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1 It is difficult to measure the corrosiveness, high viscosity, flammability, volatile and toxic liquid level, liquid-liquid interface, solid-liquid interface continuous measurement and bit type measurement, which is difficult to measure. The use of ultrasonic level gauges, but not suitable for liquid level fluctuations in the occasion;
2 Ultrasonic liquid level gauges are suitable for medium measurement which can fully reflect sound waves and propagate sound waves, but should not be used in vacuum applications, and should not be used for volatile liquids containing bubbles, suspended solids and liquids containing solid particles;
3 For process equipment with internal obstacles affecting sound wave propagation, ultrasonic level gauges should not be used;
4 For ultrasonic instruments that continuously measure the liquid level, when the temperature and composition of the liquid to be measured change significantly, the change in the propagation speed of sound waves should be compensated to improve the measurement accuracy;
5 For the connection cable between the detector and the converter. Anti-electromagnetic interference measures should be taken;
6 The ultrasonic level gauge model, structure type, probe selection, etc., should be determined based on the characteristics of the measured medium and other factors.
(2) The choice of capacitive level gauge or radio frequency level gauge may be used, but the following requirements shall be met:
1 Continuous measurement and position measurement of liquid level in corrosive liquids, sedimentary fluids, and other process media. Capacitance level gauges or RF level gauges can be used.
2 When used for interface measurement, the electrical properties (dielectric constant, etc.) of the two liquids must meet the technical requirements of the product.
3 Capacitance level meter or radio frequency level meter shall be determined according to the conductivity of the measured medium, the material of the process vessel and other factors.
4 Capacitive level gauges should not be used for conductive liquids that adhere to the electrodes.
5 Capacitance, RF level gauges are susceptible to electromagnetic interference, and electromagnetic interference measures should be taken.
6 Capacitance level meter or radio frequency level meter for level measurement should adopt horizontal installation type; for continuous measurement of capacitance level meter or radio frequency level meter, vertical installation type should be adopted.
(3) The buoyancy level gauge may be used, but it should meet the following requirements:
1 In the case of a wide range of density and operating pressure, the fluid level of the general medium should be measured at the interfacial level. Float-type liquid level gauges should be used. However, in situations where the density changes significantly, float-type level gauges should not be used. The buoyancy level gauge should be used in the following situations:
a Measurement range within 2000mm, continuous measurement of the liquid level with a density difference of 0.5--1.5;
b Continuous measurement of the liquid interface where the measurement range is within 1200 mm and the density difference is 0.1-0.5;
c Liquid level measurement of vacuum, negative pressure, or easily vaporized liquids.
2 For cleaning liquids, an external buoyancy level gauge should be used, and the "side-on-side" flange connection type is preferred.
3 For viscous, easily condensable and easily crystallized medium, float buoy level gauge should be used, and buoyancy level gauge with steam jacket type can also be used.
(4) In case of large disturbances of the liquid to be measured, the inner buoyancy level gauge shall be equipped with a smooth casing that can prevent disturbance.
5 Electric float level gauges are used for occasions where the measured level fluctuations are frequent, and the output signal should be added with a damper.
6 Electric buoy level gauge should be equipped with fins when the temperature of the measured medium is higher than 200°C, and the extension tube should be provided when the temperature is lower than 0°C.
(4) Differential pressure level gauges may be used, but they should meet the following requirements:
A liquid level (interface) measurement, should use differential pressure transmitter;
b For corrosive liquids, viscous liquids, molten liquids, and precipitated liquids, etc., differential pressure transmitters may also be used when taking isolation, blowing, or flushing fluids.
c For corrosive media, viscous liquids, easy-to-gasify liquids, liquids containing suspended solids, flat flange differential pressure transmitters should be used;
d For easy-to-crystallize liquids, high-viscosity liquids, gel-binding liquids, and precipitated liquids, insert-type flange differential pressure transmitters should be used.
e When the measured object has a large amount of condensate or precipitates, double flange type differential pressure transmitter should be selected;
f When using a differential pressure meter to measure the level of the boiler drum, a double chamber balance vessel shall be used;
The differential pressure transmitter of g liquid level should be equipped with a migration mechanism. The positive and negative migration amount should be determined when selecting the range of the instrument.
h Differential pressure transmitters should not be used for mediums where the liquid density changes significantly under normal conditions.
When using standard signal transmission, pressure (differential pressure) transmitters should be used.
Second, the corrosive and viscous liquid pressure transmitter table selection:
In explosion hazardous situations, flameproof or intrinsically safe electric pressure transmitters should be used. Pneumatic pressure transmitters can also be used.
Small pressure, small negative pressure measurement, should use differential pressure transmitter.
For sticky, easily crystalline, solid particles or corrosive media, a flanged pressure transmitter should be used.
When adopting measures such as filling the isolation liquid, blowing air or rinsing liquid, a general pressure transmitter should be used.
Corrosive liquid pressure level sensor selection considerations
Corrosion and viscous liquid level measurement sensor selection precautions (1) The application of ultrasonic level gauge. However, its selection should meet the following requirements: