Electrical Control Systems and Motor Protection

Practice vocabulary flashcards based on HVACR electrical control devices, system fundamentals, thermostats, motor controls, and motor protection units.

Direct Digital Control (DDC)

A system that uses sensors, controllers, and controlled devices to operate an HVACR or automated building system using low-voltage and/or low-current signals.

Open-loop control system

A control system that relies on an operator to manually trigger changes in operation.

Closed-loop control system

A control system that uses feedback from sensors in the conditioned space to modify system output.

Sensor

A DDC system component that detects a specific variable in a conditioned space and sends signals to the controller.

Controller

A component that responds to changes in signals from sensors and sends signals to controlled devices.

Controlled device

A component that operates based on signals received from the controller.

Normally open switch

An electrical switch that must be actuated to provide power to a circuit.

Poles and throws

The structural characteristics upon which electrical switches are arranged and operate.

Relay

An electrical switch that operates under the control of an outside electrical signal.

Solenoid

An electromagnetic device commonly used to operate valves.

Cut-in

The temperature or pressure value at which a device begins operation.

Cut-out

The temperature or pressure value at which a device ceases operation.

Range

The set of numbers between and including a control system's cut-in and cut-out values.

Differential

The difference between the cut-out value and the cut-in value in a control system.

Range adjustment

A modification to a control system that affects the system's average temperature.

Thermostat

A sensing device that reacts to temperature change.

Bimetal strip

A temperature-sensing component that reacts to temperature change by changing shape to actuate a reed or mercury switch.

Low-pressure safety control

A device that switches off the compressor motor if the low-side pressure drops below a safe limit due to refrigerant loss or evaporator freeze-up.

Pressure transducers

Devices used to program high and low pressure cut-in, cut-out, and differential at the controller.

Current relay

A relay operated by the change in current flow through a motor's run winding.

Potential relay

A relay that closes its contacts using counter emf when a single-phase motor reaches $\frac{3}{4}$ of its normal operating speed.

Motor starter

An electrical component equipped with built-in overload protection, unlike a standard contactor.

PTC relay

A relay that, once heated, increases its resistance and causes the start winding current to flow through the run capacitor.

Fast-acting fuse

A type of fuse that blows immediately after its maximum rating is exceeded.

Time-delay fuse

A type of fuse that blows after its maximum rating has been exceeded for a certain period of time.

NTC thermistor

A device that decreases its resistance to current flow as the motor's temperature rises, which can operate a relay to open the motor circuit.