FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An electronic device for continuously monitoring the neutral to earth voltage of an electronic or electrical equipment operating on AC mains
APPLICANTS
Mahindra & Mahindra Ltd, Gateway Building, Apollo Bunder, Mumbai 400001, Maharashtra, India, an Indian company
INVENTORS
Chaudhary Sumeet Ashok, Plot "No 136, Anusaya "Niwas, Vaibhav Nagar, Dhighory, Nagpur - 440034, Maharashtra, India and Dagli Dhara Deepak, 189, Arihant building Ekori ward, Ambedkar chowk, Chandrapur - 442402, Maharashtra, India, both Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to an electronic device for continuously monitoring the neutral to earth voltage of an electronic or electrical equipment operating on AC mains.
This invention also relates to an electronic device for continuously monitoring the neutral to earth voltage of an electronic or electrical equipment operating on AC mains and disconnecting the AC mains from the equipment under neutral to earth over voltage conditions.
The description in the provisional specification of this application including the drawings accompanying the provisional specification are incorporated herein by reference in entirety and form part of this specification.
BACKGROUND OF THE INVENTION
In the case of an AC power supply, the potential difference between the neutral and earthing lines thereof is expected to be zero in ideal conditions. However, it can be less than 1 V for practical purposes. The potential difference may exceed the desirable limits due to various fault conditions like loose wiring or absence of earthing. When the potential difference values of neutral and earthing are less than 1 V they are not normally harmful to the associated electronic or electrical equipments. However, when the voltage value of neutral to earth exceeds 1 V, it will not only steadily decrease the performance of the equipment but will also gradually damage the equipment. It may also cause electrical shocks and accidents.

The practice generally or conventionally followed is to check the neutral to earth wiring of such equipments at the time of installation thereof or periodically after the installation. If, in the meantime, the earthing or neutral wiring becomes loose, then the neutral to earth voltage may exceed the desirable value and create problems as discussed above. There is thus need for a device that continuously monitors the neutral and earth voltage of such equipments so as to take remedial action at the appropriate time and thereby obviate or prevent problems as discussed above.
SUMMARY OF THE INVENTION
According to the invention there is provided an electronic device for continuously monitoring the neutral to earth voltage of an electronic or electrical equipment operating on AC mains, comprising a voltage amplifier configured to receive and amplify the voltage across the neutral and earthing of the equipment, a voltage rectifier configured to receive and rectify the voltage from the amplifier, a voltage comparator configured to compare the rectified voltage received from the rectifier with a reference DC voltage preset in the comparator and give a low output or a high output depending on whether the rectified voltage is below the reference voltage or at or above the reference voltage, a semiconducting switch configured to remain in open position when the comparator output is low and to switch to closed position when the comparator output is high and a relay comprising a common contact, a normally closed (NC) contact and a normally open (NO) contact, the amplifier being configured to receive power from a DC power supply, the voltage comparator and common contact of the relay being powered by a DC voltage source, the NC contact of the relay being connected to a first indicator and the NO contact of the relay being connected to a second indicator.

According to the invention there is also provided an electronic device for continuously monitoring the neutral to earth voltage of an electronic or electrical equipment operating on AC mains and disconnecting the AC mains to the equipment under neutral to earth over voltage conditions, comprising a voltage amplifier configured to receive and amplify the voltage across the neutral and earthing of the equipment, a voltage rectifier configured to receive and rectify the voltage from the amplifier, a voltage comparator configured to compare the rectified voltage received from the rectifier with a reference DC voltage preset in the comparator and give a low output or a high output depending on whether the rectified voltage is below the reference voltage or at or above the reference voltage, a semiconducting switch configured to remain in open position when the comparator output is low and to switch to closed position when the comparator output is high and a relay comprising a common contact, a normally closed (NC) contact and a normally open (NO) contact, the amplifier being configured to receive power from a DC power supply, the voltage comparator and common contact of the relay being powered by a DC voltage source, the NC contact and NO contact of the relay being connected to a tripping device connecting the equipment to the AC mains.
Examples of electronic equipments include programmable logic controls (PLCs), computer numeral controls (CNCs), microprocessors or microcontroller cards. Examples of electrical equipments include motors, generators or power distribution boards.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 of the drawings accompanying this specification is a block diagram of an electronic device for continuously monitoring the neutral to earth voltage of an electronic or electrical equipment according to an embodiment of the invention; and
Fig 2 is a circuit diagram of the electronic device of Fig 1 without the voltmeter and first and second indicators.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The electronic device 30 as illustrated in Figs 1 and 2 of the drawings accompanying this specification comprises a voltage amplifier 32 configured to receive and amplify the potential difference or voltage across the neutral 14 and earthing 16 of an electronic or electrical equipment (not shown) operating on AC mains (not shown). 37 is a voltage rectifier configured to receive and rectify the voltage received from the amplifier. 34 is a voltage comparator configured to compare the rectified voltage received from the rectifier with a reference DC voltage preset in the comparator and give a low output or a high output depending upon whether the rectified voltage is below the reference voltage or at or above the reference voltage.
A semiconducting switch 54 is configured to remain in open position when the comparator output is low and to switch to closed position when the comparator output is high. 36 is a relay comprising a magnetic coil 36a, a common contact C, a normally closed (NC) contact and a normally open (NO) contact. The contacts of the

