Compact Logix embedded IO Analog

Getting ready to build a machine and use a Allen Bradley Compact Logix
1769-l24er-qbfc1b
It has a embedded HSC and Analog. Using the HSC on a encoder.
Need a 0-10v analog signal to control a VFD.
Would it be best recommended to order a Analog Module or use the Embedded Analog.
Both will work and the OF4 Analog In/Out module i just got quoted at $713.
Ouch
The only advantage i see to install the module is if you have a analog issue or sort or anything happens you dont have to replace the whole PLC, just the module
Any advice.
Sticking with the model of PLC since that is what is in some other machines and we have spares in the part room.

Wait, whoah, hang on.

Encoder to an HSC, analog to a VFD.... are you trying to use a general-purpose PLC as a position controller ?


Most folks who use the High Speed Counter for such a purpose are surprised / disappointed that it's not a Motion device; it's built to turn on discrete outputs in a specific count window.

My reading of the manuals shows that the 1769-OF4 and the embedded analog outputs both have 15 bit resolution, where +32767 = 10.5V DC.

I would use the onboard analog output, as long as there's no long cable run in a damage/short-prone environment.

Thanks Ken
Basically a very slow moving linear slide, only about 20 inches in 3 seconds.
Encoder just counting pulses to know the position of the slider as it moves out to desired position. When reaches desired position, return back to home.

Analog output to control the speed of a VFD that is controlling a Blackmax, break motor and gearbox that is being used to move the slide. Has a 1000ppr encoder mounted on it.
This is something that is already built that was taken off of another used machine that our Director said to use.

Actually was going to use a Yamaha servo and linear slide setup, but was told it was too costly, to use what we have laying around. Hopefully, i can still slide the Yamaha in some how but for now going direction as directed.

Ken Roach said:

Wait, whoah, hang on.

Encoder to an HSC, analog to a VFD.... are you trying to use a general-purpose PLC as a position controller ?


Most folks who use the High Speed Counter for such a purpose are surprised / disappointed that it's not a Motion device; it's built to turn on discrete outputs in a specific count window.

My reading of the manuals shows that the 1769-OF4 and the embedded analog outputs both have 15 bit resolution, where +32767 = 10.5V DC.

I would use the onboard analog output, as long as there's no long cable run in a damage/short-prone environment.

Click to expand...

Ken
Starting to see what you mean. As a test i have a compact logix L24 here on my bench and connected a Allen Bradley 845T-dz33acn Encoder, which is a 1000 ppr encoder. I have A0 and B0 connected to the A and B from the encoder. On the embedded counter terminal block i have the A0- and B0- connected together and going to the Common of the DC24vdc.
If i turn the encoder by hand i can see the Current 0 current count as i turn the encoder 1 revolution and it does say 1000.
Now here is the tricky thing. If i connect encoder on the end of a motor that is turn about 18 rev per minute and make a mark on the encoder so i know for sure when the encoder turns just one time and start the motor to run, the counter 0 current count will read about 2500. Has me confused.
The counter 0 is configured as Encoder X1 and scaler is set to 1.
I called AB tech support and woman i spoke to spent some time then said she did not know.
Any thoughts or suggestion are greatly appreciated... Thanks

Ken
Disregard. Bad hair day. Actually ended up being a bad encoder. I just could not turn it fast enough by hand. Got another encoder and replaced and it works like a charm.
Thanks for your replies. Actually i print them out as PDF files and save as reference.

As long as you have reasonable expectations, you can do this sort of low speed positioning reasonably well. But it makes folks who do motion control cringe a little.

When you're spinning up an encoder for the first time, make sure you've carefully examined any filter settings. I've had lots of situation where "it worked fine when I turned it by hand, but once it was on the motor shaft it wouldn't count all the pulses".

Thanks