Problems in the verification of Gas turbine flowmeter

                                      Problems in the verification of gas turbine flowmeter

1 Overview

In measurement science and technology, flow measurement is one of its important components. Doing a good job of flow measurement is the key factor to improve production efficiency and ensure product quality. At present, there are two main types of gas turbine flowmeter used in the market: one is integrated or intelligent electronic gas turbine flowmeter, that is, turbine flowmeter without mechanical counter; Another gas turbine flowmeter is one with mechanical counter. As a kind of velocity flowmeter, turbine flowmeter accounts for the majority in gas flow measurement. Because gas turbine flowmeter is often used in the process of natural gas handover, the accuracy of turbine flowmeter is directly related to the economic interests of both parties of natural gas handover. Therefore, in the verification process of flowmeter, the measurement error of flowmeter should be reduced as much as possible. Aiming at some problems existing in the verification of turbine flowmeter, combined with the usual working experience, this paper puts forward relevant countermeasures to make the verification work carry out normally and smoothly.

2 problems and solutions in the verification process of gas turbine flowmeter

During the verification of turbine flowmeter, the indication error is often encountered. When calculating with instrument coefficient K, the indication error of unqualified flowmeter occurs, or the standard signal cannot be directly collected and may not be displayed directly. Although this phenomenon occurs in the turbine flowmeter, it does not mean that the flowmeter is unqualified. Therefore, if we want to draw the final verification conclusion, we need our flowmeter verification personnel to carefully analyze these phenomena.

3.1 the indication error of flowmeter calculated by instrument coefficient K is unqualified

During the verification of turbine flowmeter, since the turbine flowmeter calibration at the factory adopts the method of water calibration, when the turbine flowmeter is verified with red oil medium in daily verification, due to the large viscosity coefficient of red oil, when the flowmeter is verified with red oil medium, the accuracy of verification cannot reach the factory accuracy. In order to meet the verification requirements, it is necessary to improve the lower limit of the flowmeter or reduce the accuracy of the flowmeter appropriately. For some flowmeters with automatic correction function, even if the indication error calculated by the instrument coefficient K is unqualified, the indication error of the flowmeter section can meet the requirements of verification accuracy and ensure that the turbine flowmeter is qualified after correction. Of course, the precondition is that the repeatability of the flowmeter should be qualified.

3.2 the signal cannot be collected by standard equipment

Collect the pulse signal output by the flow sensor through the standard equipment, and provide 12 / 24V DC for the turbine flowmeter to be verified. When the output signal of the flowmeter cannot be collected by the standard equipment of the verified turbine flow meter, first check whether the signal line is correctly connected. If the signal line is correctly connected, test whether there is a signal output from the flowmeter. If the signal is not output, it means that the amplifier or flowmeter has been damaged, and the verification result is that the flowmeter is unqualified. If there is an output signal, first test the frequency and amplitude of the flowmeter signal, and then adjust the "pulse signal amplification factor selection" and "pulse signal amplitude selection" on the standard equipment console to make them correspond to the corresponding amplification factor and amplitude value until the signal is collected by the standard equipment. When the signal cannot be collected by adjusting the standard equipment, the frequency of the output signal of the flowmeter can be collected by the frequency meter, and then the standard flow value and frequency are substituted according to the formula k = f / QV to calculate the instrument coefficient of the flowmeter.

3.3 the display result of secondary instrument is out of tolerance or not displayed

If the wiring of the verification instrument is incorrect, the flow value detected by the secondary instrument will not be displayed. Firstly, check whether the power supply and flow signal are connected correctly. If the line is correctly connected and the flow value still cannot be displayed, the secondary instrument may have been damaged. In addition, the coefficient of the instrument needs to be set correctly in the verification process, otherwise the flow value displayed by the secondary instrument may exceed the difference in the verification process. When the instrument has the function of subsection correction, at least one instrument coefficient value should be input for each flow section according to the verification results, not only one point, but three points must be verified. In this way, it can ensure that the flow indication error of the whole range is qualified.

3.4 others

Usually, in order to reduce the mechanical friction of bearings, high-precision turbine flowmeter generally adopts high-quality bearings. At the same time, solid impellers are usually used to bear the pressure of air flow. Therefore, during the verification process, pay attention to the on-site maintenance of these turbine flowmeters, which are usually lubricated and maintained once a quarter. This is mainly to reduce the increase of mechanical friction of flowmeter bearing due to dirt and other reasons, so as to affect the metering speed of flowmeter and produce metering error.

4 Conclusion
To sum up, in order to make the gas turbine flowmeter work in the best state, measures must be taken to optimize its flow measurement performance to ensure its measurement accuracy. Since there are many kinds of turbine flow meters, the specific verification methods are not the same. Therefore, the verification of some turbine flow meters should be carried out according to the specific conditions, and the specific verification measures should be taken.