According to the JG1037 -
2008 'turbine
flowmeter verification procedures' requirement, the linear error is a basic error is an important part of turbine flow sensor, from set out actually, in the case of repetitive content, linear range of turbine flow sensor greatly reduced, this will reduce the use of turbine flow sensor value.
To this end, the calibration process of turbine flow sensor, in the case of repetitive meet their error of one 5, using piecewise linearization processing method, not only can increase the turbine flow sensor measurement range and accuracy of measurement, also can increase the use value of turbine flow sensor, for enterprises to reduce the waste of resources caused by turbine flowmeter verification is unqualified.
1.
The linear characteristic of turbine flowmeter sensor with piecewise linearization 1.
The linear characteristic of turbine flow sensor K - 1
F - Qv, characteristic curve
Qv, nonlinear characteristic curve of full range, high viscosity medium, in particular, and has certain regularity, as shown in figure 1, according to theoretical analysis, the turbine flow sensor K -
Qv, ideal characteristic curve is parallel to the axis of the straight line, but because of the influence of the fluid viscous force characteristics and the results of the blocked by moment on the impeller, the actual curve has the characteristics of the peak, peak appears in the sensor maximum flow rate of 20% 30%, the reasons of the peak features are: when the flow rate decreases to a certain numerical usually is 20% ~ 30% maximum flow)
When the rotation of the torque acting on the turbine and viscous drag torque are reduced accordingly.
But viscous drag torque decreased more significantly, so the speed of the turbine indeed improve, characteristic peak, with the further decrease of flow rate, this effect on the turbine makes all relative to highlight the influence of resistance moment, the turbine speed drop quickly, characteristic curve decreases significantly, on the contrary, when flow rate increases to more than a certain value, the effect on the turbine rotation torque increase, when with the resistance torque balance, characteristic curve is relatively flat.
In order to obtain high measurement accuracy, the use of turbine flow sensor range should fall in the characteristic curve of the linear segment.
In addition, the current body physical characteristics have an effect on turbine flow sensor is linear, the fluid viscosity influence * is large, it must be clear, because the fluid is sticky, makes the fluid viscous resistance on the turbine from, by the change of the flow of body, the influence is bigger, the characteristics of the flow meter of qualitative analysis, with the increase of fluid viscosity, for any diameter of the sensor, its linear range, for a certain diameter of the sensor, the viscosity changes of the lower limit of linear characteristic curve of flow influence * big, influence decreases with the increase of flow rate.
For different diameter of the sensor, the diameter, the greater the viscosity change of linear feature is smaller, the influence of the smaller diameter, the greater the impact, as shown in figure 2.
Thus it can be seen that no matter what kind of fluid medium, viscosity has influence on the linear characteristic of sensor, therefore, within the scope of the full range, in accordance with the JG1037 -
2008 request, the digital flow secondary instrument can only use meter coefficient K of the linear segment Qmax, more than 30%, to 30% Qmax.
And good repeatability under nonlinear segments, cannot use, greatly narrowed the scope of the use of turbine flowmeter, causing the waste of resources.
In order to expand the using range of turbine flow meter, can be like figure 3, the turbine flowmeter flow measurement range piecewise linearization premise is a turbine flow sensor calibration, meet the precision of the repetitive one 5)
, on the basis of turbine flowmeter K -
Qv, theory characteristics curve law, divided into more than 3 pieces, with 10 or 20 intelligent flow secondary instrument of every block, f -
Qv, variations in, can achieve the goal of full range meet the precision, using the piecewise linearization method of turbine flowmeter, can extend the measuring range of turbine flowmeter, reduce scrap, turbine flowmeter can save resources for the factory.
1.
Two nonlinear processing method: piecewise linearization in the process of actual measurement data processing, * small squares is the cornerstone of the linear data processing, in the process of nonlinear sensor output, piecewise linearization of sensor output in a full range accuracy increase with special contribution.
In fact, in the process of turbine flow calibration, with a turbine flow sensor, fluid non-electricity signal ー a velocity (
V)
Is converted into electricity signal f (
Hz)
。
We according to actual traffic Qv,
我/分钟)
The flow sensor to transform power signal frequency f (
Hz)
Corresponding relation, that is, f -
Qv, function relationship, monadic linear regression analysis, fitting out of the turbine flow sensor & int;
-
Qv, characteristic curve, found the turbine flow sensor f -
Qv, curve and the turbine flow sensor K -
Qv, characteristic curve reflects the regularity of consistent, as shown in figure 1 and figure 4 corresponding relationship, they have the characteristics of nonlinear, and the flow rate more than 30% Qmax, with linear characteristics, therefore, we can use the whole range of the piecewise linearization method, each paragraph using small squares treatment f and Qv, ZUI data, fitting out f -
Qv, fitting a curve, as shown in figure 4.
Turbine flowmeter piecewise linearization processing flow chart shown in figure 5.
2.
Turbine flowmeter piecewise linearization results assessment theoretically, piecewise linearization of nonlinear sensor can be applied to all linearization, the risk of this result lies in: (1) turbine flow sensor calibration, full range for f -
The risks of Qv, the measured curve real inflection point.
(2) the risks of turbine flow sensor repeatability limit flow.
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