Scaling Problem

We have to replace 2 pressure transmitters before we were using 0-200 no we have to use -30 to 30 and we need a value of 0.3 psi at blower.
Program is made in Rslogix 5000. As you know after replacing pressure transmitters we need to do scaling.


Please help me how to do scaling. As i am new in this field. Help me !!
Input?

Input min -32767
Input max 32767
Scaled min ??
Scaled Max??
Out ?

If some one is interested in helping me. I can also send the program to you guys.

y = mx+b

I tried but did not get the answer





DataOffset -32767
value at 4 mA DataMax
32767
value at 20 mA DataSpan
65534
Max - Offset If you know please help me how to get the answer. and also please help me in add on instruction

It has been covered many times in here. Please use search first, then if there is something you do not understand, ask.

based on what you've posted so far, try this:

Input MULTIPLIED BY 0.000915555 ...

if that doesn't work, we'll need more details about your system in order to help you ...

Thanks Ron!! how to attach program here. So i can attach program here and than you can help me.

Greetings jamalshahid.

Scaling is done using the line equation y=mx + b where x is the input variable, m is the line slope, and b is the y intercept coordinate.

To compute the value of the slope we need to know the scaled span divided by the inputs span, or

m = (Scaled_Maximum - Scaled_Minimum) / (Input_Maximum - Input_Minimum).


and

b = Scaled_Minimum - (m*input_Minimum)

So we have m = (30 - (-30)) / (32767 - (-32768)) = 60/65535 = 0.0009155

b = (-30) - (m* (-32768)) = (-30) - (-30) = 0

So we have y = 0.0009155 * x

That's how Ron came up with his numbers.

Simply multiplying the raw analog input by that value using a MUL instruction will properly scale your input.

Now tell us a little bit about which ControlLogix processor you are using. If you are using a ControlLogix with 1756 Analog inputs then you don't need to do any scaling in your program - you can configure you analog input card to do it for you. If you are using Flex IO or other remote IO, or a CompactLogix with a 1769 analog input then you will have to scale in your program. If you are using RSLogix 5000 version 16 or higher then you can dowload an SCP Add On Instruction (AOI) from the Fockwell website that works like the SCP instruction on the SLC platform.

Thanks for your reply. I must appreciate your help. I am using 1769 compact logix processor. I also added add on instruction but still confused how to do scaling. If you don't mind i already made program can i send you that. Please have a look and help me.

jamalshahid said:

Thanks for your reply. I must appreciate your help. I am using 1769 compact logix processor. I also added add on instruction but still confused how to do scaling. If you don't mind i already made program can i send you that. Please have a look and help me.

Click to expand...

Zip the file and post it here. See how-to below.

http://www.plctalk.net/qanda/faq.php?faq=vb3_reading_posting#faq_vb3_attachments

Here is the program
Before we were using 0-200 pressure transmitter and now we are going to change 2 transmitter from -30 to 30 and we need 0.3 on blower

Scaling issue..

Processor we are using is 1769 compactlogix

jamalshahid said:

Here is the program
Before we were using 0-200 pressure transmitter and now we are going to change 2 transmitter from -30 to 30 and we need 0.3 on blower

Scaling issue..

Processor we are using is 1769 compactlogix

Click to expand...

In the "SCP" instruction in the file you just posted where the scaled min and scaled max are 0-200. Just change that to -30 to 30. Rung 10 if that's the one you are talking about. I would also make any adjustment necessary to rung 11's offset value.

jamalshahid said:

Thanks Ron!! how to attach program here. So i can attach program here and than you can help me.

Click to expand...

Mickey said:

In the "SCP" instruction in the file you just posted where the scaled input and scaled max are 0-200. Just change that to -30 to 30. Rung 10 if that's the one you are talking about. I would also make any adjustment necessary to rung 11's offset value.

Click to expand...

-----------------------------
what changes i have to make in offset. actually i need 0.3 on blower. Frankly speaking i am new to plcs and recently graduated and my boss gave me this task. That first he was using 0-200 pressure transmitter and now he is going to use -30 to 30 because he need 0.3 on blower. i don't know what i have to do. I did research for almost 20 hours but still helpless.

what changes i have to make in offset. actually i need 0.3 on blower. Frankly speaking i am new to plcs and recently graduated and my supervisor gave me this task. That first he was using 0-200 pressure transmitter and now he is going to use -30 to 30 because he need 0.3 on blower. i don't know what i have to do. I did research for almost 20 hours but still helpless.

If you don't mind can you teach me how to make changes in offset and what is add on instruction.