CN204142300U - A kind of heat type gas flow measurement mechanism - Google Patents

Abstract

The utility model relates to a kind of heat type gas flow measurement mechanism, adopt+24V direct current single power supply, comprise sampling module, MSP430F149 system module, display module, communication module and magnitude of current signal output module, the voltage signal input MSP430F149 system module of acquisition module collection carries out A/D conversion, and the digital quantity that MSP430F149 system module inputs is converted to 4 ~ 20mA current-mode analog quantity and exports by magnitude of current signal output module; It is characterized in that in sampling module, devising constant temperature feedback control circuit and equivalent wheatstone bridge circuits.Improve the sensitivity of thermal flowmeter, improve stability and the accuracy of systematic survey.

Description

A kind of heat type gas flow measurement mechanism

Technical field

The utility model relates to a kind of heat type gas flow measurement mechanism, belongs to industrial flow and measures and control field.

Background technology

The Common Instrument that thermal flowmeter is measured as industrial flow, uses widely.Now conventional in the industry thermal flowmeter mainly adopts 2 hot type reference resistances as sensitive element, and adopt bridge-type loop, utilize constant temperature method measuring principle to measure flow, measuring principle figure as shown in Figure 1.

Electric bridge loop has the function of temperature self-compensation, and Rw is as measuring sensor, and Rc is as temperature-sensing element.But also there is following shortcoming in prior art: when adopting bridge diagram, in order to reduce the electric current compensating branch road, compensating resistance is not generated heat, Rc resistance value is larger, normal employing PT1000 and PT20 or PT1000 and PT45 etc. are as measuring sonde, but the platinum resistance thermometer sensor, thermal inertia that resistance value is larger is comparatively large, and cause system responses slow, sensitivity is low; Measuring sensor Rw and temperature-sensing element Rc different resistive values are too large, limit the design of circuit, affect stability and the precision of signals collecting; Control circuits etc. have much room for improvement, to improve overall measurement effect.

MSP430, as a super low power consuming single chip processor, applies in industrial intelligent instrument in a large number.MSP430 operating voltage is 3.3V, and a large amount of peripheral hardware operating voltage is about 5V, there is the problem of voltage matches; In addition, AD circuit and digital quantity are converted into the noise ubiquity of analog quantity, and signal to noise ratio (S/N ratio) is the important parameter of evaluation system quality.

Summary of the invention

The technical matters solved

In order to avoid the deficiencies in the prior art part, the utility model proposes a kind of heat type gas flow measurement mechanism.

Technical scheme

A kind of heat type gas flow measurement mechanism, adopt+24V direct current single power supply, comprise sampling module, MSP430F149 system module, display module, communication module and magnitude of current signal output module, the voltage signal input MSP430F149 system module of acquisition module collection carries out A/D conversion, and the digital quantity that MSP430F149 system module inputs is converted to 4 ~ 20mA current-mode analog quantity and exports by magnitude of current signal output module; It is characterized in that in sampling module, devising constant temperature feedback control circuit and equivalent wheatstone bridge circuits, wherein OP07, R20, R19, LM317T, 1N4148 constitute constant temperature feedback control circuit, OP07 gathers bridge voltage signal, utilizes the output characteristics of LM317T to be operated in constant temperature mode by changing bridge voltage E control heating probe; R14, R13, OP07, R11, R8, Rc, R9, R10, R12, LM324N form the compensation branch road of equivalent wheatstone bridge circuits, R16, Rw form the measurement branch road of equivalent wheatstone bridge circuits, R13, R14 are by bridge voltage E dividing potential drop, OP07 forms voltage follower and R13 dividing potential drop is carried in compensation branch road, reduce compensation branch voltage, LM324N will compensate the dividing potential drop multiples such as branch road output voltage and amplify, as an input voltage Uc of constant temperature feedback control circuit.

Sampling module adopts PT20 to pop one's head in Rw, PT100 as temperature probe Rc as heating, is connected respectively on the bridge road of equivalent Wheatstone bridge.

Add 6N137 photoisolator in magnitude of current signal output module, isolation mimic channel and digital circuit, reach the effect of voltage matches, improves signal to noise ratio (S/N ratio) and the stability of system.

Beneficial effect

A kind of heat type gas flow measurement mechanism that the present invention proposes, can improve the sensitivity of thermal flowmeter, improves stability and the accuracy of systematic survey.

