Analysis on the reason of the decline of the measurement accuracy of the turbine flowmeter
2016-11-29
Turbine flowmeter is a kind of economic speed instrument, it is used in many occasions, the accuracy of turbine flowmeter is in the reference condition (or standard working conditions) determine, turbine flowmeter, reference conditions generally include:
A. environmental conditions (ambient temperature of 15 degrees Celsius to 35 degrees Celsius, relative humidity 75% ~ 45%, atmospheric pressure 86kPa, ~ 108kPa, no electric field, magnetic field interference, no vibration);
B. power source conditions (220V + 10% or 110V, 50HZ + 1, or 24VDC);
C. fluid conditions (when using the fluid standard timing, calibration pipeline for the industrial circle tube, single phase Newton fluid, full full tube, fully developed turbulent velocity, axial symmetrical distribution, no swirl, no disturbance, steady flow.
Fluid temperature is generally room temperature, fluid pressure is generally below 0.25MPa. It is clear that the actual working conditions of the turbine flowmeter are usually different from the reference condition, which will cause the change of the turbine flowmeter's precision.
Turbine flow meter in the use of the process of decline in accuracy, may be the following reasons:
1. The change of fluid temperature and pressure may make the liquid escape pipe containing air or due to the internal pressure of the pipe below the saturated vapor pressure of the fluid, so that part of the liquid into steam, medium pressure may also be due to the outside air is sucked in the pipeline, the gas with the measured liquid flow caused by the instrument indication there is increasing error, the disadvantage of fluid.
2, fluid in the fibrous or viscous impurities attached to the rotating part of the flow meter, so that the rotation resistance increases, resulting in a reduction in the value of the instrument, a negative error, adverse to the fluid side.
Generally, 3 medium have some impurities, wear to the bearing and the shaft to increase, the gap between the two, a dynamic balance is destroyed, the speed dropped, or dirt into the gap, so that increasing the resistance movement, speed down. All of these causes the decrease of the instrument display value, the negative error, and the disadvantage of the supplier.
4, the working environment is bad, for example, electromagnetic interference, dust, high temperature, vibration, humidity, may cause a malfunction or failure of turbine flow sensor, directly caused by turbine meter indication error, the error is positive may also be negative, may not be obvious, or completely failure. For the above phenomenon, in the more serious, can be found from the comparison of the working state of the process, it is easy to take appropriate measures. However, in the early stage of the problem, not to take special measures can not find the problem.
According to the principle of turbine flowmeter and field work experience, in the initial installation of the turbine flowmeter, the tube wall in the upstream and downstream of the flowmeter is 2 times the diameter of the pressure, when needed and differential pressure gauge is in working condition, flowmeter indication value and differential indicator comparison between value, if at this time everything is normal, put this as contrast after check whether the normal work of the flowmeter.
For the dirty fluid or may produce gas liquid flow in the installation time, can filter or a getter device, gas collector installed in its upstream, strengthen the daily maintenance work, regular cleaning of filters, and eliminate the gettering gas collector in the gas or debris, to ensure the normal operation of the flowmeter.
A. environmental conditions (ambient temperature of 15 degrees Celsius to 35 degrees Celsius, relative humidity 75% ~ 45%, atmospheric pressure 86kPa, ~ 108kPa, no electric field, magnetic field interference, no vibration);
B. power source conditions (220V + 10% or 110V, 50HZ + 1, or 24VDC);
C. fluid conditions (when using the fluid standard timing, calibration pipeline for the industrial circle tube, single phase Newton fluid, full full tube, fully developed turbulent velocity, axial symmetrical distribution, no swirl, no disturbance, steady flow.
Fluid temperature is generally room temperature, fluid pressure is generally below 0.25MPa. It is clear that the actual working conditions of the turbine flowmeter are usually different from the reference condition, which will cause the change of the turbine flowmeter's precision.
Turbine flow meter in the use of the process of decline in accuracy, may be the following reasons:
1. The change of fluid temperature and pressure may make the liquid escape pipe containing air or due to the internal pressure of the pipe below the saturated vapor pressure of the fluid, so that part of the liquid into steam, medium pressure may also be due to the outside air is sucked in the pipeline, the gas with the measured liquid flow caused by the instrument indication there is increasing error, the disadvantage of fluid.
2, fluid in the fibrous or viscous impurities attached to the rotating part of the flow meter, so that the rotation resistance increases, resulting in a reduction in the value of the instrument, a negative error, adverse to the fluid side.
Generally, 3 medium have some impurities, wear to the bearing and the shaft to increase, the gap between the two, a dynamic balance is destroyed, the speed dropped, or dirt into the gap, so that increasing the resistance movement, speed down. All of these causes the decrease of the instrument display value, the negative error, and the disadvantage of the supplier.
4, the working environment is bad, for example, electromagnetic interference, dust, high temperature, vibration, humidity, may cause a malfunction or failure of turbine flow sensor, directly caused by turbine meter indication error, the error is positive may also be negative, may not be obvious, or completely failure. For the above phenomenon, in the more serious, can be found from the comparison of the working state of the process, it is easy to take appropriate measures. However, in the early stage of the problem, not to take special measures can not find the problem.
According to the principle of turbine flowmeter and field work experience, in the initial installation of the turbine flowmeter, the tube wall in the upstream and downstream of the flowmeter is 2 times the diameter of the pressure, when needed and differential pressure gauge is in working condition, flowmeter indication value and differential indicator comparison between value, if at this time everything is normal, put this as contrast after check whether the normal work of the flowmeter.
For the dirty fluid or may produce gas liquid flow in the installation time, can filter or a getter device, gas collector installed in its upstream, strengthen the daily maintenance work, regular cleaning of filters, and eliminate the gettering gas collector in the gas or debris, to ensure the normal operation of the flowmeter.