Fatek Incremental encoder error

[Camran90]

I am using fatek PLC model 32MNT2. I need to interface a high speed maximum 5000 rpm magnetic disc stepper motor model DM50 Diamatec and with the shaft of stepper motor there is a 500ppr incremental disc encoder 9100A attached. I am using HSCTR function for taking encoder pulses. My aim is to find the RPM of stepper motor. I tried everything even, the code given in the manual but, there is too much variation in the RPM. For example, if the RPM of stepper is 3000 then the calculated RPM by the PLC will be varying between 2500 to 4000. I tried by changing time duration for 1ms to 5seconds but nothing works. Please, help me in this regard. I would be grateful.

 

[KlausST]

Hi,

the problem most likely is "maximum input frequency".

What is the maximum expectable frequency from the encoder?
What is the maximum input frequency specified by the PLC?

Klaus

 

[Camran90]

I don't think that's the issue because of frequency because fatek 32MNT2 is specially designed for high speed devices and it is capable to handle 920K hertz. As compared to other PLCs which are only capable to handle Maximum 200KHertz.

 

[FvM]

Yes 920 kHz counter speed versus 42 kHz encoder output should work. Of course there can be still configuration or interface level issues, which we can't assess without knowing the documentation details.

 

[KlausST]

Hi,

what does "handle" mean?
counting pulses may be simple.
but you need to "gate" them or process them with precise timing.

basically what you try to do is some kind of frequency measurement.
If you process the data in a random loop (wihtout timing) then the looptiming will determine frequency measurement precision.

Example: input 10kHz.
when the loop timing varies between 15ms and 20ms then then count value will vary between 150 and 200.

With a gating (don´t know whenter this is possible with a PLC) you count pulses nly for a fixed period of time. maybe 10ms.
Then the count value always is 100 independent whether the loop lasts 15 or 20ms.

Klaus

 

[Camran90]

I have attached the winproladder code file and pictures of my code I used to find the RPM.