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Old September 15th, 2011, 07:37 PM   #1
ddeshi2
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1769-IF16C module

Hi all, I'm using a Compactlogix PLC with 1769-L32E processor, 1769-IF16C, 1769-OF8C input and output modules.I'm using RSLOGIX5000 to develop the program. It is a 12-bit system. I'm configuring all the input channels to " scaled for PID". I'm using PID instruction in my program and trying to configure it.My question is what should I enter in the fields of Unscaled Min. and Unscaled Max. for PV. Is it 0-16383 or 0-4095? One of my friends told me that as it is a 12 bit-system and my channels are "scaled for PID" I should enter 0-4095 And if it is a 32-bit system it would be 0-16383. Is he right? Should I enter 0-4095? Please help.

Thank you,

Ding
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Old September 15th, 2011, 08:23 PM   #2
sthompson
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For the 1769-IF16C refer to Page 42 (PDF 42)of the Manual.

http://literature.rockwellautomation...m018_-en-p.pdf

For the 1769-OF8C refer to Page 4-27 (PDF 109) of the Manual.

http://literature.rockwellautomation...m002_-en-p.pdf

Stu....
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Old September 15th, 2011, 08:44 PM   #3
ddeshi2
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@Sthompson

So, is it 0-16383 even for 12-bit system? Please help

ThankYou!

Ding
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Old September 15th, 2011, 08:57 PM   #4
sthompson
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Quote:
Originally Posted by ddeshi2 View Post
@Sthompson

So, is it 0-16383 even for 12-bit system? Please help

ThankYou!

Ding
Don't get hung up on how many Bits it is, just read the Manual. Allen Bradley should know how it works.

The Table on Page 4-33 (PDF 115) might be a little more helpful for the OF8C.
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Old September 16th, 2011, 12:21 AM   #5
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if it is the 12 bit system, the range is 0--4095, be equal to
2­11
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Old September 16th, 2011, 12:28 AM   #6
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be equal to 2 of 11 powers
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Old September 18th, 2011, 07:49 PM   #7
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@ all

Thank you!

@Zhoudq

I'm trying to scale my readings of the pressure transmitter (4-20 ma to 0-750psi)for displaying on to the HMI. I'm using 1769-IF16C analog module and SCL instruction. What will be my Input Raw Max. and Input Raw Min. values? Will it be 0-4096 or -32767 to 32767? In the manual it was given as -32767 to +32767 but I'm not sure whether it is for 12bit system or not. Can you please help me with it.
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Old September 18th, 2011, 10:21 PM   #8
Mickey
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Raw data depends on how you have configured the card. Your picture above shows the choices. So how have you configured it? 0-4095 is not one of them.
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Old September 19th, 2011, 08:42 AM   #9
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@Mickey

This is not the manual that came with my PLC. I have lost the manual and when I searched online I found this. I don't think it is for a 12bit system. I have a compactlogix 12 bit system. I have configured 4 of my input channels as 4-20ma,60HZ, Raw/Proportional data. I want to display my Pressure transmitter readings (0-750psi) on the HMI and for displaying I need to scale the values. I'm using SCL function block for scaling. What would be my Input Raw Max and Input Raw Min values. Will it be 0-4095 or -32767 to 32767? Please help.

Thank you!
Ding
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Old September 19th, 2011, 08:55 AM   #10
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Agree with sthompson, don't care about the bits !

As you may see in the table you posted, configuring the module as 4-20 mA input and RAW/Proportional data, it will return values using the following considerations:

3,2 mA = -32767
21 mA = 32767

The full range of raw/proportional counts (-32767 to + 32767) applies to the full range, not the normal operating range for an input. While the normal operating range of a 4-20mA current input is 4-20mA, the full range is actually 3.2-21mA. As a result, a 4mA raw/proportional input channel will actually read around -29800, not -32767.

Hope this clears things,

- fuzzy logic
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Old September 19th, 2011, 11:30 AM   #11
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See picture below for data format values. I would use the scaled for PID or engineering units myself.
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File Type: jpg DataFormat.jpg (65.5 KB, 72 views)
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Old September 19th, 2011, 12:40 PM   #12
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See below for a very useful tool for checking the scaling and data values.

Created by John Soltesz

http://www.plctalk.net/qanda/showpos...23&postcount=1
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File Type: xls scaling chart.xls (49.5 KB, 41 views)
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Last edited by Mickey; September 19th, 2011 at 12:45 PM.
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Old September 20th, 2011, 08:48 AM   #13
ddeshi2
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@ all

Thanks for the help.
@ Mickey,fuzzylogic

How did you come up with -29,822 to 29,085. Is it just by following the manual or is there any calculation involved?

Thank you!
Ding
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Old September 20th, 2011, 09:48 AM   #14
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Ding, manual gives you the needed value... anyway you may calculate those values, using a formula.

Here below a scaling formula you may use.
  • In = Input value
  • InRawMax = Maximum attainable input value(21 mA)
  • InRawMin = Minimum attainable input value (3.2 mA)
  • InEUMax = Maximum scaled value(32767)
  • InEUMin = Minimum scaled value(-32767)
Example 1: want to know which value corresponds to 4 mA

(4-3.2)x(65534/17.8)+(-32767)
0.8 x 3681.7 -32767
-29821.64

Example 2: want to know which value corresponds to 20 mA

(20-3.2)x(65534/17.8)+(-32767)
16.8 x 3681.7 -32767
29085.56

- fuzzy logic
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File Type: jpg scaling.JPG (6.0 KB, 55 views)

Last edited by fuzzy logic; September 20th, 2011 at 10:19 AM.
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