In order to select the best liquid level sensor, we need to understand not only the characteristics and state of the liquid to be measured, but also the advantages and limitations of different detection methods, so as to be able to select the most suitable sensor. Here are some of the most common detection technologies on the market today.
TDR (Time Domain Reflectance) / Guided Wave Radar / Microwave Principle Measurement
There are a variety of different names in the professional world in its name, which has the benefits of laser measurement, such as: easy installation, calibration, good flexibility, etc., in addition, it is better than laser detection, such as no need to repeat calibration and multi-function output, etc., it is suitable for a variety of foam-containing liquid level detection, not affected by the color of the liquid, and can even be used for highly viscous liquids, which is relatively disturbed by the external environment, but its measurement height is generally less than 6 meters.
Ultrasonic measurement
Because the principle is to calculate the liquid level height by detecting the time difference between the transmission and reflection of ultrasonic waves, it is simply affected by the energy loss transmitted by ultrasonic waves. It is also characterized by simple installation and high flexibility, and can usually be installed at a height for non-touch measurement. However, when used in environments containing vapor and powder layers, the detection interval will be significantly shortened, and it is not recommended to use it in absorbing environments, such as foam.
Tuning fork oscillation measurement
The tuning fork measurement is only a switching output and cannot be used for continuous monitoring of liquid height. The principle is as follows: when the resonance frequency changes when the liquid or bulk material fills the two oscillating forks, the switching signal is announced by the change in the detection frequency. It can be used for the height monitoring of high-viscosity liquids or solid bulk materials, mainly for overflow alarm, low liquid level alarm, etc., does not provide analog output, in addition, in most cases, the opening device is required next to the container.
Photoelectric refraction measurement
In this detection method, the light source is announced inside the sensor, and the light source is fully reflected to the sensor receiver through the transparent resin, but when it encounters the liquid level, part of the light will be refracted to the liquid, so that the sensor detects the decrease in the amount of light reflected back to monitor the liquid level. This detection method is inexpensive, simple to install and debug, but it can only be used for clear liquids, and only output switching signals.
Hydrostatic measurement
The measurement method selects a pressure sensor installed at the bottom, detects the liquid pressure at the bottom, converts and calculates the liquid level height, and the reference value of the liquid pressure at the bottom is the atmospheric pressure or known atmospheric pressure communicated with the top. This detection method requires the selection of high-precision, flush pressure sensors, and the conversion process requires continuous calibration, which has the advantage that it can detect without being limited by the height of the liquid level, but the higher the height, the higher the accuracy of the sensor, and the need for repeated calibration when using for a long time or replacing the liquid.
Capacitive measurement
Capacitive measurement is mainly measured by detecting the change of capacitance value caused by the change of liquid level or bulk material height to measure the material level. They are available in a variety of types, including capacitive level gauges that can output analog quantities, level capacitive proximity switches, and capacitive proximity switches that can be installed on the side of the container for non-touch detection. When it is necessary to pay attention to the fact that capacitive sensors are simply affected by different container materials and solution characteristics, such as plastic containers and hanging materials that simply affect the analog output of capacitive sensors.
Float detection
This method is the simplest and oldest test and is relatively inexpensive. First of all, it is to detect the change of liquid level through the up and down lifting of the float, which is a mechanical detection, the detection accuracy is simple and affected by buoyancy, the repeatability is poor, and different liquid needs are calibrated from scratch. It is not suitable for viscous or impurity-containing liquids, which simply form float blockage, and at the same time, does not meet the requirements of food hygiene occupations.
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