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Micrologix 3 counters

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Thanks in advance. I'm looking for a direction to proceed here.

I have a micrologix 1100.

I need to obtain 2 rpm counts then subtract them to obtain a relative speed. 1st is a prox with a max frequency of 1200 Hz (180 ppr). 2nd is a prox with max frequency of 300 Hz (40 ppr). My initial thought was to a/b them in a HSC but the ppr are not the same (one is 4.5 times the other).

I also have an encoder I need to add for linespeed but it is only 200 Hz. max (60 ppr). I think I can just use a regular input for that.

Do I need to use an interupt? How should I proceed?

Thanks so much.

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I am thinking that unless you already own the micrologix you may want to look at the CompactLogix for this application.  Even your 200hz input is at a 5ms pulse interval which is awfully fast for std i/o to recognize.

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32 minutes ago, BobLfoot said:

I am thinking that unless you already own the micrologix you may want to look at the CompactLogix for this application.  Even your 200hz input is at a 5ms pulse interval which is awfully fast for std i/o to recognize.

It seems this is asking a lot out of it but yes, the 1100 is already installed in this machine. I see other 1100's here running 2 encoders and thought I could make this work.

The only plc's they have in this plant are the 1100 and 1400.

Thanks for your time.

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The 1100 has only 1 counter according to what I read.  Now the 1400 has three HSC and would do what you want relatively easy I am thinking.  I would suggest the switch.

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1 hour ago, BobLfoot said:

The 1100 has only 1 counter according to what I read.  Now the 1400 has three HSC and would do what you want relatively easy I am thinking.  I would suggest the switch.

Thanks BobLfoot. I know the 1100 only has the 1 hsc but I see other applications in the plant using 2 encoders with the 1100 so I did some research here and found this:

Looks like Tim has the idea. I looked at the other programs in the plant quickly and noticed they were using interrupts.

Didn't know if someone could help me to determine if it was feasible.

The 1400 will definitely do it. Not sure i'm ready to give up on this yet.

Thanks.

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