Turn a TTL into a RPM output

[Team Stoney]

Hardware

cDAQ NI 9172

Module: NI 9401

Monarch Instrument’s Remote Optical Sensor (for measuring RPM/pulse counts)

Software

NI Sound & Vibration Assistant

NI Signal Express

LabView

Experience Level

Beginner

My objective is to read and record accelerometer and engine speed data together so they are time stamped the same.  Setting the accelerometer up was easy… the RPM, not so easy.

I have been trying to convert a 5v TTL signal from an optical sensor, which is used to measure RPM, in NI Sound & Vibration Assistant.  The optical sensor is a stand alone, self powered system with a output signal of “TTL compatible pulse (0 to 5VDC)”.

I’ve started a project in NI Sound & Vibration Assistant, “Add Step”, “Acquire Signal”, “Digital Input” and “Line Input”.  On the Step Setup Tab/Configuration Tab, I’ve selected my channel, Acquisition Mode set to Continuous Samples, Rate set to 1.3kHz.  Then on the Step Setup Tab/Advanced Timing I had to select “On Demand” for Sample Clock Type due to error message(s).  “On Demand” is the only way to get the signal to appear on the Step Setup Tab’s graph.  The signal is a square wave represented by 0 and 1 (0s and 1s are overlaid on the graph).  When I block the optical sensor view, the signal goes flat represented by 1.

I’ve also messed around “Acquire Signal”, “Counter Input” and “Edge Count” with the same results.

Question:  How do I convent this TTL signal to a RPM output… either as a numeric display?

Thank you in advance for any help.

[Wayne.C]

There are several examples that ship with LV that demonstrate how to use counters to measure frequency using DAQmx vi's.  These can be found under the help menu in LV.    Help > Find Examples

Just remember that the frequency  ( Cycles per Second ) you measure using DAQmx needs to be converted to RPM.

[Team Stoney]

I’ve searched, maybe not correctly, the Find Examples without much luck.  I did find example “Read Dig Chan.vi” and was able to confirm an incoming signal.  Sorry if this seem trivial but I just can’t see how to.

Can you suggest a VI to use or a step(s) to use in Sound and Vibration Assistance?

[Wayne.C]

Just use the DAQmx vi's and LabView.  See this link  http://zone.ni.com/devzone/cda/epd/p/id/5000