Airfield Lighting Circuit Arrangements

Abstract

An airfield lighting circuit arrangement in which a plurality of lamp units are connected in the form of a loop circuit to which power supply means is connected, gating means being provided to which voltage waveforms corresponding to the loop current and the loop supply voltage are applied for affording an output signal which is indicative of the phase difference between said waveforms and therefore indicative of the number of lamp unit failures in the loop circuit.

Description

This invention relates to circuit arrangements and relates more especially to circuit arrangements for use in airfield lighting series loop circuits.

The individual lamps used in airfield lighting for illuminating perimeter runways, lane routes, etc., are normally connected in one or more series loop circuits fed from a constant current regulator (C.C.R.) and it is becoming increasingly important to know that no more than a fixed percentage of lamps fail at any one time. The present invention is directed to circuit arrangements for affording an indication of the number of failures due to open circuit lamps in such a circuit.

According to the present invention there is provided a circuit arrangement comprising power supply means for supplying power to a loop circuit which includes a plurality of lighting units, and means for affording an output signal in dependence upon the phase difference between the loop current and the loop supply voltage. The output signal thus afforded is indicative of the number of open circuit lighting units in said loop circuit.

In one arrangement for carrying out the invention the output signal will be afforded in dependence upon the power factor of the circuit arrangement.

In one preferred arrangement according to the present invention the means for affording the output signal in dependence upon the phase difference between the loop current and the loop supply voltage will comprise balanced modulator means to which voltage waveforms corresponding to the loop current and loop supply voltage are applied, said modulator means affording an output signal which is indicative of the phase difference between said voltage waveforms.

In another preferred arrangement according to the present invention, the means for affording the output signal in dependence upon the phase difference between the loop current and the loop supply voltage will comprise gating means to which voltage waveforms corresponding to the loop current and loop supply voltage are applied, the gating means affording an output signal which is indicative of the phase difference between said voltage waveform.

In an especially preferred arrangement according to the aforesaid another preferred arrangement, the gating means will comprise a first gate which is arranged to be turned "on" by one of the voltage waveforms applied thereto and "off" by the other of the voltage waveforms applied thereto, and a second gate connected in series with a fullwave rectified alternating current signal and operable under the control of the first gate for affording an output signal which, when integrated, is proportional to the volt/seconds of the open circuit lamp units in the loop circuit. Advantageously level detector means e.g. cross-over detectors may be provided operable individually on the voltage waveforms corresponding to the loop current and loop supply voltage respectively, the output from the level detector means being used to control the first gate.

In carrying out the invention according to both of the aforesaid preferred arrangements, the output signal may be used to cause indicator means to be operated and conveniently means associated with the output signal may be provided whereby an indicated output is only afforded when a predetermined number of lighting units have become open circuit.

In practice each of the lighting units may comprise a lamp connected in the loop circuit via an isolating transformer and advantageously the power supply to the loop circuit may be afforded by a constant current regulator .

Some exemplary embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a partially block schematic circuit diagram of one form of circuit arrangement according to the present invention,

FIG. 2 is a partially block schematic circuit diagram of another form of circuit arrangement according to the present invention, and

FIG. 3 shows waveforms existing at various points in the arrangement of FIG. 2.

In the circuit arrangement shown in FIG. 1 of the accompanying drawings, part of a series loop lighting circuit 1 is shown which includes two lamps 2 each fed by individual isolating transformers 3, the primary windings of which are connected in series with the loop. The loop is fed from a constant current regulator CCR of conventional form, the output transformer of which is shown at 4, the lighting circuit 1 being connected to a secondary winding 5 of the output transformer 4.

The power factor of the lighting circuit is fixed by the components used in the series loop and the leakage inductance of the CCR output transformer 4. A lamp failure nearly always results in the lamp going open circuit with the result that the power factor and hence the phase difference between the loop current and loop supply voltage is modified. Therefore by monitoring this phase difference an indication can be obtained of the number of lamps or isolating transformers that have failed by going open circuit.

