Measurement of variables are made by sensors, conditioned by transducers, and then transferred to another location using a transmitter. In the case of process control, the accuracy of transmission of the value of the variable is very important; any errors introduced during transmission will be acted upon by the controller and will degrade the accuracy of the signal. There are several meth- ods of transmitting data. The chosen solution will depend on the sensor, appli- cation of the signal, the distance the signal needs to be sent, the accuracy requirements of the system, and cost. Unfortunately, the accuracy of the system can be degraded by poor transmission.