Before a pressure switch can send a signal to monitoring or control equipment, it must first generate an electrical signal to send to that equipment. The generation, strength and type of signal are expressions of the kind of pressure to which the pressure switch is reacting. The process of converting the mechanical energy that gets registered by the switch to the electrical energy that gets reported by the switch is called transduction. Transduction is, simply, the conversion of one kind of energy to another kind of energy. In the context of pressure switches, transduction involves the conversion of mechanical energy to electrical energy.
It may be hard to mentally arrest the concept of transduction, but as it turns out, you’re probably doing a lot of transducing just sitting where you are. If you don’t suffer from diminished hearing ability, your ears are transducing every hour of every day. In fact, the operation of pressure switches and the operation of your ears aren’t terribly different. After all, sound is nothing more than air pressure waves that strike the tympanic membranes of our inner ears. Those waves cause the membrane to vibrate, and the vibration of the tympanic membrane is interpreted by the nerves in our ears as sound. This process of interpretation involves the transduction of that vibration, which is mechanical energy, into neurological signals. This is more or less what happens in a pressure switch; it experiences a change in its environment, and this change affects the condition of a sensory faculty in the pressure switch. This sensory change is transduced into an electrical signal, which gets reported to control and monitoring equipment.
It could be said that ears are pressure switches for our bodies, and pressure switches are ears in industrial processes. In both cases, an environmental change is interpreted and used to induce a behavior in a system.