Means and method for detecting capacitance connected to ac power

Abstract

The present invention relates to a novel means and a novel method for detecting a capacitance connected to AC power, which detect a sensor capacitance on the basis of a charge sharing phenomenon occurring due to a difference between voltages applied to a sensor capacitor and an auxiliary capacitor connected to a detection system when an AC voltage applied to the detection system alternates. According to the present invention, since the sensitivity of a signal detected by a detection system is improved, a magnitude and a change amount of a sensor capacitance are stably acquired.

1 . A means for detecting capacitance, comprising:
 a fixed capacitor configured to have fixed capacitance;   a variable capacitor configured to generate variable capacitance varying in response to an opposing distance or an opposing area from an external object; and   a signal detector configured to detect a change in voltage due to a charge flowing between the fixed capacitor and the variable capacitor in synchronization with an alternating current voltage applied to the fixed capacitor.   
     
     
         2 . The means of  claim 1 , further comprising:
 a switching device configured to charge the fixed capacitor with a DC voltage or keep a floating state to conserve a charged charge after the charging,   wherein the signal detector acquires the variable capacitance of the variable capacitor on the basis of the detected change in voltage.   
     
     
         3 . The means of  claim 2 , further comprising:
 a sensor configured to sense the change in voltage,   wherein the variable capacitor is formed between an electric conductor contacting the object and the sensor.   
     
     
         4 . The means of  claim 3 , wherein an interval between the object and the electric conductor or a contact area between the electric wire and the object is acquired on the basis of the variable capacitance of the variable capacitor acquired by the signal detector. 
     
     
         5 . The means of  claim 1 , wherein the fixed capacitor has equivalent capacitance to a capacitance of a parasitic capacitor generated by a connection to the signal detector and a capacitance of a storage capacitor in which the charge is stored. 
     
     
         6 . The means of  claim 1 , further comprising:
 a first ground; and   a second ground,   wherein the fixed capacitor is grounded to the first ground and the variable capacitor is grounded to the second ground.   
     
     
         7 . The means of  claim 6 , wherein the first ground is the same frequency as the alternating current voltage and in-phase with the alternating current voltage and keeps an amplitude difference of a constant size to apply a DC voltage based on the first ground to the fixed capacitor. 
     
     
         8 . The means of  claim 6 , wherein the second ground is an earth ground in which the DC voltage is zero or a DC voltage having a constant amplitude. 
     
     
         9 . The means of  claim 6 , wherein the first ground and the second ground are connected to each other at the time of outputting a result of the signal detector and the AC voltage keeps the DC voltage having a constant amplitude. 
     
     
         10 . The means of  claim 7 , wherein the first ground and the AC voltage have a first frequency during a first duration, have a second frequency different from the first frequency during a second duration different from the first duration, and the first frequency and the second frequency are alternated. 
     
     
         11 . The means of  claim 1 , further comprising:
 a sensor configured to include two opposing sensing surfaces and be connected to one sensor signal line to sense the change in voltage, wherein two variable capacitors are generated by different objects contacting each sensing surface.   
     
     
         12 . The means of  claim 1 , further comprising:
 a plurality of sensors configured to sense the change in voltage,   wherein a plurality of variable capacitors are generated by the plurality of objects applied to the plurality of sensors.   
     
     
         13 . The means of  claim 3 , wherein the signal detector senses a first voltage of the sensor or each sensor among the plurality of sensors when the variable capacitance is not generated and a second voltage of the sensor or each sensor among the plurality of sensors when the variable capacitance generated by the object is generated and acquire the variable capacitance or the plurality of variable capacitances on the basis of a difference between the first voltage and the second voltage. 
     
     
         14 . The means of  claim 13 , wherein the first voltage is a sum of a first charging voltage (first V chg ) which is the DC voltage having a constant amplitude and the AC voltage and the second voltage is a difference between the first voltage and a voltage sensed by the sensor after a flow of the charge between the fixed capacitor and the variable capacitor is completed. 
     
