For the instrument manufacturing process - simplify the calibration process, compensate for sensor defects (such as linearization, environmental factor compensation, etc.), improve instrument performance, reduce manufacturing costs, and form multi-parameter composite meters.
Installation and commissioning process for the instrument - simplify the installation and commissioning process (such as alignment, clearing), reduce installation and commissioning costs.
The operation process of the instrument - improve the measurement quality, facilitate the soft measurement, facilitate the maintenance and verification of the instrument
The selection of the pressure/differential pressure transmitter is mainly based on: the nature of the measured medium is subject to the standard, to save money, easy to install and maintain as a reference. If the measured medium is high viscosity, easy to crystallize and corrode, the isolated transmitter must be selected.
When selecting the type, consider the corrosion of the medium to the bellows metal. Be sure to choose the material of the bellows. The diaphragm material of the transmitter is made of ordinary stainless steel, 304 stainless steel, 316L stainless steel, and diaphragm box material.
In the selection, the temperature of the measured medium should be considered. If the temperature is high, it is generally 200 ° C ~ 400 ° C, the high temperature type should be used, otherwise the silicone oil will vaporize and expand, making the measurement inaccurate.
The working pressure level of the equipment should be considered when selecting the type, and the pressure level of the transmitter must be consistent with the application. From the selection range of the selected transmitter, the general transmitter has a certain range adjustable range. It is better to set the range of the range to 1/4~3/4 of its range, so that the accuracy will be guaranteed. It is even more important for differential pressure transmitters. In practice, some applications (level measurement) need to migrate the measurement range of the transmitter, calculate the measurement range and migration according to the site installation position, and migrate the positive and negative migration.
The transmitter output is fixed at 20.8 mA, indicating that the current main process variable is greater than the sensor's set range upper limit and the meter is in output saturation. The following checks can be made:
1) Check whether the set sensor range upper limit or sensor limit range is greater than or equal to the current measured signal, and determine the correctness of the selected sensor model and set range;
2) Check the pressure guiding tube for leaks or blockages. If using the pressure regulating valve, check if the valve is fully open.
3) Confirm that the introduced signal under test is a stable input; if it is measured as a liquid, confirm that there is no residual gas; if it is measured, dry the gas, confirm that there is no liquid;
4) Check the sensor flange for the presence of sediment and whether the flange is corroded;
5) If it is a remote flange type transmitter, check whether there is a difference between the two measured signals, and calculate whether the differential pressure caused by the difference is greater than the sensor range;
6) Check if the power supply is between 12V and 24VDC;
7) Use the handheld operator to perform self-test and parameter reading on the meter to verify whether the intelligent electronic components are faulty or not initialized.
The maintenance work of the transmitter mainly includes the following aspects:
1) Tour inspection:
The meter indicates the situation, and the instrument indicates whether the value is abnormal;
Whether the air supply pressure of the pneumatic transmitter is normal;
Whether the power supply voltage of the electric transmitter is normal;
Ambient temperature, humidity, cleaning conditions; leakage and corrosion between instrument and process interface, pressure guiding tube and valve.
2) Regular maintenance:
Regularly check the zero point and check it regularly;
Regular discharge, condensing, and venting;
Regularly purge the pressure guiding tube of the easily blocked medium and periodically inject the isolation liquid.
3) Equipment inspection:
Check the quality of the instrument to achieve accurate and sensitive, indicating error, static pressure error meets the requirements, and the zero position is correct;
The instrument parts are intact, no serious rust and damage, the nameplate is clear, the fasteners are not loose, the connectors are in good contact, the terminals are securely connected; the technical information is complete, accurate and meets the management requirements.
The mass flow controller (MFC) is provided with a gas flow regulating valve. The valve can adjust the flow through the controller from zero to the measured full scale. During the working process, a flow is generated between the inlet and the outlet of the controller. Air pressure drop, that is, pressure difference. The working pressure difference of MFC is usually 0.1-0.3MPa. If the pressure difference is lower than the lowest value (0.1 MPa), it may control the full-scale value; if it is higher than the highest value (0.3MPa), it may be closed. Can't be less than 2% FS. When the user uses MFC, regardless of whether the reaction chamber of the user's work is vacuum or high pressure, the pressure difference between the two ends of the MFC inlet and outlet should be kept within the required pressure difference range, and the air pressure is required to be relatively stable.