relay are isolated from the magnetic coil thereof. Therefore, the contacts are potential free contacts. The amplifier is configured to receive power from a DC power supply 31. The DC power supply is derived from the AC mains through a metal oxide varistor MOV2, spike suppressor 100, voltage step down transformer 33 and a rectifier 35. The varistor MOV2 is of 230 V rating used to protect the components of the DC supply from over voltage. It blows off when the AC supply exceeds 230 V. The spike suppressor is of 250 VAC, 50 Hz, 3A and suppresses spikes in the AC supply. 31a is a DC voltage source stepped down and derived from the DC power supply. 38 and 40 are a first indicator and a second indicator connected to the NC contact and NO contact of the relay, respectively.
The amplifier 32 preferably comprises a voltage summing amplifier 50 having two input pins 2 and 3, an output pin 6, and two supply terminals 4 and 7 connected to the DC supply 31. The input pin 3 is connected to the earthing 16 via resistance Rin4 of a rating of 5W. R is to prevent reverse flow of current from earthing 16. In case of reverse flow of current from the earthing, the resistance Rin4 gets fused. The input pin 2 is connected to the neutral 14 via parallel resistances Rin4 1 , Rin2 , and Rin3 The values of the above resistances are in the order of kilo ohms and are generally provided in order to have a voltage of increased magnitude at input pin 2. The input pin 2 is further connected to the output pin 6 via resistance Rf. The value of Rf determines the factor by which the input neutral to earth voltage is amplified. Preferably, the input neutral to earth voltage is amplified by a factor of 7-10 to detect neutral to earth voltage variations of two decimal places. MOVi is a metal oxide varistor of 25 V rating connected across the neutral 14 and earthing 16 to protect the amplifier 32 from over voltage. MOVi blows off when the voltage exceeds 25 V.

The rectifier 37 is preferably a diode rectifier. During operation of the device the diode rectifier 37 converts the amplified voltage of pin 6 to a DC voltage. The device optionally comprises a filter 19, preferably a low pass filter comprising a capacitor C\ provided to filter out any high frequencies or high frequency ripples present in the rectified voltage.
The comparator 34 preferably comprises an operational amplifier 52 having two input pins 2 and 3, an output pin 6 and voltage supply terminals 4 and 7 connected to the DC voltage source 31a. The input pin 3 is connected to DC voltage node 51 via a voltage divider network consisting of resistors RC1, RC2 RC3 and RC4 The input pin 2 is connected to the voltage supply terminal 7 via resistors RC5 and RC6. The value of resistors RC5 and RC are set in such a manner that a fixed reference voltage of 4.4V appears at the input pin 2. The comparator continuously compares the rectified voltage received from the rectifier with the fixed reference voltage of 4.4V appearing at the input pin 2.
DC voltage source 31a is also connected to the common contact C of the relay and serves as a reference voltage for the comparator.
The values of resistors RC1, RC2 ,RC3 and RC4are set in such a manner that a DC voltage appearing at the input pin 3 is less than the reference voltage 4.4 V when the potential difference between neutral and earth lines 14 and 16 is less than 1 V, and the DC voltage appearing at the input pin 3 is more than the reference voltage 4.4 V when the

potential difference between neutral and earth lines 14 and 16 is the same or more than 1 V. The output at the pin 6 of the comparator 34 is considered as high when it generates a voltage of more than or equal to 3.3 V (approx), else it is considered to be low. The output at the pin 6 is high when the voltage at pin 3 is greater than the voltage at pin 2, and vice versa.
The semiconducting switch 54 preferably comprises a field effect transistor (FET) having the base terminal B connected to the output pin 6 via resistors Roi, and R^, and collector terminal C1 connected to the magnetic coil of the relay 36 and the emitter terminal E unearthed. The FET 54 operates as a switch which remains in open position when the comparator output is low. The FET 54 switches to closed position and conduct current when the comparator output is high.
When the voltage across the neutral and earthing of the equipment is below the reference voltage, the comparator gives a low output and the semiconducting switcgh remains in open position. The NC contact of the relay continues to remain closed and the first indicator continues to glow indicating the healthy state of the neutral and earthing. When the rectified voltage is the same as the reference voltage or above the reference voltage, the comparator gives a high output and the semiconducting switch closes triggering the NC contact of the relay to open and the NO contact of the relay to close. As a result, the second indicator starts glowing indicating the unhealthy condition of the neutral and earthing. The first indicator and second indicator are preferably LEDs. In order to give a visual difference, the first indicator LEDs may be green and the second indicator LEDs may be red.

