andy257

Hi Everyone,

I am a little confussed as to how to measure inout and output resistance.

I think i have managed to measure the input ressitance but the output is confussing.

In the circuit i am trying to measure, to get the input resistance i have used a variable resistor in series with the input to find out when the voltage becomes half. (using voltage divider rule) when the voltage becomes half i measure the variable resistor and this is my input resistance.

However my problem is with output resistance

can i use the same theory as input resistance to measure the output? I have placed a variable resistor in series with the output but the voltage does not fall by half, it almost increases by half? is this correct?

if anyone could give me a quick fix on this i would be very greatful

cheers

andy

Nigel Goodwin

The variable resistor shouldn't be in series, it should go from the output down to 0V.

You musn't do this on anything with a low output impedance, you could well damage it - it a case like that you would use a higher value resistor and measure the very small signal drop it causes, then use ohms law to work it out.

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