1756-IF16 Single Ended Mode Scaling

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1756-um009_-en-p.pdf

In the above 1756-IF16 document on page 43, it says the scaling for 4-20ma in single-ended mode is 20.58ma = 32,767 counts and 0ma = -32,768 Counts.

So if I was using a scale block in a function block, I would use...
20ma = 30920 Counts = Device EU Units High
4ma = -20030 Counts = Device EU Units Low

Is this correct?





Stack Overflow scale formula
https://stackoverflow.com/questions/13137348/scaling-range-of-values-with-negative-numbers

from_max = 20.58 Milliamps
from _min = 0 Milliamps
to_max = 32767 Counts
to_min = -32768 Counts
Scale Formula
Counts at x Ma = (x - from_min) * (to_max - to_min) / (from_max - from_min) + to_min

Looks like you are using Integer mode, is that correct? Why not floating point mode?

The single-ended mode has all 16 channels available, while in single-ended mode, the card only allows integer values.

The differential mode allows floating-point values, but only eight channels available. (Each diff channel is composed of two single-ended channels)

We only have simple two-wire transducers, so to keep costs down, we went for single-ended mode. I prefer differential mode because of the loop flexibility (2-4 wire) and floating-point values.

Yes, the arithmetic is correct; 4.0mA = -20030 counts

Thank you very much

Have an awesome day!

id10t_error said:

The single-ended mode has all 16 channels available, while in single-ended mode, the card only allows integer values.

The differential mode allows floating-point values, but only eight channels available. (Each diff channel is composed of two single-ended channels)

We only have simple two-wire transducers, so to keep costs down, we went for single-ended mode. I prefer differential mode because of the loop flexibility (2-4 wire) and floating-point values.

Click to expand...

I'm not sure which PLC you are using.

On our 1756-L61, L63, L73 and L83 the 1756-IF16 can be configured for:

Float Data - Differential Mode (as you describe for 8 channels)
Float Data - Single-ended Mode - No alarm (which I use)
Integer Data - Single-ended mode
and another 15 choices as shown in the attached capture

I would delete your card, add it again, and choose float data, single ended, no alarm. Scaling is quite nice.

id10t_error said:

from_max = 20.58 Milliamps
from _min = 0 Milliamps
to_max = 32767 Counts
to_min = -32768 Counts

Click to expand...

Scaling (see attached) is 20 ma = scaled engineering units
and 4 ma = scaled engineering units

I would not use above 20 mA, and below 4 ma ... unless you are using some strange non-standard instrument.

I'll chime in with Ken Moore and thingstodo. You certainly can use single ended mode and still get float data. I also agree with thingstodo that "Float Data - Single-ended Mode - No alarm" is the choice I prefer.

I generally do something a little different in how I set up the card. I prefer my scaling as: High Signal = 20ma, Low Signal = 4ma, High engineering = 20, Low engineering = 4. This lets me configure all the cards the same and *leave them that way*. Changing ranges on a running system has some consequences (the entire card resets to accept the change) so I just don't do it. I find it easier to scale analogs in the IO mapping routines anyway. I also find being able to read in milliamps very useful in commissioning and troubleshooting.

In case you were thinking that alarming on the card was something you wanted to use, it has the same card reset issue.

This is good stuff,

Danw, thanks for confirming my values.

thingstodo, thanks for pointing out the Float option for single-ended great idea. I missed this in the setup.

Mellis, I'm really like the idea of using 4-20 on both the raw and EU high/low units. It makes perfect sense to be able to view it as a raw signal.