Only Control P

This is the basic modulating control, and what most commercial pneumatic and analog electronic systems utilize. It is essentially an error-sensing device with a fixed gain or amplification. A control mode is used with equipment that is either on or off. A nominal set point exists but is rarely actually achieved, except in passing. A range of control values must be tolerated to avoid short-cycling the equipment, and temperature ranges are often fairly wide for this reason. In the case of equipment that cannot be modulated, this is often the only choice. The smoothness of control depends strongly upon the system capacitance; systems with very low capacitance can experience short cycling problems using two position control.

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