Classical Control Components Quiz: Relay and Contactor

A closed contact is recorded in memory as logic 1 and an open contact as logic 0.

When the states of the input contacts provide logic continuity from left to right across the rung, the output coil memory location is given a logic 1 value and the output module interface contacts will close.

When there is no logic continuity of the program rung, the output coil memory location is set to logic 0 and the output module interface contacts will be open.

The completion of one cycle of this sequence by the controller is called a scan.

The scan time, the time required for one full cycle, provides a measure of the speed of response of the PLC.

Generally, the output memory location is updated during the scan, but the actual output is not updated until the end of the program scan during the I/O scan.

Fused power lines, of the specified voltage type and level, are connected to the controller's L1 and L2 terminals.

The pressure switch, temperature switch, and pushbutton field input devices are hardwired between L1 and controller input terminals I1, I2, and I3, respectively.

The motor starter coil connects directly to L2 and in series with Q1 relay output contacts to L1.

The ladder logic program is entered using the front keypad and LCD display.