ACTUATOR: A mechanical device that drives a control valve open or closed via a command signal from a positioner or I/P transducer.

AIR SET: An adjustable pressure regulator that ensures a stable source of air to the positioner.

BOOSTER: A device that amplifies the amount of air (gas) going to a pneumatic actuator, producing a faster response. Having a separate air supply than the positioner, a booster typically is used with larger actuators that have larger volumes to fill.

CALIBRATION: The process of removing errors from a device or system during setup or at different time intervals, ensuring the accuracy of the device.

DIAGNOSTICS: Information extracted from a device or sensor that can be used to troubleshoot or diagnose a problem.

DOUBLE-ACTING: A type of actuation that uses air on both sides of a piston to drive a control valve open or closed.

ELECTROPNEUMATIC: A type of digital valve positioner that receives an analog signal and converts it to a pneumatic output. That output is used to drive an actuator, which in turn opens or closes a control valve.

EXPLOSION-PROOF: A certification that ensures a device has the ability to contain an explosion within itself so it does not ignite its hazardous surroundings.

HART: HART (Highway Addressable Remote Transducer) is a communications protocol that converts a 4-20mA analog signal into a digital signal, making communication to smart field devices possible.

INTEROPERABILITY: The ability of different types of devices from different manufacturers to communicate and interact with one another because they adhere to a common set of standards.

INTRINSIC SAFETY: A set of standards that ensures a particular device is unable to create enough energy to ignite a flammable gas-rich environment.

LIMIT SWITCH: Prevents a valve from opening or closing once a specified electrical or mechanical condition has been met.

LOOP-POWERED: A loop-powered device draws its power from the system and does not require a separate power supply.

MOUNTING KIT: A mechanical bracket that attaches a positioner to an actuator. The mounting kit is a vital part of the valve assembly because the position of the positioner relative to the actuator directly affects the performance of the system.

PROFIBUS: A digital communications protocol used primarily in Europe for digital devices.

REMOTE-MOUNT: An installation in which a positioner is not mounted directly on the actuator, but in a location some distance away. This can be done for convenience or to protect the electronics of the device from harsh conditions, such vibration or radiation.

SMART: Refers to the intelligence of a digital positioner that is capable of assessing the health of the control valve it is controlling and providing diagnostic information to the end-user.

VALVE SIGNATURE: The graphical representation of a valve’s performance. This includes, but is not limited to, friction, travel, actuator pressure, and such errors as hysteresis, overshoot and linearity.

WIRELESS HART MODULE: A wireless adaptor used in conjunction with digital positioners, particularly in wired analog (4-20mA) systems. The module uses HART communication to extract from the positioner diagnostics and process data that would otherwise be trapped in a wired analog system.

The terms and definitions for this glossary were contributed by Michael Patterson, director of marketing of Digital Solutions for Dresser Masoneilan (, a provider of process control valves and solutions for more than 125 years. Mr. Patterson’s responsibilities include digital positioners, emergency shutdown devices, and other smart instruments. He can be reached at