Digital I/O

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VI to convert input signal from NI 9402 into a rpm value based on pulse frequency

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I am looking for a VI to convert an input signal from NI 9402 into a rpm value based on pulse frequency. Is there such a thing that exists in the national instruments library?


I am running LAbview 2014 embedded control and monitoring suite on a cRIO 9802 high performance integrated system with NI 9402, 4-Channel, 50 ns, LV TTL Digital Input/Output Module, ultra high-speed digital I/O module for cRIO. 


Any help would be greatly appreciated.

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Would you give us more details of the external sensor/transducer that you are trying to read? How many outputs does it have? What are you trying to measure?




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Hello yes, here is the detail,


The sensor that i am trying to read is a speed probe with details below,


There are 3 (probes) being read into three channels on the NI 9402, the signal frequency range is  0.05 to 12kHz. the speed probe functions by non contact sensing of a rotating steel profile, Frequency signal output is a square wave with constant high and low level over the entire speed range. The push-pull output stage pulls the external load up towards supply voltage during high state, and down to zero in its low state.
This results in a low impedance.
Maximum output power: 25 mamps
Maximum output load
Ub = 24 volts : 1 kohms
Ub = 12 volts : 500 ohms


I am trying to get an accurate reading in RPM, any help is great. Thanks

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Accepted by topic author turbineconsultant

The simplest way is to use the FPGA to get the time between rising edges of your pulse (shift registers to hold the current state and time will be necessary).  That will give you the period.  If it is a single pulse per revolution, then the rpm is just 60/T, where T is the period in seconds.

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