CN205175478U - Hot type gas sensor for mass flow meter based on adjustable constant current source - Google Patents

Abstract

The utility model relates to a hot type gas sensor for mass flow meter based on adjustable constant current source, including constant current source module and sensor signal output module, the sensor signal output module reference resistance of establishing ties by speed measuring probe platinum resistance, temperature probe platinum resistance, with speed measuring probe platinum resistance and the reference resistance of establishing ties with temperature probe platinum resistance, be in according to the loading the corresponding four ways voltage signal of magnitude of voltage output of four resistance, the constant current source module include that one provides invariable drive current constant current source and an adjustable constant current source that provides adjustable drive current for speed measuring probe for the temperature probe branch road. Adopt the utility model discloses a flowmeter has the characteristics of the accuracy of measurement, measurement wide range.

Description

Based on the thermal type gas quality flow meter sensor of tabilized current power supply

Technical field

The utility model belongs to flow measurement technology field, relates 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

Utility model content

The utility model improves prior art, proposes a kind of sensor can widening thermal mass flow meter flow metering scope.

The technical solution of the utility model is as follows:

Based on a thermal type gas quality flow meter sensor for tabilized current power supply, comprise constant current source module, sensor signal output module, described sensor signal output module comprises 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 _b, the magnitude of voltage according to being carried in four described resistance exports corresponding four road voltage signals, 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 utility model 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 circuitry theory diagram of the thermal type gas quality flow meter that Fig. 1 sensor of the present utility model is suitable for.

Fig. 2 typical application circuit figure.

Embodiment

Below in conjunction with drawings and Examples, the utility model is described.

Adopt the mass flowmeter of sensor of the present utility model, 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 utility model 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 sensor for tabilized current power supply, comprise constant current source module and sensor signal output module, described sensor signal output module comprises 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 _b, the magnitude of voltage according to being carried in four described resistance exports corresponding four road voltage signals, 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. thermal type gas quality flow meter sensor according to claim 1, it is characterized in that, the XTR110 chip that tabilized current power supply adopts Burr-Brown company of the U.S. to release, by external for pin 8 adjustable resistance, obtains required electric current by regulating this resistance.