AB Micrologix 1100 and absolute encoder

Some info: carton packaging machines, speed up to 150RPM or 2.5 per sec.(linear speed 0.5m/s ) , scan time around 20ms.

So far I’ve been using PLS systems such as Electrocam for positioning, but lately started to look for cheaper options on some slower machines.

So idea of absolute encoders with grey code output came along and after some reading I still have few questions which somebody here might help:

• Are encoder outputs connected on regular PLC inputs (not high speed inputs)?

ML1100 has only 4 fast inputs so if that’s the case I’m probably out of luck since they have no fast inputs expansion IO.

• Any suggestion at encoder pulses/resolution considering the speed and scan times

(the 8-bit 256 pulse per rev. encoder is more than enough but I don’t now how to calculate and see If that not too much with 20ms scan time and 2.5 rev./s speed)

I was looking at AB 845G series encoders (I like the remote set zero pin)



Thanks

That's still 0.0015625 seconds per count (1/(2.5 * 256)). Much less than you 20ms scan. If you need 1 count resolution you'll probably still need something like the Electrocam.

Hello Bernie,
Do you know if normal DC Inputs are used for connections?
Thanks again

With an absolute encoder you don't need to be specifically concerned with scan time or input response causing a loss of information. However, as bernie_carlton said, you may need to be concerned with how quickly your program can react.

You won't be able to act on a specific count. There will be cases where you won't see every position. You will need to trigger an action either on a range or when the count exceeds a certain value.

Keith

That's fine because no high precision is needed on these machines.
I was more concerned about some values getting lost due to the scan time,
but I guess that's not gonna be the case.
From that I guess I could use standard inputs, right?

shilok said:

From that I guess I could use standard inputs, right?

Click to expand...

Right.

Alaric said:

Right.

Click to expand...

What if all the inputs don't latch at the same time? Is there a need for gray scale?

Peter Nachtwey said:

What if all the inputs don't latch at the same time? Is there a need for gray scale?

Click to expand...

I'd use a Grey scale and "offset" the value of it if need be.
It'll work with regural inputs (no-high speed)but it may need something more than a micrologix itself (12 bit will require 12 inputs), I'm sure some of those are used for your machine cotrols, an expansion card will do.

shilok said:

, scan time around 20ms.

Click to expand...

for all ML1100 I worked with it never crossed my mind to check the scan time because there was no need.

however I remember an older post somebody was complaining about ML1100 having 80ms and more, and when he asked AB they replied sometimes is happening due to ethernet port overhead.

you might want to check that

Do somebody have an example of a pls (Position limit switch) using the high speed counters on a micrologix 1100.