Re: Impedance Measurement

On Mar 30, 5:54 pm, Pete M <p...@xxxxxxxx> wrote:
I would like to measure the resistance (impedance) of a soldering iron tip
to ground with power on - When I use a standard ohm meter I am getting
fictitous readings.

With no power I get a 1 ohm (typcical)dc resistance. When I power I get
readings all over the place. Any suggestions on a circuit?

Thanks

Hi, Pete. You might be seeing the effects of leakage current on your
ohmmeter when the power is on. You should try measuring with power
off.

Using a cheapie DMM to measure low ohms can be kind of chancy. If the
measurement is critical, and you don't have a Kelvin (4-terminal)
ohmmeter, use a 10V supply with a series 10 ohm, 10 watt resistor as a
voltage/current source, and then measure the actual voltage you get
from tip to GND when you apply current. You can then infer resistance
using Ohms law. That will be accurate to within the tolerance of the
resistor.

Good luck
Chris

.

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