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?


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

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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.

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  • \$\begingroup\$ not getting the same answer as the value calculated by the website \$\endgroup\$ – Siddharth Bardiya Jun 30 '16 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 Jun 30 '16 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\$ – Siddharth Bardiya Jul 1 '16 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 Jul 1 '16 at 9:09

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