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Posted by Tomi Engdahl (194.100.23.17) on December 28, 2001 at 01:20:06:
In Reply to: HOW DO I MEASURE THE IMPEDANCE OF ANY CIRCUIT ??????????/ posted by UNMESH RAJPUT on December 27, 2001 at 01:41:14:
: HEY PPL,
: I AM HAVING A PRACTICAL PROBLEM HERE.WE CAN ALWAYS MEASURE THE RESISTANCE OF A CIRCUIT. BUT HOW THE HELL DO I MEASURE THE INPEDANCE OF ANY CIRCUIT...LIKE eg THE INPUT IMPEDANCE OF AN AMPLIFIER OR TRANSFORMER OR ANY OTHER CIRCUIT...COZ UNLESS WE HAVE INPEDANCE MATCHING MAXIMUM POWER WONT B TRANSFERRED TO THE LOAD RESULTING IN UNWANTED POWER LOSSES...ILL B REALLY GRATEFUL TO ANY ONE WHOLL HELP ME OUT ON THIS.
: UNMESH
The input or output impedance of a two terminal network (for example a circuit input or output)can be determined by measuring the small signal AC currents and voltages. For the input, the voltage is measured across the input terminals and the current measured by inserting the meter in series with the signal generator.
For audio frequency measurements use a fixed frequency say 1kHz and set the generator level to around 20 mV RMS. For example, if you read 20mV RMS and 10uA for current, then the impedance is 2k. An easy way to measure small input currents,is to use a fixed resistor (for exmaple
10 kohm, 1 kohm or something like this).
The same principle can be used for other frequencies and other impdances.
Output impedance may also be determined using a similar technique.
There are also other ways to do the measurement,
some of them are more suitable to some applications than other. The links on the web page listed below will give more information on impedance measurements.