# US 2013/0154612 A1 · Foreign body detecting

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- Number: US 2013/0154612 A1
- Document ID: US20130154612A1
- Status: Published application
- Kind: A1
- Application number: 13/330,293
- Filed: 2011-12-19
- Published: 2013-06-20
- Earliest claimed: 2011-12-19
- Assignees: NCR Corporation
- Inventors: Barrie Clark; Jim Henderson
- Web page: https://patentgrep.com/patent/US20130154612A1

## CPC

- G07F 19/207: {Surveillance aspects at ATMs}
- G07F 19/2055: {Anti-skimming aspects at ATMs}
- G07F: COIN-FREED OR LIKE APPARATUS (coin sorting G07D3/00; coin testing G07D5/00; {handling coins or paper currencies apart from payment activated apparatus G07D; payment architectures, schemes or protocols G06Q20/00})

## Abstract

A method of operating a sensor 112 having a first transmit plate 114, a second receive plate 115 and a dielectric material between the two plates 114, 115. The method comprises the steps of: applying an alternating across the transmit and receive plates 114, 115, thereby to create an alternating electric field, which applied voltage results in a current Iz flowing through the two plates 114, 115; producing a voltage signal corresponding to the resultant current Iz; determining the average value of the product of the corresponding voltage signal and a reference voltage signal Vref3; and adjusting the phase of the reference voltage Vref3 until a null condition is achieved, at which condition the average value is approximately zero. A sensor 112 is also disclosed.

## Claims

### Claim 1

A method of operating a sensor comprising a first transmit plate, a second receive plate and a dielectric material between the two plates, the method comprising the steps of:
applying an alternating voltage across the transmit and receive plates thereby to create an alternating electric field, which applied voltage results in a current flowing between the two plates;
producing a voltage signal corresponding to the resultant current;
determining the average value of the product of the corresponding voltage signal and a reference voltage signal; and
adjusting the phase of the reference voltage until a null condition is achieved, at which condition the average value is approximately zero.

### Claim 2 (depends on 1)

A method according to claim 1, wherein the phase of the reference voltage is readjusted to restore the null condition when a foreign body is so positioned relative to the field as to affect the field and cause a different current to flow between the plates, and wherein the readjustment is indicative of the type of foreign body.

### Claim 3 (depends on 1)

A method according to claim 1, wherein the sensor is desensitised by adjusting the phase of the reference voltage such that a null condition is achieved when a particular foreign body is so positioned relative to the field as to affect the field and cause a different current to flow through the plates, wherein an additional foreign body is so positioned relative to the field as to affect the field and cause another different current to flow through the plates, wherein the phase of the reference voltage is further readjusted to restore the null condition, and wherein the further readjustment is indicative of the type of foreign body.

### Claim 4 (depends on 1)

A method according to claim 1, wherein the applied alternating voltage has a symmetric alternating waveform.

### Claim 5 (depends on 1)

A method according to claim 1, wherein the reference voltage has a symmetric alternating waveform.

### Claim 6 (depends on 1)

A method according to claim 1, wherein the reference voltage may lag or lead the applied voltage by 90°.

### Claim 7

A sensor comprising:
a first transmit plate;
a second receive plate;
dielectric material between the two plates;
a voltage generator for generating an alternating voltage applied across the transmit and receive plates thereby to create an alternating electric field, which applied voltage results in a current flowing between the two plates;
a convertor producing a voltage signal corresponding to the resultant current;
a calculating arrangement determining the average value of the product of the corresponding voltage signal and the alternating reference voltage signal; and
a phase shifter adjusting the phase of the reference voltage signal until a null condition is achieved, at which condition the average value is approximately equal to zero.

### Claim 8 (depends on 7)

A sensor according to claim 7, wherein the dielectric is air.

### Claim 9 (depends on 7)

A sensor according to claim 7, wherein the applied alternating voltage is applied via an amplifier.

### Claim 10 (depends on 7)

A sensor according to claim 7, wherein the converter is a trans-impedance amplifier.

### Claim 11 (depends on 7)

A sensor according to claim 7, wherein the calculating arrangement comprises a mixer and an integrator.

### Claim 12 (depends on 1)

A self-service terminal operated according to the method claim 1.

### Claim 13 (depends on 8)

A self-service terminal comprising a sensor according to claim 8.

### Claim 14

A method of operating a sensor comprising a first transmit plate, a second receive plate and a dielectric material between the two plates, the method comprising the steps of:
applying an alternating voltage across the transmit and receive plates thereby to create an alternating electric field, which applied voltage results in a current flowing between the two plates;
producing a voltage signal corresponding to the resultant current;
determining the average value of the product of the corresponding voltage signal and a reference voltage signal; and
adjusting the phase of the reference voltage until a particular condition is achieved.