Instead of visual indicators, the relay may be connected to audio alarm such as hooters or the relay may be connected to both visual indicators and audio alarm. The device of the invention optionally comprises a voltmeter 20, preferably a digital voltmeter to receive and indicate the voltage across the neutral and earthing of the equipment continuously.
According to the invention, the neutral to earth voltage of the equipment is continuously monitored so as to take prompt remedial action in case the voltage increases beyond the permissible limits. This helps to maintain performance level of the equipment and prevent damage to the equipment. It also prevents electrical shocks and accidents. The device of the invention is a proactive measure for indicating the slow detoriation of earth wire by continuously monitoring the neutral to earth voltage and generating a visual indication as soon as the neutral to earth voltage becomes unhealthy. It can be used in a wide variety of electronic or electrical circuits, ranging from electronic cards to distribution panels. It can also be used to determine the maximum number of electric machines that can be connected to a common earthing pit by determining the number of machines for which the neutral to earth voltage remain within limit of 1 V.
Instead of having the first indicator and second indicator and connecting the NC and NO contacts of the relay to the first indicator and second indicator, respectively the NC and NO contacts of the relay are optionally connected to a tripping mechanism such as circuit breaker (not shown) whereby the equipment is connected to the AC mains. The tripping mechanism will shut the power supply to the equipment as soon

as the rectified voltage received by the comparator matches with the reference voltage or increases beyond the reference voltage in the comparator and the comparator gives a high output thereby protecting the equipment against damages and also preventing or obviating the various other problems discussed.earlier. Alternatively, the first indicator and second indicator are connected to the NC contact and NO contact of the relay, respectively along with the tripping mechanism in which case visual indication of the neutral to earth voltages also will be available.
Based on voltages between neutral and earthing lines 14 and 16, the voltages at various stages of the device of the invention at fixed values of resistances of the device are illustrated in the Table below:
Table

Voltage Amp ifier voltage Comparator voltage Base voltage of FET (DC
V)
between neutral
and earthing lines 14 and 16 Pin no 6 (AC
V) After diode
rectifier Dl
(DCV) Pin no 2 (DC
V) Pin no 3 (DCV) Pin no 6 (DCV)

0.1 1.1 1.4 4.4 0.6 -3.2 -3.2
0.2 1.7 2.3 4.4 1 -3.2 -3.2
0.3 2.4 3.3 4.4 1.4 -3.2 -3.2
0.4 3.4 4.6 4.4 1.9 -3.2 -3.2
0.5 3.7 5 4.4 2.2 -3.2 -3.2
0.6 4.5 6.2 4.4 2.7 -3.2 -3.2
0.7 4.9 6.8 4.4 3 -3.2 -3.2
0.8 5.7 7.8 4.4 3.4 -3.2 -3.2
0.9 6.2 8.6 4.4 3.8 -3.2 -3.2
1 7.1 9.8 4.4 4.4 4.0 4.0
1.5 8.5 10.7 4.4 4.7 4.0 4.0
2.5 9.3 10.7 4.4 4.7 4.0 4.0
5 9.7 10.7 4.4 4.7 4.0 4.0
10 9.9 10.7 4.4 4.7 4.0 4.0

It is seen from the Table that the voltage at the base of the FET turns positive only when the potential difference between neutral and earthing lines 14 and 16 reaches 1 V. For values less than 1 V, the voltage at the base of the FET is negative and thus the FET does not switch on and remain in open position. As soon as the FET is switched on. the relay 36 gets energised and an indication is provided by the second indicator that the neutral and earthing lines 14 and 16 are in unhealthy condition. Thus, the device of the invention facilitates to indicate all values of neutral to earth voltages and to detect even minor variations in neutral to earth voltages.
It will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from the spirit and scope of the invention. Thus it is intended that the invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

