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Old February 20th, 2013, 03:51 PM   #1
m.peric87
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1756 if16 Analog Input

I need a help to calibrate analog input 4-20mA.
This is how it should be 4mA=0;20mA=940,
but I'm getting a mistake on input.
4mA=-77; 20mA=863.
How to calibrate current input when there is only voltage calibration on card.
Please help
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Old February 20th, 2013, 04:28 PM   #2
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Sounds like you are more interested in "scaling" of the analog input channels than in "calibrating" the channels. As for current inputs, they are really only voltage inputs anyway from the module's point of view. Your 4-20mA signal is converted to a 1-5 VDC signal via a 250 ohm resistor across the input terminals.
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Old February 20th, 2013, 07:13 PM   #3
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If, and a big IF, you are confident that 4.00mA and 20.00mA inputs give you those values you have quoted, then by all means attempt the calibration procedure detailed in the manual for the module. You WILL need an accurate voltage/current source to do this.

However, you readings are so far away from "expected" that i think your 4 and 20mA signals are not 4 and 20mA.

How have you measured these?
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Old February 20th, 2013, 07:44 PM   #4
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have you installed the proper jumpers as part of the wiring on the module's terminal strip? ...

the 250 ohm resistor that's been mentioned above is located INSIDE the module - and the only way to include it in the circuit is by properly using a jumper as part of the wiring ...

and be sure that you consider whether you're using DIFFERENTIAL or SINGLE-ENDED wiring for your system ... there is a separate wiring diagram for each method ...

.
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Last edited by Ron Beaufort; February 20th, 2013 at 07:53 PM.
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Old February 21st, 2013, 01:36 AM   #5
m.peric87
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I used a accurate curent source to see is there is a mistake on input. (also used a digital multimetar to check curent source)
Signal is good, but problem still exist.
4mA= -77 ; 20mA= 863 =>77+863=940.
Channel which I need to calibrate is 11. That mean 26 IN and 25iRTN.
I read a manuall. But I'm not really sure what to do.
Do I need to set voltage calibrator on 25 IN(+DC) & 9 RTN(-DC), and set 0 V for Low Reference(Volts), and 10 V for High Reference(Volts) in calibration tab on the module properties.
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Old February 21st, 2013, 03:08 AM   #6
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The 1756 Analog Cards can be Scaled in the Card.

You don't just have some weird Scaling Values in that Channel do you?

Stu....
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Old February 21st, 2013, 03:31 AM   #7
m.peric87
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I also tried on free input channel 15(36 IN & 35 iRTN) with 4-20mA and there is the same result. 4mA= (-77); 5,6mA=14 and 20mA=863.
I also try to put a new Analog 1756 and the results are the same with low diference. 5.6mA=18; 20mA=867
For rest I will do measurement. Scaling is as in figure.
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Last edited by m.peric87; February 21st, 2013 at 03:45 AM.
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Old February 21st, 2013, 04:12 AM   #8
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..

Last edited by ianingram; February 21st, 2013 at 04:26 AM. Reason: wrong info given
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Old February 21st, 2013, 04:19 AM   #9
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Quote:
Originally Posted by ianingram View Post
Is there an option under Input Range of 4-20mA.

The config above will give 0 with 0mA, not 4mA
Hi Ian:

Actually, 0-20mA is the only selection for Current Input. The setup shown will give you 0 at 4 mA, it is just the way things work on the 1756-IF16.

Stu....
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Old February 21st, 2013, 04:38 AM   #10
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I will try again..
Should the low signal = -235
then the high signal =940

Copy & paste from excel..


0 -235
1 -176.25
2 -117.5
3 -58.75
4 0
5 58.75
6 117.5
7 176.25
8 235
9 293.75
10 352.5
11 411.25
12 470
13 528.75
14 587.5
15 646.25
16 705
17 763.75
18 822.5
19 881.25
20 940
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Old February 21st, 2013, 05:50 AM   #11
Ron Beaufort
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so apparently you're using Single-Ended wiring for current ... here's the diagram ...

Quote:
Channel which I need to calibrate is 11. That mean 26 IN and 25iRTN.


actually it means 26 IN and 25iRTN - AND - a jumper from 25iRTN to RTN ...

so ... did you install the jumper? ...

I HIGHLY recommend that you quit thinking about "calibration" and look at the wiring - and the scaling ... the big question would be "how did the module get THIS FAR out of calibration in the first place?" ... unless someone has already been messing around with the calibration settings, the chances are VERY slim that "calibration" is going to fix your problem ...

.
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Last edited by Ron Beaufort; February 21st, 2013 at 06:03 AM.
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Old February 21st, 2013, 06:49 AM   #12
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Quote:
Originally Posted by m.peric87 View Post
I used a accurate curent source to see is there is a mistake on input. (also used a digital multimetar to check curent source)
Signal is good, but problem still exist.
4mA= -77 ; 20mA= 863 =>77+863=940.
Channel which I need to calibrate is 11. That mean 26 IN and 25iRTN.
I read a manuall. But I'm not really sure what to do.
Do I need to set voltage calibrator on 25 IN(+DC) & 9 RTN(-DC), and set 0 V for Low Reference(Volts), and 10 V for High Reference(Volts) in calibration tab on the module properties.

You perform the calibration for 0-10 VDC and this will assure proper calibration of the channel for all possible configurations. That said, small deviations in your voltage dropping resistors could still result in slight inaccuracy. Since this module's only current input selection is for 0-20mA, you will need to scale the input appropriately to account for the zero offset.

If it were my choice, I'd set the module up to return full 16 bit resolution and then scale the analog input to Engineering Units in my program logic or HMI. That would allow you to easily compensate for any deviation in input resistor value from channel to channel.
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Old February 21st, 2013, 08:13 AM   #13
m.peric87
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I have done measurements another two channels.
Channel 12: Zone 2 Air flow
Scaling for Low 4mA=0; High 20mA=4000
But with input 9.32mA I have 1186 instead of 1330.
Channel 13: Zone 2 Gas flow
Scaling for Low 4mA=0; High 20mA=360
But with input 10.6mA I have 121 instead of 148,64.
That mean all input are wrong.

What than I should to do to fix this?
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Old February 21st, 2013, 08:44 AM   #14
m.peric87
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Quote:
Originally Posted by Ron Beaufort View Post
so apparently you're using Single-Ended wiring for current ... here's the diagram ...



actually it means 26 IN and 25iRTN - AND - a jumper from 25iRTN to RTN ...

so ... did you install the jumper? ...

I HIGHLY recommend that you quit thinking about "calibration" and look at the wiring - and the scaling ... the big question would be "how did the module get THIS FAR out of calibration in the first place?" ... unless someone has already been messing around with the calibration settings, the chances are VERY slim that "calibration" is going to fix your problem ...

.
I still didn't try to install jumper. I need to wait weekend when factory stop Furnace. Until then I need to prepare what to do. But I'm without idea if calibration is not right solution, because I checked wiring, and signal. And everything seems to be ok, unless reading on 1756
And what do you mean to look in the scaling?
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Last edited by m.peric87; February 21st, 2013 at 08:51 AM.
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Old February 21st, 2013, 09:04 AM   #15
dmargineau
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Find the respective Analog Input module within the RSL5K hardware "tree", right-click it, choose Properties and pick the Configuration tab; within the resulting applet you will find the scaling for each of the module's points.
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