A number of control signals have been developed and used as technology has evolved. Control signals are a standardized method of conveying information from one device to another. A control signal is the data sent from one device to another by a specific method. In industrial process instrumentation, transmitted information is data. Data can be transmitted in many formats and over many different types of media. In addition, the data may be analog or digital in form. This paper will discuss the most common types of control signals used in the natural gas industry