Re: Measuring the varying Resistance of a DC motor

Rich256 wrote:

troyrivera@xxxxxxxxx wrote:

I have a DAQ that uses LABVIEW. I need to calculate the changing
current going to a DC motor. I cannot measure the current directly
because it is too high for my DAQ to handle. Basically I need to
continuously monitor the varying resistance of the motor, so that I can
calculate the current the motor is pulling. Does anybody have any idea
how I could do this? I was considering breaking open an ohmmeter, but
I'm not sure how an ohmmeter works. Does the ohmmeter send a certain
voltage with certain resistances?

Thanks in advance


It isn't motor resistance that changes. It's back emf. As a motor is loaded the back emf decreases, drawing more current.

Search the web for 'current shunt' -- that should help. Basically you want to measure a small voltage across a very small resistance with a big current flowing through it. You keep the resistance small so your measurement doesn't disturb the system, which means you need a good low-offset amplifier in the DAQ or out.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/
.

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