GB2054141A - Road lamp checking device - Google Patents

Abstract

Light-tight hood 16 fits over a standard road lamp, turning it on if it is controlled by a light sensitive switch. Light dependent resistor 32 is mounted against hole 26 in the hood opposite a lens enclosure of the lamp, to receive light therefrom. When the lamp flashes, light emitting diode D1 flashes in synchronism, indicating correct operation. If the power of the lamp is below a first predetermined level, such that the batteries would be likely to fail if left over a weekend, this is detected and light emitting diode D3 is turned on. If the power of the lamp is below a second, lower predetermined level, such that the batteries would be likely to fail if left overnight, light emitting diode D3' is turned on. <IMAGE>

Description

SPECIFiCATION Road lamp checking device This invention relates to a device for checking the operation of road lamps, and particularly road lamps used to warn motorists of hazards.

A common form of such road lamp has a casing containing Leclanché dry cell batteries. On top of this is provided a double-sided lens enclosure containing a light bulb. The casing also includes circuitry for causing the bulb to flash, which both provides a more noticeable warning and increases battery life. Furthermore, a light sensitive switch is provided either in the casing or the lens enclosure which is arranged to turn the bulb and the flashing circuit on only when darkness falls, so that the batteries are not wasted during the hours of daylight. Other forms of road warning lamps are continuously lit (i.e. they have no flashing circuit) and/or they are switched on manually instead of by a light sensitive switch.

Naturally, a problem with all such road lamps is that the battery life is limited and thus in time the battery voltage will fall as the internal resistance of the battery increases.

When a road lamp is left to warn of hazard, therefore, it is essential to know firstly that it is functioning correctly; and secondly that enough power remains in the batteries to maintain an adequate light intensity throughout the hours of darkness, or for longer periods of time if for example the lamp is to be left over a weekend.

One way of checking that lamps are functioning correctly which has been used in the past is to cover the lamp, e.g. with the operator's coat. This covers the light sensitive switch so that the lamp turns on and starts flashing. However, in bright sunlight it will still be very difficult to see that the lamp is flashing, and probably the lamp will be obscured by the coat. Such a method of course is very haphazard.

My invention provides a road lamp checking device comprising a hood or canopy for fitting over the lamp in a substantially light-tight arrangement, having a light sensitive element arranged to receive light from within the hood; and indicator means acted on by the light sensitive element to produce an indication when light is received from a road lamp within the hood or canopy.

The indicator means may comprise one or more indicating lamps or light emitting devices. It may operate in synchronism with any flashing of a road lamp within the hood or canopy. Alternatively or additionally, it may provide an indication of whether the amount of light received from a road lamp within the hood or canopy by the light sensitive element is above or below a predetermined level. There may be two such indicators which each operate when the light received from within the hood or canopy falls below respective different pre-determined levels.

Road lamp checking devices according to my invention will now be described by way of example, with reference to the accompanying drawings, wherein: Fig 1 shows a hood forming part of such a device, in position over a road lamp; Fig. 2 is a diagrammatic vertical cross-section through the device of which the hood in Fig 1 forms part, taken along the line Il-Il in Fig 1; Figs. 3 to 5 are circuit diagrams of respective parts of circuitry used in the device; Figs. 6A, 7A, and 8A are front views of three standard types of road lamp; and Figs. 6B, 7B, and 8B show diagrammatically hoods that can be used with the roadlamps of Fig.

6A,7A and 8A, respectively.

Fig. 1 shows a standard design of road lamp 10 comprising a double sided lens enclosure 12 mounted on top of a battery casing 14. Over this fits in a substantially light-tight relationship a generally box-like hood or canopy 16, which has a carrying handle 1 8 for ease of fitting over and removal from the lamp 10. Inarticular the lower, open end portion of the hood 16 is a reasonably close fit over the battery casing 14 so as not to admit an undue amount of ambient light and so as to cover and actuate a light sensitive switch (not shown) of the road lamp. In the bottom edge of the hood 16, semi-circular cut-outs 20 are provided to accommodate a fixing bolt 22 provided on the standard design of road lamp 10.

The road lamp 10 is shown as having legs 24 forming a tripod base, but the hood 16 could equally be fitted over a road lamp 10 without such a base.

