A chemical company is designing a new filling station to transfer liquid chemica

ID: 3281688 • Letter: A

Question

A chemical company is designing a new filling station to transfer liquid

chemicals from their production process to tanker trucks. The chemicals are contained

in a large holding tank and emptied from there into the trucks. You must design the

logic control for the pump motor used for the tanker truck filling system in ladder

logic using the truth table approach.

The pump motor control relay is controlled by the following sensors:

• A: Position sensor to sense if the truck is in position. This sensor is a

normally closed weight sensor.

• B: Limit switch in the holding tank to sense whether there is enough

chemical to fill a tanker truck. This switch is a normally open sensor.

• C: Limit switch on the filler tube nozzle to sense whether the chemical

level in the tanker is at the proper level (to sense if the tanker is filled).

This switch is a normally open sensor.

• CR: The pump motor control relay (CR), which is normally open.

The pump motor should turn on when the tanker is in position and there is a proper

amount of chemical in the holding tank. The pump motor should turn off when the

tanker is full.

1. Construct the truth table to evaluate the effect of each set of input conditions on the

output (pump motor control relay).

2. Convert the truth table into a Boolean expression. Simplify the expression.

3. Draw the ladder logic rung to control the pump motor control relay (CR).

Solution:

A B C CR T T T T T T F F T F T F T F F F F T T F F T F F F F T F F F F F

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