Just to close this out. The old HMI software is Lookout 6.7.1 (not the Lookout Direct variant) and the Hart device is accessed with a 3rd party software by FieldComm group called HartServer. I talked to them about migrating the product and found out that their latest version doesn’t appear to play well with Windows 64 bit operating systems, so even if I upgraded, it might not be reliable.
So, wired the analog sensor to a 16 bit analog input on their DL06 PLC and got it scaled to match what is being read from the Hart interface. I did add some first order filtering logic in the PLC to take the jitter out and the end result side-by side comparing Ignition to Lookout are a match. This means I don’t have to come up with a software solution but a solution that relies just on PLC hardware and code is much more comforting to me anyway.