Micro 850 Instead of 1794-AENT?

Just a thought, if you had a system controlled primarily from a compactlogix L32E, and you wanted remote Ethernet communications to 10 inputs, and 10 outputs, wouldn't it be much cheaper to use a micro 850 in place of a 1794-AENT Flex Ethernet module?

Basically what I'm asking is if anyone has ever successfully setup a micro850 as a dummy that just sends and receives MSG instructions to an L32E, for the purpose of having a really cheap remote I/O module.

1794-AENT costs $779 (without any input/output modules, or power supply)

Micro850 costs $455 (comes with 14 inputs and 10 outputs, no power supply)

Seems like it could be a very cost effective solution.

The Micro 850 can't act as a cyclic I/O adapter. That's simply not what it's for.

In my opinion, using MSG instructions instead of cyclic I/O connections is an unreliable and disfavored engineering practice. I have only done it as an engineering workaround for migration of obsolete equipment.

I wouldn't do it to save a few hundred dollars on a couple of units, and I also would not design a large-scale or high-volume system that was based on such a technique.

I'm a notable curmudgeon on the topic, so I promise ahead of time to not give anyone grief if their opinions differ.

Ken Roach said:

The Micro 850 can't act as a cyclic I/O adapter. That's simply not what it's for.

In my opinion, using MSG instructions instead of cyclic I/O connections is an unreliable and disfavored engineering practice. I have only done it as an engineering workaround for migration of obsolete equipment.

I wouldn't do it to save a few hundred dollars on a couple of units, and I also would not design a large-scale or high-volume system that was based on such a technique.

I'm a notable curmudgeon on the topic, so I promise ahead of time to not give anyone grief if their opinions differ.

Click to expand...

So your saying it's possible? lol

The idea is to remove a bunch of old time delay relays that control the level of an outdoor water tank, which is not even connected to the existing PLC, but we often have a lot of trouble with it.

It would be nice to run the time delay's program on the micro 850 and then send info back to the L32e for indication and manual control on the panelview.

+1 to what Ken said, curmudgeon-ly.

That being said, why not talk directly to the Micro850 from the PanelView? I don't think there's a native driver, yet, but Modbus/TCP should be a good fit for this application.

JordanCClark said:

+1 to what Ken said, curmudgeon-ly.

That being said, why not talk directly to the Micro850 from the PanelView? I don't think there's a native driver, yet, but Modbus/TCP should be a good fit for this application.

Click to expand...

I have a lot of bad luck with PV processor shortcuts disappearing or otherwise not working, but yeah that could be done as well.

provided you have logic within the micro to detect communications failure and act accordingly, I don't see why not.

Messaging should just pass setpoints / status data back and forth.

For what you're doing I think it's fine. You're basically replacing relay controls with a local PLC control. Just do the logic in the micro and command and control from the CompactLogix

I haven't seen this in terms of remote IO, but have seem a similar setup with Siemens CPU's to be able to cope with the number of connections required on the ethernet links and it worked fine.

It isn't ideal, but it could be a solution... in your case, I would potentially use the micro as part of a distributed system where it received information from the main controller (not just commands for outputs) and act accordingly, basically distributing the control to that CPU.

I would accept something like that, even if the remote controller only took over when the main controller died or comms went down, but possibly wouldn't accept putting a PLC doing a remote IO's job as you make savings on the installation, but whoever runs it will have to deal with a more complex system and the savings aren't passed on.

I've often had the same thought- use a micro or micrologix as a poor man's remote IO. And maybe if it was my own personal plant I would, but when someone else is paying the bills anyways... nah

If you want remote IO but don't want to pay out the a$$, look into Omron. If memory serves, you can get what you're looking for for not much more than the mico850. And it will set up in the
RSL5000 tree just like an AENT, and have all the fail safe stuff configured just the same.

rupej said:

I've often had the same thought- use a micro or micrologix as a poor man's remote IO. And maybe if it was my own personal plant I would, but when someone else is paying the bills anyways... nah

If you want remote IO but don't want to pay out the a$$, look into Omron. If memory serves, you can get what you're looking for for not much more than the mico850. And it will set up in the
RSL5000 tree just like an AENT, and have all the fail safe stuff configured just the same.

Click to expand...

I will defiantly check into the OMRON stuff. Thanks Guys!

I also think.... it depends a lot on the actual project

I have used MicroLogix's and Automation Directs for this in the past, my biggest was a DL06 talking to about 15 DL05 via Ethernet (Modbus I/P) I was only doing a read/write on the network when there was a change in the I/O, it was all digital so if someone on the other end of the plant pushed a button it would send a state change to the 'master', worked great, I did not do any analog or process control on that system, but it was a cheap way of making it work