Accompanying drawing explanation

Fig. 1 thermal flowmeter measuring principle

Fig. 2 the utility model scheme block diagram

Fig. 3 sonde configuration schematic diagram

Fig. 4 power circuit

Fig. 5 signal acquisition circuit

Fig. 6 MCU circuit

Fig. 74 ~ 20mA current output circuit

Fig. 8 display, communication and key circuit

Fig. 9 program flow diagram

Figure 10 integrated flow calculates schematic diagram

Embodiment

Now in conjunction with the embodiments, the invention will be further described for accompanying drawing:

A kind of heat type gas flow measurement mechanism, as shown in Figure 2, comprise sampling module, MSP430F149 system module, display module, communication module and magnitude of current signal output module, the voltage signal input MSP430F149 system module of acquisition module collection carries out A/D conversion, and the digital quantity that MSP430F149 system module inputs is converted to 4 ~ 20mA current-mode analog quantity and exports by magnitude of current signal output module.

Sampling module adopts PT20 to pop one's head in Rw, PT100 as temperature probe Rc as heating, is connected respectively on the bridge road of equivalent Wheatstone bridge, as shown in Figure 3.

This device adopts+24V direct current single power supply, as shown in Figure 4, exports+15V voltage by 7815 (U1), and R1 and R2 dividing potential drop exports+5V voltage VCC5V, and AMS1117-3.3 exports+3.3V voltage VCC.

As shown in Figure 5, for thermal mass flow meter, its flow detection is according to heat balance principle to signal acquisition circuit, and electric current flows through heat that Heat―Film Probe produces and should equal fluid and flow through the heat that Heat―Film Probe takes away.Under constant temperature mode of operation, can obtain becoming with flow the voltage of certain corresponding relation to export.

In the signal acquisition circuit of this device, devise constant temperature feedback control circuit, OP07 (U5A), R20, R19, LM317T (U3), 1N4148 forms constant temperature feedback control circuit, OP07 (U5A) gathers bridge voltage signal, utilizes the output characteristics of LM317T to be operated in constant temperature mode by changing bridge voltage control heating probe.

Rc (PT20) and Rw (PT100) are sensor probe, and Rc is temperature probe, and Rw is heating probe.Rw is operated in higher temperature, and the electric current flow through is larger; Rc is as temperature probe, and the electric current flow through should very little (being not more than 4mA), makes it be unlikely to generate heat and affect the measurement of environment temperature.

In order to neither change the temperature self-compensation characteristic of electric bridge, greatly reduce again the electric current compensating branch road, the equivalent wheatstone bridge circuits of this apparatus design, R14, R13, OP07, R11, R8, Rc, R9, R10, R12, LM324N form the compensation branch road of equivalent wheatstone bridge circuits, R16, Rw form the measurement branch road of equivalent wheatstone bridge circuits, and measuring branch voltage is directly provided by bridge voltage E; R13, R14 are by bridge voltage dividing potential drop, and OP07 (U4) forms voltage follower and R13 dividing potential drop is carried in compensation branch road, so just substantially reduces compensation branch voltage; LM324N (U3B) will compensate the dividing potential drop multiples such as branch road output voltage and amplify, as an input voltage Uc of constant temperature feedback control circuit; Uw is as another input voltage, and whole circuit working process and the equivalence of common bridge diagram, be analyzed as follows:

When bridge balance, from analyzing above, compensating branch voltage is the output voltage compensating branch road is:

$\mathrm{Uc}=E\frac{R13}{R13+R14}\·\frac{\mathrm{Rc}}{\mathrm{Rc}+R8}\·\frac{R12+R10}{R10}$

Measuring branch road output voltage is

$\mathrm{Uw}=E\frac{\mathrm{Rw}}{\mathrm{Rw}+R16}$

Work as R13=R10, during R14=R12, again because bridge balance can obtain:

$\mathrm{Uw}=E\frac{\mathrm{Rw}}{\mathrm{Rw}+R16}=E\frac{\mathrm{Rc}}{\mathrm{Rc}+R8}=\mathrm{Uc}$

Namely during bridge balance, electric bridge exports equal, and when bridge balance is destroyed, constant temperature feedback control circuit gathers voltage signal control electric bridge and is again in equilibrium state.

Regulate R16 can the working temperature of control Rw.Equivalent electric bridge circuit has the function of temperature self-compensation.When gas flow rate changes, Rw temperature change, change in resistance, constant temperature feedback control circuit gathers the voltage signal of electric bridge, and control LM317T output voltage changes, thus changes the electric current that bridge voltage regulates Rw, makes it be operated in steady temperature.Gas flow is larger, and the heat taken away is more, and the watt current flowing through Rw is larger, the temperature remained constant of guarantee Rw; Otherwise gas flow is less, the heat taken away is fewer, and the watt current flowing through Rw is less, therefore gas flow becomes one-to-one relationship with the electric current flowing through Rw, also just becomes corresponding relation with each voltage signal of electric bridge.

The effective voltage of LM324N (U3A) Acquisition Circuit regulates rear input single-chip microcomputer to carry out A/D conversion.

Add 6N137 photoisolator in magnitude of current signal output module, isolation mimic channel and digital circuit, reach the effect of voltage matches, improves signal to noise ratio (S/N ratio) and the stability of system.

