CN105222843A - A kind of thermal type gas quality flow meter based on tabilized current power supply - Google Patents

Abstract

The invention relates to a thermal gas mass flowmeter based on an adjustable constant current source, comprising a constant current source module, a sensor signal output module, a signal conditioning module, an A/D sampling module and a main control unit, and the sensor module consists of The platinum thermal resistance of the speed measuring probe, the platinum thermal resistance of the temperature measuring probe, the reference resistance connected in series with the platinum thermal resistance of the speed measuring probe, and the reference resistance connected in series with the platinum thermal resistance of the temperature measuring probe, output corresponding The four-way voltage signal, the signal conditioning module includes a four-way conditioning circuit, the four-way voltage signal that meets the sampling requirements after conditioning is sent to the A/D sampling module for analog-to-digital conversion, and then sent to the main control unit, which is calculated by the main control unit For the flow value, the constant current source module includes a constant current source that provides a constant driving current for the branch circuit of the temperature measuring probe and an adjustable constant current source that provides an adjustable driving current for the speed measuring probe. The invention has the characteristics of accurate measurement and wide measurement range.

Description

A kind of thermal type gas quality flow meter based on tabilized current power supply

Technical field

The invention belongs to flow measurement technology field, relate to a kind of mass-flow gas meter.

Background technology

Thermal type gas quality flow meter is driect type mass flowmeter, has that measurement range is wide, crushing is little, reliability is high, can measure mixed gas, is applicable to various pipeline and transships the plurality of advantages such as harmless, be widely applied ^[1].Current, the research of thermal type gas quality flow meter mainly concentrates on four aspects: one is temperature techniques Compensation Research; Two is sensor design research, the accuracy adopting different materials and processing technology to ensure to measure and reliability; Three is measuring method and Study on Data Processing ^[2], under the prerequisite ensureing Measurement Resolution and precision, the data gathered are processed; Four is Sensor Model research, if can obtain the corresponding model of sensor, then effectively can improve measuring accuracy and reduce to measure difficulty.

In sum, people pay close attention to the design of sensor and the compensation of software algorithm, and metering system major part is based on constant temperature differential or constant power type.Constant temperature differential mainly contains two shortcomings: one is adopt wheatstone bridge configuration, will affect bridge balance when environment temperature changes, and showing as zero point unstable and low discharge precision cannot ensure, must add corresponding temperature-compensation circuit; Two is that the flow upper limit is restricted, and along with the continuous increase of flow, heating power is corresponding increase also, and the difficulty that will increase circuit design when heating power is excessive affects the stability of circuit simultaneously.The major defect of constant power type adopts larger heating power when being to measure low discharge, heat transfer free convection between temperature probe and holes probe can not be ignored, cannot ensure the measuring accuracy of low discharge, power control algorithm has certain hysteresis quality simultaneously, the sensitivity that impact is measured.

Thermal mass flow meter carries out flow measurement according to heat transfer theory, and the main transfer mode of its heat is thermal convection.Thermal convection refers to fluid in the process of flowing, and because cold and hot distribution there are differences, cold fluid and hot fluid contacts with each other and produces the process of heat transmission.Convection heat transfer' heat-transfer by convection is divided into again natural convection and the large class of forced convertion two, and the flowing caused because internal fluid each several part density is different is natural convection; The flowing that fluid produces under external force is forced convertion.When rate of flow of fluid is larger, natural convection, heat radiation, heat transfer can be ignored.But when rate of flow of fluid is less, free convection heat transfer just can not have ignored.The fundamental formular of convection heat transfer' heat-transfer by convection is Newtonian Cooling formula:

Q＝hA(T _W-T _C)(1)

Q is the heat flux in the unit time, W; H is surface coefficient of heat transfer, W/ (m ²* k); A is heat interchanging area, m ²; T _wfor the temperature of object wall, be holes probe temperature in thermal flowmeter, K; T _cfor fluid temperature (F.T.), K.

Thermal flowmeter heats holes probe, and its thermal value is:

$Q=I_W^2{R}_W---\left(2\right)$

I _wrepresent the heating current of holes probe, A; R _wrepresent the resistance value of holes probe, Ω.

RogerCBaker provides hA in formula (1) in book at " Flowmeasurementhandbook " and can be expressed as:

hA＝A ₁+B ₁(q _m) ^0.5(3)

Then can obtain flow rate calculation formula:

$q_m={\[\frac{1}{B_1}\left(\frac{I_W^2{R}_W}{T_W-T_C}\right)-\frac{A_1}{B_1}\]}^2---\left(4\right)$

In formula: A ₁, B ₁for constant, drawn by flux experiment device normalization.

Thermal mass flow meter is mainly divided into constant temperature differential and constant power type.When fluid flow is less or be zero time, if the excessive holes probe that will cause of heating current is overheated, and then make ambient temperature obviously increase, the free convection heat transfer so between holes probe and temperature probe just be can not ignore; When fluid flow is larger, if heating current is too small, it is too much that fluid takes away heat, makes the temperature difference between temperature probe and holes probe very little, causes probe insensitive to the change of flow.For above problem, the impact of free convection heat transfer be ignored, under the prerequisite ensureing certain range ratio, not relate to complicated control algolithm, and suitably improve the reaction velocity of instrument.

Patented claim CN201410301881.0 gives a kind of constant flow method thermal type gas quality flow meter and gives its measuring method.

