Ml1100/1200

I am new to this forum, I have been reading for a while, but now it's time to admit I am stuck. I have an ML1100 program i am working on (My first PLC project) and I cannot quite grasp the concept of the A/D Module and its requirements. I am trying to monitor two temp readings and set of a warning alarm and then a shut down alarm when temp reaches a higher level. I have a tendency to make things difficult and over think the problem. I would like some help to get me back on track. Many thanks in antisipation

Post the complete catalog number of the analog module your using.
If you can post your code(.RSS file, zip it and post). The more info we have the more complete the help.

What analog module are you working with ??

Mickey said:

Post the complete catalog number of the analog module your using.
If you can post your code(.RSS file, zip it and post). The more info we have the more complete the help.

Click to expand...

I have an AB 1762-IF4 Analog module using only one temp input

I'm not sure of the workings of this forum yet but I replied to Mickey
that I have an AB 1762-IF4 Analog module using only one temp input

What are you using for a temperature sensor? Make and model.
What is its output and range?
Do you have any additional expansion IO on your PLC?

The more detail you can give us right up front the better, it will save the twenty questions and we can get to what you want faster, which is getting an answer to your question instead of answering our questions.

I am using an Omega TX91A-J2 Temp sensor mounted in an Omega NB2-ICSS-14U-4 housing. The ML1100 is a 1763-L16AWA controller with a 1762-OW8 expansion module. This is all going to be operated by a Panel View micro 300.

Great info. That Omega temperature transmitter is going to convert the millivolt input from your Type J thermocouple into a 4-20 mA current loop signal. The 1762-IF4 module will then sample that current loop signal and produce an integer value inside the Input data table of the MicroLogix.

What's important to you now is "what integer value will show up in the MicroLogix input table for a given temperature ?". That's partially about the MicroLogix data range and scaling, and partially about the Seebeck voltage from the thermocouple.

The 1762-IF4 module specifies a -21 to +21 mA range for a 15 bit bipolar data resolution. This means that a 15-bit integer value will correspond to 21 mA of input span.

0 to 21 mA = 0 to 32767 (decimal) in the MicroLogix input data table.

Let's say that's 1560.38 counts per milliampere.

So the data value in the MicroLogix at the low end of the transmitter temperature span (zero degrees F) will be 4 mA x 1560.38 = 6242.

The data value in the MicroLogix at the high end of the transmitter temperature span (200 degrees F) will be 20 mA x 1560.38 = 31208.

Configure your 1762-IF4 in accordance with your omega device in this case 4-20 mA, download the manual 1762-IN012A-EN-P from www.ab.com and configure internal swithes to work with 4-20 mA.

On your rslogix go to IO configuration on the left pane and then look for your 1762-if4 if there, if it´s not configured then choose it from right pannel of IO config and then add it to your ML1100, when your board has been added then go to adv config and there you will see something like attached figure.


In this case 4-20 mA ( Channel 0) because of your omega device, data from the IF4 range from 0-16384 being 0 minimun data from your omega device and 16384 maximum, from that point on you can scalize your data and your alarms.

OK, let talk about your hardware for a minute.

You are using a transmitter that accepts a J type thermocouple input and amplifies it, outputting a 4-20 millamp current. The first problem you are going to encounter with this hardware selection ss that your trasmitter does not lienarize the thermocuple signal. That means that you will not be able to easily scale your input signal into a meaningful temperature. Linearizing a J type thermocouple generally requires that you solve three polynomials, a 9th order equation, an 8th order equaton, and a 6th order equation. You can do this in a PLC that supports floating point math, but its probably not for a beginning programmer unless he is a fast study and good at polynomial equations.

The simplest hardware will be to wire the thermocouple directly into a thermocouple input module on your PLC, in this case a 1762-IT4. Once properly set up the module will give you the temperature wihtout the need to do any conversions or scaling. But if you are a long distance from the thermocouple you will need the transmitter. If you have to use a transmitter then I suggest you first select a model that will linearize the thermocouple for you.

Okay, I was off by a couple of counts: RA Knowledgebase Article ID # 19719.

You might think you're ready to scale this input data to Degrees F and start writing your alarm logic. But you have to consider and important fact of that Omega transmitter: the Seebeck voltage (the millivolt signal) of a thermocouple is not linear to temperature, and the Omega transmitters you chose do not provide a linearization function.

More sophisticated thermocouple signal transmitters provide a linearization using a lookup table or a polynomial equation. This is also what happens inside the more expensive thermocouple input modules for PLCs.

Since you are just trying to detect a threshold and a less-than-threshold temperature, you might just find a way to apply those temperatures and read the raw values inside the MicroLogix, or use a thermocouple calibrator or millivolt source to provide an emulation of the thermocouple input to your Omega transmitter.

Just to add to the above post here's another view,
First config card ( I used scaled for PID)


Below is some logic to scale your input and set an alarm

If you don't actually need the temperature in the PLC but just want limit alarm then there are a variety of inexpensive limit relays on the market that will accept your thermocouple input and energize a relay when the set temperature is reached.

http://www.actionio.com/

To all that have helped in the above query, I appreciate the responses and have put them to good use. I will be back with more questions as I progress thru this maze. Again Many Thanks to All.