Liquid level measurement and monitoring play an increasingly important role. Liquid level measurement and monitoring directly affect the quality of the production process.
Liquid level measurement is required for process control in many industries. Use liquid level sensors for liquid level measurement. They are divided into two categories: point level measurement and continuous level measurement.
Sino-Inst offers a variety of Solutions for Liquid Level Measurement. If you have any questions, please contact our sales engineers.
8 Types Liquid level measurement methods
- Floating ball measurement:
This method is the simplest and oldest detection method, and the price is relatively cheap.
Mainly through the up and down movement of the float to detect the change of the liquid level. It is a mechanical detection, the detection accuracy is easily affected by buoyancy, and the repeat accuracy is poor. Different liquids need to be recalibrated.
It is not suitable for viscous or impurity liquids, which can easily cause blockage of floating balls. At the same time, it does not meet the application requirements of the food hygiene industry.
- Tuning fork vibration measurement:
Tuning fork measurement is only a switch output and cannot be used to continuously monitor liquid height. The most representative one is the tuning fork level switch.
The principle is: when the two vibrating forks are filled with liquid or bulk material, the resonance frequency changes, and the switching signal is sent out depending on the detection frequency change.
It can be used to monitor the height of high-viscosity liquids or solid bulk materials, mainly for anti-overflow alarms, low-level alarms, etc. It does not provide analog output. In addition, in most cases it is necessary to install holes on the side of the container.
- Ultrasonic measurement:
Since the principle is to calculate the liquid level by detecting the time difference between ultrasonic transmission and reflection, it is susceptible to the energy loss of ultrasonic propagation.
It has the characteristics of easy installation and high flexibility. Usually can be installed in high places for non-contact measurement.
But when used in environments containing steam and powder, the detection distance will be significantly shortened. Therefore, it is not recommended to use it in a wave-absorbing environment with foam.
- TDR (time domain reflection)/guided wave radar/microwave principle measurement:
Its name has many different names in the industry, and it has the advantages of laser measurement. Such as: easy installation, calibration, flexibility, etc.
But it is better than laser detection, such as no need to repeat calibration and multi-function output. Suitable for all kinds of liquid level detection with foam. Not affected by liquid color.
It can even be applied to highly viscous liquids, with relatively little interference from the external environment. But its measuring height is generally less than 6 meters.
- Laser measurement:
The laser sensor is based on the principle of optical detection and detects light by reflecting light from the surface of the object to the receiver. The light spot is small and concentrated, easy to install, calibrate, and flexible. It can be applied to continuous or limit alarm of bulk material or liquid level.
But it is not suitable for transparent liquids. Transparent liquids easily refract light, causing the light to not be reflected to the receiver. Use in foam or steam environment (cannot penetrate foam or easily interfered by steam), fluctuating liquid (easy to cause malfunction), vibration environment, etc.
- Photoelectric refraction measurement:
This detection method emits a light source inside the sensor. The light source is totally reflected by the transparent resin to the sensor receiver.
But when encountering the liquid surface, part of the light will be refracted to the liquid. Therefore, the sensor detects the decrease in the amount of total reflected light to monitor the liquid level. The detection method is cheap and simple to install and debug. But it can only be applied to transparent liquids, and it only outputs switching signals.
- Capacitive measurement:
Capacitive measurement mainly measures the height of the material level by detecting the change in capacitance value caused by the change of the liquid level or the height of the bulk material.
There are many types, including capacitive level gauges and capacitive proximity switches that can output analog quantities. Capacitive proximity switches can be installed on the side of the container for non-contact detection.
When choosing, it must be noted that capacitance sensors are easily affected by different container materials and solution properties. For example, plastic containers and hanging materials can easily affect capacitance sensors with analog output.
- Static pressure measurement:
This measurement method uses a pressure sensor installed at the bottom. By detecting the bottom liquid pressure, the liquid level is converted and calculated. The bottom liquid pressure reference value is the atmospheric pressure connected to the top or the known pressure.
This measurement method requires the use of a high-precision, flush-type pressure sensor. At the same time, the conversion process requires continuous calibration.
Its advantage is that the detection is not limited by the height of the liquid level. But the higher the height, the higher the accuracy requirements of the sensor. Repeated calibration is required when using for a long time or changing liquid.
Read more about: Hydrostatic level measurement: Measuring Principle
Featured liquid level measurement devices/instruments
Liquid level measurement in a closed tank
Differential Pressure Level transmitter for closed containers
For airtight containers, the inside is isolated from the atmosphere. When the process fluid fills or empties the tank, the pressure in the tank may change from positive pressure to vacuum. This change in tank pressure will directly affect the measured liquid level unless it is compensated for. This can be done by connecting the low-side pipe of the differential pressure transmitter to the top of the tank. Therefore, when measuring the liquid level of a closed tank, a differential pressure transmitter must be used.
Double flanges are used to measure the liquid level of a closed tank.
The calculation method of the differential pressure range: the height of the liquid level to be measured (unit: m) × acceleration of gravity (9.8) × (the density of the measured medium-the density of the capillary filling liquid) (unit: g/cm3) = differential pressure range (unit: KPa).
The selection must know the measurement medium, measuring range, medium temperature, pressure, capillary length, the size and pressure rating of the process connection flange and the flange standard
If you need to measure river water level, open channel level, etc. The Ultrasonic Liquid Level Sensor can be used for non-contact continuous level monitoring.
Portable Ultrasonic Liquid Level Gauge
Portable ultrasonic liquid level indicator is best choice for tanks or pipes level measurement. It is designed to measure the presence or absence of liquid at a certain height position in a tank or in pipelines. Non-contact ultrasonic detection technology.
SI-ML works perfect for detection of dangerous toxic or corrosive liquids. Under ordinary conditions, the maximum wall thickness of measurable containers is 30mm. The product is suitable for the detection of various types of liquids. Liquids are non-crystalline or other particulate matter. For example CO2 Tank. Thanks to non-contact detection technology, this level indicator is ideal for detecting hazardous toxic or corrosive liquids.
Read more about: 7 Level Senors for Tank Level Measurement
Liquid Level Measurement Converter Tools
Converter Tools used to convert and calculate liquid level values or for calculations that require liquid level measurement to obtain other measurement parameters. Help users choose suitable Level sensors and transmitters!
Selection of liquid level measuring sensor
The issues that need to be considered before choosing a level measurement sensor include:
- Measuring liquid or solid?
- What is the temperature and pressure range of the application environment?
- Need point level measurement or continuous measurement?
- How much liquid level measurement range is required?
- Is the tested material conductive?
- Will the tested material cover or accumulate on the surface?
- Will there be turbulence, foam or steam on the surface of the liquid?
- Do you need contact or non-contact level measurement?
- What kind of output is needed, analog, relay, digital display or other?
Sino-Inst offers over 10 Solutions for Liquid Level Measurement. About 50% of these are float liquid level meters, 40% is the level switches.
A wide variety of Solutions for Liquid Level Measurement options are available to you, such as free samples, paid samples.
Sino-Inst is a globally recognized supplier and manufacturer of Solutions for Liquid Level Measurement instrumentation, located in China.
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