1. A Soft Start uses an SCR (silicon-controlled rectifier) to turn on an AC Moto

Question

1. A Soft Start uses an SCR (silicon-controlled rectifier) to turn on an AC Motor using three phase 480 VAC. Describe the use of the SCR in this device.

a. The SCR will shut down upon motor overload

b. The motor speed is changed by the SCR at any time.

c. The motor speed is slowly increased upon start up, using a slow voltage increase controlled by the SCR.

2. A Triac output device installed in a PLC output module or SSR ( solid state relay), can have multiple failure modes. In general, a Triac can.

a. Fail in a mode that shows the sotput as open

b. Fail as the output is short or closed.

c. Both a and b

3. In a typical VFD design, IGBT's are used to control the output to the motor. For a 3 phase 480 VAC motor, how many IGBT's would expect to see in the circuit?

a. one

b. three

c. six.

4. A proximity switch is an industrial sensor that signals when it is physical close to

a. Any metal

b. plastic

c. ferous metal.

5. What is an example of an AC inductive load used in industry today, that is controlled by a PLC output module using a Triac?

a. pilot light

b. solenoid

c. heating elment.

Explanation / Answer

Ans 1: (c) The motor speed is slowly increased upon start up, using a slow voltage increase controlled by the SCR.

Ans2 :(c) Both a and b

Ans3: (c) Six

Ans 4: (a) Any metal

Ans 5: (b) Solenoid

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