitherto been possible for the consumer on account of the parallel connection. Systems such as "central building conduction technology" or "house conduction technology" are known. The transmission of signals from the individual lights to the central supply unit is problematic and in this case either cables have to be additionally and, in the case of existing systems, subsequently laid or the supply lines to the lights have to operate in accordance with carrier frequency technology.

Both methods are cost-intensive and only worthwhile if several pieces of information or control or regulating functions can also be dealt with. A disadvantage of the carrier frequency system also lies in the fact that, according to the regulations of the Post Office Telecommunications Engineering Department, only signal powers of S 5mW can be used. This low power does not provide sufficient freedom from interference in industrial power systems.

The object of the invention is to provide a simple monitoring circuit for a safety lighting system which comprises a plurality of lights connected in parallel and allows a continuous indication of the operation of each light and a fault signal, which is free from interference, to be sent to the central supply unit of the lighting system, without the necessity of providing additional wiring material, such as cables etc.

This object is solved according to the invention in that a current measuring resistor for measuring the current flowing through the parallel-connected lights during stand-by service is connected downstream of a constant voltage source connected between the mains and the switch, in which the measured value of the current can be evaluated by a comparator with an amplifier connected upstream and an indicating device can be triggered if a predeterminable value is exceeded.

The monitoring circuit for each lamp is characterised in that the lamp of each light is connected via a switch to the lines of the supply unit, that the switch is triggered buy a potential divider which is connected to the lines and comprises a Zener diode, that a resistor with a pilot lamp connected downstream is arranged in parallel with the switch and that a threshold switch with a multivibrator connected downstream are provided and are connected on one hand to the lines and the lamp/switch connection point and on the other to the pilot lamp and, via a further resistor, to one of the lines.

The monitoring system according to the invention for a safety lighting system has the advantage of enabling a short circuit in the lines between the lights and the supply unit to be detected. A broken filament in one or more of the lamps of the lights is also detected. The fault in a defective light is registered in the actual light and in the supply unit and the fault is indicated in the central supply unit without the need for additional wiring, i.e. only the lines already provided are required for this. The lights and lines are continuously controlled during stand-by service, i.e. when the lamp is switched off.

An embodiment of the invention is explained in the following with reference to the drawings.

Figure 1 shows a block diagram of a safety lighting system with a bank of batteries or a central battery.

The lights 6 are fed from the supply unit 1 from the battery 4 during emergency service. The battery 4 is charged by a charger 2 when a mains voltage is provided. The mains monitoring device 3 switches over to emergency operation via the switch 5 in the case of a mains failure.

If a mains voltage is provided the lights are supplied from the constant voltage source 7 via a shunt 8 and the switch 5 with a voltage which is lower than the battery voltage 4.

If the current at the shunt exceeds a threshold value (evaluation by the amplifier 9 and the comparator 10), a fault is signalled in the unit by a lamp 11 (or a buzzer etc.) and can simultaneously be signalled to a central monitoring device via a contact 12.

The fault-signalling operation is described with reference to Figure 2: All the lights 6 are supplied in parallel via the two lines 20, 21. The lamp 25 is switched on by a switch 26 (transistor or relay), i.e.

connected to the lines 20,21. This is, however, only possible if the supply voltage between the lines 20, 21 is greater than the base voltage of the transistor 26 and the threshold voltage of the Zener diode 23.

The base of the transistor 26 is connected to the line 20 via a resistor 24 and to the line 21 via a Zener diode 23 with a resistor 22 connected downstream.

The components 22, 23, 24 can also be replaced by a relay coil and the component 26 by a relay contact.

A test current flows through the resistor (27) and the pilot lamp (28) via the cold resistance of the filament lamp (25). The pilot lamp (28) is extinguished if there is a break in the filament of the lamp (no emergency light operation). The threshold switch (29) triggers a multi-vibrator (30), which intermittently loads the lines 20, 21 with the resistance (42) and simultaneously lets the pilot lamp (28) flash. The resistor (42) is dimensioned such that it causes a current to flow through the shunt (8) in the supply unit (1) which is greater than the threshold value of the comparator (10). A fault is thus signalled to the central supply unit (1).

