The Sump Pump Resource Center

Sump pumps are used to expel water in dwelling basements where water can accumulate under several conditions. To date, there are two typical systems that sense the levels of water in the sump pump recess that operates the pump.

The first is of a primitive nature (but the most reliable) that incorporates a “float” riding on top of the water surface. When the “float” achieves a pre-determined critical upper level height, a ball inside the float rolls into two contacts supplying power to the pump motor. As the water is discharged from the sump pump recess, the “float” descends with the level of the water, and when it reaches a critical lower level height, the ball rolls away from the electrical contacts and the pump ceases to operate.

The second system involves a pressure switch mounted at the base of the sump pump assembly and serves the same purpose as our “floating” switch.

Recently hired by the Sump Pump and Jump Company LLC, you have been assigned the task of designing the control logic for their flagship product – of course – a Sump Pump. Upon creating the design you find out some interesting facts:

The “Jump” part of the company name was adopted to reflect the predictable electrical shock experienced by previous company service personnel while engaged in the installation process of the product.
The Sump Pump as three inputs, one of which serves as an output as well.
The Sump Pump is to operate as follows: The recess in which the sump pump is positioned has two water level sensors, one for the low level, the other for a high level. Water in the recess is expelled when the pump motor is “ON” caused by the opening of the “LOW” and “HIGH” sensors. The motor can only be switched “OFF” by the closure of the lower sensor.
Testing the control circuit starts with both level sensors being closed, i.e. a logic zero or “LOW”. While the water begins to rise in the of the sump pump recess, the lower sensor (S1) is covered with water which “OPENS” the sensor and the logic state transists from a “LOW” to a “HIGH”. The LED which represents the pump motor remains OFF. After some time allowing for the buildup of water in the pump recess, the high level sensor (S2) is covered with water which “OPENS” the sensor and the logic state transists from a “LOW” to a “HIGH”. This causes the pump motor to turn on. As the water level begins to fall, closing or opening the high level sensor has no effect on the motor and continues to pump water out until such time that the low level sensor closes again or goes “LOW”

which then and only then turns off the motor.

Inputs Output Action
HIGH LOW MOTOR MOTOR
0 0 0 1 Motor is “ON”, turn Motor “OFF”
0 0 1 1 Motor is “OFF”, leave it “OFF”
0 1 0 0 Motor is “ON”, leave it “ON”
0 1 1 1 Motor is “OFF”, leave it “OFF”
1 0 0 0 Sensor error, turn Motor “OFF”
1 0 1 0 Sensor error, turn Motor “OFF”
1 1 0 0 Sensors are covered, Motor is “ON”, leave it “ON”
1 1 1 0 Sensors covered, turn Motor is “OFF”, turn it “ON”

From the truth table on the previous page, we can construct the logic necessary for implementation using Boolean techniques.

1 1
0 1
0 0
0 0

C C

A B

A B = ( A * B) + (A * C)

A B

A = HIGH switch

B = LOW switch

C = Motor Output

A B

The following schematic demonstrates the logic and wiring required for the

LOGICAL SUMP PUMP

For your grade, you are to explain via text and attached to an e-mail in detail the COMPLETE OPERATIONS of the Logical Sump Pump

To start, determine the output of the sump pump motor for its initial conditions i.e.

The water level is below the LOW switch
Both HIGH and LOW switches are LOW or “CLOSED”