0
\$\begingroup\$

Im developing a capacitive sensor of concentric cylindrical plates type.I know its dimensions(length & diameter). How i can calculate its capacitance without using any multi-meter or LCR-meter?

\$\endgroup\$

1 Answer 1

2
\$\begingroup\$

It's the same as for a length of coax: -

enter image description here

enter image description here

Information taken from here

Where "L" is the length of the "tube" and "k" is the dielectric constant aka \$\epsilon_r\$.

See also this website.

\$\endgroup\$
4
  • \$\begingroup\$ not getting the same answer as the value calculated by the website \$\endgroup\$ Commented Jun 30, 2016 at 15:25
  • \$\begingroup\$ How long/round is the sensor and what frequency are you using? Also "not getting the same answer" is meaningless - put some numbers on it. Explain in detail how you measure it. \$\endgroup\$
    – Andy aka
    Commented Jun 30, 2016 at 17:06
  • \$\begingroup\$ length is 146mm, od=50mm, id=16mm, dielectric is air only so constant is 1.and why frequency is required when we are calculating from formula? \$\endgroup\$ Commented Jul 1, 2016 at 5:12
  • \$\begingroup\$ I get 48.8 pF/m or 7.128 pF for 146 mm. What did you calculate and what did you measure? Frequency is important - ever heard of transmission line effects? Too high a frequency will turn your capacitor into an inductor. At 146 mm your "capacitor" will have an impedance of zero ohms with a frequency of about 600 MHz. Even at one-tenth of this there will be an error due to reflections. \$\endgroup\$
    – Andy aka
    Commented Jul 1, 2016 at 9:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.