One expects a configurable range TT nowadays, so the question comes up as to what is needed to change the range. Is the TT itself $100 or $150 and the software and cable for configuring the unit $500? I avoid those like the plague. PACTware is gaining acceptance as an easily available HART configuration tool, although the mfg has to provide the DTM file for their product.
The advent of widespread USB and the disappearance of RS-232 serial ports on PCs would make a USB comm connection with a standard USB 'printer' cable a nifty idea. I don't know if USB is technically feasible on a loop powered device, though.
Tiny ring terminals, in addition to the terminal screws, to which one can connect spring clip test probes or spring clip HART probes or spring clip DC power wires when configuring the unit would be an inexpensive, but neat feature for those who test and configure, to avoid the necessity for connecting to screw terminals for test or config.
A diode between a couple of "test" terminals for reading the 4-20mA without having to break into the circuit is a sign of a 'better quality' TT.
I prefer terminal screws with square washers that can't rotate against a barrier because I only have two hands and round washers tend to let the wire slip out as the washer tightens, requiring the three hands of a Martian.
If you go HART, you might consider
- reporting CJ temp as the 2nd variable
- doing thermocouple drift analysis and reporting the T/C condition as a HART variable. This technology deserves wider use.
A flat, non-glossy surface onto which the range could be written would be handy.
Cheap and convenient DIN rail mounting is a necessity, as is DIN Form B head mounting dimensions.
The sensor market is fragmented amongst different type T/Cs and 100ohm Pt RTDs.
I personally won't use a non-isolated TT, life's too short to deal with ground loops and common mode. But I suspect that non-isolated out sell isolated models because of the price difference.