The hood 16 has a small hole 26 in its front 30, which is so positioned in relation to the interior dimensions of the hood 16 that with the standard design of road lamp 10 for which the hood is intended it is positioned opposite the centre of the lens enclosure 12.

In addition to the hood 16 as shown in Fig. 1, the device comprises a box 28 (Fig 2) which is secured to the front face 30 of the hood 16 over the hole 26. The box 28 contains the electronic circuitry of the device, mounted on a board 34.

This includes a light dependent resistor 32 of type ORP 12, which is so positioned in the box 28 that when the box is secured on the hood 1 6 the light dependent resistor 32 is held close to the hole 26.

There are also three light emitting diode indicators D1, D3, D3' protruding through the box 28. A photodiode or phototransistor could be used in place of the light dependent resistor 32 if desired.

In use, a person wishing to check the operation of a number of road lamps 10 of the flashing type operated by a light sensitive switch, positioned around a hazard such as roadworks, will take the device by the carrying handle 1 8 and place the hood 16 over each road lamp 10 in turn. As soon as it is covered by the hood 16, the road lamp 10 will turn on and will start to flash, assuming it is functioning correctly. If the road lampl-0 10 is of the manually operated variety the user will of course turn it on first: The light dependent resistor 32 then reacts to the light emitted from the road lamp 10 as will now be described.

Fig 3 shows the light dependent resistor 32 which is connected in a voltage divider circuit with a resistor R1 and a variable resistor P 1. Thus, when the road lamp 10 emits a flash of light, the resistance of the light dependent resistor 32 will fall, turning a transistor T1 on. Current flows through the transistor T1 and causes the light emitting diode D1 to flash in synchronism wjth the road lamp 10. This indicates to the user whether the road lamp is flashing normally. The sensitivity of the circuit can be adjusted by P 1.

Of course, to some extent the brightness of the light emitting diode D1 will tell the user about the condition of the battery in the road lamp 10, since if the battery voltage is very weak the lamp will not flash very brightly and accordingly the light emitting diode D1 will not flash very brightly. The circuit of Fig 3 could thus be used by itself as a very simple road lamp checking device.

In the present device, however, an output is taken at a point A in Fig 3 (the junction between the light dependent resistor 32 and the resistor R1) and is taken to an input resistor R4 of a peak detector circuit shown in Fig 4. The function of this circuit is to provide an analogue output which varies with the height of the peak of the pulses produced by the light dependent resistor 32 in response to the flashing of the road lamp 10. The input from point A is taken through the resistor R4 to the non-inverting input of an operational amplifier Al suitably of type Lem 101. At the output of the amplifier Al there are arranged a diode D2, a capacitor C1 and a feedback resistor R5.This arrangement builds up a charge on the capacitor C1 through the diode D1 during every positive peak, which charge is then-maintained until the next peak occurs. Accordingly, the voltage on C1 varies with the height of the incoming peaks. This voltage is taken as an output from the circuit of Fig 4 at a point B to each of two circuits as shown in Fig 5.

The input of the circuit of Fig 5 at point B is taken through a resistor R8 to the non-inverting input of a comparator A2. This is suitably provided.

by an operational amplifier type 741, or more preferably, since the circuit of Fig 5 is duplicated, each may be provided by one half of a dual operational amplifier integrated circuit of type 747. The inverting input of the comparator A2 is fed with a preset voltage taken from a resistive divider comprising resistors R6, R7 and a potentiometer P2. By varying the setting of the potentiometer P2, the input voltage at point B at which the output of the comparatorA2 changes state can be varied. A feedback resistor R9 provides a small degree of hysteresis in the operation of the comparator A2. When the level of the voltage at the input point B rises above the level preset by potentiometer P2, the amplifier A2 will turn on the light emitting diode D3, or (in the duplicate circuit of Fig 5) D3'.

To set up the checking device, first of all the variable resistor P1 in the circuit of Fig 3 is preset so as to give the light dependent resistor 32 a desired amount of sensitivity to suit the standard design of road lamp to be tested. Then, a road lamp which is powered not by batteries but by a variable power supply is inserted in the hood 16.

