What are the advantages of intelligent pressure/differential pressure transmitters over analog transmitters?
For instrument manufacturing process -- simplify adjustment process, compensate sensor defects (such as linearization, environmental factor compensation, etc.), improve instrument performance, reduce manufacturing cost, and form multi-parameter composite instrument.
For instrument installation and debugging process -- simplify the installation and debugging process (such as alignment, zero clearing), reduce the cost of installation and debugging.
For instrument operation process -- improve measurement quality, facilitate soft measurement, facilitate instrument maintenance and calibration and asset management (need the support of system and equipment management software).
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The selection of pressure/differential pressure transmitter is mainly based on: the property index of the medium under test shall prevail, and the reference shall be to save money, facilitate installation and maintenance.If the medium under test is of high viscosity and prone to crystallization and strong corrosion, the isolated transmitter must be selected.
In the selection of the medium to consider the corrosion of the film box metal, must choose the film box material, the transmitter film box material has ordinary stainless steel, 304 stainless steel, 316L stainless steel, tantalum film box material.
In the selection course,the temperature of the measured medium should be considered , if the high temperature of 200 ℃ ~ 400 ℃, should choose high temperature type, or silicone oil will produce vaporizing expansion, making measurements is not allowed.
In the selection of the equipment to consider the working pressure level, the pressure level of the transmitter must be consistent with the application situation.From the choice of transmitter measurement range, generally transmitter has a certain range adjustable range, it is best to use the range of the range set in its range of 1/4 ~ 3/4 paragraph, so the accuracy will be guaranteed, for the differential pressure transmitter is more important.In some practical applications (liquid level measurement), it is necessary to transfer the measuring range of the transmitter. The measuring range and the migration amount can be calculated according to the on-site installation position. The migration can be divided into positive migration and negative migration.
The transmitter output is fixed at 20.8mA, indicating that the current main process variable is greater than the upper limit of the set range of the sensor, and the meter is in the output saturation state.The following tests can be performed:
1) check whether the upper limit of the sensor range or the limit range of the sensor is greater than or equal to the currently measured signal, and find out the accuracy of the selected sensor model and the set range;
2) check whether the pressure guide pipe is leaking or blocked, and if the pressure guide valve is used, whether the valve is fully opened;
3) confirm that the input signal is stable;If measured as a liquid, make sure there is no residual gas;If the dry gas is measured, confirm that there is no liquid;
4) check whether the sensor flange is precipitated and corroded;
5) if it is a long-distance flanged transmitter, check whether there is a bit difference between the two measured signals and calculate whether the difference pressure caused by the bit difference is greater than the sensor range;
6) check whether the power supply is between 12V and 24VDC;
7) use the handheld operator to self-check the instrument and read the parameters to check whether the intelligent electronic components fail or are not initialized.
The maintenance of the transmitter mainly includes the following aspects:
1) itinerant inspection:
Instrument indication, whether there is any abnormal value;
Whether the air source pressure of pneumatic transmitter is normal;
Whether the power supply voltage of the electric transmitter is normal;
Environmental temperature, humidity and cleanliness;There is no leakage or corrosion between instrument and process interface, pressure guide pipe and valve.
2) regular maintenance:
Check zero point and check regularly;
Regular discharge, coagulation and emptying;
The pressure guide pipe which is easy to block medium should be purged regularly and the isolation fluid should be filled regularly.
3) equipment overhaul:
Check the quality of the instrument, to achieve accurate, sensitive, indicating error, static pressure error meet the requirements, zero is correct;
The instrument parts are intact, free from serious rust and damage, the nameplate is clear and unmistakable, the fasteners shall not be loose, the connectors are in good contact, and the terminals are firmly connected;Complete technical data, accurate, in line with management requirements.
Mass flow controller (MFC) is equipped with a gas flow regulation valve, which can adjust the flow through the controller from zero to the full range of measurement. In the process of work, there will be a pressure drop between the inlet and outlet of the controller, that is, the pressure difference.The working pressure difference range of MFC is usually 0.1 ~ 0.3mpa. If the pressure difference is lower than the lowest value (0.1mpa), it may not reach the full range.If it is higher than the highest value (0.3mpa), it is possible that the flow cannot be less than 2%F.S when it is closed.When users use MFC, no matter whether the reaction chamber they work in is vacuum or high pressure, the pressure difference between the two ends of the inlet and outlet gas of MFC should be kept within the required pressure difference range, and the pressure should be relatively stable.
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