Allen Bradley Analog input

I am generaly using micrologix or SLC processors with analog input cards, and using SCP to scale the card for my sensors.
I have always used 0-16383 for scaling (scaled for PID). I have seen other engineers use 3120 to 15600 for the same analog card (there loic being that 0 is equal to 0 mA and 16383 is equal to 21 mA) I am having trouble finding documentation in the AB manuals to clear this up for me. how do you determine what the scale should be for the module? (say a 1762 if2of2 or a 1769 if4)

Search the SCP or scaling function in this forum. It has been discussed quite a bit.
It really depends on the resolution of the transmitter, ie 8 bit, 16bit...etc.
1024 counts....this will determine your ranges, either for PID or engineering units.

It is sometimes tough to find, but the A-B documentation for each analog module includes a table like the attached. You get similar information in the set up section for the input cards in RSLogix 500

Let's assume in this case the analog input card is 0-20 mA. So, if you are formatted for Raw Data, a value of 4 mA theoretically returns data of 6552 and a value of 20 mA gives 32760.

Sounds simple, right. Oh no, not so fast my friend! The relationship is very much card model dependent. In some cards the card actually returns 32760 at a value of 21 mA input. In some cases 0 input data occurs at 4 mA.

The moral is, make sure you get the configuration table for the exact card you are using. When in doubt, contact your A-B distributor. And, just to make sure, I always use a 4-20 mA simulator on each analog input channel during panel testing. This not only makes sure that I have done the math right, it allows me to compensate for the errors in input card calibration if I want to get my results to the gnat's eyebrow.

I did do a search and I can find many post saying 4mA is 0 and 20 mA is 16383 (scaled for PID), BUT I also See post saying 4mA is 3277 and 20 mA is 16383 (scaled for PID), and I also saw reference to 21mA. I just was wondering if there was a standard to the cards?

Hi Tom,

Thanks,

I do need a little further education on the Data tables. What colum tells you if the 0 to 32760 is 4-20, 0-20, 0-21, or 4-21?

Thanks for the help

KIRK the number you use for a 1762 if2of2 will depend on how you set it up. Look here and on page 8 well tell you how to set it up on voltage or current. Now go to page 16 here you select raw or pid and this depends on bit 13. Now go to page 14 now depending on what bit 13 is in the configuation file will be the numbers you use when programming. If you`ve choosen raw the #`s will be 0 to 32760 or if you choose pid the numbers will be 0 to 16380. i could be wrong about all this, but this is the way i understand it. If i am one of the more knowledgeable ones will help us. i would say you always have to get the numbers to use from the literature for the card. It confusing because it says this card is 12 bits and it is it just not the first 12 bits that they are using. Now it`s going to take some one like Ken or Ron to explain this.

Thomas Sullens said:

KIRK the number you use for a 1762 if2of2 will depend on how you set it up. Look here and on page 8 well tell you how to set it up on voltage or current. Now go to page 16 here you select raw or pid and this depends on bit 13. Now go to page 14 now depending on what bit 13 is in the configuation file will be the numbers you use when programming. If you`ve choosen raw the #`s will be 0 to 32760 or if you choose pid the numbers will be 0 to 16380. i could be wrong about all this, but this is the way i understand it. If i am one of the more knowledgeable ones will help us. i would say you always have to get the numbers to use from the literature for the card. It confusing because it says this card is 12 bits and it is it just not the first 12 bits that they are using. Now it`s going to take some one like Ken or Ron to explain this.

Click to expand...

I have a possible project using a analog card and am confused.
On page 8, set it up for voltage or current, is something that I understand, but on page 16 here you select raw or pid and this depends on bit 13 -- maybe its just one of those mornings, but not quite grasping this, does this mean that if bit 13 is high or low, is how the card knows to operate on 0-32760, or 0-16380.
also, bit 13 of which word.
just not quite able to fully understand. i just thought you used the scp to scale what you wanted the card to see.

On page 8, set it up for voltage or current, is something that I understand, but on page 16 here you select raw or pid and this depends on bit 13 -- maybe its just one of those mornings, but not quite grasping this, does this mean that if bit 13 is high or low, is how the card knows to operate on 0-32760, or 0-16380.
also, bit 13 of which word.

just not quite able to fully understand. i just thought you used the scp to scale what you wanted the card to see.

Click to expand...

Back in the good old days, the Allen-Bradley card operation mode was fixed at the factory Then someone had the bright idea that if it is an Input card, the equivalent "Output" word at the same memory location is not used, so why not use that Output word to "program" the Input card and tell it how you want it to work. So that is how you configure the card: use an Output with the same address as the Input you wish to set (or use a later version of the software that can do it from a menu).