03-11-2012, 02:30 PM
INSTANT SALINITY CHECKER
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INTRODUCTION
Salinity checker is a device that is used to check the quality of water. This project is aimed at determining the quality of water for the drinking purpose by taking into account the conductivity of the water.
It’s a simple circuitry consisting of a sensor which is immersed into the sample/water whose salinity is to be measured. The supply voltage is made into a rich alternating current and is stepped up with the help of a transformer and fed into the sensor. The AC supply will play a crucial role in avoiding polarization that can occur in the sensor. The output of the sensor is compared with a reference voltage and given to the comparator whose output is displayed in the LCD display.
The value which is displayed in the LCD should be less than 500 micro moles if the water is drinkable. However a value of 0-1999 can only be displayed.
The usual procedure to determine the salinity of water is by taking samples and checking it in the lab. But this is a hectic job as the samples need to be collected and named and carried to the lab in order to do so. This is where our projects comes into play, instant salinity checker determines the conductivity of water at the spot itself helping to take immediate actions if any required. Another important application is to determine the area were pollution is spread in a water body. The device can be carried through a boat with the sensor immersed into the water, since instantaneous values are noted the area where the pollution is spread can be determined by simply moving the boat in the direction of flow.
BLOCK DIAGRAM EXPLANATION
Instant salinity tester (ISC) essentially consists of:
• Oscillator section
• Emitter follower
• Sensor
• A/D converter
• Comparator/Amplifier
• LCD display
Now we look into each section in detail,
OSCILLATOR SECTION: An electronic oscillator is an electronic circuit that produces a repetitive electronic signal. The harmonic, or linear, oscillator produces a sinusoidal output. The basic form of a harmonic oscillator is an electronic amplifier connected in a feedback loop, with its output fed back into its input through an electronic filter. When the power supply to the amplifier is first switched on, the amplifier's output consists only of noise. The noise travels around the loop, being filtered and re-amplified until it increasingly resembles the desired signal. Very quickly the signal in the loop becomes a sine wave at a single frequency.
In inductive-capacitive or LC oscillators, the filter is a tuned circuit (often called a tank circuit) consisting of an inductor (L) and capacitor © connected together. Charge flows back and forth between the capacitor's plates through the inductor, so the tuned circuit can store electrical energy oscillating at its resonant frequency. The feedback from the amplifier creates a negative resistance that compensates for the internal resistance of the LC circuit, sustaining the oscillations. LC oscillators are typically used when a tunable frequency source is necessary,
EMITTER FOLLOWER: An emitter follower circuit is widely used in AC amplification circuits. The input and output of the emitter follower are the base and the emitter, respectively, therefore this circuit is also called common-collector circuit.
A circuit that uses a common-collector transistor amplifier stage with unity voltage gain, large input resistance Ri, and small output resistance Ro . In its behavior, the emitter follower is analogous and very similar to the source follower in metal-oxide-semiconductor (MOS) circuits. Many electronic circuits have a relatively high output resistances and cannot deliver adequate power to a low-resistance load, or do suffer unacceptable voltage attenuation. In these cases, an emitter follower acts as a very simple buffer.
SENSOR: The sensor is Platinum electrode sensor the external part of the salinity checker. It’s used to sense the conductivity of water . Depending on the conductivity of the solution under test, the resistance offered by the sensor to the circuit varies. And this sensed value is given as the input to inverting terminal of comparator. The other input of the comparator being a reference voltage
A/D CONVERTER: An analog-to-digital converter (abbreviated ADC, A/D or A to D) is a device which converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement. The reverse operation is performed by a digital-to-analog converter (DAC).
Typically, an ADC is an electronic device that converts an input analog voltage or current to a digital number proportional to the magnitude of the voltage or current. However, some non-electronic or only partially electronic devices, such as rotary encoders, can also be considered ADCs.
A simple A/D converter is used here. Its essential components are diodes D1 and D2 and capacitor. Say diode D1 is connected in the main path of the circuit. The negative of diode2 is connected to the positive of diode 1 as shown in the circuit diagram. During the positive half cycle diode1 is forward biased and the capacitor charges to its maximum.
During the reverse bias, diode1 is reverse biased. But now diode2 is forward biased, current flows to the ground through it.
COMPARATOR/AMPLIFIER: As its name suggest it compares its input’s and produce appropriate output. An LM358 IC is used for this purpose. The output from the sensor is given to the IC via A/D converter. Sensor is connected to the inverting terminal while the other arm of the bridge circuit is given to the non- inverting terminal of LM358. Output produced from this section is in range of 0-4.5v
PRINTED CIRCUIT BOARDS
The miniaturization in electronic equipment design has introduced a new technique known as PRINTED CIRCUIT BOARD. Printed circuit board is used to interconnect various electronic circuit printed on it and is provided with holes to accommodate various electronic components.
Printed circuit board (PCB) consists of an insulating base substrate, which is rigid, with metallic circuitry photo chemically formed up on the substrate. Interconnections between components are achieved by means of conducting paths (thin Cu film) running on or through the substrate called tracks.The width of the tracks depends on the amount of current it has to carry. The tracks meet components to which they are to be connected by means of Land or pads which takes form of larger area of Cu. The lands may be of different shapes and sizes and have holes drilled through them.These holes can either accommodate component leads or via-holes. The via -holes also known as plated through holes (PTH) provide connections through the substrate to other track areas. These aroused in case of double sided and multilayer PCBs only.