Selection of transmitters under special working conditions
The selection of the transmitter under several special conditions is as follows
High temperature and high vacuum:
The life of the transmitter is very low at high temperatures and high vacuum. Because the filling liquid in the sealing
system is heated after the contact between the high temperature medium and the diaphragm, the volume expands,
and when it exceeds the limit, it will be squeezed out from the sealing portion, so that the filling liquid is reduced,
the pressure transmission is affected, and the measurement error is increased. When vacuum is applied, the
diaphragm is subjected to an outwardly attracted force because it is not supported by the backing plate, and the
diaphragm is externally used for a long time, which reduces the life of the transmitter. Therefore, in chemical
applications, when selecting a remote transmitter under high temperature and high vacuum conditions, the all-
welded sealing structure, that is, the capillary tube and the transmitter, should be selected, and the connections
between the process connecting members are all sealed by welding to eliminate possible leakage points. ***
Control the filling amount of the filling liquid according to the application conditions. In order to solve the problem
of expansion of the filling liquid at high temperature, according to the application conditions of the user and the
characteristics of various filling liquids, the filling amount of the filling liquid is appropriately reduced by precise
calculation to compensate for the influence of the filling liquid expansion. Special pretreatment of the filling liquid
to minimize the dissolved gas content
2. The medium contains hydrogen
Under the action of static pressure, hydrogen can penetrate the metal diaphragm and invade the sealing cavity of the
sensor. Once the external static pressure disappears, the pressure in the cavity will expand or rupture. Hydrogen is
insoluble in gold, and gold plating on the surface of the diaphragm can effectively prevent the hydrogen nucleus from penetrating the membrane. The gold plating layer must be dense and free of any micropores. Or a ceramic insulating
film is coated on the outside of the gold plating layer to isolate the hydrogen ions in the medium from the electrons in
the film to prevent them from bonding. in use
(1) It is not recommended to use a diaphragm.
(2) Electroplated parts should not be used near the transmitter, and the shunt branch parts should be made of nickel-
chromium stainless steel.
(3) The temperature of the measured medium should be lowered to room temperature when it reaches the transmitter.
(4) The transmitter should avoid direct sunlight and reduce the ambient temperature.
3. The medium contains ammonia
Ammonia is one of the important inorganic chemical products. In a practical use, the fluorine rubber used in the sealing
ring is quickly corroded into powder after ammonia corrosion, and the sealing effect is lost. When measuring the ammonia medium, the isolation diaphragm can be selected as 3l6L, but the sealing ring of sensitive parts should be selected from PTFE.
4. Oxygen and chlor-alkali
In order to ensure the safe operation of the air separation plant, the instrument for the oxygen generator must be degreased. Pure oxygen and liquid oxygen are products of air separation plants. They are strong oxidants, the oxidation reaction is extremely intense, and a large amount of heat is released. Oxygen is prone to combustion and explosion when it encounters combustible materials. In a pure oxygen environment, the spontaneous combustion point of combustibles will decrease, the range of explosion limits will increase, and the risk of explosion will increase. Therefore, in the case of measuring oxygen, the transmitter must be degreased. The medium in the production process of chlor-alkali includes strong alkali, strong acid and chloride. These mediums are highly corrosive. For this situation, the anti-corrosion strategy of the instrument is to choose corrosion-resistant materials, including corrosion-resistant metals and alloy materials, non-metallic materials. Change the
way of liquid connection, including selecting the appropriate instrument structure, such as remote transmission type or radar measurement, gas and liquid isolation, inner wall coating and isolation diaphragm.
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