Level measurement instrument is a kind of industrial automation instrument, mainly used to measure the level height of liquid and powder granular materials. Generally, people will measure the height of powder, particles and other solid materials, or the surface position of the instrument called level meter or level switch; will measure the height of the liquid in the tanks, towers and tanks and other containers or the liquid level position of the instrument called level meter; and will measure the two containers of insoluble liquids or solids and liquids in the interface position of the instrument is called the phase interface meter. So, how should the level measurement instruments be selected to better meet the requirements of level measurement?

To do a good job of level measurement instrumentation selection, usually start with the following points:

　　1. If the need to measure the material surface, this should be based on the particle size of the material, the angle of repose of the material, the conductivity of the material, the structure of the silo form and measurement requirements for selection.

　　If the measurement is liquid level and interface, this time should be selected vibration type instrument, differential pressure type instrument, float type instrument and float type instrument. If the above instrumentation can not be measured, capacitive, resistive (electrical contact), acoustic wave type instrumentation.

　　2. Level measurement instrumentation in the selection, should have an in-depth understanding of the process conditions, the nature of the measured medium, measurement and control system requirements, in order to make a full evaluation of the technical performance of the instrumentation and economic effects, in order to help ensure production stability, product quality and economic efficiency and other aspects of the enhancement.

3. According to the characteristics of the measured medium, choose to determine the structure of the instrument used by the form and material. In the selection should focus on the following factors: the measured medium pressure, temperature, corrosivity, electrical conductivity; density and density changes; the liquid contains the number of suspended solids; the degree of liquid surface disturbance and solid material particle size; the existence of polymerization, viscosity, precipitation, crystallization, film, gasification, foaming and other phenomena.

　　4. In determining the range of the instrument, should be based on the actual need to display the range of process objects or the actual range of change. In addition to volumetric measurement for the level of instrumentation, the normal level should generally be in the instrument range of about 50%.

　　5. In determining the display mode and function of the instrument, it should be based on the requirements of process operation and system composition. When the requirements of signal transmission, depending on the situation, you can choose to use analog signal output function or digital signal output function of the instrument.

6. Instrumentation measurement accuracy should be selected according to process requirements, but for volumetric measurement of the level of instrumentation, its accuracy level should generally be above 0.5 level.

　　7. Electronic level instrumentation for combustible gases, vapors and combustible dust and other explosive hazardous areas, should be determined in accordance with the category of hazardous areas and the degree of danger of the measured medium, select the appropriate explosion-proof structure or take appropriate protective measures.

　　8. Electronic level instrumentation for corrosive gases and hazardous dust and other places, according to the instrument should be used in the environmental conditions, select the appropriate shell protection type.