Diagnostics Large Oven

Hey Guys,
I have several thermoforming ovens I am working on. These ovens have 24 heating zones. Each zone may be from 2 heaters in series, to 20 heaters in series parallel configuration. These are what we call cal rods, resistive heaters. 480V system where one zone has 2 SSRs, and L2 doesnt go through an SSR, but is connected (I can upload examples of the wiring if needed.

i have been tasked with setting up diagnostics through the HMI. I am having trouble getting started on this. Space is limited, and I would rather not install new SSRs.

My first through is to use CT(current transformer) connected to analog inputs to the PLC. Can a CT output be connected to a 0-20ma input? I have found some compact CTs that are rated 0-100A with 26ma max output. the highest fuse rating on a zone at the moment is 40amps.

My theory is to have a base amps the zone pulls, and if its out of tolerance we can show a warning for the operator to act on.

Thanks for any input.
Jerry

So, the thought just hit me. Im measuring AC, and the CT output will be AC, not DC current for my PLC input.....Any suggestions?

I have seen CTs with built-in transducers that convert the current to a 4-20 ma signal and I have also seen standalone transducers that take the standard 0-5 amps and convert it to a 4-20 ma signal. I just can't remember any makes for either right now.

Automation direct

Check this out from automation direct http://www.automationdirect.com/adc...ansducers/AC_Current_Transducers/ACT050-42L-F

Amps in 4-20MA DC out If cost is and issue they have go/nogo descrete.

More options....

http://www.plctalk.net/qanda/showthread.php?t=102389&highlight=ct