The potentiometers P2 in the two circuits of Fig 5 are then each adjusted so that one light emitting diode D3 turns on when the power supply voltage is reduced to approximately 3.7 volts, which the other potentiometer P2 is adjusted until the light emitting diode D3' is turned on when the power supply voltage to the lamp is reduced to about 3.2 volts. These values are chosen to correspond with those battery voltages which would satisfactorily power the road lamp 10 over a weekend or overnight respectively. Of course, for other types of road lamps or other batteries, or if it is desired to indicate different lengths of time for remaining battery life, then the potentiometers P2 can be adjusted accordingly.

To make the checking device simper to use, the three light emitting diodes D1, D3, D3' are preferably different colours. Suitably the diode D1 is green (since it indicates that the road lamp 10 is flashing normally); the diode D3 is yellow: and the diode D3' is red (indicating that there is insufficient battery life to last through one night).

Although visible indicators are most convenient, audible indicators can also be used.

To achieve best operation of the checking device, it is important that the hole 26 and the light sensitive resistor 32 should be positioned in a reproducible location relative to the lens enclosure 1 2, and preferably opposite the centre of the lens enclosure 12. With the arrangements shown in Fig. 1 and 2, this can only be ensured if the hood 1 6 is used only over one particular standard design of road lamp 10. It will be a fairly simple matter to make a hood 16 of a different size to suit each different standard design of road lamp. The box 28 containing the electronic circuitry could be standardised to fit any of these hoods. However, Figs. 6B, 7B, 8B show very diagrammatically how one hood 16 could be adapted to fit any of three standard designs of a road lamp 10 shown in Figs.

6A, 7A, 8A. The distance H 1 (in Fig. 6B) from the top of the hood 1 6 to the hole 26 corresponds to the distance from the top of one of the road lamps 10 to the centre of its lens enclosure 12. By fitting a spacer 40 which has a thickness F1 in the upper end of the hood 16, as shown in Fig. 7B, an effective distance H2 is produced form the hole 26 to the spacer 40, and this corresponds with the distance from the top of a second type of road lamp 10 to the centre of its lens enclosure 12 (Fig.

7A). By including a third spacer 42 of a thickness F2 (Fig. 8B) the effective distance from the spacer 42 to the hole 26 is reduced to a distance H3, which corresponds with the height of a third form of road lamp 10 (Fig. 8A) from the centre of its lens enclosure 12 to its top.

Of course, many modifications can be made to the devices described. For example, instead of a hole 26, the light dependent resistor 32 could be mounted inside the hood 16 and be connected by wires within the hood to the circuitry mounted in a box on the top of the hood. The carrying handle 18 could then be omitted. Also, to speed up the operation of the circuitry, the peak detector of Fig.

4 could be followed by a buffer, e.g. an operational amplifier connected as a voltage follower, with feedback to the input of amplifier Al.

Claims (8)

1. A road lamp checking device comprising a hood or canopy for fitting over the lamp in a substantially light-tight arrangement, having a light sensitive element arranged to receive light from within the hood; and indicator means acted on by the light sensitive element to produce an indication when light is received from a road lamp within the hood or canopy.

2. A device according to claim 1 wherein the indicator means operates in synchronism with any flashing of a road lamp within the hood or canopy.

3. A device according to claim 1 or claim 2 wherein the indicator means operates when the amount of light received by the light sensitive element from within the hood or canopy falls below a pre-determined level.

4. A device according to claim 3 wherein the indicator means comprises two indicators which each operate when the amount of light received from within the hood or canopy falls below respective different pre-determined levels.

5. A device according to claim 3 or claim 4 including a peak detector circuit which provides an analogue output in accordance with the height of the peaks of a signal produced from the light sensitive element when the hood or canopy is over a flashing road lamp, the analogue output being taken to a circuit or circuits which operate the indicator means when the analogue output reaches a level or levels corresponding to said pre-determined light level or levels.

6. A device according to any one of the preceding claims wherein the indicator means comprises one or more indicator lamps or light emitting devices.

7. A device according to any one of the preceding claims wherein the hood or canopy has one or more spacers removably located therein whereby the hood or canopy may fit over more than one type of road lamp with the light sensitive element generally in a similar positional relationship thereto.

8. A road lamp checking device substantially as described herein with reference to Figs. 1 and 2; Figs. 1 to 5; or Figs. 1 and 2 as modified by Figs.

6B, 7B and 8B, of the accompanying drawings.