compute motor speed

[mos89 0]

Hi I have a CJ1 GCPU42H with CTO21 high speed counter connected to a motor encoder I am using my counter as simple counter (linear) I want to compute motor speed in rpm, i am not sure how to do, with timer ? thanks

[scottmurphy 1]

No, a timer is not needed, you can use the rate measurement function of the CTO21 module. If you look at the CTO21 manual, 3-7-2- Rate measurement, this will give you a description of how to do it. You will have to use the IORD instruction to get the rate measurement, then do some math as the example shows to get the actual rpm. I have done this before, but cannot remember / find how I set up the IORD instructions the way i did. It was nearly 2 years ago. edit Just searched the manual and my notes again, section 4-5-3-special data gives some more information. Edited 19 Feb 2007 by scottmurphy

[BITS N BYTES 66]

The first thing you need to do is read the manual on the COT21 unitl! The second is to define how you can use it in YOUR application! If you cannot find what you really need then post your questions. Here is the pertinent section - CTO21_Rate_Measurement.pdf

[mos89 0]

I can not use IORD function for the rate measurment when using in simple counter . i will try to use in linear counter , but the count direction is inverted ...

[Pak 0]

Hi mos89 we are doing the same thing. got any progress yet?

[mos89 0]

i did it with a timer 1 get CCV at T0 and read it after a certain time T1 CCV2 and do few math to compute it

[Nibroc 4]

.... Hi Mos, (yes - you cannot use the linear counter and rate measurement feature together) Some other ideas over using a standard timer (some inaccuracies exist with standard timers and PLC scan rates etc) - You could use - 1. Timed Interrupt 2. Free running millisecond timer Another note is if you have a low pulse count per rpm you may get fluctuating results - some averaging may be required ... (or a higher resolution encoder) ... the trick is that any averaging will slow the response of your result!! Nibroc