The value of the resistor 42 must be smaller than the voltage at 20, 21 during mains operation divided by the sum of all the operative resistances in the light 6 during mains operation (sum IR27 < lR42).

The example of use in Figure 3 (only the light part 6 is illustrated) shows how this can be simply put into effect.

The components 31 to 41 represent the functional blocks from Figure 2. A resistor 34 and a diode 40 are connected to the line 20. The resistor 34 is connected at the other side to a capacitor 36, a transistor 45 and the base of a transistor 38. On the other side the diode 40 adjoins resistors 32, 39 and 42 via a transistor 41. The base of the transistor 41 is connected viaa diode 31 to the connection point of the lamp 25/transistor 26/resistor 27 and also adjoins the line 21 via a resistor 37 and the transistor 38. The resistor 39 and the capacitor 36 are connected together. The resistor 32 adjoins the connection point of the resistor 27/pilot lamp 28 via a diode 33.

The transistor 45 is connected to the line 21. Its base adjoins the connection point of the resistor 22/Zener diode 23 via a resistor 43 and the line 21 via a resistor 44.

The voltage at 20, 21 is lower during mains operation than the threshold voltage determined by the components 22, 23, 24, 26, i.e. the transistor (26) is inhibited and the lamp (25) remains switched off.

A test current flows through the resistor (27) and the pilot lamp (28) via the cold resistance of the lamp (25), i.e. the lamp indicates the intact lamp filament by a steady light. The transistor (41) remains inhi bited on account of the cold resistance of the lamp (25) and the diode (31).

The components 34 to 42 form a stable multivibrator with complementary transistors, i.e. the two transistors 38 and 41 are either both conductive or both inhibited. The current in each light (6) is limited by the resistor (27). All the other consuming devices (22 - 42) are inoperative in this operating condition.

if the filament of the lamp (25) is broken the transistor (41) is enabled and the resistor (42) thus connected in time with the multivibrator via the transistor (41) and the diode (40) to the lines 20, 21 and thus in parallel with all the lights. The pilot lamp (28) is firstly inhibited in parallel with the resistor (42) via the resistor (32) and the diode (33) and then flashes, also at the clock frequency of the multivib rator.

The battery voltage 4 is applied to the lines 20, 21 during emergency service. As this voltage is higher than the test voltage during mains operation, the transistor (26) is rendered conductive and the lamp (25) switched on. The multivibrator (30) is simultaneously inhibited by the transistor (45).

Claims

1. Safety lighting system comprising a plurality of lights which are connected in parallel and sup plied by a supply unit connected to the mains, the supply unit being provided with a battery, a charger and a mains monitoring circuit with a switch connected downstream for switching over from standby service to emergency service, characterised in that a current measuring resistor (8) for measuring the current flowing through the parallel-connected lights (6) during stand-by service is connected downstream of a constant voltage source (7) connected between the mains and the switch (5), in which the measured value of the current can be evaluated by a comparator (10) with an amplifier (12) connected upstream and an indicating device (11, 12) can be triggered if a predeterminablevalue is exceeded.

2. Safety lighting system according to claim 1, characterised in that the lamp (25) of each light (6) is connected via a switch (26) to the lines (20, 21) of the supply unit (1), that the switch (26) is triggered by a potential divider (22, 24) which is connected to the lines (20, 21) and comprises a Zener diode (23), that a resistor (27) with a pilot lamp (28) connected downstream is arranged in parallel with the switch (26) and that a threshold switch (29) with a multivibrator (30) connected downstream are provided and are connected on one hand to the lines (20, 21) and the lamp (25)/switch (26) connecting point and on the other to the pilot lamp (28) and, via a further resistor (42), to one of the lines (21) (Figure 2).