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How to find RPM of the MOTOR



I need to find the RPM of the AC motor. Does any one know how to write labview program for that. Thank u

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LabVIEW alone can not do this. You will need to buy a sensor that will allow you to measure the rotation. An encoder would be the easiest way to do this measurement. If you order a quadrature encoder and you buy a DAQ card that has quadrature inputs it will be very easy to do. Do you have any hardware?

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Thanks for your reply. I am planning to use tachometer or hall effect sensors . I am using compactRIO and c series modules. Do you have any example programs. Thank u

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Do you currently have any of the C-Series modules? If the sensors output digital pulses, you should be able to track speed by reading these pulses with a DAQ module, as Tim suggested. If you are using a C-Series motion controller to control the motor, you may also have Digital I/O lines that could be used to read pulses from the sensor.


Please fill us in on your hardware so we might be able to make some more specific suggestions.

NI Community Team
National Instruments
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Thank you very much for ur reply sir. I am using NI 9234 accelerometer module and cRIO . I am not planning to use DAQ. I am using cRIO . Any suggestion ?


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The answer here will depend on the sensor that you are using to monitor the rotations. If the sensor has an analog output, it may be possible to read from your current NI 9234, but this may not be ideal. The signal cannot exceed +/-5 V and synchronizing acquisition with other device may be require more detail. Using a quadrature encoder and reading the pulses with a Digital or Counter Module would very likely be a preferred solution. You may want to take a look at the Quadrature Encoder Measurements: How-To Guide document as well. 

NI Community Team
National Instruments
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Here is a quick and dirty idea on how to use a IEPE input for a refective optical sensor CNY70


rpmsensor 02.png


But since the LED might need more current  than the 2mA another try with an external powersupply (here as a currentsource, for a 5V supply add (5-1.6)/20mA ~ 150 Ohm in series)



This is not tested!  But if you have a free input on the 9234 and a optical sensor is possible (Hall Sensors are more robust) maybe worth a try 😉



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