1769IF8 scaling

chad k

Member
Join Date
Aug 2005
Location
edmonton
Posts
16
I configure the module as 4-20mA Raw/proportional data format.
it supposed to read -32767-32767 correspont 4mA-20Ma respectivly.
but, When I connect current source 4-20mA to any input channel, I red value as -29838-29025. I just use these values as min and max to do the AI scale.

any problem with that? why that wired value?

thanks
 
Take note of full range values. The -32767 to +32767 corresponds to 3.2 to 21 ma.
So the values for 4 to 20 ma are somewhere in between your values look close but should be
closer to -29456 to +29456, you might double check your ma readings.
I personally like to use the engineering units because it follows the ma signal.
4000 to 20000 = 4 to 20 ma. If your going to use this for PID control then use scaled for PID.

FullRange.jpg
 
Mickey said:
Take note of full range values. The -32767 to +32767 corresponds to 3.2 to 21 ma.
So the values for 4 to 20 ma are somewhere in between your values look close but should be
closer to -29882 to +29085 (corrected values), you might double check your ma readings.
I personally like to use the engineering units because it follows the ma signal.
4000 to 20000 = 4 to 20 ma. If your going to use this for PID control then use scaled for PID.



FullRange.jpg

EDIT: Your values for 4 to 20ma are correct
 
The best way I find to scale a transducer is to first figure out the full scale range of your transducer.

Example: Lets say I have a Loadcell with a range of 0 - 2000 lbs. The output of my transducer is 4 - 20ma, 0 lbs being 4ma and 2000 lbs equaling 20ma.
With a milli-amp meter hooked in series between your transducer and analog input card set your transducer (loadcell) to your zero position (no load). Adjust your loadcell amplifier with the zero pot so your milliamp meter reads 4 ma. Look at your analog input raw counts in the data table and write it down.

Apply a known load of 2000 lbs to the loadcell usually using a master loadcell to verify the load is at 2000 lbs. Adjust your span pot on the loadcell amplifier so your milliamp meter reads 20 ma. Again look at your raw counts and write down the full scale reading.

Now you just calibrated your transducer to your amplifier so your output will be linear and you just figured out your analog input calibration factors to be used in the SCP function block or your own math CMP statement.

If you are using the Scale with Parameters "SCP", the first raw counts reading you wrote down in the data table when at zero load should be entered in the "Input Min".
The second reading written down while load was at 2000 lbs will be in your put in the "Input Max".
(0) should be entered in the "scaled min".
(2000) should be entered in the "scaled max".

Now you should have a perfect linear calibration of your analog input and can be verified with your master loadcell.
This same procedure will work with any transducer such as a LVDT, Vacuum or pressure transducer hooked to the analog card. To setup you will just have to find a known standard such as guage blocks for the LVDT or manometer for the Vacuum or pressure.


Hope this doesn't confuse you more, I just think it is easier to relate to examples.
 
Last edited:
I have attached a picture using RS500 that shows the adv conf of the 1769-IF8.
Hope this helps.
 
Last edited:
No wonder I don't see this. I'm using RSLogix5000, not RSLogix500.

This is what my I/O Configuration looks like.


This is what the Properties window show.


How do I get my I/O Configuration to show as you indicated (without resorting to RSLogix500)?
 
novice said:
How do I get my I/O Configuration to show as you indicated (without resorting to RSLogix500)?

Well you will have to stay with Logix5000 since you are using a Compactlogix. I'll check Monday at work for you.
 
What version of RsLogix 5000 are you running?

You still should be able to configure it in the Controller Tags, Local:X:C
 

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