Capacitive fill level sensor

Patent metadata

Field	Value
Publication number	US-9658095-B2
Application number	US-201414783200-A
Country	US
Kind code	B2
Filing date	Apr 8, 2014
Priority date	Apr 9, 2013
Publication date	May 23, 2017
Grant date	May 23, 2017

Abstract

A capacitive fill level sensor for measuring the fill level of a medium in a container has an electrode unit, which contains a strip-shaped measurement electrode, a strip-shaped counter electrode and a strip-shaped shielding electrode, the shielding electrode at least partially surrounding the measurement electrode. A first AC voltage source having a predefined frequency and amplitude is provided, to which the shielding electrode is connected such that a shielding capacitor formed between the shielding electrode and the measurement electrode has a shielding capacitance that is proportional to the length of the shielding electrode. A second AC voltage source of equal frequency and a predefined second amplitude is provided, the second amplitude being in phase opposition to the first amplitude, to which AC voltage source the counter electrode is connected, such that a measurement capacitor formed between the counter electrode and the measurement electrode has a measurement capacitance that is proportional to the fill level. The measurement electrode voltage present at the measurement electrode is used to determine the fill level.

First claim

The invention claimed is:

1. Capacitive fill level sensor ( 10 ) for measuring the fill level (H 1 , H 2 ; H 1 ′, H 2 ′) of a medium ( 16 ) in a container ( 14 ), having an electrode unit ( 12 ), which has a strip-shaped measurement electrode ( 22 ), a strip-shaped counter electrode ( 24 ) and a strip-shaped first shielding electrode ( 26 , 28 , 40 ), wherein the first shielding electrode ( 26 , 28 , 40 ) surrounds the measurement electrode ( 22 ) at least partially, wherein a first AC voltage source ( 60 ) having a predefined frequency and amplitude is present, which is applied to the ground ( 62 ) and to which the first shielding electrode ( 26 , 28 , 40 ) is connected such that a shielding capacitor ( 54 , 56 , 58 ) formed between the first shielding electrode ( 26 , 28 , 40 ) and the measurement electrode ( 22 ) has a shielding capacitance that is proportional to the length of the first shielding electrode ( 26 , 28 , 40 ), wherein a second AC voltage source ( 66 ) of the same frequency and with predefined second amplitude is present, wherein the second amplitude is in phase opposition to the first amplitude, which is applied to the ground ( 62 ) and to which the counter electrode ( 24 ) is connected such that a measurement capacitor ( 52 ) formed between the counter electrode ( 24 ) and the measurement electrode ( 22 ) has a measurement capacitance, which is proportional to the fill level (H 1 , H 2 ; H 1 ′, H 2 ′) and wherein the measurement electrode voltage ( 72 ) applied to the measurement electrode ( 22 ) in relation to the ground ( 62 ) is used to determine the fill level (H 1 , H 2 ; H 1 ′, H 2 ′).

2. Capacitive fill level sensor according to claim 1 , further comprising a second strip-shaped shielding electrode ( 40 ), which is arranged on the rear side of the measurement electrode ( 22 ) facing away from the container ( 14 ) and covers the measurement electrode ( 22 ).

3. Capacitive fill level sensor according to claim 2 , further comprising a third strip-shaped shielding electrode ( 28 ), wherein the first shielding electrode ( 26 ) is arranged on the one side next to the measurement electrode ( 22 ) and the third shielding electrode ( 28 ) is arranged on the other side next to the measurement electrode ( 22 ) and wherein the first, second and third shielding electrodes ( 26 , 28 , 40 ) are electrically connected to one another.

4. Capacitive fill level sensor according to claim 3 , wherein the counter electrode ( 24 ), the measurement electrode ( 22 ) as well as the first and third shielding electrode ( 26 , 28 ) are arranged on a carrier layer ( 48 ).

5. Capacitive fill level sensor according to claim 4 , wherein an insulation layer ( 50 ) is present at least in the region between the second shielding electrode ( 40 ), on the one hand, and the first shielding electrode ( 26 ), the measurement electrode ( 22 ) and the third shielding electrode ( 28 ), on the other hand.

6. Capacitive fill level sensor according to claim 5 , wherein the insulation layer ( 50 ) is implemented as foam material adhesive strip.

7. Capacitive fill level sensor according to claim 2 , wherein the rear side of the second shielding electrode ( 40 ) and the counter electrode ( 24 ) is coated with a protective layer ( 42 ).

8. Capacitive fill level sensor according to claim 1 , wherein the electrode unit ( 12 ) has an adhesive layer ( 18 ) on the side facing the container ( 14 ) to fix the electrode unit ( 12 ) on the outer wall ( 20 ) of the container ( 14 ).

9. Capacitive fill level sensor according to claim 1 , wherein the measurement electrode ( 22 ), the counter electrode ( 24 ) as well as the shielding electrode ( 26 , 28 , 40 ) are connected on a printed circuit board ( 44 ) of a first electronic unit ( 30 ), which is arranged directly on the container ( 14 ).

10. Capacitive fill level sensor according to claim 1 , wherein a plug connector ( 34 ) is present for connecting the electronic unit ( 30 ).

11. Capacitive fill level sensor according to claim 1 , wherein the second AC voltage source ( 66 ) is implemented as an inverter, the input of which is connected to the first AC voltage source ( 60 ).

12. Capacitive fill level sensor according to claim 11 , wherein the inverter has a gain factor of one.

13. Capacitive fill level sensor according to claim 11 , wherein the frequency of the AC voltage sources ( 60 , 66 ) is set to a value between 0.1 MHz and 30 MHz.

14. Capacitive fill level sensor according to claim 13 , wherein the frequency is set to 1 MHz.

15. Capacitive fill level sensor according to claim 1 , wherein a rectifier ( 74 ) is provided for rectifying the measurement electrode voltage ( 72 ) occurring at the measurement electrode ( 22 ) and wherein the DC voltage (UDC) occurring at the output of the rectifier ( 74 ) is used as an output signal ( 36 ), which is a measurement for the fill level (H 1 , H 2 ; H 1 ′, H 2 ′).

16. Capacitive fill level sensor according to claim 15 , wherein an impedance transformer ( 70 ) is present between the measurement electrode ( 22 ) and the rectifier ( 74 ).

17. Capacitive fill level sensor according to claim 15 , wherein the first AC voltage source ( 60 ) is implemented as a controlled AC voltage source ( 60 ), wherein the amplitude of the first AC voltage source ( 64 ) is changeable as a function of a control voltage (UR), wherein a comparator ( 84 ) is present, which compares the DC voltage (UDC) with a reference voltage (URef) and sets the control voltage (UR) as a function of the comparison result, whereby a control circuit results, which maintains constant the measurement electrode voltage ( 72 ) and wherein the control voltage (UR) is used as an output signal ( 36 ), which is a measurement for the fill level (H 1 , H 2 ; H 1 ′, H 2 ′).

Assignees

• Balluff Gmbh

Inventors

• Winkens Frank
• Glock Juergen

Classifications

• G01F23/263 Primary

  by measuring variations in capacitance of capacitors · CPC title

• G01F23/268

  mounting arrangements of probes · CPC title

• G01F23/266 Primary

  measuring circuits therefor · CPC title