How to measure a capacitance of an isolated object?

In summary: You need to measure the capacitance of your "isolated" object with respect to something. I believe that the capacitance of a single object is measured wrt a sphere of large radius approaching infinite. E.g. the capacitance of the Earth is around 710 uf, IIRC from memory. The large sphere enclosing the object is 1 electrode, with the object being the other. Taking the limit as the radius of the sphere approaches infinite gives the capacitance of the object. I believe Halliday & Resnick physics texts have illustrative examples of this.Did I help?
  • #1
Artlav
162
1
How can you measure a capacitance of an isolated object, like a conductive sphere or a coil?

Can it be done using a typical RLC meter?
I've tried touching only one end of the probe to the object in question, and that seems to give sporadic readings, but within the order of magnitude of the theoretical expectation.

How to do it reliably, if there is a way?
 
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  • #2
Artlav said:
How can you measure a capacitance of an isolated object, like a conductive sphere or a coil?

Can it be done using a typical RLC meter?
I've tried touching only one end of the probe to the object in question, and that seems to give sporadic readings, but within the order of magnitude of the theoretical expectation.

How to do it reliably, if there is a way?

By definition, capacitance is between two objects or surfaces. You need to measure the capacitance of your "isolated" object with respect to something.
 
  • #3
I believe that the capacitance of a single object is measured wrt a sphere of large radius approaching infinite. E.g. the capacitance of the Earth is around 710 uf, IIRC from memory. The large sphere enclosing the object is 1 electrode, with the object being the other. Taking the limit as the radius of the sphere approaches infinite gives the capacitance of the object. I believe Halliday & Resnick physics texts have illustrative examples of this.

Did I help?

Claude
 
  • #4
hi claude! :smile:

but how do you measure it?
 
  • #5
tiny-tim said:
hi claude! :smile:

but how do you measure it?

I'm not sure as to how it is measured. Capacitance of a single object is valid theoretically, but I'm not sure about it being a measurable quantity. I would say a good approximation is to enclose said object inside a sphere whose radius is large compared with the object dimensions, then measure capacitance between object & sphere. That should get you in the ball park. Of course as the sphere radius increases, the measurement gets more accurate, eventually converging. Maybe tonight I'll look this subject up. I have several good reference texts. Off the cuff, that would be my approach. Comments welcome.

Claude
 

1. How do I measure the capacitance of an isolated object?

To measure the capacitance of an isolated object, you will need a capacitance meter or a multimeter with a capacitance function. You will also need two insulated probes to connect to the object.

2. What is the unit of measurement for capacitance?

The unit of measurement for capacitance is farad (F). However, for most practical purposes, capacitance is measured in microfarads (μF) or picofarads (pF).

3. Can I measure the capacitance of any object?

No, you can only measure the capacitance of objects that can hold an electric charge, such as capacitors, conductors, and dielectrics. Insulators, such as rubber or plastic, do not have measurable capacitance.

4. How do I account for stray capacitance?

Stray capacitance refers to the unintentional capacitance that exists between components and wires in a circuit. To account for it, you can use a guard ring or shield around the object being measured. You can also use a multimeter with a relative measurement function to subtract the stray capacitance from your measurement.

5. What factors can affect the accuracy of capacitance measurement?

The accuracy of capacitance measurement can be affected by factors such as temperature, humidity, and external electromagnetic interference. It is important to ensure a stable and controlled environment when measuring capacitance for accurate results.

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