Programmable Logic Controllers

Question 1

Before PLC’s what was used to help with automation?

Answer 1

1. Hard wired system of switched relays and timers. The wiring was extremely complicated, and fault finding was very time consuming.

Question 2

What are the main requirements when selecting a PLC?

Answer 2

1. Cost
2. complexity of the process
3. speed of processing
4. input and output requirements
5. communication requirements
6. interface requirements

Question 3

What are some types of communication requirements fora PLC.

Answer 3

1. 1st would have to know if it would have to interface to other PLC’sor a central computer. Does it communicate with a serial link , ethernet , USB ,or RS422 cable.

Question 4

What are the 3 main types of PLC’s

Answer 4

a. all in one (very simple all-in-one)
b. modular ( usualyy built into a crate and some additional modules can be added)
c. rack mounting (similar to modular but Larger racks that can be expanded upon and placed away from central unit).

Question 5

What is the software for PLC’s refererred to as?

1. IDE’s
2. BLT’s
3. IPA’s

Answer 5

1. IDE’s (Integrated Development Environment). SOFTWARE or IDE’s are not interchangeable. some are more difficult than other’s.

Question 6

What are analogue signals usually used for in PLC’s

Answer 6

Physical measurements such as temperature, pressure, flow, weight, and motion.

Question 7

What are the types of signal’s used in a PLC

1. 480 V
2. 220 V
3. analogue 4-20mA , 0 to 10V, -10V to +10V, 0 to 5 V
4. 24v DC

Answer 7

3. analogue 4-20mA ,0 to 10V, -10V to +10V, 0 to 5 V, Physical measurements such as temperature, pressure, flow, weight, and motion.

4. 24v DC usually digital, on or off, switch outputs, or sensor inputs, relay and contactor signals or lamp indicator lamps out of the PLC.

High voltage is usually segregated somewhere else in the control panel to ensure that no electrical noise can affect the signal.