CN110057870A - Intelligent liquid vaporation-type VOC gas test characterization instrument based on STM32 - Google Patents

Abstract

The intelligent liquid evaporative VOC gas test characterization instrument based on STM32 belongs to the field of gas sensor performance testing. The technical solution is as follows: including: a gas distribution and liquid inlet controller, a gas distribution box, a gas sensing test system, an N2 gas cylinder, a host computer, and a liquid evaporation furnace, the liquid evaporation furnace is built in the gas distribution box, and the gas distribution The liquid inlet controller is connected with the liquid evaporation furnace, the inlet of the gas distribution box is respectively connected with the gas sensing test system and the N2 gas cylinder through a three-way valve, and the outlet of the gas distribution box is connected with the gas sensing test system. The system is connected, and the gas-sensing test system is connected with the upper computer. The beneficial effects are: the present invention evaporates the liquid VOC gas into a gaseous VOC gas by the method of liquid evaporation, and controls the flow rate pump by the single chip STM32 to control the flow velocity of the liquid injection and the speed of evaporation; The good mixed gas is evenly sent into the gas sensor test box for component testing.

Description

Intelligent liquid evaporative VOC gas test and characterization instrument based on STM32

technical field

The invention belongs to the field of gas sensor performance testing, and in particular relates to an intelligent liquid evaporative VOC gas testing and characterizing instrument based on STM32.

Background technique

VOC gas detection is very important. Semiconductor gas sensors are used to test VOC gas dynamic test systems. Due to the influence of environment, geographical location, gas safety, bulky, high cost and many other factors, the research and analysis of the performance of gas sensors is urgently needed. A test instrument that can overcome the problems caused by the above factors, can evaporate liquid VOC gas into gaseous VOC gas through liquid evaporation, and can effectively control the flow rate of liquid injection and the speed of evaporation.

SUMMARY OF THE INVENTION

In order to overcome the problems caused by the above-mentioned various factors, the present invention provides an intelligent liquid evaporative VOC gas test and characterization instrument based on STM32, which evaporates the liquid VOC gas into For the gaseous VOC gas, the flow pump is controlled by the microcontroller STM32 to control the flow rate of liquid injection and the speed of evaporation; the flow rate of the carrier gas is controlled by the microcontroller to evenly send the evaporated mixed gas into the gas sensor test box for component testing.

The technical solution is as follows:

An intelligent liquid evaporative VOC gas test and characterization instrument based on STM32, including: a gas distribution and liquid inlet controller, a gas distribution box, a gas sensing test system, an _N2 gas cylinder, a host computer, and a liquid evaporation furnace, the liquid evaporation furnace It is built in the gas distribution box, the gas distribution and liquid inlet controller is connected with the liquid evaporation furnace, and the inlet of the gas distribution box is respectively connected with the gas sensing test system and the N gas cylinder through a three _- way valve, The outlet of the gas distribution box is connected with the gas-sensing testing system, and the gas-sensing testing system is connected with the upper computer.

Further, the gas distribution and liquid inlet controller adopts STM32 single-chip microcomputer as the core control unit.

Further, the gas-sensing test system includes a test box and a gas-sensing element, the gas-sensing element is built in the test box, the gas-sensing element is connected to the upper computer, and the test box is provided with a test box inlet 1 . , the test box inlet 2 and the test box exhaust port.

Further, the gas sensor includes a pair of heating electrodes and two pairs of test electrodes.

Further, the liquid evaporation furnace includes a liquid evaporation pool, an AC ceramic heating plate, a C-type 304 steel frame and a signal line, the C-type 304 steel frame is connected to the AC ceramic heating plate, and the AC ceramic heating plate is The liquid evaporation pool is set, and the signal line is set on the C-type 304 steel frame.

The beneficial effects of the present invention are:

The intelligent liquid evaporative VOC gas test and characterization instrument based on STM32 of the present invention evaporates the liquid VOC gas into gaseous VOC gas by means of liquid evaporation, and controls the flow pump through the single chip STM32 to control the flow rate of liquid injection and the speed of evaporation ; The flow rate of the carrier gas is controlled by the single chip microcomputer, and the evaporated mixed gas is evenly sent to the gas sensor test box for component testing.