MCU circuit as shown in Figure 6, is the minimum system of MSP430F149 single-chip microcomputer.P1 interface is the JTAG download port of single-chip microcomputer, provides the download program of single-chip microcomputer; The voltage signal that signal acquisition circuit gathers enters single-chip microcomputer by A0 (P6.0) passage and carries out A/D conversion.

As shown in Figure 7, single-chip microcomputer carries out SPI by P5.0, P5.1, P5.3 and AD420 and communicates 4 ~ 20mA current output circuit.AD420 chip operation is set at 4-20mA current output mode.MSP430F149 single-chip microcomputer operating voltage is 3.3V, AD420 logic voltage is about 5V, therefore communication both being connected by 6N137 photoisolator, reach the effect of voltage matches.The digital quantity that single-chip microcomputer transmits is converted to 4 ~ 20mA current-mode analog quantity and exports by AD420 chip.In addition, because whole system is made up of digital circuit and mimic channel, 6N137 can also play the effect of isolation mimic channel and digital circuit, can improve signal to noise ratio (S/N ratio) and the stability of system like this.

This device also added display module, communication module and key circuit, and as shown in Figure 8, whole system forms a complete measurement mechanism.

Make hardware unit according to circuit theory diagrams, package casing and mounting condition etc. can be made according to actual needs.After hardware completes, in code test platform is demarcated device, uses least square method to fit out the family curve of device.Adopt the family curve of models fitting device, wherein V is sampled voltage, and U is the flow velocity of gas, is the corresponding relation corresponding relation of flow (or with) of sampled voltage and flow velocity.This family curve is the calculated curve of instantaneous delivery.

Software programming controls.The voltage signal input single-chip microcomputer that signal collection modulation circuit exports carries out A/D conversion, completes the calculating of instantaneous delivery and integrated flow in single-chip microcomputer; Single-chip microcomputer and AD420 carry out SPI and communicate, and industrial standard analog output instantaneous delivery being converted to 4-20mA passes to host computer, drive 12864 liquid crystal display instantaneous delivery and integrated flows simultaneously; Program constantly inquires about the operational order whether had from host computer, to be modified and upgrade by MAX485 chip to parameters.The process flow diagram of program as shown in Figure 9.

The calculating of instantaneous delivery calculates by demarcating the equipment energy characteristic curve obtained.The calculating of integrated flow as shown in Figure 10.From integral principle, the integrated flow in t1 to the t2 time period is the integration of U1 to U2 segment of curve in t1-t2.Due to the expression formula of U-t accurately cannot be known, straight line is adopted to replace the method for curve to calculate compared with the integrated flow Δ S in minor time slice.The integrated flow of each time period is added, namely total integrated flow.

After completing hardware making, Experimental Calibration and software programming, flow measurement can be carried out.After device powers on, by button to device initialization, measuring condition and parameter are set.

Claims (3)

1. a heat type gas flow measurement mechanism, adopt+24V direct current single power supply, comprise sampling module, MSP430F149 system module, display module, communication module and magnitude of current signal output module, the voltage signal input MSP430F149 system module of acquisition module collection carries out A/D conversion, and the digital quantity that MSP430F149 system module inputs is converted to 4 ~ 20mA current-mode analog quantity and exports by magnitude of current signal output module; It is characterized in that in sampling module, devising constant temperature feedback control circuit and equivalent wheatstone bridge circuits, wherein OP07, R20, R19, LM317T, 1N4148 constitute constant temperature feedback control circuit, OP07 gathers bridge voltage signal, utilizes the output characteristics of LM317T to be operated in constant temperature mode by changing bridge voltage E control heating probe; R14, R13, OP07, R11, R8, Rc, R9, R10, R12, LM324N form the compensation branch road of equivalent wheatstone bridge circuits, R16, Rw form the measurement branch road of equivalent wheatstone bridge circuits, R13, R14 are by bridge voltage E dividing potential drop, OP07 forms voltage follower and R13 dividing potential drop is carried in compensation branch road, reduce compensation branch voltage, LM324N will compensate the dividing potential drop multiples such as branch road output voltage and amplify, as an input voltage Uc of constant temperature feedback control circuit.

2. a kind of heat type gas flow measurement mechanism according to claim 1, is characterized in that described sampling module adopts PT20 to pop one's head in Rw, PT100 as temperature probe Rc as heating, is connected respectively on the bridge road of equivalent Wheatstone bridge.

3. a kind of heat type gas flow measurement mechanism according to claim 1, it is characterized in that adding 6N137 photoisolator in described magnitude of current signal output module, isolation mimic channel and digital circuit, reach the effect of voltage matches, improves signal to noise ratio (S/N ratio) and the stability of system.