Impedance Calculator


 
Output Impedance Measurement Calculator
Open circuit voltage (V) (=V1): Load resistance (ohm) (=Rload): Loaded circuit voltage (V) (=V2): Output Impedance (ohm) (=Rsource):

Measurement circuits:
                  o-------------------------+
                  |                         |
               SOURCE(Rsource)         AC voltmeter (V1)
                  |                         |
                  o-------------------------+


                  o----------------+--------+
                  |                |        |
               SOURCE(Rsource)   Rload   AC voltmeter (V2)
                  |                |        |
                  o----------------+--------+

Output impedance may be determined using this simple technique: A load resistor is used to load the signal source. The output voltage is measured first with full load (V1), then without the load (V2).

Just fill the values you get plus the resistance value to the form above to get the output impedance value.

Note on selecting resistor: Do not select too low resistance value, because this can load the output too much (can cause equipment damage). Do not select too high load resistance value, because this cause the voltage changes to be very small (causes large measurement error). For normal audio amplifier speaker output testing 8-10 ohms resistance value is very good. For line level audio signals 1-2 kohms is usually a good value.


 
In/Out Impedance Measurement Calculator
Generator signal (V) (=V1): Series resistance (ohm) (=Rtest): Signal after resistor (V) (=V2): In/Out Impedance (ohm) (=LOAD):

Measurement circuit:

         +-----------+---- Rtest -----+--------+
         |           |                |        |
AC voltmeter (V1)  Sine gen.        LOAD   AC voltmeter (V2)
         |           |                |        |
         +-----------+----------------+--------+

The input or output impedance of a two terminal network can be determined by measuring the small signal AC currents and voltages. The classical measuremetn for the the input is the following: the voltage is measured across the input terminals and the current measured by inserting the meter in series with the signal generator. With high impedance circuits, the current will become very small and difficult to measure.

Usually a better method when measuring high impedance circuits is to to use a fixed resistor as in the diagram above. Measure the AC voltage at points V1 and V2. Fill in those values and the resistance value you used to the form above.

Output impedance may also be determined using a similar technique. Connect the equipment output to be tested as the the load. The output to be teste must not be outputting any signal (any signal from it causes measurement error as extra signal combined to V2 voltage) but is active on.

Select suitable measurement resistance value. For typical audio equipment input/output interface measurements resistance values from 1-100 khohms range are usually most suitable values for Rtest.


 

Notes: Please enter decimal separator as "."
Calculators done with 2 decimals accuracy.
There is no guarantee of the correctness of the calculations.