Sclae w/Parameters (SCP)

Here is the setup:
We have a MicroLogix 1100 (1763-L16AWA). It has a voltage range of plus/minus 10 Volts. It has a range of -31206 to 31206. It is recieving information from a load cell which has a max force of 50,000 pounds. The load cell sends a signal of plus/minus 5 Volts. Although we are only using the positive side. The program (rss?) was written quite a while ago. My experience with PLC's is very limited and happened years ago. I was tasked yesterday with improving the setup.

The system has opererated pretty much okay. However, in order to change the maximum load and minimum load being applied during the test you had to enter some number between 0 and 31206. What we would like to do is enter (for instance) a 1000 lbs for the min and 15,000 lbs for the max. In other words, enter the ACTUAL loads we want during the test. The rss has a SCP on one of the rungs. It was set up like this:
Input I:1.0
3453<
Input Min. 0
0<
Input Max. 31206
31206<
Scaled Min. 0
0<
Scaled Max. 31206
31206<
Output N7:0
3453<

It seems to me it should be setup like this:
Input I:1.0
3453<
Input Min. 0
0<
Input Max. 31206
31206<
Scaled Min. 0
0<
Scaled Max. 50000
50000<
Output N7:0
3453<
However, I recieve an error of "Operand sizes do not match."
Some one said it is because 50000>31206. Is that true? I could buy that.
My other question is should the input max actually be 15603 or HALF of 31206? Since the load cell is only going to give a max of 5 volts and the MicroLogix has a max of 10 volts?

Try Two SCPs:
Input: [LoadCellRawAdress]
Input Min: -31208
Input Max: +31208
Output Min: -10.0
Output Max: +10.0
Destination: [Float of your choice]"Load Cell Volts from +-10vdc input"

Then SCP
Input :[Float of your choice from above]
Input Min:0.0
Input Max:+5.0
Output Min: 0
Output Max: 50000
Destination: EDIT [DINT or float of your choosing]"Load cell pounds"

EDIT: You will find the voltage values handy for set up and troubleshooting, although there may be a trade off in precision using my interim float in the 2nd SCP.
The errors you got are due to the exceeding the positive range of your N address (INT). You can use an INT to hold positive values from 0-65535, but you will have to take extra steps to force them to be handled that way in math instructions.

I have to say, that seems like a pretty good solution. Maybe even billiant. I will certainly give it a try. Thanks.

Welcome to the forum.

If you are going to be changing the range parameters from time to time I suggest that you use either F registers or L registers for output min and max instead of using constants.

----+-SCP-------------+

    |Input       I:1.0|

    |Input Min       0|

    |Input Max   15603|     

    |Output Min   F8:1|

    |Output Max   F8:2|     

    |Destination  F8:0|

    +-----------------+

F8:1 = 0.0
F8:2 = 50000.0

If you need to change the scaling then you only need to change the values in F8:1 and F8:2 instead of editing the rung. (Choose any address you want, you don't have to use F8:0, F8:1 and F8:2, however you should use an F data type or an L data type)

Notice that I changed the Input Max to 15603 for 5V. That doesn't change the analog input range in anyway, it just establishes the point 5V = 50000 lbs.


One of our distinguished forum colleagues has put together the best scaling tutorial on the internet. You can find it if you go to his website www.ronbeaufort.com, click sample lessons on the left hand side, and click scaling with y=mx+b part 1 and part 2. He covers various methods of scaling including using the SCP instruction.



I am a little perplexed by this statement.

mbuis said:

However, in order to change the maximum load and minimum load being applied during the test you had to enter some number between 0 and 31206. What we would like to do is enter (for instance) a 1000 lbs for the min and 15,000 lbs for the max. In other words, enter the ACTUAL loads we want during the test.

Click to expand...

This is very important to understand: You set up scaling on an analog input according to the hardware attached to the input channel. So unless you are changing out the load cell and using load cells of different ranges for different tests then you don't change the scaling.

Your test parameters are most likely set elsewhere in your program and are compared to the actual scaled force.

Can you attach a copy of the program to this thread? You'll need to zip the .RSS file first.