GB2288667A

GB2288667A - Voltage detector

Info

Publication number: GB2288667A
Application number: GB9407723A
Authority: GB
Inventors: Graham John Barr
Original assignee: WIRE WATCHER CO Ltd
Current assignee: WIRE WATCHER CO Ltd
Priority date: 1994-04-19
Filing date: 1994-04-19
Publication date: 1995-10-25
Anticipated expiration: 2014-04-19
Also published as: GB9407723D0; GB2288667B

Abstract

An induced voltage detector has an indicator activated as the induced voltage rises above a first threshold and deactivated only when the voltage drops below a second lower threshold. As described flashing light and audio indicators warn a driver of vehicle proximity to power lines. An override button may be activated to disable the warning while below the first threshold, a red/green light indicating whether the second level is still exceeded. As shown detector 14 initially directly connected to probe 11, trips switch 13 when actuating the warning, lowering the threshold by connecting preamplifier 12 into circuit. <IMAGE>

Description

VOLTAGE DETECTOR This invention relates to a voltage detector. It can be used to warn a vehicle operator of his approach to conductors carrying a voltage of a value such that contact or even a close approach could cause injury.

A known voltage detector has an indicator and a sensor responsive to an induced voltage above a given threshold value to activate the indicator only when the induced voltage is above the threshold. This has the disadvantage that as the sensor moves from a region of an induced voltage above the threshold to one below it, the indicator will be disabled, but in some situations, such as in the region immediately below parallel conductors carrying three phase alternating current, there is a phantom low induced voltage area even though conductors carrying dangerously high voltages are still in the vicinity.

, > The present invention therefore improves the known detector by arranging the sensor to be responsive to induced voltages of two thresholds - activating the indicator as the induced voltage rises past a first threshold and only deactivating the indicator when the induced voltage drops past a second, lower, threshold.

Even though the induced voltage in the "phantom" low induced voltage area may drop below the first threshold, the second threshold can be selected so that it is below all induced voltages encountered in the phantom areas, so that the indicator will remain activated insuch areas.

The detector can be arranged to operate differently when the induced voltage is above or below the first threshold.

For example, means may be provided to discontinue the output of the indicator responsive to the sensor to be operative only when the induced voltage is below the first threshold.

An example of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagram of prior art, Figure 2 is a corresponding diagram of the example of the invention.

An indicator comprises a red flashing warning light and a status light which light is adapted to change colour to indicate change of status. A probe is connected across a detector circuit to earth. The detector circuit compares the voltage induced at the probe with a first reference voltage representing a first threshold and with a second lower reference voltage representing a second threshold.

When the detector including the indicator and sensor described in the preceding paragraph is far from any high voltage conductor, the status indicator shows a green light. The induced voltage rises as the conductor is approached. The detector ignores the rise of the corresponding voltage in the detector circuit past the second reference voltage, but when it rises past the first reference voltage, it sends an activating signal to the indicator to cause the red light to flash and the green light to change to red. Additional alarms may be added to the indicator, including audio alarms, and there may be warning indicators outside a vehicle carrying the detector duplicating that on the inside.

Once the indicator has been energised, the sensor does not de-energise it until the induced voltage drops sufficiently for the voltage induced in the detecting circuit to drop past the second reference voltage. This means that if the detector assembly moves into a phantom area where the induced voltage drops in spite of the close presence of high voltage conductors, the indicator will remain energised even though the voltage in the detecting circuit drops below the first reference voltage. Provided the second reference voltage is sufficiently low that the detecting circuit voltage never reaches it in a phantom area, the indicator will ignore the phantom area.

An override button is provided. If pressed for two seconds, it may be effective to cancel the energisation of the red flashing warning light and any associated alarms.

It will not be effective when the detected voltage is above the first reference voltage, so that the warning light and alarms can only be made ineffective when the detected voltage is between the first and second reference voltages.

When the light and alarms are made ineffective, an intermittent indicator operating, for example, at intervals of 30 seconds is energised so that the operator is given a regular warning that the detected voltage is still above the second threshold.

The status light shows green when the detected voltage is below the first reference voltage and it shows red when it is above it. The status light is not affected by the second reference voltage.

The difference between the two thresholds can be achieved by a preamplifier which is selectively connected between the probe and the detecting circuit. When there is a direct connection from the probe to the detecting circuit, the voltage V at the detecting circuit which causes it to trip is the first reference voltage at the probe. When the preamplifier is connected, amplifying the voltage at the probe by a factor of N to present the amplified voltage at the detecting circuit, the detecting circuit trips when the voltage at the probe is V/N. The tripping of the detector circuit when the voltage induced at the probe reaches the first reference voltage V causes the preamplifier to be connected. Thus although the detecting circuit will trip back to its original state when the voltage at its input drops below V, the voltage at the probe must drop below V/N for this to happen, and V/N is the second reference voltage. When the detecting circuit is tripped back to its original state, the preamplifier is disconnected again, so that the induced voltage must rise again to the first reference voltage V to cause the detecting circuit to trip once more.

In Fig. 3, the probe is shown at 11, the preamplifier at 12 and a selector switch 13 which can be activated to connect the preamplifier between the probe 11 and the detector 14. The detector 14 has a trip output 15 which is used to operate the switch 13, as well as to operate the alarms not illustrated in this figure.

Claims

1. A voltage detector comprising an indicator and a sensor responsive to induced voltages, adapted to activate the indicator as the induced voltage rises past a first threshold and only deactivating the indicator when the induced voltage drops past a second threshold lower than said first threshold.

2. A detector as claimed in claim 1 comprising means to disable the indicator when the induced voltage is below said first threshold.

3. A detector as claimed in claim 2 comprising a further indicator, not responsive to said disabling means, to indicate when the induced voltage is above said second threshold.

4. A voltage detector substantially as hereinbefore described with reference to the accompanying drawings.