List of references

[1] Wang Liheng, Li Changxi. thermal gas flowmeter temperature Compensation Study [J]. sensing technology journal .2008,21 (8): 1379-1382

[2] civilian Xiao Ling, Liu Cuimei, Yi Xianjun, etc. the nonlinear compensation algorithm analysis [J] of platinum resistor temperature measuring. sensor and micro-system .2009,28 (8): 33-36

Summary of the invention

The present invention improves prior art, proposes a kind of thermal flowmeter of the adjustable constant-flow source technology that can be operated in wider flow range.Technical scheme of the present invention is as follows:

Based on a thermal type gas quality flow meter for tabilized current power supply, comprise constant current source module, sensor signal output module, Signal-regulated kinase, A/D sampling module and main control unit, described sensor signal output module is by holes probe platinum resistance thermometer sensor, R _w, temperature probe platinum resistance thermometer sensor, R _c, with holes probe platinum resistance thermometer sensor, R _wthe reference resistance R of series connection _aand with temperature probe platinum resistance thermometer sensor, R _cthe reference resistance R of series connection _bmagnitude of voltage according to being carried in four described resistance exports corresponding four road voltage signals, Signal-regulated kinase comprises four road modulate circuits, the four road voltage signals meeting sampling request after conditioning are sent into A/D sampling module and carries out analog to digital conversion, be sent to main control unit, calculate flow value by main control unit, it is characterized in that, described constant current source module comprises one for temperature probe branch road provides constant drive current I _cconstant current source and one provide adjustable drive current I for holes probe _wtabilized current power supply.

The XTR110 chip that tabilized current power supply can adopt Burr-Brown company of the U.S. to release, by external for pin 8 adjustable resistance, obtains required electric current by regulating this resistance.

The present invention sets different heating currents to carry out flow measurement to holes probe, to make flow meters work at wider flow range under adopting and carrying out flow measurement and different in flow rate point to the mode of holes probe constant current-supplying.

Accompanying drawing explanation

The schematic block circuit diagram of Fig. 1 thermal type gas quality flow meter of the present invention.

Fig. 2 typical application circuit figure.

Embodiment

Below in conjunction with drawings and Examples, the present invention will be described.

Mass flowmeter of the present invention, its circuitry principle as shown in Figure 1.

Complete machine is divided into sensor signal output module, constant current source module, voltage source module, main control unit and peripheral module thereof, A/D module, Signal-regulated kinase.R _cfor the resistance of temperature probe, it can thus be appreciated that gas medium temperature Tc; R _wfor the resistance of holes probe, it can thus be appreciated that holes probe temperature Tw; R _a, R _bfor reference resistance, resistance 100 Ω, precision 0.01%, temperature drift 5ppm.

$R_c=\frac{U_c*R_b}{U_b}---\left(5\right)$

$R_w=\frac{U_w*R_a}{U_a}---\left(6\right)$

The setting of reference resistance efficiently reduces the impact of constant current source fluctuation on experimental result.Adopt the AD7193 chip of 24 to carry out analog to digital conversion, its resolution is 0.298 μ V, by SPI communication, sampled result is passed to 430 single-chip microcomputers, fully ensure that sampling precision.In single-chip microcomputer, realize the tasks such as signal transacting, setting parameter, model calculating, eventually through liquid crystal, 485 and pulse signal three kinds of modes export.Consider anti-interference and stability that is circuit simultaneously, add house dog protection circuit and power-down protection circuit.

The key of complete machine is the tabilized current power supply of powering for holes probe.

The XTR110 that the present invention adopts Burr-Brown company of the U.S. to release.This chip internal is made up of Voltage to current transducer module, electric current/current transformation module, precision resistance mixed-media network modules mixed-media and precision+10V voltage reference module etc.Fig. 2 is its typical application circuit, and its output current is:

$I_w=50\frac{V_{IN2{/}_2}}{R_{span}}---\left(7\right)$

By external for pin 8 adjustable resistance, obtain required electric current by regulating this resistance.

Experimental calibration result is as shown in table 1, and range ratio reaches 100, and precision meets basic 1.0%, and only when minimum flow point, precision is 1.5%.

Nominal data under table 1 each section of heating current

Tab1Thecalibrationdataunderdifferentheatingcurrent

Claims (2)

1. based on a thermal type gas quality flow meter for tabilized current power supply, comprise constant current source module, sensor signal output module, Signal-regulated kinase, A/D sampling module and main control unit, described sensor assembly is by holes probe platinum resistance thermometer sensor, R _w, temperature probe platinum resistance thermometer sensor, R _c, with holes probe platinum resistance thermometer sensor, R _wthe reference resistance R of series connection _aand with temperature probe platinum resistance thermometer sensor, R _cthe reference resistance R of series connection _bmagnitude of voltage according to being carried in four described resistance exports corresponding four road voltage signals, Signal-regulated kinase comprises four road modulate circuits, the four road voltage signals meeting sampling request after conditioning are sent into A/D sampling module and carries out analog to digital conversion, be sent to main control unit, calculate flow value by main control unit, it is characterized in that, described constant current source module comprises one for temperature probe branch road provides constant drive current I _cconstant current source and one provide adjustable drive current I for holes probe _wtabilized current power supply.

2. flowmeter according to claim 1, is characterized in that, the XTR110 chip that tabilized current power supply adopts Burr-Brown company of the U.S. to release, and by external for pin 8 adjustable resistance, obtains required electric current by regulating this resistance.