Why Is There a Huge Discrepancy in My Capacitor's Measured Capacitance?

In summary: I think the huge error was due to the paper material used as a dielectric which is not a very good dielectric material. In summary, the conversation involved the creation of a capacitor using aluminium foils separated by paper dielectric with a dielectric constant of 3.8. The calculated capacitance was 3.3 nano Farad, but when measured, it was 125 micro Farad. The reason for this large error is still unknown, but it is suspected to be due to the use of paper as a dielectric material and possible errors in the measurement process.
  • #1
eexmr7
2
0
Hello,

I have made a capacitor with two aluminium foils separated with paper dielectric with,

dielectric constant (K) = 3.8 for paper material
paper thickness, D = 0.1mm = 1e-4 m
plate or foil area, A = (12.1 x 8.3)cm = 0.010043 m
air permitivity, Eo = 8.85e-12 F/m

Calculated capacitance = (K Eo A)/d = 3.3 nano Farad

When I measured the capacitance i got,

Measured capacitance = 125 micro Farad

Can anybody explain why this huge error is existing? I have tried with different foil areas but could not find the reason of error.

I m looking forward, Cheers.
 
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  • #2
eexmr7 said:
Hello,

I have made a capacitor with two aluminium foils separated with paper dielectric with,

dielectric constant (K) = 3.8 for paper material
paper thickness, D = 0.1mm = 1e-4 m
plate or foil area, A = (12.1 x 8.3)cm = 0.010043 m
air permitivity, Eo = 8.85e-12 F/m

Calculated capacitance = (K Eo A)/d = 3.3 nano Farad

When I measured the capacitance i got,

Measured capacitance = 125 micro Farad

Can anybody explain why this huge error is existing? I have tried with different foil areas but could not find the reason of error.

I m looking forward, Cheers.
!
It's not just huge error, It's a huge value of capacity for described capacitor. My guess is you made a serious error in measurement procedure, readings or misuse of the instruments .
 
  • #3
For one thing, this is incorrect: "plate or foil area, A = (12.1 x 8.3)cm = 0.010043 m" Convert the two lengths to meters before multiplying, and your final area units need to be m^2.

Also, how did you measure the capacitance? What type of meter are you using? What do you measure for the resistance between the plates? How are you holding the plate stack together? Can you post a picture?
 
  • #4
eexmr7 said:
Hello,

I have made a capacitor with two aluminium foils separated with paper dielectric with,

dielectric constant (K) = 3.8 for paper material
paper thickness, D = 0.1mm = 1e-4 m
plate or foil area, A = (12.1 x 8.3)cm = 0.010043 m
air permitivity, Eo = 8.85e-12 F/m

Calculated capacitance = (K Eo A)/d = 3.3 nano Farad

When I measured the capacitance i got,

Measured capacitance = 125 micro Farad

Can anybody explain why this huge error is existing? I have tried with different foil areas but could not find the reason of error.

I m looking forward, Cheers.

Just by looking at your numbers, my feeling (based on 50 years of electronics experience) is that your calculated value is in the correct range. There is absolutely no chance at all that you can create a capacitor yourself with a value of 125μF.
 
  • #5
I'm actually not exactly sure how devices measure capacitance (RC circuit? Or LC?), but I wouldn't be surprised if they don't show the same accuracy across all ranges (kinda how you have to dial in the right resistance range to get an accurate reading of a resistor).
 
  • #6
rumborak said:
I'm actually not exactly sure how devices measure capacitance (RC circuit? Or LC?), but I wouldn't be surprised if they don't show the same accuracy across all ranges (kinda how you have to dial in the right resistance range to get an accurate reading of a resistor).

My personal inexpensive B&K LCR meter definitely needs to be put on the capacitance range that is closest to (but not less than) the capacitor to be measured. It also has a D (= 1/Q} measurement setting to let you know if the capacitor you are measuring is very lossy. If it is too lossy, that messes up the capacitance measurement. That's why I asked the resistance question in my earlier post... :-)
 
  • #7
rumborak said:
I'm actually not exactly sure how devices measure capacitance (RC circuit? Or LC?), but I wouldn't be surprised if they don't show the same accuracy across all ranges (kinda how you have to dial in the right resistance range to get an accurate reading of a resistor).

I once built an LCR meter based on a Wien bridge. If anybody is interested, I could try to dig up the schematics.
 
  • #8
berkeman said:
For one thing, this is incorrect: "plate or foil area, A = (12.1 x 8.3)cm = 0.010043 m" Convert the two lengths to meters before multiplying, and your final area units need to be m^2.

Also, how did you measure the capacitance? What type of meter are you using? What do you measure for the resistance between the plates? How are you holding the plate stack together? Can you post a picture?
hi,

0.010043 is in meter-sq not in meters. the unit was wrong sorry for that. I measuring capacitance with LCR meter.
 

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Related to Why Is There a Huge Discrepancy in My Capacitor's Measured Capacitance?

What is a capacitor?

A capacitor is a passive electronic component that stores energy in an electric field. It consists of two conductive plates separated by an insulating material called a dielectric.

What is the purpose of a capacitor?

The main purpose of a capacitor is to store and release electrical energy. It is commonly used in electronic circuits to filter out unwanted signals, stabilize voltage, and block DC current while allowing AC current to pass through. It also helps to improve the efficiency and performance of electronic devices.

How is a capacitor constructed?

A capacitor is constructed by placing two conductive plates parallel to each other with an insulating material in between, such as ceramic, plastic, or electrolytic material. The plates are then connected to the circuit, and the insulating material is used to prevent direct contact between the plates.

What factors affect the capacitance of a capacitor?

The capacitance of a capacitor is determined by the surface area of the plates, the distance between the plates, and the type of dielectric used. The larger the surface area and the smaller the distance between the plates, the higher the capacitance. Different types of dielectric have different permittivity, which also affects the capacitance.

How is the capacitance of a capacitor measured?

The capacitance of a capacitor is measured in farads (F), named after the scientist Michael Faraday. In practical applications, capacitors are usually measured in microfarads (μF) or picofarads (pF) due to their small size. The capacitance can be measured using a multimeter or a capacitance meter.

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