Measurement and point detection devices for monitoring liquid level and activating switch contacts at predetermined liquid level thresholds.
A 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 an warning lamp, activate an audible alarm, or switch on/off a pump.
There are two basic types of liquid level switches, those that detect the presence of liquid known as point level detection, and those that are continuously monitoring the variation in level to detect when a threshold has been reached.
Point level switches have to be mounted so that the sensing probe makes contact with the fluid. They are simpler to set-up and calibrate, since the installation position dictates the switch point, however this also limits where the point level sensor can be installed.
There are many applications on a liquid storage tank where a switch provides a lower cost and simpler installation for managing tank contents because there is no need for additional signal conditioning instrumentation, and some switch types are mechanically activated and require no electrical supply or electronic circuits to function.
Capacitive Liquid Level Switches - Capacitive switches for opening or closing electrical contacts at a preset liquid level thresholds.- Conductivity Liquid Level Switches - Conductive devices for monitoring liquid level and opening and closing switch contacts at predetermined liquid level thresholds.
Ultrasonic Liquid Level Switches - Ultrasonic devices for monitoring liquid level and activating the opening and closing of switch contacts at predetermined liquid level thresholds.
Vibrating Tuning Fork Liquid Level Switches - Vibrating tuning fork devices for monitoring liquid level and activating switch contacts at predetermined liquid level thresholds.
Hydrostatic Liquid Level Switches - Hydrostatic pressure sensing switches for activating switch contacts at predetermined liquid level thresholds.
Float Liquid Level Switches - Float actuated devices for monitoring liquid level and activating switch contacts at predetermined liquid level thresholds.
Product Type Comparison Table
Please use the table below to compare the advantages and disadvantages of each liquid level switch technology type versus application and specification parameters.
| float | conductivity | capacitive | hydrostatic | tuning fork | ultrasonic | |
|---|---|---|---|---|---|---|
| media contact | yes | yes | yes | yes | yes | no |
| moving parts | yes | no | no | yes | yes | no |
| surface disturbance sensitive |
no | no | no | no | no | yes |
| pressurised vessel | yes, low pressures | yes | yes | more difficult | yes | yes |
| vacuum evacuated vessel | yes | yes | yes | more difficult | yes | no |
| installation position | top, side, bottom | top, side, bottom | top | side, bottom | top, side, bottom | top, side |
| thick fluids | no | no | no | yes with flush diaphragm | no | yes |
| protrusion into tank | yes | yes | yes | no | yes | no |
| sg density variation sensitive | no | no | yes | yes | yes | no |
| fouling degrades performance | yes | yes | yes | yes | yes | no |
| multiple point level detection | vertical entry yes, side entry no | vertical entry yes, side entry no | yes | yes | vertical entry yes, side entry no | top entry yes, side entry no |
| accuracy | low | low | low | high | high | high |
| cost | low | low | high | high | high | high |
| power supply required | no | yes | yes | yes | yes | yes |
Browse other help pages associated with the same topic group as this Liquid Level Switches page.
- Hydrostatic Liquid Level Sensors
- ftH2O – Feet of Water Column at 4 deg C Pressure Unit
- mH2O – Metres of Water Gauge at 4 deg C Pressure Unit
- cmH2O – Centimetres of Water Column at 4 deg C Pressure Unit
- Using Hydrostatic Pressure Transducers for Measuring Fluid Level
- Are all IP68 Water Resistant Protection Ratings the same
- Determining water tank volume using hydrostatic pressure
- Measuring the volume of liquid in a horizontal cylinder tank
- How to determine milk tank level and volume from pressure
- mmH2O – Millimetres of Water Column at 4 deg C Pressure Unit
- Measuring liquid level in a sealed tank with a hydrostatic pressure sensor
- Liquid Level Sensors
- Float Fluid Level Detection
- Vibrating Tuning Fork Fluid Level Detection
- Conductive Fluid Level Detection
- Capacitive Fluid Level Measurement
- Hydrostatic Pressure
- Specific Gravity
- Considerations for monitoring Landfill Water Level
- How do you measure the volume of a liquid using pressure
- Difference between vented and non-vented water level measurement
- Converting non-vented depth readings & barometric pressure to true depth
- Why are Submersible applications so demanding of Pressure Transducers?
- Determining the hydrostatic pressure range for a tank level sensor
- Using a screw in or waterproof pressure transmitter to measure liquid level
- Using absolute pressure sensors to measure hydrostatic level
- Determining the Signal Cable Length of a Suspended Liquid Level Transducer
- How does changes in Local Gravity affect Hydrostatic Pressure
- Improve the electrical termination of vented submersible pressure sensors
- Problem with zero drift when installing submersible pressure sensor
- Liquid Level Measurement