The function of the manipulating device is to influence the process variable. Its main purpose is to regulate a mass or energy flow. Mass flows can be either in gaseous or liquid state e.g. steam, natural gas, fuel oil, etc.
The energy flows typically take the form of electrical energy. The energy supply can be varied discontinuously through contacts, relays or contactors or continuously by means of variable transformers, variable resistors or thyristor units.
Examples of Manipulators and Actuators commonly used in Instrumentation and Control Systems have been discussed below.
Contents
Mass Flow Manipulators
Manipulators for mass flow include: dosing pump, valve, flap and slide. They are illustrated in the Figure below:
Energy Flow, Discontinuous Manipulators
Here the manipulators may include: Contact, Relay/contactor or a Thyristor.
Continuous Variable Manipulators
Examples of the manipulators that are used here are: Variable resistance and variable transformer.
Recommended: The Ultimate Guide to Electrical Maintenance
Actuators
The manipulating device is often operated by an actuator where the controller cannot operate it directly, for example, if it cannot provide enough power or where the output of the controller is in the wrong energy form for driving the manipulator. The controller then operates either a mechanical-pneumatic or electrically powered driver. For instance, the relays built into switching controllers can typically handle currents up to 5A; external contactors or solid state relays are then used to control the higher power required by the process.
Electric Actuators
These may include: Electromagnet, magnet, 3-phase motor drive, single-phase motor drive as illustrated in the figure below:
Related: Electric Solenoid Actuator – Features & Operation
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Pneumatic/Hydraulic Actuators
Examples include: Diaphragm (spring loaded), Diaphragm (double-acting), piston spring-loaded, etc.
Table 1.0 an overview of controllers and their various manipulators/drivers
| Controller Type | Operated Manipulators/Drivers |
| Continuous controllers | Thyristor unit Adjustable resistor Speed-controlled motors Valves, flaps, slides |
| 2-State controllers | Contact Relay, contactor, solenoid valve Solid-state relay |
| 3-state controllers | Relays |
| Modulating controllers | Actuating motors (AC, DC, 3-phase, etc.) |
Also Read: Pneumatic Actuators
