Measuring system and a method for detecting static electricity and/or change thereof in a measuring object and use thereof

• US 6,031,378 A
• Filed: 11/13/1997
• Issued: 02/29/2000
• Est. Priority Date: 05/26/1995
• Status: Expired due to Term

• Current Assignee: Foster Wheeler North America Corporation (John Wood Group PLC)
• Original Assignee: TR-Tech Int. Oy (John Wood Group PLC)
• Inventors: Rosin, Tomas
• Primary Examiner(s): Do, Diep N.
• Application Number:
  US08/952,744
• Time in Patent Office: 838 Days
• Field of Search: 324/452, 324/453, 324/454, 324/455, 324/456, 324/457, 324/72, 324/109, 340/561, 340/562, 340/567
• US Class Current: 324/452
• CPC Class Codes: G01R 29/12 Measuring electrostatic fields or voltage-potential
• CPC Class Codes: G01R 29/24 Arrangements for measuring quantities of charge

Abstract

A method and a measuring system for detecting static electricity in a measuring object includes at least a sensor, a voltage meter, and a processor unit with a signal processing unit connected to the voltage meter. The sensor includes a sensing element arranged so that the electric field of the measuring object induces in the sensing element an electric signal which is proportional to the change in the electric charge of the measuring object. The sensor includes a detector including a capacitive circuit, such as a capacitor circuit, having an integrating effect on the measuring values which are read off by the voltage meter, connected between the sensing element and the voltage meter.

Claims

1. A measuring system for detecting at least one of static electricity and change of static electricity in an object, comprising:

a voltage meter which reads charge measuring values;

a processor unit with a signal processing unit connected to said voltage meter;

at least one sensor comprising;

a sensing element positionable with respect to an object to be evaluated so that the electric field of the object induces in said sensing element an electric signal indicating a change in electric charge which is proportional to the electric charge of the object; and

a detector comprising a capacitor circuit having a capacitance connected between said sensing element and said voltage meter for transmitting to said voltage meter the signal induced in said sensing element indicating a change in electric charge, for measuring the change in the charge; and

a resistance R connected in parallel with said capacitor circuit so that the time constant T=R*C of said capacitor circuit at discharge falls within the range of 0.01-5 seconds, so that said capacitor circuit has an integrating effect on the measuring values which are read by said voltage meter.

2. A measuring system according to claim 1 wherein said resistance R is connected to said capacitor circuit so that the time constant T=R*C of said capacitor circuit falls within the range of 0.1-1 seconds.

3. A measuring system according to claim 1 wherein the capacitance C of said capacitor circuit is 1-50 nF, and wherein said capacitor circuit includes a resistance between 1-100 Mohm.

4. A measuring system according to claim 3 wherein said detector further comprises a signal cable which transmits current induced in said sensing element to said voltage meter, said signal cable having a capacitance between 1-50 nF.

5. A measuring system according to claim 1 wherein said voltage meter transmits measuring signals for more than 100 digitized measuring points, for calculation of a numerical value of the electrical field E of the object for a given time period, to said signal processing unit so that said voltage meter reads measuring values in a time interval dt of less than 0.01 seconds for a time period of between 1-10 seconds.

6. A measuring system according to claim 1 further comprising a biasing unit, which is controlled by said processor unit, connected to said detector for compensating the current (I) over a resistor in said capacitor circuit, so that the voltage over the resistor in said capacitor circuit=0 when no external signal is present, so that a biasing current (I_b) is conducted from said biasing unit to said detector over a biasing resistor (R_b '"'"'), the value of which corresponds to the value of said resistor in said capacitor circuit, and wherein the magnitude of the biasing current (I_b) is controlled according to the magnitude of the electric field (E).

7. A measuring system according to claim 6 wherein said measuring system comprises a plurality of sensors and biasing units, each biasing unit being connected to one of said sensors.

8. A system as recited in claim 1 which analyzes at least one of the chemical and physical conditions of an object;

and further comprising means for using the integrated measuring values read by said voltage meter to determine at least one of the chemical and physical characteristics of an object.

9. A system as recited in claim 1 in combination with an object comprising at least one of a powdery medium, flowing gas, and web of material.

