In order to select the best liquid level sensor, we need to understand not only the characteristics and conditions of the liquid to be measured, but also the advantages and limitations of different detection methods, and then we can select the most suitable sensor. Here are some of the most common inspection technologies on the market today.
TDR (Time Domain Reflectance) / Guided Wave Radar / Microwave Principle Measurement
There are a variety of different names in the name of the occupation, which has the advantages of laser measurement, such as: easy to device, calibration, good flexibility, etc., and 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 liquid color, and can even be applied to highly viscous liquids, which is relatively small by external environmental interference, 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 ultrasonic transmission and reflection, it is slightly affected by the energy loss of ultrasonic propagation. It also has the characteristics of simple and flexible equipment, and can usually be installed at a height for non-contact 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 wave-absorbing environments, such as foam.
Tuning fork vibration 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 liquid or bulk material fills the two vibrating forks, when the resonance frequency changes, the switching signal is announced based on the change of 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, and 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 transparent resin, but when it encounters the liquid level, part of the light will be refracted to the liquid, and then the sensor detects the decrease in the amount of light reflected back to monitor the liquid level. This detection method is inexpensive, and the device and debugging are simple, but it can only be applied to transparent liquids, and only the switching signal is output.
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 that is connected with the top. The detection method requires the selection of high-precision, flush pressure sensors, together with the conversion process needs to be continuously calibrated, its advantage is 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 or replacing liquids for a long time.
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. There are various types of them, including capacitive level gauges that can output analog quantities, capacitive proximity switches, and capacitive proximity switches that can be installed on the side of the container for non-contact detection. When selecting, it must be noted that capacitive sensors are slightly affected by different container materials and solution characteristics, such as plastic containers and capacitive sensors that simply affect the analog output of the capacitive sensor.
Float detection
This method is the simplest and oldest detection method, and it 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 slightly affected by buoyancy, the repeatability is poor, and different liquid needs to be recalibrated. It is not suitable for viscous or impurity-containing liquids, which may form float blockage and meet the application requirements of food hygiene occupations.
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