Description of drawings

Fig. 1 is the structure diagram of the intelligent liquid evaporative VOC gas test characterization instrument based on STM32 of the present invention;

Fig. 2 is the principle block diagram of the VOC gas liquid evaporation gas distribution characterization control system based on STM32 of the present invention;

Fig. 3 is the structure diagram of the liquid evaporation furnace of the present invention;

Fig. 4 is the temperature measurement control circuit schematic diagram of the present invention;

Fig. 5 is the temperature control circuit schematic diagram of the present invention;

6 is a schematic diagram of the hardware structure of the gas distribution system of the present invention;

Fig. 7 is the flow chart of the gas distribution test process procedure of the gas distribution system of the present invention;

8 is a plan view of a gas sensor of the present invention;

FIG. 9 is a test circuit diagram of the gas sensor of the present invention.

Detailed ways

The following is a further description of the intelligent liquid evaporative VOC gas test and characterization instrument based on STM32 in conjunction with accompanying drawings 1-9.

Example 1

An intelligent liquid evaporative VOC gas test and characterization instrument based on STM32, including: a gas distribution and liquid inlet controller, a gas distribution box, a gas sensing test system, an _N2 gas cylinder, a host computer, and a liquid evaporation furnace, the liquid evaporation furnace It is built in the gas distribution box, the gas distribution and liquid inlet controller is connected with the liquid evaporation furnace, and the inlet of the gas distribution box is respectively connected with the gas sensing test system and the N gas cylinder through a three _- way valve, The outlet of the gas distribution box is connected with the gas-sensing testing system, and the gas-sensing testing system is connected with the upper computer.

Further, the gas distribution and liquid inlet controller adopts STM32 single-chip microcomputer as the core control unit.

Further, the gas-sensing test system includes a test box and a gas-sensing element, the gas-sensing element is built in the test box, the gas-sensing element is connected to the upper computer, and the test box is provided with a test box inlet 1 . , the test box inlet 2 and the test box exhaust port.

Further, the gas sensor includes a pair of heating electrodes and two pairs of test electrodes.

Further, the liquid evaporation furnace includes a liquid evaporation pool, an AC ceramic heating plate, a C-type 304 steel frame and a signal line, the C-type 304 steel frame is connected to the AC ceramic heating plate, and the AC ceramic heating plate is The liquid evaporation pool is set, and the signal line is set on the C-type 304 steel frame.

It also includes a micro injection pump, and the micro injection pump is arranged at the inlet and outlet of the gas distribution box, the inlet 1 and the inlet 2 of the test box.

The present invention also includes a test method for an intelligent liquid evaporative VOC gas test characterization instrument based on STM32, using the above test characterization instrument for testing, and the steps are as follows:

S1. Open the air inlet and air outlet channels, and let in N ₂ to keep the N ₂ environment in the air distribution box, keep the air out, and keep the air pressure in the test box and the air distribution box constant;

S2. When the gas distribution process starts, the carrier gas N ₂ turns to the inlet 1 of the test box, the inlet and outlet of the gas distribution box are kept closed, the micro-injection pump maintains the advancing speed corresponding to the evaporation speed of the target liquid, and pushes the target liquid into the evaporation furnace evaporation;

S3, when the advancing time is equal to the concentration of the propelled gas and reaches the target gas concentration, the inlet and outlet of the gas distribution box are opened, the carrier gas N ₂ turns to the inlet of the gas distribution box, the outlet of the gas distribution box leads to the inlet 2 of the test box, and the test timing starts;

S4. After the test process is over, _N2 turns to the inlet 1 of the test box for scavenging, and the inlet and outlet of the gas distribution box are closed;

S5. When the test concentration increases, on the basis of the original concentration in the box, increase the liquid injection amount, and adjust the advancing speed of the injection pump consistent with the target gas concentration;

S6. When the gas concentration in the box reaches the target concentration, the carrier gas channel turns to the inlet of the test box, the outlet of the distribution box turns to the test box, and tests are performed in sequence.

Further, the steps of the gas distribution test process are as follows:

T1, set the target gas concentration;

T2. Calculate the propulsion speed V of the micro injection pump and the propulsion time Xs;

T3. Connect the _N2 valve switch to the test box;

T4. When the ventilation time N is greater than or equal to the propulsion time Xs, the _N2 valve turns to the inlet of the gas distribution box, and the outlet of the gas distribution box leads to the test box;

T5. Set the air distribution time Ys, when the ventilation time N is greater than or equal to the propulsion time Ys, the _N2 valve turns to the test box, and the inlet and outlet of the air distribution box are closed;

T6, set the scavenging time Zs, when the ventilation time N is greater than or equal to the scavenging time Zs, the test process ends.

Example 2

The structure diagram of the intelligent liquid evaporative VOC gas test and characterization instrument based on STM32 is shown in Figure 1.

