AZL Book: Electrical Math - Kelvin Double Bridge
The Kelvin Double Bridge (wired as shown above) is a probe/wire configuration I like to use when taking analog measurements over a significant distance. If my probe wires are more than 3m in length, I will tend to use this.
Here is a site that goes into greater detail if you would like to learn more.
Ultimately, whet this does is allows you to take a measurement which takes into account the resistance of the wire. Over longer distances, the resistance of the wire can have a negative impact on the end reading; this setup is designed to mitigate this factor.
I use the HP34401-A meter for fast and easy setup when I do this. It has the option to specify a Kelvin Double Bridge connection, and does the calculation for you.
Last time I used it, I was testing the temperature of a motor using the Rise by Resistance method. This requires that you run the motor to steady state temperature, then shut of and take several measurements of the motor winding resistance, starting with the moment of shut down and documenting the time in between each subsequent measurement. These days I write software to take the measurements for me, so now I can take several hundred measurements with something like 500 ms between each reading. But back in the day this was not an option, so I would get the resistance of the motor at shutdown, and then once every ten seconds for 0.5-1.0 minute.
The change in resistance as the motor cools down can be used to back-calculate the temperature of the motor.
I’m sure there are other uses for the Kelvin Double Bridge, but this is what I’ve used it for traditionally.
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