Introduction: A Simple RPM Counter for FLOWSTONE Using a Labjack U3.

It's always useful to know how fast a rotating equipment is actually moving. This can be a motor, generator, flywheel, tire etc.

I will present here, a very small schematic in Flowstone to calculate RPM via a voltage signal measured at a labjack U3.

My intended purpose is for measuring the RPM of a small wind turbine generator I plan to evaluate. You can use this software schematic for other applications.

Step 1: Basic Schematic Blocks.

The core of this measurement schematic are the Tick, Counter and Trigger Sample/Hold primitives. The aim here is to take samples and count them.

The samples come directly from the labjack U3 AIN or FIO terminals. Whether its rising or falling edge, all that is needed is to know if the voltage is above or below a defined threshold value. This signal can be a half wave rectified alternator voltage, a hall proximity swtich or an infrared proximity switch. You can use your imagination to obtain that pulse in order to get the RPM reading. Whatever the means to obtain the signals, just never exceed the voltage limits of the labjack U3. A good idea is to keep the pulse voltages at 5.0VDC.

After counting the samples, its necessary to hold the samples counted and clear the counter. Using some basic maths, the RPM is obtained.

Step 2: The RPM Schematic.

Without boring you on the schematic details any further, here is the RPM schematic I'm using for an upcoming project. The actual measured signal will be sent to the Inc input of the Counter primitive.

This is just the segment of the schematic I'm going to plug into my home automation schematic. I have attached the flowstone schematic file for your use! Enjoy!

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