1. Temperature control of liquid evaporation furnace:

Hardware: evaporating dish, 304 steel, heating material: AC constant temperature PTC ceramic heating plate, as a heating module, the size is about 15mm*30mm (0～200), the power is 220V.

The temperature of the heating furnace is controlled by STM32 to increase and decrease the temperature. Different VOC gases have different boiling points, and the temperature control range of the evaporator is 0°C to 250°C; a K-type thermocouple temperature sensor is used as the large temperature sensing element. When it is working, the thermocouple sensor senses the temperature of the heating plate, which is processed by cold junction temperature compensation, signal amplification, analog-to-digital conversion, etc., and then input to STM32 and compared with the set value; the temperature control circuit adopts a PID control algorithm based Solid state relay, and output the control signal to the actuator, by controlling the output current, to achieve the purpose of controlling the temperature of the resistance furnace. Its temperature measurement control circuit is shown in Figure 4, and the temperature control circuit is shown in Figure 5.

2. Gas distribution process and flow rate control:

System hardware: N ₂ gas cylinder (purchased from Guangming Special Gas); valve controller, two-way valve and three-way valve, and the schematic diagram of the hardware structure of the gas distribution system is shown in Figure 6.

Description of liquid-gas distribution process:

From the beginning of the test process, open the inlet and outlet channels, and pass N ₂ through the mass flow controller at a flow rate of 1000sccm to keep the N ₂ environment in the box, keep the gas outlet, and keep the air pressure in the test box and the gas distribution box constant.

A. When the gas distribution process starts, the carrier gas N ₂ turns to the inlet 1 of the test box, the inlet and outlet of the gas distribution box are kept closed, and the micro-injection pump maintains the advancing speed (V) corresponding to the evaporation rate of the target liquid to advance the target liquid into The evaporation furnace evaporates, and the test process begins when the advancing time is equal to the advancing gas concentration reaching the target gas concentration.

B. The test process starts, the inlet and outlet of the distribution box are opened, the carrier gas N ₂ turns to the inlet of the distribution box, the outlet of the distribution box leads to the inlet 2 of the test box, the test timing starts, and the test response time is generally 5 minutes;

C. After the test process, _N2 turns to the test box inlet 1 for scavenging, and the gas box inlet and outlet are closed;

When the test concentration increases, the liquid injection volume is increased on the basis of the original concentration in the box, and the advancing speed of the injection pump is adjusted to be consistent with the target gas concentration. When the gas concentration in the box reaches the target concentration, the carrier gas channel turns to the inlet of the test box, the outlet of the distribution box turns to the test box, and tests are performed in sequence. The flow chart of the gas distribution test process of the gas distribution system is shown in Figure 7.

(Take the preparation of 1ppm ethanol gas as an example to illustrate the gas distribution process

A. When the gas distribution starts, the carrier gas _N2 is turned on, and turns to the inlet 1 of the test box, the inlet and outlet of the gas distribution box are kept closed, and the micro-injection pump maintains the advancing speed corresponding to the target liquid evaporation speed (V=1.26ml/ The flow rate of m) pushes the ethanol liquid into the evaporation furnace for evaporation. When the push time is 18.65min of ethanol, the micro-injection pump pushes 2.35 μl of the ethanol liquid, and the concentration of ethanol gas in the box reaches the target concentration of 1ppm.

B. When the 18.65th minute is reached, the test process starts, the inlet and outlet of the distribution box are opened, the carrier gas _N2 turns to the inlet of the distribution box, the outlet of the distribution box leads to the inlet 2 of the test box, the test timing starts, and the test response time is normal 5 minutes;

C. After the test process is over, _N2 turns to the inlet 1 of the test box for scavenging, and the inlet and outlet of the gas distribution box are closed;) 4. Liquid micro-injection pump control

Accessories: Micro-injection pump, analytically pure 99.9% ethanol, formaldehyde, acetone solution, etc., based on STM32 control, injected into the evaporating dish through the micro-injection pump.

The propulsion speed of the injection pump and the calculation method of the gas distribution process are as follows

The injected liquid is evaporated into gas through the evaporation furnace, and then enters the test box driven by the carrier gas. The volume of the evaporation box is 1L, the mass flow rate of the carrier gas is N2, and the flow rate is 1000sccl/m, then the target gas concentration is

In formula (1), m is the molecular weight of the injected gas, the unit is g, d is the liquid density, the unit is g/cm-3, p is the purity of the liquid, and it is assumed that under the test conditions, 1mol of liquid is completely converted into 22.4L of liquid. gas. TK is the room temperature, and Tb is the gas box temperature. In this way, the number of milliliters of liquid injected into the evaporation pond of the test container can be converted into the corresponding gas volume ratio.

