Overview
The ET87 series liquid level transmitter is an input type liquid level measuring instrument that introduces advanced foreign technology and imports key components for assembly and production. This product passed the national level product appraisal and explosion-proof appraisal in 1989, and passed the marine appraisal and acceptance of the National Navy Equipment System Department in 1992. It was selected as a specialized product for naval ship liquid level, providing reliable basis for timely control of ship navigation status. At present, the product has formed mass production, with advanced technology, unique structure, and wide applicability, which can be widely used in industries such as ships, oil tanks, petroleum, chemical, power, metallurgy, etc.

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As shown in equation (1), if the atmospheric pressure Po changes, the ceramic diaphragm will be affected like a liquid level change. In order to eliminate the error caused by atmospheric pressure changes, the transmitter uses a gas pipe to introduce the atmospheric pressure Po into one side (upper side) of the ceramic diaphragm, so that the total pressure Ph borne by the ceramic diaphragm is:
Ph＝0.098ρh （2）
As shown in equation (2), Ph is only related to the density and height of the liquid. If the liquid density ρ is constant, Ph is proportional to h. As long as Ph is measured, the depth of the liquid can be determined.

Technical parameters

Measurement range 0-200m
Output signal 4-20mA (two-wire system) 0-20mA (three wire system)
Accuracy ± 0.2% FS, ± 0.5% FS
Power supply 24VDC ± 5%
Lag better than 0.01% FS
Power supply 24VDC ± 5%
Stability better than 0.1% FS per year
Dead zone<0.1% S
Environmental temperature affects every 10 ℃<0.1% FS
Capable of withstanding working vibrations with frequencies of 5-60HZ, 2.5 ± 0.25mm, and acceleration in three directions for two hours, without affecting accuracy
Medium temperature -20-+80 ℃
The temperature of the medium affects every 10 ℃<0.1% FS
Protection level IP65
Explosion proof grade ia IIbT6

Debug
Zero point and full-scale adjustment
Zero point and full-scale adjustment are achieved by connecting a standard ammeter (with an accuracy of 0.05%) in the circuit. The specific steps are as follows:
1. Connect the wires according to the system wiring diagram and turn on the power
2. The liquid level transmitter is adjusted to zero position without pressure (or when the container is emptied). Rotate potentiometer Z to make the standard ammeter indicate zero current (4mA or 0mA). The zero adjustment range is ± 5%.
3. According to the actual usage of the user, use the following formula:
Ph＝0.098ρ? h
Calculate Ph and apply pressure to the transmitter using a standard pressure source until Ph is reached. Rotate the full range potentiometer S to indicate the full range current (20mA) on the standard ammeter, or when the container is full (liquid level h), rotate the potentiometer S to display 20mA on the standard ammeter. The full range adjustment range is 40% -100%