# US 2018/0023992 A1 · A method and system for sensing a liquid level

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- Number: US 2018/0023992 A1
- Document ID: US20180023992A1
- Status: Published application
- Kind: A1
- Application number: 15/549,417
- Filed: 2016-02-19
- Published: 2018-01-25
- Earliest claimed: 2015-03-30
- Assignees: Koninklijke Philips N.V.
- Applicants: Koninklijke Philips N.V.
- Inventors: WEI BIAN; KIN LEONG YIP; YAO HEAN CHIAH; KWONG LIM CHIN; GARY CHI YANG LIM
- Web page: https://patentgrep.com/patent/US20180023992A1

## CPC

- G01F 23/265: {for discrete levels}
- G01F 23/266: {measuring circuits therefor}
- G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME

## Abstract

The present application relates to a system (10) for sensing liquid level in a receptacle (16). The system comprises a capacitive sensing probe (12), for sensing a capacitance between the capacitive sensing probe (12) and an electrically conductive portion of the receptacle (16). The system also comprises a control circuit (15) connected to the capacitive sensing probe (12) for detecting a level of the liquid in the receptacle (16) based on said capacitance, a non-isolated AC power supply (11) arranged to power the control circuit (15), the non-isolated AC power supply (11) having an electrical connection between its input and its output, and at least one filter capacitor (C1, C2) connected in series between the capacitive sensing probe (12) and the control circuit (15).

## Claims

### Claim 1

A system for sensing liquid level in a receptacle, said system comprising:
a capacitive sensing probe for sensing a capacitance between the capacitive sensing probe and an electrically conductive portion of the receptacle;
a control circuit connected to the capacitive sensing probe for detecting a level of the liquid in the receptacle based on said capacitance;
a non-isolated AC power supply arranged to power the control circuit, the non-isolated AC power supply having an electrical connection between its input and its output; and
at least one filter capacitor (C1, C2) connected in series between the capacitive sensing probe and the control circuit.

### Claim 2 (depends on 1)

The system as claimed in claim 1, wherein the control circuit is arranged to receive an AC voltage from a mains supply and convert the AC voltage into a zero-crossing signal used to trigger the capacitive sensing.

### Claim 3 (depends on 2)

The system as claimed in claim 2, wherein the capacitive sensing is triggered with a time delay after a zero-crossing point of zero-crossing signal is detected, the time delay is a pre-determined value or range.

### Claim 4 (depends on 1)

The system as claimed in claim 1, wherein the control circuit 0 is arranged to perform a capacitive sensing measurement at a rising edge and/or a falling edge of the zero-crossing signal.

### Claim 5 (depends on 1)

The system as claimed in claim 1, wherein the control circuit is arranged to detect whether an edge of the zero-crossing signal is a rising edge or a falling edge, and the control circuit is arranged to detect the level of the liquid in the receptacle based on the capacitance of the capacitive sensing probe based on results of the detection.

### Claim 6 (depends on 1)

The system as claimed in claim 1, wherein the at least one filter capacitor (C1, C2) is a Y-capacitor.

### Claim 7 (depends on 1)

The system as claimed in claim 1, wherein the non-isolated AC power supply is at least one of a switched mode power supply, a capacitive power supply, and a resistive power supply.

### Claim 8 (depends on 1)

The system as claimed in claim 1, wherein the control circuit and the non-isolated AC power supply are located on a printed circuit board assembly.

### Claim 9 (depends on 1)

The system as claimed in claim 1, wherein the capacitive sensing probe acts as a first electrode (E1) of a sensing capacitor, and a grounded electrically conductive portion of the receptacle acts a second electrode (E2) of the sensing capacitor.

### Claim 10 (depends on 1)

A boiler system comprising a receptacle and a system as claimed in claim 1, wherein the capacitive sensing probe is located within the receptacle and is electrically insulated from the receptacle.

### Claim 11

A method of detecting a level of liquid with a system comprising a capacitive sensing probe, a control circuit arranged to receive an AC voltage from a mains supply, and a non-isolated AC power supply arranged to power the control circuit wherein the non-isolated AC power supply has an electrical connection between its input and its output, and at least one filter capacitor (C1, C2) connected in series between the capacitive sensing probe and the control circuit, the method comprising:
using the control circuit to convert AC voltage from the mains supply into a zero-crossing signal, and
performing capacitive sensing using the capacitive sensing probe at a time determined by the zero-crossing signal.