1771 ofe2/b , plc5/20e

I swapped out a 1771 ofe1 with a 1771 ofe2/b. Got the config in and the btw/btr rslogix created.
I am having an issue with the scaling registers. 4095 max keeps pushing 16533 to the data file registers of the btw. Conversely, if I change the value in the data file to 16533 it pushes 1655 to the max scale of that channel in the i/o config.

Any idea where/how this is happening? It is set for BCD data type. I tried two's complement binary option without much change.

This is what I believe to be causing my issues with output current not stepping in a linear fashion. I have to be around half of the scale to get 20mA to drop. It seems a little better on low end but still doesn't oscillate with changing values in btw data file registers.

Ladder 2 rungs 255/256 in attachment.

Any ideas/insight would be appreciated.

Thanks!,

Ben

First, change it from BCD to 2's compliment, otherwise you are going to get confused by what you are seeing in the data tables.
You will see that value that you thought was around 50% is really double the max output.

short on time ...

regarding THIS part of your confusion:

Any idea where/how this is happening?

Click to expand...

go to the data table and change the Radix setting (lower right corner) to HEX/BCD ... notice that in that format, the 16533 entries are now shown as 4095 ...

here's why in BASIC terms ...

WAY BACK when that module was designed, HEX/BCD was the numerical "format of choice" ... now the setting for Two's compliment (Decimal) is more common ... so what WE usually see in the data table is 16533 - but the same bit pattern appears as 4095 when it gets sent over to the module ...

haven't had time to look at your program code yet ... retirement takes up a lot more time than you'd think ...

Reading this thread:

http://www.plctalk.net/qanda/showthread.php?t=5981

I've changed to two's complement. Will I need to do TOD/FRD in addition? My application is HMI integer inputs scaled on that side into data file registers of output channel bits of BTW.

Thanks for the help!!

Also, just so I'm clear, per the manual there are no jumpers or dip switches to be moved onf 1771 ofe2/b? Maybe just the fault jumper(mid-high-low)?

Since you changed to 2' complement, the need for TOD and FRD went away, if you go online and look at your data table.
Write a CPT for the scaling: Let's use N7:0 as the desired setpoint (0-100). Use limits in your HMI to ensure the max is not above 100.

(N7:0 /100)* 4095, destination N226:3

You could also change the scaling on the card from 0-4095 to 0-100, and write 0-100 directly to the card address.

Thanks for the suggestions! I think I'll try the writing of 100 straight to the card with changed scaling.

As always, much appreciated Ron and Ken!!

If you were using a floating point as your setpoint, I would not recommend the scaling change. But since you are using an integer as your setpoint, you don't need the added resolution.