GB2231672A

GB2231672A - Voltage spike detector

Info

Publication number: GB2231672A
Application number: GB8904310A
Authority: GB
Inventors: Bhikhu Ardeshir Unvala; Chin Lai Lang; Francis Minoru Saba
Original assignee: MATELECT Ltd; NPM International
Current assignee: MATELECT Ltd; NPM International
Priority date: 1989-02-24
Filing date: 1989-02-24
Publication date: 1990-11-21
Anticipated expiration: 2009-02-24
Also published as: GB2231672B; GB8904310D0

Abstract

A detector for detecting spikes on a mains electricity supply and for counting the number of spikes occurring during a period of time includes a zener diode (Z2, Z3) connected in series with a resistor (R4) and a counter (IC1) having an input connected across the resistor. The zener diode and resistor are connected in series to the mains supply and the zener diode has a breakdown voltage of a magnitude such that under normal conditions it does not breakdown but upon occurrence of a spike in excess of a predetermined magnitude the zener diode breaks down and provides an input to the counter. <IMAGE>

Description

INTERFERENCE DETECTOR This invention relates to detectors for detecting the occurrence of interference signals and in particular to the detection of interference voltage spikes on mains electricity supplies.

The occurrence of interference signals may cause malfunctioning of electronic equipment. For example data in personal computers may be corrupted and the operation of sensitive instruments may be adversely affected by such interference. Such interference may be radiated and received by the equipment but is often borne on the mains supply used to power the equipment. Mains borne interference may be due to operation of other equipment from the same mains supply, for example from electric motors used to drive machinery. Accordingly prior to using equipment which may be adversely affected by voltage spikes on the mains supply it is desirable to determine whether the mains supply is sufficiently clean for use of such equipment or whether it will be necessary to insert suitable filters in the mains supply to remove the voltage spikes.Also it may be found that existing equipment is mal-functioning and it is desired to determine whether it is as a result of mains borne voltage spikes.

According to one aspect of the invention a detector for detecting voltage spikes on an electrical circuit including first means operative in response to a voltage spike in the electrical circuit in excess of a predetermined magnitude to generate a signal and counting means responsive to said signal to provide an indication of the number of voltage spikes detected.

According to another aspect of the invention a detector for detecting voltage spikes on a main electricity supply including first means connectable to a supply to be tested to generate from the supply a voltage level which has a first magnitude when the mains supply is energised and a second magnitude when the mains supply is energised and a voltage spike is present on the supply; second means operative in response to the second magnitude of voltage level being at a predetermined value in excess of the first magnitude to generate a count input signal; and a counter operated by the count input signal to provide an indication of the number of occurrences of voltage spikes having a magnitude in excess of said predetermined value.

An embodiment of the invention will now be described by way of example with reference to the drawings in which:- Figure 1 is a circuit diagram of a voltage spike detector and Figure 2(a) and 2(b) show front and side views respectively of a convenient physical construction and housing for the detector.

Referring to Figure 1 of the drawings, the circuit is connected to an alternating current mains supply which it is desired to test for the occurrence of voltage spikes.

The mains supply is applied between a live input terminal L and a neutral input terminal N. The alternating mains supply input is rectified by a bridge rectifier consisting of diodes D1, D2, D3, D4, the connection from the live terminal L being through a fusible resistor R1 to prevent excessive current flow in the event of failure of a component in the circuit. A negative output from terminal 10 of the bridge rectifier is connected to a common zero volt line 1z and a positive output from terminal 11 of the bridge rectifier is connected to input point 13 of the detector circuit. With a 240 volt A.C. mains input the peak rectified voltage at point 13 is approximately 350 volt.Upon occurrence of an interference voltage spike on the mains supply, the voltage at point 13 will rise to a peak voltage dependent upon the amplitude of the voltage spike.

