Apparatus for detecting liquid level
An embodiment of the invention provides a liquid-level sensor to detect liquid-level information of a liquid to be tested in a container. The sensor includes an electrode, a sensing circuit, an amplifier and a controller. The electrode is disposed on the outer surface of the container, comprising a first electrode and a second electrode. The sensing circuit is coupled to a first electrode and a second electrode, and receives a clock signal to generate a first voltage signal and a second voltage signal. The amplifier receives the first voltage signal and the second voltage signal to output an output voltage. The controller acquires liquid-level information of the liquid to be tested according to the output voltage and a voltage-volume table.
1. A liquid level sensing device to detect liquid-level information of a liquid to be tested in a container, comprising:
a first electrode and a second electrode disposed on an outer surface of the container to detect a variation volume of the liquid to be tested;
a sensor coupled to the first electrode and the second electrode to receive a clock signal generated by a clock source to generate a first voltage signal and a second voltage signal;
an amplifier to receive the first voltage signal and the second voltage signal to generate an output voltage; and
a controller to acquire the liquid-level information according to the output voltage and a voltage-volume table, wherein the first electrode and the second electrode are comb electrodes, and both the first electrode and the second electrode comprise a body and a plurality of extension parts, wherein W 1 is a width of each extension part, D is a length of each extension part, W 2 is a width of the body, S 1 is a distance between two adjacent extension parts, S 2 is a distance between the extension parts of the first electrode and the extension parts of the second electrode, A is a cross-sectional area of the container, ΔV is the variation volume of the liquid to be tested, and W 1 , W 2 , A, S 1 , S 2 , ΔV and D meet the requirements below:
( W 1 +S 1 )× A=ΔV,
D>W 2 , and
( D+W 2 )/4< S 2 <( D+W 2 )/2.
2. The liquid level sensing device as claimed in claim 1 , further comprising a low pass filter to receive the output voltage, filter out high frequency noise of the received output voltage and transmit filtered output voltage to the controller.
3. The liquid level sensing device as claimed in claim 1 , wherein the voltage-volume table stores a remaining volume or a reduced volume of the liquid to be tested in a storage device.
4. The liquid level sensing device as claimed in claim 1 , wherein the sensor comprises:
a first resistor having a first terminal coupled to a first node and a first input terminal of the amplifier, and a second terminal coupled to a third node;
a second resistor having a first terminal coupled to the third node, and a second terminal coupled to a second input terminal of the amplifier;
a variable capacitor having a first terminal coupled to the first node and the first electrode, and a second terminal coupled to a second node and the second electrode, wherein variable capacitor is an equivalent capacitor formed by the first electrode, and the second electrode, and the liquid stored in the container; and
a reference capacitor having a first terminal coupled to the second node, and a second terminal coupled to the second input terminal of the amplifier;
wherein the clock is fed to the second node and the third node receives a common mode voltage.
5. The liquid level sensing device as claimed in claim 1 , wherein the first electrode and the second electrode are formed on the outer surface of the container by a metal printing technology.
6. The liquid level sensing device as claimed in claim 1 , wherein the first electrode and the second electrode each has an adhesive layer formed on one side thereof, and the first electrode and the second electrode are stuck on the outer surface of the container by the adhesive layer.
7. A liquid level sensing device to detect liquid-level information of a liquid to be tested in a container, comprising:
a first electrode disposed on an outer surface of the container to detect a variation volume of the liquid to be tested;
a sensing circuit coupled to the first electrode to receive a clock signal generated by a clock source to generate a first voltage signal and a second voltage signal;
an amplifier to receive the first voltage signal and the second voltage signal to generate an output voltage; and
a controller to acquire the liquid-level information according to the output voltage and a voltage-volume table, wherein the first electrode is a comb electrode, and the first electrode comprises a body and a plurality of extension parts, wherein W 1 is a width of each extension part, D is a length of each extension part, W 2 is a width of the body, S 1 is a distance between every two adjacent extension parts, A is a cross-sectional area of the container, ΔV is the variation volume of the liquid to be tested, and W 1 , W 2 , A, D, S 1 and ΔV meet the requirements below:
( W 1 +S 1 )× A=ΔV , and
D>W 2 .
8. The liquid level sensing device as claimed in claim 7 , further comprising a low pass filter to receive the output voltage, filter out high frequency noise of the received output voltage and transmit filtered output voltage to the controller.
9. The liquid level sensing device as claimed in claim 7 , wherein the output voltage is varied according to the clock signal to form an output voltage signal, and the liquid level sensing device further comprises a clamper to transform negative voltage parts of the output voltage signal into positive voltages and outputs a second output voltage.
10. The liquid level sensing device as claimed in claim 7 , wherein the voltage-volume table stores the remaining volume or the reduced volume of the liquid to be tested in a storage device.
11. The liquid level sensing device as claimed in claim 7 , wherein the sensor comprises:
a first resistor having a first terminal coupled to a first node and a first input terminal of the amplifier, and a second terminal coupled to a second node;
a second resistor having a first terminal coupled to the second node, and a second terminal coupled to a second input terminal of the amplifier;
a variable capacitor having a first terminal coupled to the first node and the first electrode, and a second terminal grounded, wherein variable capacitor is an equivalent capacitor formed by the first electrode, ground and the liquid stored in the container;
a first reference capacitor having a first terminal coupled to the first node, and a second terminal coupled to a third node; and
a second reference capacitor having a first terminal coupled to the third node, and a second terminal coupled to the second input terminal of the amplifier;
wherein the clock signal is fed to the third node and the second node receives a common mode voltage.
12. The liquid level sensing device as claimed in claim 7 , wherein the first electrode is formed on the outer surface of the container by a metal printing technology.
13. The liquid level sensing device as claimed in claim 7 , wherein the first electrode has an adhesive layer formed on one side thereof, and the first electrode is stuck on the outer surface of the container by the adhesive layer.