(Note: Problem solutions are available at

1. Given a clear plastic bottle, list 3 different types of sensors that could be used to detect it.

2. List 3 significant trade-offs between inductive, capacitive and photooptic sensors.

3. Why is a sinking output on a sensor not like a normal switch?

4. a) Sketch the connections needed for the PLC inputs and outputs below. The outputs include a 24Vdc light and a 120Vac light. The inputs are from 2 NO push buttons, and also from an optical sensor that has both PNP and NPN outputs.

b) State why you used either the NPN or PNP output on the sensor.

5. Select a sensor to pick up a transparent plastic bottle from a manufacturer. Copy or print the specifications, and then draw a wiring diagram that shows how it will be wired to an appropriate PLC input card.

6. Sketch the wiring to connect a power supply and PNP sensor to the PLC input card shown below.

7. Sketch the wiring for inputs that include the following items.

3 normally open push buttons

1 thermal relay

3 sinking sensors

1 sourcing sensor

8. A PLC has eight 10-60Vdc inputs, and four relay outputs. It is to be connected to the following devices. Draw the required wiring.

• Two inductive proximity sensors with sourcing and sinking outputs.

• A NO run button and NC stop button.

• A 120Vac light.

• A 24Vdc solenoid.


9. Draw a ladder wiring diagram (as done in the lab) for a system that has two push-buttons and a sourcing/sinking proximity sensors for 10-60Vdc inputs and two 120Vac output lights. Don’t forget to include hard-wired start and stop buttons with an MCR.

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