Hi guys,
We’re in the middle of choosing new PLC’s for monitoring levels, temperatures and pressures in our storagetanks, all in all something like 24 analog inputs.
I’ve talked with our supplier of PLC’s, but they didnt know a lot about the Allen Bradley product line, which i’d chosen since it seems ignition supports them more than other brands.
My problem is that all these different plc’s seem to favor digital inputs, and what i really need is analog.
My question is:
Is there a cost effective solution to get:
24 analog IO ports,
Ethernet capability,
Tag browsing
Or should i try to limit the amount of inputs?
For such small applications I generally recommend the CompactLogix 5370 series processors. The L16 with some side-mounted analog modules (12 channels) and some ethernet connected modules (for the other 12) would meet your needs. Or a pair of L16s might be more convenient.
If you want to leave more room for expansion, consider the L24 or above.
Thanks for the reply,
So a setup could be
1x CompactLogix 5370 L1(i assume the only relevant difference between the units is the memory capability?)
3x 1734-IE8C (which is an 8 channel analog I/O module, i couldnt find any 12 port?)
The L16 allows up to six Point I/O modules on the side. The L18 allows eight. I didn’t think of the 4ch or 8ch modules – they’re relatively new. (Watch out for backplane current load – you probably will need an EF24DC power injector.)
If you’re just doing analog stuff another good option is Opto 22 Snap PAC.
They are much more competitive price wise and they hold up very well. I use them a lot specifically for analog monitoring (temperatures, flows and levels primarily).
Pros:
The systems are relatively cheap and well made
The programming software is free
Very good at analog
Very easy to get up and running quickly
Cons:
You’ll need some 3rd party OPC software like Kepware to get the tag values into Ignition or purchase Opto’s OPC server.
The programming is very much different from what PLC programmers are used to (no ladder logic)
If you’re not used to looking at high level language code then digital logic can be confusing.
It might be worth a look at some point in time.
I really would like most to avoid too much programming, im not much of a programmer, which was also why i liked ignition, it seems that most functions are accessible from the UI.
To keep things simple, i just need an analog logger which will feed the data on to the server, preferably with tag browsing.
If you’re just trying to feed analogue values into Ignition, avoid using PLCs. They are expensive for analogues and it sounds like you’re not wanting to do any control.
Use any data acquisition module that supports Modbus TCP. I know this protocol doesn’t support browsing, but setting up 24 I/O in Ignition will take you all of 10 minutes, generally with no programming on the I/O side 
Unless you just have to have Allen-Bradley, I would just as soon use the Modicon M340 (Specifically the BMX P34 2020) with three BMX AMI 0810 cards (8 isolated high speed analog inputs). While there are pros and cons to both brands of PLCs, for just the raw hardware/software cost you’ll save a mint going the M340 route over just about any Allen-Bradley solution (imho).
Yes the M340 can’t do direct tag browsing, but I created a simulation PLC using the M340 to create my base objects and it’s a simple thing to take a PLC export of the database from an M340 processor and import it back into Ignition under a tag folder.
In fact, attached is the excel spreadsheet I made to let me rapidly take an export from an M340 and import it back into ignition.