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Frequency Measurement on VisiLogic

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Hello together,

i try to measure the Speed of Rotation (between 1000 1/min and 8000 1/min) with a Samba SM43-J-TA22 and an capacitiv sensor with one srew on the Motor shaft.

When i use the High Speed Input in the Hardware Configuration (Frequency Measurment 1000msec) i have an very bad Resolution (Value 16 * 60 = 960  and next  Value 17 *60 =1020).

I've tried to use the "Freq<- HSC" building block, but it doens't work with my values. For example im not sure what i have to chose for the Channel A, because I can chose HSC 0, HSC1 and HSC2 there but I only have two HS channels on my Samba Controller. 

Is this the right way to measure the Speed of Roation more exactly?

If yes can you give me an example how i have to config the block, and if i have to set up the High Speed Input in the Hardware Config?

Thank you very much.

Kind regards




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  • MVP 2023

You can increase the accuracy by increasing the number of bolts on the motor shaft.

Use 6 bolts and you will have accuracy of approximately 10 turns per minute.
However, make sure that the sensor has the appropriate frequency range.
Or use an optical sensor and a perforated wheel.

Using a 2.5ms interrupt to determine the sensor signal period will not increase the accuracy of the readings.

It is also possible to use your sensor, diode, RC link, and send a signal to the analog input of the PLC.

This is not very accurate, but this solution has advantages.
A similar scheme is used in tachometers of old cars.

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  • 5 years later...
  • MVP 2023

To answer your question, the block is the "Frequency measurement based on HSC" block.  It is located in the Utils->Immediate menu, and there's a good Help page on how to set it up.  There is also an example program under Help->Examples called "V570_Frequency precise meter".

But first you have to verify that you can see the tachometer signal from the fan.  If this is one of those little computer fans with a tach wire you'll need to get the output type and voltage level of it to interface with the HSC input on the PLC, which is expecting a +24V signal for the tach pulses.

Joe T.

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