Precautions for chemical companies to select ultrasonic level sensor gauges

- Jun 11, 2019-

ultrasonic sensor for liquid level detection


Industrial chemical plants often use ultrasonic level gauges to measure the level of tanks and reactors because ultrasonic has the following advantages.


1. Non-contact measurement. It can be measured without touching the liquid. The density and viscosity of the liquid do not affect the measurement.
2. It is easy to install. It only needs to be installed at the top of the tank. It can eliminate the need to clean the liquid in the tank and solve the cumbersome process of installing on flammable liquid.

Among the large number of chemical companies we have contacted, because the ultrasonic level gauge is not fully understood, the following common mistakes have been made during use.


1. Use an ultrasonic level gauge on a highly volatile liquid.

Many chemical storage tanks are organic solvents such as toluene, xylene, alcohol, and acetone. Most organic solvents are highly volatile. General chemical companies only consider his explosion-proof requirements and do not consider the impact of volatility on the measurement.


Because the ultrasonic level gauge is based on the time of transmission and reception of the entire process × speed of sound ÷ 2 = the actual measured distance.


For example: a 6 m high tank, installed with an explosion-proof and anti-corrosion ultrasonic level gauge. The entire process of transmitting and receiving is 0.03 seconds, and the speed of sound in the air is 334 m/s. Then the distance from the probe to the surface of the liquid is 0.03 × 334 ÷ 2 = 5.01 m.

However, in the storage tank, after the organic solvent is volatilized, there is a large amount of organic solvent in the air, and the speed of sound changes. If he is 400 meters per second, then at a distance of 5.01 meters, the ultrasonic level gauge emits and receives the entire The time of the process is shortened, 5.01 × 2 ÷ 400 = 0.025 seconds.


The ultrasonic level gauge is still calculated based on the original sound velocity of 334 m / s, so the distance from the probe to the liquid surface is: 0.025 × 334 ÷ 2 = 4.17 m.


5.01-4.17=0.83 meters. That is, the actual data measured by the entire tank will have an error of 0.83 meters.


2. Only consider explosion protection without considering anti-corrosion requirements


Chemical companies generally consider explosion-proof requirements when selecting ultrasonic level gauges, as most are flammable and explosive liquids. It is common to consider corrosion protection in liquids of hydrochloric acid, sulfuric acid and hydrofluoric acid. In fact, when measuring organic solvents such as toluene, xylene, alcohol, acetone, etc., anti-corrosion should also be considered. Most organic solvents are soluble in ordinary plastic materials. We saw dissolved probes in the same chemical industry as many glues.


3. The selected range is only selected according to the actual height.


Basically, all enterprises choose the ultrasonic level gauge according to the height of the tank, and there is no reserve.


In a highly volatile canister such as hydrochloric acid, a large amount of fine liquid particles are suspended in the air in the can due to the volatilization of the liquid, and the ultrasonic waves emitted from the ultrasonic level gauge are scattered by the suspended liquid particles. This will cause a phenomenon that when the liquid in the tank drops to a lower position, the ultrasonic level gauge will not receive the echo. In this case, it is generally necessary to increase the measured large distance by 30-50%, for example, a 6-meter-high can, and an ultrasonic level gauge of 8 to 10 meters is selected for measurement.


In addition, because the probe of the ultrasonic level gauge is a mechanical vibrating component, its performance will decrease over time. After a year and a half, the larger measurement distance originally selected will not be measured. Therefore, when selecting an ultrasonic level gauge, add a few meters to the actual height of the can. For example: a 6-meter-high can, you can choose an 8-meter ultrasonic level gauge.


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