Taking the ethanol solution as an example, the known conditions are that the density d of the ethanol liquid is 0.789g/cm-3, the injected gas is the molecular weight of the ethanol liquid, m is 46.07g, and the purity p of the ethanol solution is 99.7%, TK is 20°C, Tb is 60 ° C, the volume percentage of the prepared ethanol gas is 1 ppm, and the volume of the injected ethanol solution is calculated by substitution. The common VOC gas parameters for preparing 1ppm are shown in Table 1:

Table 1. Preparation of 1ppm common VOC gas, injection liquid preparation parameters table

molecular formula molecular weight liquid density Injected liquid volume formaldehyde HCOH 30.03 0.815g/cm³ 1.45μl Ethanol C2H5OH 46.07 0.789g/cm³ 2.35μl acetone CH3COCH3 58.08 0.7845g/cm³ 2.95μl

Carrier gas N ₂ , assuming that the carrier gas flow rate is 1000sccm, it means that 1000ml of the gas to be tested with a concentration of 1ppm flows out of the evaporation box per minute, then 1000ml of target gas contains mass m=1000ml×1mg/1000ml=1mg, ethanol liquid density 0.789g/cm3*, the loss of pure ethanol liquid is 1.26×10 ^-3 ml. To keep the concentration in the evaporation box unchanged, the micro-injection pump needs to continuously replenish 1.26×10 ^-3 ml of ethanol solution within 1 minute. Then the advancing speed of the micro injection pump is 1.26×10 ^-3 ml/m. The calculation formula is as formula (2)

During gas distribution, firstly, 2.35 μl of ethanol was advanced by the micro-injection pump at a flow rate of 1.26 ml/m, and the advancing time was 18.65 minutes, at the 18.65th minute. Turn the carrier gas channel to the inlet of the gas distribution box. Driven by the carrier gas, the target gas is passed into the test box from the outlet of the gas distribution box, so that the prepared ethanol gas with a concentration of 1 ppm enters the test box. During the test gas process, the advancing speed of the micro-injection pump was kept at 1.26×10 ^-4 ml/m to keep the ethanol gas concentration in the evaporation box constant;

5. Gas sensor test control:

The gas sensing test system consists of a test box, a gas sensing element, a test inlet 1, an inlet 2 and an outlet. The gas sensor and the test are placed in the test box. The gas sensor has two structures, one pair of heating electrodes and two pairs of test electrodes. In order to avoid the corrosion and oxidation of VOC gas, the test circuit board is placed outside the test box, and the output voltage signal of the electrode is measured. The plan view of the gas sensor is shown in Figure 8, and the test circuit of the gas sensor is shown in Figure 9.

The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (5)

1. a kind of intelligent liquid evaporative VOC gas test characterization instrument based on STM32, is characterized in that, comprises: gas distribution controller, air distribution box, gas _- sensing test system, N gas cylinder, host computer, liquid evaporation furnace , the liquid evaporation furnace is built in the gas distribution box, the gas distribution and liquid inlet controller is connected with the liquid evaporation furnace, and the inlet of the gas distribution box is connected to the gas sensing test system, The N ₂ gas cylinder is connected, the outlet of the gas distribution box is connected with the gas-sensing testing system, and the gas-sensing testing system is connected with the upper computer. 2. The intelligent liquid evaporative VOC gas test characterization instrument based on STM32 as claimed in claim 1, wherein the gas distribution and liquid inlet controller adopts STM32 single-chip microcomputer as the core control unit. 3. The intelligent liquid evaporative VOC gas test characterization instrument based on STM32 as claimed in claim 1, wherein the gas-sensing test system comprises a test box and a gas-sensing element, and the gas-sensing element is built in the test box, The gas sensor is connected to the upper computer, and the test box is provided with a test box inlet 1, a test box inlet 2 and a test box exhaust port. 4. The STM32-based intelligent liquid evaporative VOC gas test characterization instrument according to claim 3, wherein the gas sensing element comprises a pair of heating electrodes and two pairs of test electrodes. 5. The intelligent liquid evaporation type VOC gas test characterization instrument based on STM32 as claimed in claim 1, wherein the liquid evaporation furnace comprises a liquid evaporation pond, an AC ceramic heating plate, a C-type 304 steel frame and a signal line, The C-type 304 steel frame is connected to the AC ceramic heating plate, the liquid evaporation pool is arranged on the AC ceramic heating plate, and the signal line is arranged on the C-type 304 steel frame.