The T120 is a 2 wire transmitter for Pt100 and Ni100 type probes, loop powered, it is included with Seneca's configuration software making it easy for the end user to control and configure the T120 parameters (start/full scale, rejection, RTD type, cable resistance, over-range, etc.).
The T121 is a converter for Thermoresistance (mA, mV, Pt100, Pt1000, Pt500, Ni100, TC's, Ohm) with 2, 3, 4 wires and convert/isolate it into 4 to 20 mA loop powered signal. It's completely configurable through PC software. T121 is suitable for in-head mounting (RTD or TC). A 2-way galvanic isolation among input and output circuits assures the integrity of your data.