Mesa IO switching rate

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08 Sep 2020 10:42 #181234 by Tesremos
Okay, so a quick question, Mesa 7i77
I was unable to find the information in the manual, and JT was unsure, and suggested asking.

i want to feed a tachometer (24v) into the Inputs on the field I/O to read the speed of something.
preferably with out using an encoder port(5v),

What is the maximum read rate of the Feild I/O inputs? is 1khz to fast for an accurate read?
approximate maximum pulse rate to be expected is 600hz.

any input is appreciated.
TIA

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08 Sep 2020 11:03 #181238 by tommylight
Replied by tommylight on topic Mesa IO switching rate
Tacho's are analogue devices that produce a certain voltage at a given rotation speed, and that value is written on them, namely the voltage per 1000 rpm.
So if a tacho has written on tit that it does 24V/k that means it will output 24V at 1000 rpm, 48V at 2000 rpm and 72V at 3000 rpm.
Since you mention Hz, most probably it would be a single optical or magnetic sensor that does 1 pulse per revolution, so that will be OK to wire to Mesa inputs, and those should do about 1000 readings per second, but should be confirmed by PCW.

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08 Sep 2020 17:12 #181302 by PCW
Replied by PCW on topic Mesa IO switching rate
You cannot read a 600 Hz signal with a 1 KHz servo thread,
The maximum frequency you can resolve is 1/2 of the servo thread
frequency, but this assumes perfect 50% square waves and 0 jitter

1/3 of servo thread frequency is a about that best you could expect with
~50% signals.
The following user(s) said Thank You: tommylight

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08 Sep 2020 21:58 #181328 by Tesremos
Replied by Tesremos on topic Mesa IO switching rate
Awesome response!

thanks very much.

ill use the encoder, :)

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