Steam flow measurement of temperature and pressure automatic compensation (
Hereinafter referred to as temperature pressure compensation)
, the domestic sixties and seventies of the 20th century has been carrying out the work, then benefit from the cell in pneumatic, electric unit combination instrument development and improvement.
With the development of computer technology, the work but also had great progress.
But the basic principle and application of some problems and has not changed.
One, the concept of temperature, pressure compensation temperature pressure compensation usually refers to the measured data of instrument is the temperature 25 degrees, under the condition of pressure for a standard atmospheric pressure for results, often the scene of the measuring temperature and pressure difference with the standard, so the general instrument can measure the temperature and pressure, and then through the calculation formula of the measurement results are automatically compensated.
Second, the essence of temperature, pressure compensation of steam temperature and pressure changes, the density of steam will change accordingly, that generates steam flowmeter
In order to reduce the error of temperature pressure compensation mode can be taken to reduce the measurement error.
Essence of temperature, pressure compensation is measured the temperature, pressure and the design of steam when using numerical discrepancy, and vapor density correction measures.
Density correction measures as well as for human, also can use instrument and DCS, automatically.
Three, temperature, pressure compensation is the premise of using orifice plate steam flow measurement, for example.
When the actual parameters (steam flow being measured
Temperature and pressure)
Do not agree with design parameters, the outflow coefficient C, the beam of linear 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, is small, influence on measuring the voltage compensation measures to achieve the ideal measuring precision.
Most of its compensation formula for empirical formula, 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 voltage compensation measures, is still difficult to meet the accuracy requirements, for specific orifice plate, at this time only to recalculate 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 of outflow coefficient C, a beam linear 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.
Four, powerless compensation measures for two-phase flow in steam flow measurement, when the steam pressure increases its density increases, the condition of steam pressure is greater than the design pressure will appear negative error, otherwise there will be a positive error.
Temperature when its density is reduced, i. e. , the change of pressure and temperature of steam density is on the contrary, the influence of the phase change can also be complementary on the error.
Generally think of superheated steam flow belongs to the single-phase flow in the pipeline, the density of superheated steam is decided by two parameters of steam temperature and pressure, sometimes also need to consider on the linear expansion coefficient & epsilon;
Is particular in temperature and pressure range is larger and the heat preservation effect is bad, often into saturated steam superheat steam, gas liquid two phase flow is made at this moment, even if a compensation measures is difficult to accurately measure mass flow.
The temperature of saturated steam pressure is of single value function, so the density of voltage compensation can be simplified as pressure compensation, but should see, when the design is usually regarded as saturated steam dryness & Chi;
= 1, it is treated as single-phase flow, but the reality is most of saturated steam is wet steam, its dryness & Chi;
1, this time the saturated steam in pipeline belongs to two phase fluid flow, the pressure compensation measures are also difficult to accurately measure the mass flow rate.
Five, the temperature pressure compensation should start from the actual production the temperature pressure compensation comprehensive consideration, such as the measurement requirements, the cost of the flowmeter USES, temperature, pressure transmitter
and other factors.
For measuring temperature pressure compensation measures must be adopted, and the persons to be good, choose the right experience formula and the precision of form a complete set of temperature, pressure transmitter, and correct, reasonable and carefully set up and calibration.
To do show that use of the 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 measures is also wrong.
Six, correctly treat extreme cases for the user, must on the frequent fluctuations of actual working condition and volatile occasions a prudent attitude.
Otherwise the temperature pressure compensation alone is still difficult to meet the requirements of measurement precision.
Self-control should suggest technology personnel find condition parameter volatility and reasons of the frequent fluctuations, and from the improvement on the process or equipment is the best policy.
If the production process, the design requirements steam pressure of 1.
2 mpa, the temperature is 220 ℃ backward section for steam, but steam supply pressure often only 0.
5 mpa, and the temperature is 300 ℃, the steam quality, and can process after normal production?
At this time should be from the production management or equipment to find the reason, and solve the problem, because it is beyond the scope of measurement and the process parameters greatly deviate from the design value, only depend on the temperature compensation is obviously not enough, moreover, even difficult to guarantee the process after production, measurement and no practical implications
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