The detector circuit includes a chain of zener diodes Zi, Z2, Z3 and a resistor network connected in series between the point 13 and the zero volt line 12. The resistor network comprises resistor R4 with resistors R5 and R6 connected in series across resistor R4. The junction of zener diodes Z1 and Z2 is connected through series resistors R2 and R3 to a zener diode s4, the other side of the zener Z4 being connected to zero volt line 12. Zener diodes zi, Z21 Z3, Z have breakdown voltages of 91, 150, 150 and 6.8 respectively.Accordingly when the circuit is powered from the mains supply, there is a potential of 6.8 volts across the zener diode 24 which is utilised to power a decade counter ICl on terminal vcc thereof. This 6.8 volt supply for powering the counter is smoothed by a capacitor Cl connected across zener diode Z4. A reset terminal Re of the counter IC1 is connected to the zero volt line 12 through a resistor R8 and is connected to the 6.8 volt supply on terminal Vcc by a capacitor C2. Asa result when mains power is initially applied between terminals L and N and the 6.8 volt supply is produced at terminal Vcc, a pulse is applied to the reset terminal Re to reset the decade counter fC1 to its zero count state.

The junction of resistors R5 and R6 is connected through a current limiting resistor R7 to a clock input terminal Cik of counter ICl. It will be appreciated that instead of two zener diodes z2 and Z3, a single zener diode of appropriate breakdown voltage may be used.

When the mains supply input is clean and there are no interference voltage spikes, the peak rectified voltage at point 13 is approximately 350 volts. With the point 13 at a voltage of this level the voltage across the zener diodes Z2 and Z3 is insufficient to cause breakdown thereof and they have high impedance.Therefore no signal is applied to the clock input terminal Clk. However when the voltage at point 13 rises, due to a spike voltage on the mains supply input, to a level at which the voltage across the zener diodes Z2 and Z3 is sufficient to result in breakdown thereof, the voltage across resistor R4 rises and an input is applied to the clock input terminal Cik of the counter IC1 to cause the counter to step to its next higher count state, The counter lCl has ten output terminals corresponding to count states of 'O' to '9' respectively. Light emitting diodes (LED) are connected to the output terminals of the counter and to the zero volt line 12 through a common resistor R9.The outputs of the counter drive the LEDs directly to cause illumination thereof so that at any time the LED connected to an output terminal corresponding to the count state of the counter is illuminated and thereby indicates the count state of the counter. The output terminal of the counter corresponding to the 9 state is connected to a count inhibit terminal Inh of the counter so that when the counter is stepped to the 9 state further counting is inhibited and counter and the count indication provided by the LEDs remains frozen at the 9 state.

With zener diodes ZI, s2 and z3 having the breakdown voltages referred to hereinbefore, the counter is stepped on each time a voltage spike in excess of approximately 50 volts is present on the input mains supply until a maximum count of '9' is obtained. However if desired by utilising zener diodes having different breakdown voltages, the counter may be caused to step in response to voltage spikes of different magnitude. While the circuit has been described as utilising a counter having a maximum count of '9', if desired, counters having other values of maximum count may be used.

The voltage spike detector circuit described hereinbefore may be housed in a housing as shown in Figures 2(a) and 2(b). The housing comprises a hollow body 14 having a base wall formed to provide a mounting for the pins 15 of a standard mains plug. An upper wall 16 of the housing is provided with ten apertures 17 through which the ten LEDs may be viewed.

When it is desired to determine the extent to which a mains power supply is effected by interference voltage spikes, the detector device is plugged into a socket of that mains supply. This causes the counter to be powered to be reset to the '0'state so that the state LED is illuminated. If voltage spikes occur, the counter will be stepped by the spikes thereby causing the LEDs to be successively illuminated to indicate the number, up to a maximum count of 9, of voltage spikes detected. The mains supply may then be cleaned by insertion of filters suitable to remove the voltage spikes and the detector device may then be used again to determine the effectiveness of the inserted filters.

Claims

1. A detector for detecting voltage spikes on an electrical circuit including first means operative in response to a voltage spike in the electrical circuit in excess of a predetermined magnitude to generate a signal and counting means responsive to said signal to provide an indication of the number of voltage spikes detected.

2. A detector as claimed in claim 1 wherein the electrical circuit is at a first potential and said first means includes a zener diode haing a breakdown voltage in excess of said first potential and approximately equal to the sum of said first potential and the predetermined magnitude.

3. A detector for detecting voltage spikes on a main electricity supply including first means connectable to a supply to be tested to generate from the supply a voltage level which has a first magnitude when the mains supply is energised and a second magnitude when the mains supply is energised and a voltage spike is present on the supply: second means operative in response to the second magnitude of voltage level being at a predetermined value in excess of the first magnitude to generate a count input signal; and a counter operated by the count input signal to provide an indication of the number of occurrences of voltage spikes having a magnitude in excess of said predetermined value.

