1771 OFE reconfiguration

Hello,

I need to reconfigure some channels on an existing 1771OFE of a PLC 5/20E. All 4 channels are 1-5vdc right now.

I know I will need to pull the module to check and possibly change the jumper positions. Confirm if it's OFE2/3. And then do some reconfig via the I/O configuration and rack, slot, all that and select the appropriate current from voltage.
My question is, can some cards not be current output capable? Can I tell this from the module type? Aside from the jumpers and the module config via the I/O config in PLC, is anything else needed to complete this?

I've been referencing the very unhelpful PN955107-82 manual. Looking for more clear explanations/direction.

I get lost on not being able to see the BTW/BTR configuration setups and then working off of default configs in the I/O configuration.

Any insight is appreciated.

1771-OFE1 only does voltage outputs, the jumpers select the range. If your card is 1-5VDC now, your only option is 0-10VDC or -10 to +10 VDC. Current is not an option.

1771-OFE2 only does 0-20mA, might have to spring for a new card.

Another option would be to install a 250 ohm resistor on the 1-5VDC and that would give you 4-20mA.

Ken,

Thanks for the reply. I'll be verifying the card next week. Currently there is a module in slot 9, setup for 4-20ma, but there is no BTW/BTR in program for Group 9(not configured?)
How hard would it be to create some block transfers to get that operational? Just some control block/data files and create the block transfers?

250 ohm resistor converts 4-20 to 1-5, but how can I get 1-5vdc to 4-20?

bigLee said:

Ken,

Thanks for the reply. I'll be verifying the card next week. Currently there is a module in slot 9, setup for 4-20ma, but there is no BTW/BTR in program for Group 9(not configured?)
How hard would it be to create some block transfers to get that operational? Just some control block/data files and create the block transfers?

Click to expand...

The newer versions of RSLogix 5, will add the transfer blocks for you. Much, much easier than the old days.

250 ohm resistor converts 4-20 to 1-5, but how can I get 1-5vdc to 4-20?

Click to expand...

There’s a variety of converters available. I recently used a few Allen Bradley 931S-C1A2D-OP. I chose them because they’re loop powered and no calibration pots, just use switches to select input range. 1-5V is not available but 0-5V is. You might have to rescale in the code or get a model with zero and span adjustments.

https://literature.rockwellautomation.com/idc/groups/literature/documents/td/931-td001_-en-p.pdf

So I swapped out the 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 chaning values in btw data file registers.

Any ideas/insight would be appreciated.

Thanks!,

Ben