Chapter 4: WATER LEVEL MEASUREMENT
4.1 BASIC LEVEL MEASUREMENT
For Few crops Like Rice a certain level of water must be present above the Ground level. Water
level above the ground can be measured by various Meathods :
• Capacitive level Measurement
• Ultrasonic water Level Measurement
• Water level sensor integrated circuit
4.2 capacitive level measurement
This simply works upon the change in dielectric medium of the capacitor. Initially when
air is present the default capacitance value has been measured now upon installation in
field the dielectric changes from air to water thus results in change of capacitance which
works as function of level.
4.3 Ultrasonic Water level sensor
As the indicate, ultrasonic sensor measures distance by using ultrasonic waves . the sensor head emits an ultrasonic wave and receives the wave reflected back from the target. Ultrasonic sensor measure the distance to the target by measuring the time between the emission and the reception.
An optical sensor has a transmitter and receiver, whereas ultrasonic sensor uses single oscillator emits and receives ultrasonic .waves alternatively. this enable miniaturization of the sensor head.
FIGURE 4.1(SONAR SENSOR)
4.3.2 About ultrasonic
Ultrasonic sensor are used around the world, indoors and outdoors in the harshest condition, for a variety of application. Our ultrasonic sensors, made with piezoelectric crystals, using high frequency sound to resonate a desire frequency and convert electric energy into acoustic energy, and acoustic energy into electric energy sound wave are transmitted to and reflected from target back to the transducer. Target can have anyreflective form, even around certain variables, such as target surface angle, changes in temperature and humidity, and reflective surface roughness, can affect the operation of the sensors.
4.3.3 Distance calculation
The distance can be calculated with using the following formula.
Distance L = ½ * T * C
Where L is the distance, T is the time between the emission and reception, and C is the sonic speed. (the value is multiplied by ½ because T is the time for go and return distance.
Characteristics enable by the detection system are following.
Transparent object detectable
Since ultrasonic waves can reflect off a glass or liquid surface and return to the sensor head, even transparent target can be detected.
Resistant to mist and dirt
Detection is not affected by accumulation of dust or dirt.
Complex shaped object detectable
Presence detection is stable even for target such as mesh trays or spring.
4.4 Types of ultrasonic sensors :
4.4.1 Proximity detection
An object passing with in the preset range will be detected and generate an output signal. The detect point is independent of target size, material or reflectivity.
4.4.2 Ranging measurement
Precise distance of an object moving to and from the sensor are measured via time intervals between transmitted and reflected bursts of ultrasonic sound. Distance change is continuously calculated and outputted.
4.4.3 Migration in ultrasonic sensing
Migration has used the advance technology of ultrasonic sensing to solve an array of a problem across a wide range of industries since 1979. Our field tested products are capable of meeting unique needs with a variety of option to help you to find a solution. Tough and reliable, we have had sensor running 24 hours a day, 7 days a week since 1980 without fail.
4.5 Migration advantage
1) Resistance to external disturbances such as vibrations, infrared radiation, ambient noise and EMI radiation.
2) Measures and detect moving objects from discrete distances.
3) Can detect small object over long operating range.
4.6 Typical application :
4.6.1 Tank level
Liquid level sensor are integral to process control and inventory management in many industries.
At migration we engineer two type level sensors (proximity sensor) and continuous level sensor (analog sensor).the type of sensor are appropriate for our liquid level measurement.
4.6.2 Production line sensor
Ultrasonic sensor can be applied to the manufacturing process for automated process control on factory floor while also being an indispensable tool for company to maximize efficiency through precise measurement and control.
Ultrasonic sensor can streamline the production process.
FIGURE 4.2(WORKING OF ULTRASOUND)
4.6.3 Distance measurement
Ultrasonic sensor can measure the distance to a wide range of objects regardless of shape color or surface texture. They are also able to measure approaching or receding objects.
4.6.4 Application using migration ultrasonic sensor
1) loop control
2) roll diameter tension control, winding and unwind
3) liquid level control
4) beam detection for high speed counting
5) full detection
6) thread or wire break detection
7) robotic sensing
8) stacking height control
9) people detection for counting
10) contouring or profiling using ultrasonic system
4.7 Use of ultrasonic sensor in industry
Ultrasonic sensor can detect movement of targets and measure the distance to them in many automated factories and process plants. Sensor can have on or off digital output for detecting the movement of objects, or a analog output proportional to distance. They can sense the edge of material as web guiding system.
Ultrasonic sensors are widely used in car as parking sensors to aid the driver in reversing into parking spaces. They are being tested for a number of other automotive uses including ultrasonic people detection and assisting in autonomous UAV navigation
Because ultrasonic sensor are use sound rather than light detection, they work in application where photoelectric sensor may not.
Ultrasonic are great solution for clear object detection, clear label detection and for liquid level measurement, applications that photoelectric struggle with because of target translucence. As well, target color or reflectivity do not affect ultrasonic sensors, which can operate reliably in high glare environment.
Passive ultrasonic sensor may be used to detect high pressure or liquid leaks, or other hazardous conditions that generate ultrasonic sound in these devices, audio from transducer (microphone) is converted down to human hearing range.
High power ultrasonic emitters are used in commercially available ultrasonic clearing devices. An ultrasonic transducer is affixed to a stainless steel pan which is filled with a solvent (frequently water or isopropanol). An electrical square wave feeds the transducer, creating sound in the solvent strong enough to cause cavitation.
Ultrasonic testing are widely used in metallurgy and engineering to evaluate corrosion, welds, and material defects using different types of scans.
4.7.1 Use in medicine
Medical ultrasonic probe come in variety of different shapes and sizes for use in making cross sectional images of various parts of the body the transducer may be passed over a surface in contact with the body. The transducer may be passed over the surface and in contact with the body, or inserted into body opening such as rectum or vagina. Clinicians who perform ultrasound guided procedures often use a probe positioning system to hold the ultrasonic transducer.
Air detection sensor are used in various roles non invasive air detection isfor the most critical situation where safety of patience is mandatory. Many of the variable which can affect the performance of the amplitude or continuous wave based sensing system, are eliminated or greatly reduced, thus yielding and repeatable detection.
One key principle of this technology is that the transmit signal consists of short bursts of ultrasonic energy. After each burst electron looks for a return signal with in small window of time corresponding to the time it take signal received during this period will qualify for additional signal processing. This principle is similar to radar range gating. 4.8 PIN DESCRIPTION:
FIGURE 4.3(HCSR04 PIN LAYOUT)