4. A detector as claimed in claim 3 in which said first means includes a rectifier.

5. A detector as claimed in claim 3 or 4 in which said second means includes.at least one zener diode which has a breakdown voltage such that the zener diode breaks down when the voltage level exceeds the second magnitude.

6. A detector as claimed in claim 5 wherein the second means includes first and second zener diodes connected in series with a first resistor; a junction between the first and second zener diodes is connected through a second resistor to a third zener diode, said first and third zener diodes and said second resistor operating to provide across the third zener diode a voltage for powering the counter; said second zener diode being in a high impedance state when the second magnitude of voltage level is less than the predetermined value above the first voltage level and being driven to a low impedance state when the second magnitude of voltage level is greater than the predetermined value above the first voltage level whereby current passes through the first resistor and generates the count input signal 7.A detector constructed and arranged to operate substantially as hereinbefore described with reference to Figure 1 of the drawings.

8. A detector constructed and arranged to operate substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the drawings.

Amendments to the claims have been filed as follows 1. A detector for detecting voltage spikes on an electrical circuit including first means operative in response to a voltage spike in the electrical circuit in excess of a predetermined magnitude to generate a signal and counting means responsive to said signal to provide an indication of the number of voltage spikes detected.

2. A detector for detecting voltage spikes on an electrical power circuit including a housing; an electrical connector integral with said housing and comprising at least first and second connector pins for connection to the electrical power circuit; an electronic circuit housed in said housing connected to said first and second connector pins and comprising first means operative in response to a voltage spike across said first and second connectors in excess of a predetermined magnitude to generate a signal and counting means responsive to said signal to provide an indication of the number of voltage spikes detected.

3. A detector as claimed in claim 1 or 2 wherein the electrical circuit is at a first potential and said first means includes a zener diode having a breakdown voltage in excess of said first potential and approximately equal to the sum of said first potential and the predetermined magnitude.

4. A detector for detecting voltage spikes on a main electricity supply including first means connectable to a supply to be tested to generate from the supply a voltage level which has a first magnitude when the mains supply is energised and a second magnitude when the mains supply is energised and a voltage spike is present on the supply; second means operative in response to the second magnitude of voltage level being at a predetermined value in excess of the first magnitude to generate a count input signal; and a counter operated by the count input signal to provide an indication of the number of occurrences of voltage spikes having a magnitude in excess of said predetermined value.

5. A detector as claimed in claim 4 wherein the first means, the second means and the counter are housed in a housing and including electrical connector pins mounted on said housing for connection to the main electricity supply.

6. A detector as claimed in claim 4 or 5 in which said first means includes a rectifier.

7. A detector as claimed in claim 4, 5 or 6 in which said second means includes at least one zener diode which has a breakdown voltage such that the zener diode breaks down when the voltage level exceeds the second magnitude.

8. A detector as claimed in claim 7 wherein the second means includes first and second zener diodes connected in series with a first resistor; a junction between the first and second zener diodes is connected through a second resistor to a third zener diode, said first and third zener diodes and said second resistor operating to provide across the third zener diode a voltage for powering the counter; said second zener diode being in a high impedance state when the second magnitude of voltage level is less than the predetermined value above the first voltage level and being driven to a low impedance state when the second magnitude of voltage level is greater than the predetermined value above the first voltage level whereby current passes through the first resistor and generates the count input signal.

9. A detector as claimed in any preceding claim wherein the counting means includes a plurality of light emission devices, said devices corresponding to different count values respectively and the counting means being constructed to energise a seiected light emission device to provide the indication of the number of voltage spikes detected.

10. A detector as claimed in claim 2 or 5 wherein the counting means includes a plurality of light emission devices mounted in said housing adjacent apertures in a first wall of said housing, said devices corresponding to different count values respectively and the counting means being constructed to energise a selected light emission device to provide the indication of the number of voltage spikes detected.

11. A detector as claimed in claim 10 wherein the connector pins extend from a base wall of the housing opposite the first wall of the housing.

12. A detector as claimed in any preceding claim and constructed as hereinbefore described hereinbefore with reference to Figures 2(a) and 2(b).

13. A detector constructed and arranged to operate substantially as hereinbefore described with reference to Figure 1 of the drawings.

14. A detector constructed and arranged to operate substantially as hereinbefore described with reference to Figures 1, 2(a) and 2(b) of the drawings.