Because it has the character of compressible gas cause of gas flow measurement is much more complicated than those of liquids.
Measured in the gas flow meter output signal in addition to the associated with the input signal, and also associated gas density, temperature and pressure and the density of the gas is (
Under the joint action of physical quantities.
So for the measurement of the gas will involve a concept of temperature, pressure compensation.
So-called Edwin voltage compensation is actually when measured density, pressure and the design of steam using numerical value does not conform to the time, and the density correction measures.
And the corrective measures can be artificial, more can use instrument and DCS, automatically.
It is recommended that output measurement and control system should be used as instrument of computerization, according to the measured gas and instrument types, choose suitable mathematical function formula, temperature automatic pressure compensation.
For the most part in the measurement of gas, can be approximately regarded as an ideal gas, the density of the gas available after correction of the ideal gas state equation.
Some gases, such as water vapor, which is different from the ideal gas, the density should not simply use the ideal gas state equation.
For gas and dry, wet, wet gas, its density in addition to related to temperature, pressure, also related to humidity.
Due to the rapid development of computer technology, significant changes, the progress of science and technology bring instrument manufacturing measuring instrument, the emergence of many intelligent temperature with pressure compensation of steam turbine flowmeter
is a kind of typical types, this instrument makes the advent of gas flow measurement temperature compensation from the previous manual calculation, and become simple and accurate, so as to improve the accuracy of measurement.
For the measurement of steam is an important aspect in the gas measurement, according to the classification of the pressure and temperature of steam for: saturated steam and superheated steam.
They have to flow metering measure can be used to measure, both saturated steam and superheated steam, steam temperature changes, the density of the steam will be along with the change.
At this time, with temperature pressure compensation as the integration of steam turbine flowmeter is produced so, in order to reduce the error.
As early as the sixties and seventies, the domestic some scientists began such studies, the end is also a success.
Is characterized by small pressure loss, wide range, high precision, working condition of the measurement volume flow is almost not affected by the fluid density, the influence of the parameters such as pressure, temperature, viscosity.
Actual measurements, we need to compensate the temperature pressure what?
When the actual parameters (steam flow being measured
Temperature and pressure)
With the design parameters, the flow coefficient & alpha;
, beam expansion coefficient & epsilon;
, aperture d contour will change.
But when the steam temperature, the pressure fluctuation is not big, the working condition of parameters deviating from the design is not too much, influence on measurement is small, the accuracy of measurement of temperature, pressure compensation measures to achieve the ideal.
Most of its compensation formula for empirical formula, in the flow meter are introduced, and the book can use directly.
But when the working condition parameters deviate from the design value too much.
Or operating conditions and frequent fluctuations too big when, even if a temperature compensation measures, is still difficult to meet the accuracy requirements, at this time for a specific orifice plate, can only to calculate the relationship between the differential pressure and flow rate.
But has more perfect compensation and correction measures can be introduced, namely through the intelligent instrument and DCS on the discharge coefficient & alpha;
, beam expansion coefficient & epsilon;
, density & rho;
To conduct a comprehensive correction, but its measuring accuracy depends on the algorithm.
To do the whole compensation or has the certain difficulty.
Need to be aware that not all measuring temperature pressure compensation, should be handled according to the actual production situation.
To comprehensively consider the temperature pressure compensation, such as: measurement requirements, purposes, factors such as temperature, pressure transmitter
For steam turbine flowmeter must adopt temperature pressure compensation measures, and the persons to be good, select the right experience formulas and the precision of form a complete set of temperature, pressure transmitter, and correct, reasonable and careful setup and calibration.
To make a display of instrument, from the reality of production requirements, the compensation will be compensated, need not and cannot compensate occasions is not compensation.
Adopt measures to compensate the compensation of the occasion is wrong, but the exaggerated effect of temperature, pressure compensation is also wrong.
For the actual data of the steam flow (being tested
Temperature and pressure)
Much fewer, and design the parameters of the available density type under the fixed.
When you adopt integration temperature pressure compensation, is to reduce the error, but one thing to remember, to avoid new error, how do you say this?
With temperature compensation are used when the pressure transmitter, at this time should be considered: the influence of atmospheric pressure and static pressure liquid column, so as to avoid the emergence of a new error.
Points above are as follows: the error due to atmospheric pressure, due to the empirical formula of temperature, pressure compensation, contains steam pressure * * the parameters, the general practice is to use pressure transmitter, the detected pressure steam tables and the local atmospheric pressure to represent * * pressure, so the mathematical model is set up, should be calculated according to the local atmospheric pressure, without justification using the approximate equal to zero.
1 mpa instead of atmospheric pressure, especially in high altitude area and low steam pressure that should attract attention.
If choose * * pressure transmitter will not produce the effect.
Liquid column static pressure caused by the error, mostly due to a variety of mouth and take pressure transmitter ontology can't be in the same height, so the condensed water static pressure affect the output of the transmitter will, and produce additional error.
Take the mouth and vertical distance of the transmitter, the greater the influence, the greater the the influence of ordinary pressure transmitter, pressure transmitter * * have influence.
Then can take zero migration and revised method to adjust the pressure transmitter, to eliminate the influence.
In this paper by embellish instrument technology co. , LTD. Arrange release.
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