To monitor the phase difference in the arrangement shown in FIG. 1, a balanced modulator 6 is provided which is arranged to compare the phase of the supply voltage with the phase of the loop current. A signal proportional to the supply voltage is derived from the output transformer 4 of the constant current regulator CCR by means of an additional secondary winding 7 and a signal proportional to the loop current is obtained by means of a further transformer 8 connected in series with the loop 1. The outputs from the secondary winding 7 and the transformer 8 are applied to a balanced modulator 6 of conventional form the net output Vo from which will be zero when the power factor is unity. In practice the power factor of the circuit arrangement with all the lamps working would normally be in the region of 0.95 but this will be modified when one or more of the lamps 2 or isolating transformers 3 go open circuit and consequently an output will be obtained from the balanced modulator 6 which is proportional to the number of open circuit lamps etc. The output Vo of the balanced modulator 6 is applied via a potentiometer 9 to an amplifier 10 in which it may be smoothed and amplified and used to cause a relay 11 to be operated, relay contacts 12 of the relay being used to actuate any convenient form of indicator, alarm etc. By adjusting the setting of the potentiometer 9, it may be arranged that the relay 11 is caused to operate when the maximum number of lamp failures has occurred.

In the arrangement shown in FIG. 2 of the accompanying drawings the output transformer 20 of a constant current regulator CCR is shown having three output windings, output winding 21 for supplying a series loop circuit 1 as in the arrangement of FIG. 1 and two further output windings 22 and 23 as will hereinafter be described. A current transformer 8 is connected in series with the loop circuit 1 also as in the arrangement of FIG. 1. The output from the winding 22 of transformer 20 (shown in FIG. 3 (a)) and the output from the current transformer 8 (shown in FIG. 3 (b)) are fed to level detectors in the form of cross-over detectors 24 and 25 respectively, the outputs from which are applied to a gate 26 which is arranged to be opened say, by the output from detector 24 and closed by the output from detector 25 so that an output waveform is obtained from the gate 26 in the form of a series of pulses, as shown in FIG. 3 (c), the width of the pulses being dependent upon the phase difference between the voltage and current waveforms obtained from the winding 22 and current transformer 8 respectively, and therefore proportional to the number of open circuit lamps in the lighting circuit.

In order to produce a constant volt/second output, the signal from the gate 26 is used to operate a second gate 27 which is connected in series with a full-wave rectified sinusoidal supply derived from output winding 23 of the output transformer 20 and a bridge rectifier 28. The output voltage from gate 27, shown in FIG. 3 (d) is then integrated by means of integrator 29 to afford an output signal at terminals 30 which is proportional to the volt/seconds of the number of open circuit lamps in the series lighting circuit. As in the arrangement of FIG. 1, the output afforded at terminals 30 may be used to cause a suitable indicator to be operated.

It will be appreciated that various modifications may be made to the arrangements described without substantially affecting the principle involved. For example, any suitable form of modulator may be used in the arrangement of FIG. 1 and level detectors other than zero-crossing detectors may be used in the arrangement of FIG. 2.

Claims

What we claim is:

1. An airfield lighting circuit arrangement comprising a plurality of lighting units connected in the form of a loop circuit, power supply means for supplying power to the loop circuit, and gating means to which voltage waveforms corresponding to the loop current and the loop supply voltage are applied, the gating means affording an output signal which is indicative of the phase difference between said voltage waveforms.

2. An airfield lighting circuit arrangement according to claim 1, in which the gating means comprises a first gate which is arranged to be turned "on" by one of the voltage waveforms applied thereto and "off" by the other of the voltage waveforms applied thereto, and a second gate connected in series with a fullwave rectified alternating current signal and operable under the control of the first gate for affording the output signal.

3. an airfield lighting circuit arrangement according to claim 2, comprising level detector means operable individually on the voltage waveforms corresponding to the loop current and loop supply voltage respectively, the output from the level detector means being used to control the first gate.

4. An airfield lighting circuit arrangement according to claim 3, in which the level detector means take the form of crossover detectors.

5. An airfield lighting circuit arrangement according to claim 3, in which the output signal is integrated to afford an output which is proportional to the volt/secononds of the open circuit lighting units in the loop circuit.

6. An airfield lighting circuit arrangement according to claim 1, comprising indicator means which is caused to be operated by the output signal.

7. An airfield lighting circuit arrangement according to claim 6, comprising means associated with the output signal whereby an indicated output is only afforded when a predetermined number of lighting units have become open circuit.

8. An airfield lighting circuit arrangement according to claim 1, in which each of the lighting units comprise a lamp connected in the loop circuit via an isolated transformer.

9. An airfield lighting circuit arrangement according to claim 1, in which the power supply means takes the form of a constant current regulator.