Ultrasonic devices for monitoring liquid level and activating the opening and closing of switch contacts at predetermined liquid level thresholds.
A ultrasonic liquid level switch is an instrument for monitoring the height of a liquid and tripping a relay contact switch or transmitting a solid state relay switch output when a maximum, minimum or intermediate level has been reached. The liquid level switch output can then be utilised by other instrumentation to open a valve, illuminate a warning lamp, activate an audible alarm, or switch on a pump.
Featured liquid level measurement products
LMK458 Marine Approved Hydrostatic Level Transmitter - Marine approved level transmitter with 4-20mA output for measuring level of contents inside ship ballast, fuel, liquid cargo or wastewater tanks
External Mounted Tank Level Sensors - External mounted level sensors for installing on the outside of a liquid storage tank to measure level of tank contents.
Ultrasonic liquid level switches are contactless measurement devices which transmit and receive high frequency acoustic waves to measure the distance to the surface of a liquid based substance.
Ultrasound liquid level switch technology transmits a high frequency sound wave pulse and receives the wave echo reflected off a liquid surface. The time taken for the acoustic pulse to traverse the distance between the transmitter and target surface, and back again to the receiver is measured.
The distance (d) between the ultrasonic liquid level switch and the liquid surface can be calculated by dividing the time taken (t) by two, and multiplying that by the speed of sound (c) in air, i.e. d = c ∙ t / 2. The liquid level in a tank (LT) can then be determined by subtracting distance (d) from the height of the ultrasonic level switch (HT), i.e. LT = HT – d.
The performance of a ultrasonic level switch is mainly affected by changes in the speed of sound and disturbances on or above the surface of the liquid.
The speed of sound will change if the air density changes. Since air density changes in the Earth’s atmosphere are directly related to changes in air temperature (measured in Kelvins), an ultrasonic fluid level switch is compensated by incorporating an air temperature sensor.
Featured liquid level measurement products
OEM sensor for diesel tank level measurement - Submersible hydrostatic level sensor for OEM integration in diesel fuel tanks. Low-power, 0.5 to 4.5V output.
DPT200 Pressurised Tank Level Differential Pressure Transmitter - Pressurised tank liquid level differential pressure cell transmitter for process plant storage.
Surface effects can be reduced by experimenting with the position of the device, installing within a stilling well or wave guide, and some ultrasonic devices include features to minimise the effects of foaming, bubbles, vapour and turbulence.
Since there is no contact with the fluid to be measured, ultrasound liquid level measurement technology can be used in applications where switches requiring contact are otherwise prohibited.
Ultrasonic liquid level switches are typically housed in a single assembly combining the acoustic transmitter and receiver in one device.
Since ultrasonic liquid level switches do not make contact with the liquid media to be measured, they are mounted above the surface of the liquid in the top of a tank or from a platform spanning the top of an open tank.
Featured liquid level measurement products
ATEX Approved Liquid Level Sensors for Hazardous Areas - European hazardous area ATEX approved sensors for liquid level measurement in intrinsically safe installations on petrochemical, pharmaceutical, landfill and sewage treatment sites.- 0-10 Volts Output Hydrostatic Sensors, Probes & Transducers - Choose 0-10V output hydrostatic sensors, probes & transducers for accurate liquid level and head pressure measurement. Ideal for industrial tanks, boreholes & process control systems.
Advantages
- No media contact for vertically mounted type, so flexibility for use on different corrosive media, thick fluids, slurries, wastewater
- High temperature fluid compatibility for vertically mounted types, since no sensitive components make contact with the fluid
- High accuracy due to high frequency pulse wave and precise transit time time measurement
- Multiple switch contacts in one device
- Operates with conductive or non-conductive fluids
- Sealed pressurised vessel will not affect performance
Disadvantages
- Foaming, splashing, vapour and humidity can affect measurement performance
- High cost compared to other technologies
- Top mounting only unless using point level type
- Minimal blocking distance limited operation when in proximity to liquid level
- Temperature compensation required to compensate for speed of sound variation with air temperature
- Sound waves cannot be transmitted through a vacuum
Featured liquid level measurement products
Water Level Transmitters with 4-20mA Output - Browse for 4-20mA water level transmitters using two-wire loop power. Ideal for wells, tanks, rivers & reservoirs with excellent noise immunity & long cable runs.
River level sensor for run-of-the-river hydropower monitoring up to 4m - Vented pressure river level sensor for measuring water level up to 0.4 bar in run-of-the-river hydroelectricity systems.
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Related Technical Terms
- Capacitive Fluid Level Measurement
- cmH2O – Centimetres of Water Column at 4 deg C Pressure Unit
- Conductive Fluid Level Detection
- Float Fluid Level Detection
- ftH2O – Feet of Water Column at 4 deg C Pressure Unit
- mH2O – Metres of Water Gauge at 4 deg C Pressure Unit
- mmH2O – Millimetres of Water Column at 4 deg C Pressure Unit
- Specific Gravity
- Vibrating Tuning Fork Fluid Level Detection
Related Online Tools
- Liquid Level to Hydrostatic Pressure Calculator
- Fluid Depth, Density, Gravity, and Pressure Calculator
- Liquid Level Transmitter 4-20mA Current Output Calculator
- Vertical Cylindrical Shaped Tank Contents Calculator
- Horizontal Cylindrical Shaped Tank Contents Calculator
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