process control

From the little information you have provided, you are sending a 3-15psi signal to a transducer with a 4-20mA output. It should be set up electronically so that your psi setting produces a comparable digital readout.

But I really don't have enough information here.

3-15 psi and 4-20 mA signals are called "live zero" signals. It offers two advantages:

1. If the signal cable or pneumatic tubing is cut, the signal drops to 0 psi or 0 mA. This will help you in troubleshooting.
2. If the signal cable or pneumatic tubing is cut, the system will surely go to the fail-safe mode. For example: if the 3-15 psi signal goes to a control valve. A 0 psi signal will force the valve to close (or open if it's air-to-close). Same principle applies for 4-20 mA instruments.

Of course, the "surely" only applies if the system fail-safe mode is properly designed.

As for the difference between "sensor" and "transducer", take your pick. For some people, they're the same thing. Others see them as different things. For me, it's not terribly important. At work, we say "sensor", never "transducer". Go figure.