I assume you are referring to this Pressure Transducer block in Simscape Electrical. You connect the A port to the location you want to measure in a fluid (gas, thermal liquid, two-phase, etc.) network, and the +/- ports will generate a voltage signal.
Alternatively, you may use the ideal sensors in the Gas (now replaces Pneumatics) domain, the uses the pressure physical signal directly. If you'd like a voltage signal as in a transducer, you may try a 1D PS look-up table to represent the transducer specification and do the conversion.
