Measurement of Capacitance by Carey Foster Bridge

  Procedure:

  1. Set the voltage (V=12V) and Frequency (500Hz) and set the unknown capacitance value from 'Set capacitor value' tab by clicking on 'set' button.

  2. Then switch on the supply to get millivoltmeter deflection.

  3. Now vary the values of R1, L1, M and R4 from the control box below or directly put the values in the boxes of respective elements.

  4. Observe the millivoltmeter pointer to achieve "Null".

  5. If "NULL" is achieved, switch to 'Measure capacitance value' tab and click on 'Simulate'. Observe calculated values of unknown capacitance (C3) and unknown internal resistance (R3) of the capacitor. Also observe the Dissipation factor of the unknown capacitor, which is defined as `w*C*R`. where, `w=2*pi*f`.

Tutorials Point

  • Set the actual values of C3: (R3 value is fixed at 5 Ohm)
      Enter the C3 values and click on the set button.
       C3 (in `muF`): 
    0.001 `muF`   0.1 F
  • The current voltmeter reading is:   mv. Now simulate to get:
         Capacitor value (in `muF`):
    Resistance value (in `Ohm`):
    Dissipation Factor:
CONTROLS
   R1 : 1 Ohm     11.5 MOhm
   R4 : 1 Ohm     11.5 MOhm
   L1 : 1 uH     1000 uH
   M: 1 uH     100 uH