24-11-2012, 11:17 AM
WATER LEVEL MONITOR
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INDIVIDUAL UNITS
The power supply stage is a linear power supply type and consist of a step down transformer, filter capacitor, and voltage regulators, to give the various voltage levels. After stepping down to 12volts and filtering with a 2200uf capacitor to remove ripples, the voltage is regulated to 12volts and 5volts respectively.
The comparator section is powered with a 12volts supply while the indicator section makes use of 5volts. The power supply circuit diagram is shown in the diagram below.
MEASURING PROBE
This unit is used in monitoring the level in a water reservoir, when the water level is not up to the level where the Ground probe and the level to measure (High and low) is placed, this indicates that the presence of no water.
The principle implored in this design is the conductivity of water with high resistance, when water comes in contact with the two probes there is a current flow, consequently a voltage is obtained, this voltage is being monitored in the comparator section to trigger the indicator section.
COMPARATOR SECTION
A comparator is achieved with an open-loop operational amplifier, this device is used to compare two voltage levels thereby using the difference to perform an action in a circuit.
A comparator has two in inputs (inverting and non inverting ) and an output, when the inverting input of an Opamp is greater that the non-inverting input the output is low and vice versa. In this design of a water level monitor, the LM 358 dual opamp is used as a comparator. The inverting input of the first comparator is connected to the low level probe, while the non inverting input is supplied with a reference voltage of 11volts. When there is no water contact between the low level probe and the ground probe, the voltage at the non inverting input is maximum of the supply i.e 12v, meaning that the otput of the comparator is low thereby the indicator led is off. But if contrary, the inverting input goes low to around 4volts then the ouput of the comparator goes high thereby powering the indicator led.
Note: This same connection is same for the second comparator to indicate the full level, and all other level when monitored.
LEVEEL INDICATOR
This section is made up of an LED to indicate the water level. When the output of the comparator is high, it biases a transistor which switches ground to the negative terminal of the led.
MODE OF OPERATION
This device monitors water level in a reservoir with the aid a of a wire probe , the changes in the input of a comparator circuit due to the presence of water between the level probe and the ground probe cause a change resistance and voltage beweeen the probe terminals and the reference voltage thereby causing an output voltage from the comparator, consequently biasing a transistor which in turn causes a led to glow, indicating a specific level of water in the reservoir with the aid of a predifined calibration of the levels and probes.