ABB ac drive 550

[jayshah376]

can anyone please help with connecting a rpm meter SELEC RX100 to the AC drive in order to display the instantaneous speed of the motor.

 

[jraef]

Well first off, "RX100" is not a good number according to the Selec website, so without knowing what that meter needs as an input, it will be impossible to tell.

But in general, if you want an accurate depiction of motor speed using only the drive, you will be required to have the drive running in some sort of "Vector mode". Without a feedback loop of some sort, the drive has no idea what the actual speed of the motor is, it only knows what frequency it TOLD the motor to run at, but that doesn't mean it is actually at that frequency, because load will affect it. With Vector control, the drive is looking at the error between commanded speed and actual speed, therefore it does know.

So if you understand what that means and you are in some form of Vector control, then you simply assign an analog output in the VFD to reflect a percentage of motor shaft speed as an analog value, let's say 4-20mA with 4mA being zero speed and 20mA being 100% speed, then feed that to a digital meter that allows for unit conversions.

Or remotely mount a display from the drive. Have you tried speaking with your local ABB sales office?

 

[DickDV]

jayshah, I'd advise a little care in acting on jraef's comments above. I'm thinking he's been spending a bit too much time around paper tensioning systems or other very accurate speed control systems.

His comments are as always, true and well intended but, you really don't need to switch to vector control if you can stand a little error in the speed readout. For example, if you have a motor with 3% nameplate slip (say 1455rpm full load) and your motor loading varies from no load to full load (very few loads actually swing this far), then your readout would vary within about 3% of actual speed. And the error would all be negative.

On the other hand, if you pick a premium efficient motor with only 1% slip (1485rpm full load, for example) and your load swings only from full load to half load, then your display error would be around .5%.

If you need better than that, follow jraef's good advice. You can get down in the range of .01% no load to full load with a good vector system.

 

[jraef]

jayshah, I'd advise a little care in acting on jraef's comments above. I'm thinking he's been spending a bit too much time around paper tensioning systems or other very accurate speed control systems.

His comments are as always, true and well intended but, you really don't need to switch to vector control if you can stand a little error in the speed readout. For example, if you have a motor with 3% nameplate slip (say 1455rpm full load) and your motor loading varies from no load to full load (very few loads actually swing this far), then your readout would vary within about 3% of actual speed. And the error would all be negative.

On the other hand, if you pick a premium efficient motor with only 1% slip (1485rpm full load, for example) and your load swings only from full load to half load, then your display error would be around .5%.

If you need better than that, follow jraef's good advice. You can get down in the range of .01% no load to full load with a good vector system.

Well Dick, he said he was looking for RPM not Hz, from a separate meter, I took the statement at face value.

So even if he has a 1% slip motor, you don't know if it is really running at that RPM, because the load on the motor may make it increase the slip if it's just in V/Hz mode. Now if he said "I want something to display the speed, +- 5% is fine", I would have advised him as you just did. But my experience is that unless someone explains it to them people tend to believe things they don't fully understand as being absolute. Between the two of us, hopefully he now realizes that he was being too vague to get a wholly useful UNQUALIFIED answer to the question as asked.