What is the best solution to interface a large number of analog inputs

Looking to interface a MUX (16ch) to a Allen Bradley point IO. The main reason behind this is to make some savings from using the PLC AI cards.

Currently the process has a main PLC - compact logix L33ER with a number of digital I/Os.

Next to that is a point IO with a few digital I/Os and a large number of AI. All of which are temp transmitters.
There are 80 transmitters in total.

In short:
L33ER-------------DeviceNetPointIO-------MUX---MUX---...

I am hoping to use a 16 channel MUX from some vendor (possibly IFM?) that can use a Ethernet based protocol (possibly IO Link) to connect to the point IO.

Which can then be received at the main (compact logix PLC).

Can anyone please share your thoughts on achieving this design this way or a better way?
What are some of the considerations I need to take in place to get this in terms of configuration, network traffic etc?

Thanks in advance.

Never used it but this looks like what you are looking for...

https://www.phoenixcontact.com/onli...f5e7f401/d921a075-be41-48f6-9c8c-d621f5e7f401

I'm not familiar with the costs of Allen-Bradley IO but you could use another brand of remote I/O if your goal is to save money. For example, Beckhoff analog inputs are about $30 per point. Combine enough modules for 80 points with an Ethernet I/P or DeviceNet bus coupler and you'd be in the $3000 range. I expect there are other brands that would offer similar savings.

for cheap have a look at arduino.
Or a lot of relais as MUX. I did this for Pt100.

If you use relays, make sure you use contacts designed for switching low current signals.

This thread has peaked my interest. So with the device that Norm posted the link for, you can take in many Analog Inputs and then output 1 signal to the PLC. What does that 1 output represent? Which input signal is outputted? I am confused on how the whole thing works.

What about the PLC program side? How do you know what signal you are seeing at any given time?

I am just trying to increase my knowledge right now. Thanks for any info that you can provide. May need this some day

Bullzi said:

This thread has peaked my interest. So with the device that Norm posted the link for, you can take in many Analog Inputs and then output 1 signal to the PLC. What does that 1 output represent? Which input signal is outputted? I am confused on how the whole thing works.

What about the PLC program side? How do you know what signal you are seeing at any given time?

I am just trying to increase my knowledge right now. Thanks for any info that you can provide. May need this some day

Click to expand...

Take a closer look at the product description:

The channels are switched over in one or two-second cycles. The channel currently switched is detected via three digital outputs using a bit pattern.

So the bit pattern tells the PLC which input the output represents at it cycles through them. Based on that information the PLC can move the data from the output of the until into memory areas which represent each of the 8 analog inputs. Makes for a very slow response, but if you are monitoring something like temperature readings update time probably isn't critical.

Now, if you were trying to control a PID loop I'd probably stick to a dedicated AI input to the PLC.

Thanks Paully,
Yea I guess some more detailed reading would have helped me I seen the DO's on the picture but didn't realize that they were to tell the PLC what channel it was sending.

Thanks for the explanation!!

How is the sync done between analog and digital as that would be affected on the logix side by scan times, rpi times of modules, module filters/delays etc. Seems a wrong value ends up somewhere. Especially if one of the three inputs fail. Definitely not to be used on anything critical.

Thanks for the replies everyone.
Yea basically wanted to know if there was something that someone has worked on a similar solution especially on the Allen Bradley hardware.

Some interesting pointers to take from this discussion.
THanks for all your help.

At this point I am looking to get a Multiplexor with an ethernet/modbus based comms that will interface with a compact logix.

Looked at the iFM - they use IO link protocol to interface back but then it is an overkill, as IO link can have bi-directional traffic meaning it can be used to configure the transmitters. But in my case it is a bunch of large number of temperature transmitters.

Oh, and the PID is very slow so the values can be updated in 10's of seconds. Its a long and process of heating in the 10's of mins.
And I have a total of 320 of these temp transmitters to be connected. :S
And YES these are PT100s tooooooo!!!!!!

Just for information -
so far I have considered the iFM and intech MUX.
Just figuring out how I can best make the connection and configure these to work via ethernet/modbus.
http://www.intech.co.nz/products/remotestations/2100-m.html

in this case, the mux uses 4 DI to tell which channel to read from. so that means for each of this MUX i need to allocate DO and AI.
Instead of hardwiring I am looking for more of a protocol based comms.

Yes the Phoenix contact also has a good solution will look into that.
Thanks

Are you able to post a link to the IFM product you are looking at?

Interested to see what it can do.

vigz said:

..
At this point I am looking to get a Multiplexor with an ethernet/modbus based comms that will interface with a compact logix.

Click to expand...

Pardon my ignorance on the task at hand, but why would you bother looking for a multiplexer with Ethernet/IP to a PLC? Plenty of bandwidth over Ethernet to read individual IO. I can only assume its a $$$ issue?

I'm with kolyur, use a remote IO rack and load it with RTD cards. Wago would another alternative.

MUX is a PITA - gave it away years ago. Individual is way better.

http://www.ifm.com/products/us/ds/AL1020.htm

Its a IO Link master module, there is a variety of it, and uses the IO link protocol which is quite similar to Profibus from what I understand. It can be used to configure instruments as it is bi-directional. A little bit of an overkill for my application unless I find the right architecture.

Hope this helps.