We claim:
1) An elelctronic device for continously monito of an electronic or electrical equipment operating on AC mains, comprising a voltage amplifier configured to receive and amplify the voltage across the neutral and earthing of the equipment, a voltage rectifier configured to receive and rectify the voltage from the amplifier, a voltage comparator configured to compare the rectified voltage received from the rectifier with a reference DC voltage preset in the comparator and give a low output or a high output depending on whether the rectified voltage is below the reference voltage or at or above the reference voltage, a semiconducting Switch configured to remain in open position when the comparator output is low and to switch to closed position when the comparator output is high and a relay comprising a common contact, a normally closed (NC) contact and a norrnally open (NO) contact, the amplifier being configured to receive power from a DC power supply, the voltage comparator and common contact of the relay being powered by a DC voltage source, the NC contact of the relay being connected to a first indicator and the NO contact of the relay being connected to a second indicator.
2) The electronic device as claimed in claim 1, wherein the voltage amplifier comprises a voltage summing amplifier.
3) The electronic device as claimed in claim 1, wherein the voltage rectifier comprises a diode rectifier.
4) The electronic device as claimed in claim 1, wherein the voltage comparator comprises an operational amplifier.

5) The electronic device as claimed in claim 1, wherein the semiconducting switch comprises a field effect transistor (FET) with the base terminal thereof configured to receive the comparator output, the collector terminal thereof configured to trigger the NC and NO contacts of the relay alternately and the emitter terminal thereof earthed.
6) The electronic device as claimed in claim 1, wherein the first indicator and second indicator each comprises LEDs, the first indicator comprising green LEDs and the second indicator comprising red LEDs.
7) The electronic device as claimed in claim 1, wherein the DC power supply is derived from AC mains and the DC voltage source is stepped down DC derived from the DC power supply.
8) The electronic device as claimed in anyone of claims 1 to 7, which comprises
a voltmeter configured to receive the voltage across the neutral and earthing of the equipment.
9) The electronic device as claimed in claim 8, wherein the voltmeter is a digital voltmeter.
10) The electronic device as claimed in anyone of claims 1 to 9, which comprises a filter configured to filter high frequency ripples in the rectified voltage from the rectifier.
1 l)The electronic device as claimed in claim 10, wherein the filter is a low pass filter.

12) The electronic device as claimed in claim 11, wherein the low pass filter is a capacitor.
13)The electronic device as claimed in anyone of claims 1 to 12, which comprises a tripping device connected to the NO and NC contacts of the relay.
14) An electronic device for continuously monitoring the neutral to earth voltage of an electronic or electrical equipment operating on AC mains and disconnecting the AC mains to the equipment under neutral to earth over voltage conditions, comprising a voltage amplifier configured to receive and amplify the voltage across the neutral and earthing of the equipment, a voltage rectifier configured to receive and rectify the voltage from the amplifier, a voltage comparator configured to compare the rectified voltage received from the rectifier with a reference DC voltage preset in the comparator and give a low output or a high output depending on whether the rectified voltage is below the reference voltage or at or above the reference voltage, a semiconducting switch configured to remain in open position when the comparator output is low and to switch to closed position when the comparator output is high and a relay comprising a common contact, a normally closed (NC) contact and a normally open (NO) contact, the amplifier being configured to receive power from a DC power supply, the voltage comparator and common contact of the relay being powered by a DC voltage source, the NC contact and NO contact of the relay being connected to a tripping device connecting the equipment to the AC mains.

15) The electronic device as claimed in claim 14, wherein the voltage amplifier comprises a voltage summing amplifier.
16) The electronic device as claimed in claim 14, wherein the voltage rectifier comprises a diode rectifier.
17) The electronic device as claimed in claim 14. wherein the voltage comparator comprises an operational amplifier.
18) The electronic device as claimed in claim 14, wherein the semiconducting switch comprises a field effect transistor (FET) with the base terminal thereof configured to receive the comparator output, the collector terminal thereof configured to trigger the NC and NO contacts of the relay alternately and the emitter terminal thereof earthed.
19) The electronic device as claimed in claim 14, wherein the DC power supply is derived from AC mains and the DC voltage source is stepped down DC derived from the DC power supply.
20) The electronic device as claimed in anyone of claims 14 to 19, which comprises a voltmeter configured to receive the voltage across the neutral and earthing of the equipment.
21) The electronic device as claimed in claim 20, wherein the voltmeter is a digital voltmeter.
22) The electronic device as claimed in anyone of claims 14 to 21, which comprises a filter configured to filter high frequency ripples in the rectified DC voltage.

23) The electronic device as claimed in claim 22, wherein the filter is a low pass filter.
24) The electronic device as claimed in claimed 23, wherein the low pass filter is a capacitor.