Proper calibrating of a 1756-IF8 Analog input card

soccernut43

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Jan 2013
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I am looking for information on the proper calibration of an 1756-IF8 analog input card, preferably the wiring of the voltage source. Rockwell suggests a -10V - +10V DC calibration source. Is the -10V even used? Our problem is we have a calibrated Rosemont transmitter measuring 0-40 MGD of water. The transmitter at zero is roughly showing 3.991 mA. But at zero flow we are showing 1.2MGD of flow on the HMI. I've used a Beta calibrator and input a 4mA signal and we are not seeing zero on a 0-100 % input on our scaling block in the RSLogix software. The percentage of error is 2.8% but we'd like to see if we could get it closer. Thanks in advance.

Mike
 
I have a 1762-IF4 analog card in a micrologix 1100. I use a laser sensor with a 4-20ma output back to the analog card for table positioning. I used a SCP instruction, ex: 4ma =0% value, and 20ma = 32267 (raw counts) or 100%
I didn't have to "calibrate" the I/O card. I just feed the correct 4-20ma it is looking for.
Make sure your filter settings and voltage/current settings are correct in the "advanced options" settings of your I/O card. Pic attached.

analog.jpg
 
Unfortunately it is set for 4 to 20mA. But for a 4-20mA input which should be 4mA equals 0% and 20mA equals 100%, a 4mA input gievs us a 3.08%. The transmitter is fine. The error seems to be on the low or 4mA end. Thanks!
 
Just for kicks you could make a new scp block and start it out at the 3.08 (as 0%) and if the transmitter goes to 20ma properly set that as your 100%
Just to see if you have a 0-100% reading at the hmi.
 
I am looking for information on the proper calibration of an 1756-IF8 analog input card, preferably the wiring of the voltage source. Rockwell suggests a -10V - +10V DC calibration source. Is the -10V even used? Our problem is we have a calibrated Rosemont transmitter measuring 0-40 MGD of water. The transmitter at zero is roughly showing 3.991 mA. But at zero flow we are showing 1.2MGD of flow on the HMI. I've used a Beta calibrator and input a 4mA signal and we are not seeing zero on a 0-100 % input on our scaling block in the RSLogix software. The percentage of error is 2.8% but we'd like to see if we could get it closer. Thanks in advance.

Mike

You should be able to configure everything in the Module Properties. If your xmitter is fine, just adjust your offset, min and max. You have the data points from your cal, just feed those to your input and adjust the high and low signal to match the high and low eng. units in the configuration tab of the IF8 in RS5000. Zero flow is 4ma? 3.991... but your range on the card is set to 0-20ma? did you set the offset or the units?
 
Even if you use the IF8, or any channels on it, in Current Input mode, the calibration procedure will use Voltage inputs, as stated at the bottom of page 215....

It is amazing how many people skip reading those IMPORTANT notifications in the literature !!

For ultimate accuracy, you will need a precision voltage source, providing 0 and 10.25 Volt signals. The zero is easy, just short out the input channel being calibrated (obviously without the voltage source being connected). The more "accurate" those voltages are, the better the calibration.

If you don't want to go down the "Calibration" route, you can always compensate for zero and gain by adjusting the Scaling parameters for each channel
 
Last edited:
The sensor needs to be within the limits of the input card.a good calibration of the sensor is needed to be able to control the sensor,
same for the input card.
together you will need to see both conversions and make a recalculation like a map instruction, or a scale .
even a perfect calibrated sensor and a calibrated input card will need a scale function.
 
The sensor needs to be within the limits of the input card.a good calibration of the sensor is needed to be able to control the sensor,
same for the input card.
together you will need to see both conversions and make a recalculation like a map instruction, or a scale .
even a perfect calibrated sensor and a calibrated input card will need a scale function.

Not so, the scaling is (can be) done on the input module itself, and you can use these scaling parameters to "adjust" a badly calibrated sensor AND a badly calibrated analog input module.

"proper" calibration of the sensor could be expensive, but providing it gives a proportional signal that is within the operating range of the analog input module, would be ok.

"proper" calibration of the analog input module requires taking the system down while calibration is performed (program mode on the PLC), so may not be an option.

"Calibration", of both the sensor and the input module is just giving them both parameters to adjust the signal conversions for gain and zero offset, so it really doesn't matter if everything is "calibrated", or not, you can just adjust end-to-end using the on-board scaling of the input module.

Of course, this does mean you have to "re-calibrate" the on-board scaling if you have to change the input sensor, or the analog input module. And because you can write to the channel scaling parameters, many times these can be updated automatically in PLC code, especially the "zero" end.

In over 30 years working with all platforms of A-B analog input and output modules, I have never had the need to "calibrate" any of them, in fact I don't think calibration existed pre- Logix5000.

It is never an "ideal" scenario scaling end-to-end, but sometimes it is the cheapest and quickest way to make an analog channel read the real-world process variable adequately.
 
for customers who use milliamp signals and have to check the calibration on these modules as part of their regular "maintenance plan" schedule, I recommend that they invest in a spare Removable Terminal Block - to use when calibrating ... that way they don't have to deal with removing and reinserting the milliamp jumpers - and take a chance on wearing out those tiny little sissy-style screws ...

just pull off the "real" RTB - and then plug it back in when finished with the module's calibration ...
 

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