Hello Chris,
Thank you for contacting National Instruments.
The first thing you need to understand is the signal that you would like to measure. Our FP-CTR-500 and FP-CTR-502 can measure signals up to 50kHz. If the frequency of your signal exceeds 50kHz, you will not be able to measure it.
More than likely, the signal that you are trying to measure is coming from a shaft encoder that produces a finite number of pulses per revolution of the shaft to which it is attached. If you shaft encoder produces 360 pulses per revolution, then you will be able to measure RPMs up to 8333rpm. You can determine this by taking 50kHz/(360pulses/rev) = (138rev/s), (138rev/s)x(60s/min) = 8333rev/min
You may need to tweak this formula depending on the number of pulses
your shaft encoder produces in one revolution.
Next you must understand your measurement device. The inputs of the FP-CTR-500 are sinking. This means that your measurement signal must source current and be connected to some type of power supply. The
FP-CTR-502 has sourcing inputs, which means that the Vin terminal provides a path to a voltage supply which means that your signal must provide a path to ground.
Here are links to the manuals for the FP-CTR-500 and 502:
http://digital.ni.com/manuals.nsf/websearch/5AE49B0DECF9430286256D4A0061F5DA?OpenDocument&node=132100_US
http://digital.ni.com/manuals.nsf/websearch/FD58CA056D4A0062510A?OpenDocument&node=132100_US
Please also see this link to this tutorial:
http://zone.ni.com/devzone/conceptd.nsf/webmain/B3E3A26BBBBF9E1586256AF00059B86E?opendocument
Saving the best for last, her is a LabVIEW example program for measuring frequency with the FP-CTR-500/502:
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=
B45EACE3EBA556A4E034080020E74861&p_node=174404&p_source=external
Regards,
Bill B
Applications Engineer
National Instruments
