Maintenance Q&As

How do sensors and actuators work together?

Answered September 06 2019

When working in tandem within a given system, actuators receive signals from sensors and perform some kind of task based on that input. To understand how that works, we’ll have to look at how both sensors and actuators function.

The role of sensors

Sensors monitor environmental conditions, such as the level of fluid in a tank, the vibrations of a ball bearing system, or the temperature of a furnace. The input from the environment is converted to an electrical signal which can be interpreted by other pieces of equipment.

For instance, a gas furnace will have a thermocouple that monitors the heat from the pilot light. As long as the pilot light keeps burning, the thermocouple generates a current. The greater the heat, the higher the voltage will be.

The role of actuators

Fundamentally, an actuator is a device that causes movement. It takes input—often an electrical signal—and energy, which it then converts into physical motion. An actuator may be pneumatic, hydraulic, electric, thermal, or magnetic.

For example, a hydraulic cylinder on an excavator uses pressure from hydraulic fluid to push and pull on the piston rod within the cylinder barrel. That lateral movement is used to move the arm on the excavator.

Actuators and sensors together

Going back to our furnace example, we can see how sensors and actuators often work together.

In furnaces, the gas shutoff valve is connected to the thermocouple. As long as the pilot light is going, the thermocouple generates a current, and that current keeps the valve open. As soon as the current stops—such as if the pilot light goes out—the valve shuts, preventing gas from accumulating in the furnace and reducing the risk of an explosion.

In this case, the sensor (the thermocouple) provides both the energy and the signal for the actuator (the shutoff valve). In other systems, the setup may be more complex with multiple sensors and actuators working in tandem to perform a given task. However, the basic principle remains—the sensor provides a signal, and the actuator adjusts based on that signal.

Likewise, the movement from an actuator may register on a sensor, allowing it to control other components of a system accordingly or provide performance data for condition-based maintenance.

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