Liquid level sensor in order to choose the best, we not only need to be aware of the properties of the liquid to be tested and, at the same time, also want to know the advantages and limitations of different detection method, which can select the most appropriate sensors. The following is the most common type of detection technology on the market at present.
Laser measurement: laser sensors based on optical detection principle, through the surface reflects light to the receiver, the light small and concentrated, easy to install, calibration, good flexibility, can be applied to the powder or liquid level of the continuous or limit alarm, etc. But it is not suitable for application in transparent liquid (transparent liquid refraction of light, easily lead to the light cannot be reflected to the receiver), including bubble or steam environment (cannot penetrate bubble or vulnerable to steam interference), volatile liquid (cause misoperation), vibration environment, etc.
TDR (time domain)/principle of guided wave radar/microwave measurements: its name in the industry with a variety of different term, it has the merits of the laser measurement, such as: easy to install, calibration, good flexibility, etc., and the more superior to laser detection, such as do not need to repeat the calibration and multifunctional output, it is applicable to various foam containing liquid level detection, is not affected by the liquid color, can be applied to high viscous liquid, even relatively small influence of the external environment, but its measurement generally less than 6 m.
Ultrasonic measurement: due to its principle for ultrasonic sending and the reflection of the time difference through testing to calculate liquid level height, so easy to be affected by the energy loss in the ultrasonic propagation. Its easy to install, high flexibility, etc, also have usually can be installed in high non-contact measurement. But when used for steam, the environment such as powder layer, detection distance will be shortened obviously, not recommended for use in absorbing environment, such as foam, etc.
Measurement for vibration measurement: a tuning fork fork type switch output, cannot be used for continuous monitoring liquid level. Its principle is: when the liquid or powder filling two vibrating fork, resonance frequency change, rely on the detection and signal switch frequency change. It can be used to the height of the high viscosity liquid or solid powder monitor, mainly for spill-proof alarm, low liquid level alarm, etc., does not provide analog output, in addition, in most cases need opening installed on the container side.
Photoelectric refractive measurement: the test way in light source, through the sensor inside the light through a transparent resin total reflection to sensor receiver, but when you meet the surface part of the light will be reflected to the liquid, and sensors to detect total reflection back less of the quantity of light to monitor liquid level. The test way cheap, simple installation, debugging, but can only be used in transparent liquid, only switch output signal at the same time.
Through the static pressure type measurement: the measurement way at the bottom of the pressure sensor, by detecting the bottom of the liquid pressure, conversion to calculate the height of liquid level, with the top in the liquid pressure at the bottom of the reference for atmospheric pressure or pressure is known. The detection way, flush type pressure sensor with high precision, calibration requires constant conversion process at the same time, its advantage is detectable level without limit, but the higher the altitude, the sensor precision demand is higher, for a long time use or replacing liquid need to repeat the calibration.
Capacitance measurements: mainly through capacitance measurement due to liquid level or bulk material height change of capacitance value measured level height change. It has many types, was to be output analog capacitive liquid level sensor, liquid level capacitive proximity switch, capacitive proximity switch can be installed on the container side for non-contact detection. When the choice must pay attention to, capacitance sensor is easily affected by the different container material and solution properties, such as plastic containers and hanging is easy to affect the analog output of capacitance sensor.
Ball float detection: this way is the simplest and most ancient detection methods, the price is relatively cheap. Mainly by floating ball of lifting up and down to detect the liquid surface, its for mechanical testing, test precision is easily affected by buoyancy, repeat accuracy is poor, the different liquid needs to be calibrated. Do not apply to the viscosity or impurities in the liquid, easy to block, the floating ball at the same time, do not meet the requirements of the application of food hygiene industry.
