Point IO Analog scaling

kjacoby

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Jul 2011
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Good Afternoon. I am working with a point IO setup with a couple temperature sensors, and pressure transmitters. I am using a 1734-IE8C Point io module. Under the scaling, I have my level sensor setup for 0-100 engineering units. I would like to get better resolution, so i started changing it from 100 to 1000, and 10000 max units. when I do this, my reading doesn't scale correctly.

My current reading is showing 46".

0-100 shows 46
0-1000 shows 475
0-10000 shows 4755

I don't know if this is a rounding issue, a firmware issue, or just something I need to deal with. I don't know what is actually the true number.

running a scaling calculation in excel, I get the same number every time, with greater resolution. I am using 3277 and 16383 as the min and max inputs from the manual.

The calculation I am using is the following

Rate = (scaled_max-scaled_min)/(input_max-input_min)
output = (input-input_min)*rate+scaled_min

There is not much information on AB's site, or KB about the 1734-IE8C.

Thanks for any help,
Kenneth
 
what platform and what scaling function are you using?
is the raw value fluctuating at all?
also what is the value of your raw count?
can you try putting a constant tag into the scale instead of an I/O signal?
 
Last edited:
Scaling
Select scaling for each channel by making the selection on the configuration
dialog. Scaling is the conversion of unscaled data to engineering units.
The high and low scalers (Engineering Units) are signed integers. There are no
restrictions on these units.
• Defaults for 1734-IE2C scalers are +3277 @ 4 mA for low
and +16,383 @ 20 mA for high.

This is what manual says - 1734-um001_-en-p.pdf, pg. 102.

It is clearly written signed integer. This is for the engineering units. So after this you divide by what you need to REAL.
 
Also, you can adjust the scaler values to give more resolution. The default values work out to ~14bits, the card is capable of 16bits.

The scaler range is a signed int, so -32768 to +32767 , Do the math to figure out what 4ma would be at that range(off the cuff, something like -19661 i would think) use that for the low engineering scaler and use 32766 for the high scaler. Then change your scaling function accordingly.

Note, assuming you are using Rs5000, change the scalers in the module config.
 
I am using a L36 V20. With the 1734-IE8C I do not have the option to adjust scalers, or even the type of scaling. I can select the current range, 0-20 or 4-20, add a digital filter, and set my high and low engineering values.

my concern is when i have a stable reading, and I change my high engineering value to 1000, or 10000, instead of giving me a similar reading, the value is higher.

0-100 shows 46
0-1000 shows 475
0-10000 shows 4755

I would expect to see 46.x or 46.xx after I divide by 10 or 100, and store as a real.
 
IMHO it's a resolution issue

16383-3277=13106

13106/100=131.06 counts per degree
13106/1000=13.1 counts per degree
13106/10000=1.3 counts per degree
 
I am using a L36 V20. With the 1734-IE8C I do not have the option to adjust scalers, or even the type of scaling. I can select the current range, 0-20 or 4-20, add a digital filter, and set my high and low engineering values.

my concern is when i have a stable reading, and I change my high engineering value to 1000, or 10000, instead of giving me a similar reading, the value is higher.

0-100 shows 46
0-1000 shows 475
0-10000 shows 4755

I would expect to see 46.x or 46.xx after I divide by 10 or 100, and store as a real.

Change your engineering values to -19661 and 32766 in the module config for the channel you are interested in, Then take the output of the analog channel and feed it into your scaling function in ladder or FB, scale to your 'actual' values and make sure the destination tag is a REAL.

Edit: I don't have a point io card to try it with, so ymmv.

sacle1.png sacle2.jpg
 
Last edited:

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