EXAMINATION QUESTION - JIGS

V. Ryan © 2006 - 2009

1. The diagram below shows a jig used on a production line to check the length of a component (the steel cylinder).
When the steel cylinder is inserted into the test jig, the green LED lights. This shows that the steel cylinder is the correct length.

The push to make switches control the LEDs.

If switch ‘C’ is not pressed none of the LEDs should light.

The red and green LEDs indicate whether the cylinder is the correct length, too short or too long.
If the cylinder is too long it will press switches A, B and C. The RED and GREEN LEDs will light.
If the cylinder is too short it will not press switches A and B.
If the cylinder is the correct length both switches B and C should be pressed.

1a. In the space below draw a circuit that shows how switches A, B and C can be connected to make the jig and its LEDs work correctly.

include all three switches, the green and red LEDs and appropriate resistors (include values)

1b. Explain the purpose of the resistors.

The resistors protect the LEDs. They reduce the flow of electricity allowing the LEDs to light rather than be damaged. Without the resistors the LEDs would ‘blow’

1c. What is the advantage of using a 9 volt power source for the jig?

A 9 volt power source means that the jig is electrically safe as electrocution of the operator cannot take place even if there is s fault. The 9 volt supply can be from a battery making the jig mobile and not requiring a mains electric connection.

1d. In the space below draw a ‘push to make switch’ and describe how it works.

As the switch is pressed a connection is made across the two terminals allowing electricity to flow around the circuit.

1e. Draw and label two other types electro mechanical switch.