     
         15 . The means of  claim 14 , further comprising:
 an earth ground which is the DC voltage having a constant amplitude,   wherein the variable capacitor accumulates the charge supplied from the fixed capacitor when the AC voltage is increased based on the earth ground and the fixed capacitor accumulates the charge supplied from the variable capacitor when the AC voltage is reduced based on the earth ground.   
     
     
         16 . The means of  claim 1 , wherein an input terminal of the signal detector has a high impedance of at least 1 MΩ or more. 
     
     
         17 . A method for acquiring variable capacitance by a system including a sensor sensing a change in voltage, a fixed capacitor having and fixed capacitance, and a variable capacitor generating variable capacitance varying in response to an opposing distance or an opposing area from an external object, the method comprising:
 charging the sensor and the fixed capacitor with a charging voltage which is a DC voltage;   applying an AC voltage to the fixed capacitor;   detecting, by a signal detector, a change in voltage due to a charge flowing between the fixed capacitor and the variable capacitor in synchronization with the AC voltage;   acquiring the variable capacitance on the basis of the change in voltage.   
     
     
         18 . The method of  claim 17 , wherein the variable capacitor is formed between an electric conductor contacting the object and the sensor. 
     
     
         19 . The method of  claim 17 , further comprising:
 turning off a switching device to keep a floating state so as to conserve the charge charged in the sensor and the fixed capacitor between the charging of the DC voltage and the applying of the AC voltage; and   acquiring an interval between the object and the electric wire or a contact area between the electric wire and the object on the basis of the variable capacitance.   
     
     
         20 . The method of  claim 17 , wherein the fixed capacitor has equivalent capacitance to a capacitance of a parasitic capacitor generated by a connection to the signal detector and a capacitance of a storage capacitor in which the charge is stored. 
     
     
         21 . The method of  claim 17 , further comprising:
 grounding a first ground to the fixed capacitor; and   grounding a second ground to the variable capacitor.   
     
     
         22 . The method of  claim 21 , wherein the first ground is the same frequency as the alternating current voltage and in-phase with the alternating current voltage and keeps an amplitude difference of a constant size to apply a DC voltage based on the first ground to the fixed capacitor. 
     
     
         23 . The method of  claim 21 , wherein the second ground is an earth ground in which the DC voltage is zero or a DC voltage having a constant amplitude. 
     
     
         24 . The method of  claim 21 , wherein the first ground and the second ground are connected to each other at the time of outputting a result of the signal detector and the AC voltage keeps the DC voltage having a constant amplitude. 
     
     
         25 . The method of  claim 22 , wherein the first ground and the AC voltage have a first frequency during a first duration, have a second frequency different from the first frequency during a second duration different from the first duration, and the first frequency and the second frequency are alternated. 
     
     
         26 . The method of  claim 17 , further comprising:
 generating two variable capacitors on each of the two opposing sensing surfaces of the sensor by contacting between two different objects.   
     
     
         27 . The method of  claim 17 , further comprising:
 generating a plurality of variable capacitors by the plurality of objects contacting the sensor which is formed in plural.   
     
     
         28 . The method of  claim 17 , wherein the signal detector senses a first voltage of the sensor or each sensor among the plurality of sensors when the variable capacitance is not generated and a second voltage of the sensor or each sensor among the plurality of sensors when the variable capacitance generated by the object is generated and acquire the variable capacitance or the plurality of variable capacitances on the basis of a difference between the first voltage and the second voltage. 
     
     
         29 . The method of  claim 28 , wherein the first voltage is a sum of the charging voltage and the AC voltage and the second voltage is a difference between the first voltage and a voltage sensed by the sensor after a flow of the charge between the fixed capacitor and the variable capacitor is completed. 
     
     
         30 . The method of  claim 29 , further comprising:
 an earth ground which is the DC voltage having a constant amplitude,   wherein the variable capacitor accumulates the charge supplied from the fixed capacitor when the AC voltage is increased based on the earth ground and the fixed capacitor accumulates the charge supplied from the variable capacitor when the AC voltage is reduced based on the earth ground.   
     
     
         31 . The method of  claim 17 , wherein an input terminal of the signal detector has a high impedance of at least 1 MΩor more.