10. A method of detecting at least one of static electricity and a change thereof in an object to be evaluated, utilizing a measuring system including a voltage meter which reads measuring values, a processor unit with signal processing, connected to the voltage meter, and at least one sensor comprising a sensing element and a detector, the detector comprising a capacitor circuit;

said method comprising;

(a) positioning a sensing element in or near the object to be evaluataed so that the electric field of the object induces an electric signal in the sensing element indicating a change in electric charge, which signal is proportional to the electric charge of the object;

(b) using the capacitor circuit to transmit the signal induced in the sensing element to the voltage meter; and

(c) integrating the measuring values which are read by the voltage meter by practicing (b) utilizing a resistance R connected in parallel with the capacitor circuit so that the time constant T=R*C of the capacitor at discharge is within the range of 0.01-5 seconds.

11. A method according to claim 10 further comprising (d) substantially eliminating the affect of external interference on the result achieved by calculating in the signal processing unit the standard deviation for measuring points in a certain desired frequency band while excluding from the calculation the standard deviation for measuring points in another, undesired, frequency band.

12. A method according to claim 10 wherein (a) is practiced by moving the sensing element in a slow motion, having a long amplitude in the electric field.

13. A method according to claim 10 wherein (a) is practiced by moving the sensing element relative to the object in a well-defined, velocity and coordinate known, manner.

14. A method according to claim 10 wherein (a) is practiced by controlling the sensing element with the signal processing unit to detect a representative field of each charged partial area of the object, and then using the signal processing unit to compile a representative value of the change in the entire charge of the object.

15. A method according to claim 10 wherein (c) is practiced by using a coaxial cable having a capacitance greater than one nF to which a resistor having a resistance of greater than one Mohm is connected so that the time constant T=R*C of the capacitor circuit is between 0.1-1 seconds.

16. A method according to claim 10 wherein the signal processing unit includes an A/D converter;

and wherein (a) and (c) are further practiced by transmitting from the voltage meter via the A/D converter a series of measuring values read within a predetermined time interval during a predetermined period of time, in digital form, and wherein the time interval is less than 0.01 seconds and the time period is between 1-10 seconds.

17. A method as recited in claim 16 further comprising (d) substantially eliminating the affect of external interference on the result achieved by calculating in the signal processing unit the standard deviation for measuring points in a certain desired frequency band while excluding from the calculation the standard deviation for measuring points in another, undesired, frequency band.

18. A method as recited in claim 10 further comprising (d) using the measuring result of the measurement of at least one of the static electricity or the change in the electric field of the object to optimize a process utilizing the object as a component.

19. A method as recited in claim 18 wherein (a)-(c) are practiced to measure at least one of the static electricity or the change in electric field of a flowing suspension of solid matter;

and further comprising using the result measured for controlling mechanical, chemical, or heat treatment of the solid matter of the suspension.

20. A method as recited in claim 18 further comprising using a measuring result from (a)-(c) to analyze at least one of the chemical and physical condition of the object, and then controlling a process containing the object after analyzing at least one of the physical and chemical conditions thereof.

21. A method as recited in claim 18 further comprising using the measuring result from (a)-(c) to control at least one of:

the supply of starting material to a process;

the supply of additives to the process;

the reaction time of the process;

the degree of grinding of the starting material in the process;

the supply of heat to a process; and

combustion in the process.

22. A method as recited in claim 18 wherein (a)-(c) are practiced utilizing a paper web in a paper making machine as the object;

and further comprising using the measuring result from (a)-(c) to control at least one of the stock fed to the paper making machine, and the operation of the paper making machine.

23. A method as recited in claim 18 wherein (a)-(c) are used to measure at least one of the velocity, the volume flow, the mass flow, the ratio between gas and powder, and the degree of turbulence, in a suspension of powder.

24. A method as recited in claim 18 wherein (a)-(c) are practiced to measure at least one of the velocity, the amount of particles, and the flow geometry, of flue gases.

25. A method as recited in claim 18 wherein (a)-(d) are practiced using a powdery medium as the object.

26. A method as recited in claim 18 wherein (a)-(d) are practiced using a flowing gas as the object.

27. A method as recited in claim 18 wherein (a)-(d) are practiced using a web of material as the object.

28. A method as recited in claim 10 wherein (a)-(c) are practiced using at least one of a powdery medium, flowing gas, and web of material as the object.