EE302 Basic EE II
Ladder Logic Homework #3
Rev. 4/15/2020

1. A pump (Q1) is used to automatically maintain the water level between “high” and “low” in a
   tank using electric sensors. There is a start (I1) and stop (I2) button which is used to enable
   and disable the automated system. The electric sensors indicate high level (I3) and low level
   (I4). The output of I4 is high when the tank is empty, low when not empty. The output of I3
   is high when the tank is full, low when not full. Develop the ladder logic to control this
   system. Keep safety in mind: the level sensors should not be able to turn on the pump if the
   system has been disabled. (5 points)

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2. A product moves on a conveyor and has a label placed on the top of the product. Design
   ladder logic which starts (I1) and stops (I2) the conveyor belt motor (Q1). When the product
   has been sensed in correct upright position (I3) and horizontal position (I4), the conveyor
   stops. The label stamper (Q2) is engaged for one second, then the conveyor resumes
   operation. (5 points)

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3. Develop ladder logic code to control a traffic light which does the following: The N/S red
   light (Q1) and the E/W green light (Q6) are on. Then, both yellow lights (Q2 and Q5) are on.
   Then, the N/S green light (Q3) and E/W red light (Q4) are on. Each light group is on for 15
   seconds. No, this is not a normal traffic light system. (5 points) Hint: you will need to select
   a PLC with more than 4 outputs to simulate this system.

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4. Your company has been asked to develop a conveyor belt system which packages six bottles
   into steel trays. A start (I1) and stop (I2) button control the operation. A steel tray travels
   down the conveyor (Q1) until the steel tray has been sensed by a proximity sensor (I3). Once
   detected, the conveyor stops, a red light is illuminated (Q2), and the automated pick-andplace system is initiated (Q3). Each time a bottle is loaded (detected by I4, not shown), the
   green light (Q4) is illuminated and counted. When six bottles have been loaded, the red light
   is turned off and the conveyor restarted. (5 points)

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5. You have been asked to develop a system to mix and bottle orange juice from concentrate. (5
   points) Hint: you will need to select a PLC with more than 4 outputs to simulate this system.
   a. Low level detectors in the water (I1) and concentrate (I2) tanks prevent operating the
   water (Q1) and concentrate (Q2) pumps.
   b. The orange juice tank has a high level detector (I4) which stops the pumps in the
   water and concentrate tanks.
   c. The conveyor belt motor (Q4) is initiated by a start (I6) and stop (I7) button.
   d. When a bottle is detected under the spigot (I5), the conveyor belt is stopped
   e. The orange juice pump (Q3) is operated for 10 seconds to fill the bottle.
   f. The conveyor belt is then restarted.
   g. The red indicator light (Q5) is illuminated if the orange juice tank has a low level
   h. The green indicator light (Q6) is indicated during normal operation.