Tachometers and 4-20 mA signals

[hec64]

I am trying to get a speed feedback from a 1 HP AC motor using a simple tachometer. I have look around but the only one I found is one that Dart Controls sells. The device is very simple. It attaches to the end of the motor and give pulses. (the model number is PU-2E for a single pulse per revolution) I do not want to buy a transducer to translate the pulse to 4-20 mA. Is there any other in the market that can give 4-20 mA directly from the tachometer?

Thanks.

 

[Barry1961]

If this is a variable speed application you may be able to get a signal from the speed controller easier the motor. The slip on the AC motor from full load to no load may be as accurate as you need if you are considering a 1PPR device.

Barry1961

 

[hec64]

This is a VFD but we did not want to get the signal from the VFD. We want a direct connection to the motor itself.

 

[cswilson]

4-20mA is not the natural output of any tachometer. A real tachometer (i.e. tachogenerator) puts out a fixed number of volts per rpm. You would need some op-amp circuitry to convert this to a current output with a 12mA bias.

In the case of the pulse-output device you have, you would first need a frequency-to-voltage converter, followed by the voltage-to-current converter mentioned above.

Curt Wilson