Test bench for measuring torque, rpm, volt and current.
Test bench for measuring torque, rpm, volt and current.
(OP)
Hi everybody!
First of all I have to excuse my english, but I hope everybody can understand me.
I'm building a test bench for AC motors, where the AC motor will be connected to a DC motor(will be running as an generator) with an adjustable load connected.
I've been trying to find a formula for calculating the torque produced by the AC motor, with just using the readings from the DC motor,but I can't find anything... I know that the torque is proportional to current, but I just can't figure out how to do this.
This is a new type of problem for me, since I have only been working with oil and gas installations, with very little motor installations, and non DC-motor installations.
The only parameters for the DC motor I have at the moment is:
Generator: 2,2kW @ 1500rpm
Motor: 2,0kW @ 1400rpm
Rotor: DC 220V 12A
Excitation DC 220V 0,8A
I would really appreciate if anyone could help me out here.
Great forum btw!
First of all I have to excuse my english, but I hope everybody can understand me.
I'm building a test bench for AC motors, where the AC motor will be connected to a DC motor(will be running as an generator) with an adjustable load connected.
I've been trying to find a formula for calculating the torque produced by the AC motor, with just using the readings from the DC motor,but I can't find anything... I know that the torque is proportional to current, but I just can't figure out how to do this.
This is a new type of problem for me, since I have only been working with oil and gas installations, with very little motor installations, and non DC-motor installations.
The only parameters for the DC motor I have at the moment is:
Generator: 2,2kW @ 1500rpm
Motor: 2,0kW @ 1400rpm
Rotor: DC 220V 12A
Excitation DC 220V 0,8A
I would really appreciate if anyone could help me out here.
Great forum btw!





RE: Test bench for measuring torque, rpm, volt and current.
Mike Halloran
Pembroke Pines, FL, USA
RE: Test bench for measuring torque, rpm, volt and current.
The old bench is analog, and I want to convert it to digital, so that I can get the parameters on a touchscreen. The touchscreen will also be connected to a VFD so that I can controll the speed of motor that is being tested.
Thanks for the reply anyways!
RE: Test bench for measuring torque, rpm, volt and current.
RE: Test bench for measuring torque, rpm, volt and current.
Tq (N-m) = kW x 9550 / RPM
But to be accurate, you would need to adjust the measured kW by the strated motor efficiency, because you want the real shaft kW (absorbed power) if you are trying to determine mechanical torque from that. So take your measured kW and multiply it by the motor rated efficiency at the percent of load that you have applied to it. Most motor mfrs will be able to provide that for you now, but if you are using an old motor that may be a challenge.
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RE: Test bench for measuring torque, rpm, volt and current.
So, it's really the simplest to calibrate the load cell with some known weights and then use it to measure the torque.
RE: Test bench for measuring torque, rpm, volt and current.
RE: Test bench for measuring torque, rpm, volt and current.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Test bench for measuring torque, rpm, volt and current.
Another question, what is the actually the difference between PLS and DAQ? I know that the DAQ is much faster, but there must be other differences?
RE: Test bench for measuring torque, rpm, volt and current.
RE: Test bench for measuring torque, rpm, volt and current.
There was a recent discussion here.
Difference between Scada-PLCs and DCS
thread830-157405: Difference between Scada-PLCs and DCS
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Test bench for measuring torque, rpm, volt and current.
Another question:
I'm going to measure te voltage going from te VFD to the motor. Since te voltage doesn't have a perfect sinus-shape, I have to use true RMS to get the right measurment. I'm familiar with RMS, but how do I measure true RMS? I've read something about using differentialprobs.
RE: Test bench for measuring torque, rpm, volt and current.
An example of an algorithm that is NOT true rms would be finding the peak and dividing by sqrt(2). That works for sinusoid but not for many other waveforms.
An algorithm that gives true rms for any waveform will ususally be based on sqrt of sum of squares of time samples over a representative interval, divided by sqrt(N) where N is number of samples.
Older analog measuring circuits often did not measure true rms (for non-sinusoidal signal). All or most modern digital measuring devices compute true rms (for any signal).
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(2B)+(2B)' ?
RE: Test bench for measuring torque, rpm, volt and current.
I don't think so. I hear the term DAQ (data acquisition) used in the test and measurement world; using stuff like PC cards with fast I/O and a software package, like National Instruments.
The typical process DCS has a sampling rate of what, 5 to 10Hz? Is that fast enough for this type of test stand?
RE: Test bench for measuring torque, rpm, volt and current.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Test bench for measuring torque, rpm, volt and current.
I'm quite new in the world of power electronics, so I was wondering what the difference between a "normal" voltmeter and a differential probe is?
RE: Test bench for measuring torque, rpm, volt and current.
Then please Red Flag your own message above, and in the dialog box that appears, ask that the message be deleted.
Thank you.
Mike Halloran
Pembroke Pines, FL, USA
RE: Test bench for measuring torque, rpm, volt and current.
RE: Test bench for measuring torque, rpm, volt and current.
However, consider that it's really a separate question that deserves its own title. Consider also that a new discussion may draw in some different viewpoints.
Mike Halloran
Pembroke Pines, FL, USA
RE: Test bench for measuring torque, rpm, volt and current.
A handheld voltmeter is differential already. Many panel voltmeters are differential as well.
A differential probe is used to isolate the ground in a scope.