Interfacing tank gauging system with SCADA

Needless to say if even your problems will be sorted out the accuracy of measuring system a whole will be worsened. Is it possible to upgrade your SCADA? It would be preferable.

So as I could understand you've got so called "wrapping data" bug's effect. Just like as in C long variable is forcedly converted/casted to short one with unpredictable output result.

Your gauging system is representing analogue signal up to 2^32=FFFF FFFF (i'm supposing it's unsigned) when your scada can handle only 2^16=FFFF as maximum.

It does no matter what's a specific protocol's been applied, but what is important how could you change data representation transmitted through one. If there're so called engineering units I'd suggest to change it (if possible) to HEX mode to be transmitted as hex to input on your PLC.

I'd not come across with Modicon so I'm wondering could it handle data on low bit level for being correctly converted/downgraded by programming from 32 bit to 16 bit. This could be done there then converted to decimal and multiplied on scale factor if needed for being sent to SCADA.

Otherwise you'd make as done this trick by writing special tag which converts 32 bit into 16 on SCADA-client level applying calculation tools. Must be noted if your PLC is also 16 bit it won't help.

As intuitive assumption could you divide readings you got from scada on 65536 then minus 1. What you get then? Could you represent us as instance sheet of readings for better figuring out what's up there?

Write a translator, or build a stand alone monitoring module.