Fermentation Temp Control

akedwards · Apr 3, 2005

I am using a Micrologix 1000 analog plc (1761-L20BWA-5A) and I was hopeing to use it for controlling and data logging the temperature on 6 fermentation tanks. I know I need to buy some RDT analog input modules, but I'm not sure the best way to go.

I was planning to log the data using RSview ME and build an HMI program to accept user defined temp setpoints.

Any thoughts much appreciated.

-Chris

mgvol · Apr 4, 2005

I don't think the ML1000 is going to work for you on all six tanks, as it only has four analog inputs and the MicroLogix 1000 does not have any expansion I/O capability. If you are installing one ML1000 per tank, then it will work, as long as your RTD's have transmitters to convert the output signal to 4-20mA or 0-10vdc and you don't have to monitor more than four temperatures per tank.

akedwards · Apr 4, 2005

Good Point

Yeah, I see what you mean. I guess my only other option with the ML1000 would be to convert the RDT signal to a digital one an then use 6 of my digital inputs. Sounds like I should look into another PLC for this application, any suggestions?

mgvol · Apr 4, 2005

The MicroLogix1200 has expansion I/O capability, and the 1762-IR4 module will accept 4-RTD inputs.

jimbo3123 · Apr 4, 2005

If you're committed to Allen-Bradley, It sounds to me like you would be best with a SLC rack with analog input cards (or thermocouple cards) Thermocouples aren't quite as accurate at the temperatures you will be dealing with, but they should read within a fraction of a degree, which I would think would be good enough for a fermentation application.
You will save the cost of transmitters, but will need to allocate more money for thermocouple wire.
It's at least worth looking into.

Edit: The ML1200 would be a good choice as well. I didn't think of that one.

akedwards said:
Yeah, I see what you mean. I guess my only other option with the ML1000 would be to convert the RDT signal to a digital one an then use 6 of my digital inputs. Sounds like I should look into another PLC for this application, any suggestions?

akedwards · Apr 4, 2005

Thanks for the info, I will look into both options, (SLC and ML1200)

Stephen Luft · Apr 4, 2005

Are you locked in to Allen Bradley?

akedwards · Apr 4, 2005

I am locked into allen bradley because I have already made the investmen in RSlogix and RSview.

Tom Jenkins · Apr 4, 2005

akedwards said:
I guess my only other option with the ML1000 would be to convert the RDT signal to a digital one an then use 6 of my digital inputs.

This is a non-trivial task, you know. Analog and discrete inputs are not interchangerable. GE and a couple others have some tricky analog to discrete converters, but you have to hae some equally tricky code in your PLC to get the analog data out of a pulsed signal from the converter.

Your best bet would be a MicroLogix 1200 - they are fairly inexpensive, have many of the math functions that the SLC has (but not all) and have RTD modules.

akedwards · Apr 4, 2005

Thanks for the help, Tom. The 1200 looks to be in my price range.

JohnW · Apr 5, 2005

I have had a problem with RTD modules for the SLC with loss of calibration, it may be the same with the ML1200. I would recommend using RTDs with 4-20 mA converters and a 4-20 mA input module.

You may find that the ML1500 is a better solution than the ML1200, especially if you need memory for data logging. It also gives you the option of 2 serial ports and SLC type math functions.

rsdoran · Apr 5, 2005

The ML 1200 also offers 2 ports on some models. It also supports alot of math functions:

MicroLogix 1200 controllers now offer:

•

Floating Point (F) Data File for use with:

compare instructions (EQU, GEQ, GRT, LEQ, LES, LIM, NEQ);

math instructions (ABS, ADD, CLR, DIV, MUL, NEG, SQR,

SUB); move instruction (MOV); file instructions (CPW, FLL);

and the message (MSG) instruction

•

Programmable Limit Switch (PLS) File for use with HSC

•

RTA - Real Time Clock Adjust

•

GCD - Gray Code

•

CPW - Copy Word

•

ABS - Absolute Value

Fermentation Temp Control

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