Micro-positive pressure explosion-proof flow transmitter and flow detection method

Abstract

The invention discloses a micro-positive pressure anti-explosion flow transmitter and a flow detection method, and relates to the technical field of anti-explosion flow transmitters. The transmitter consists of an upper part, a middle part and a lower part, wherein the lower part comprises a three-way base, a thermal mass flow chip (sealed by ceramic and encapsulated by epoxy resin) and a shell joint cover; the middle part comprises a PCB (integrated operational amplification and signal conversion circuit) in an explosion-proof cavity and a shell cylinder; and the upper part comprises a cable and a brass nickel-plated explosion-proof stuffing box. According to the detection method, based on the thermal mass flow chip, the constant temperature difference principle and the Min's law (P / deltaT = K1 + K2f (qm) K3), the micro-positive pressure (50-500 Pa) gas flow is calculated by detecting the temperature difference and heating current change when gas flows through the chip, a 4-20 mA signal is output to the positive pressure controller, and flow monitoring, gas replacement judgment and fault alarm are achieved. The problem that an existing transmitter cannot detect micro-positive pressure gas is solved, the explosion-proof performance is excellent, and the transmitter can directly work in a dangerous area.

Description

Technical Field

[0001] This invention relates to explosion-proof flow transmitters, specifically to a micro-positive pressure explosion-proof flow transmitter. It also relates to a flow detection method for the explosion-proof flow transmitter. This invention is applicable to the ventilation stage of positive pressure explosion-proof equipment in flammable and explosive environments, enabling accurate detection of the gas flow rate at the exhaust port under micro-positive pressure (50-500 Pa) to ensure that the hazardous gas in the positive pressure chamber is fully purged and replaced, meeting explosion-proof performance requirements. Background Technology

[0002] Positive pressure explosion-proof equipment is widely used in flammable and explosive environments such as petroleum, chemical, and coal mines. In these environments, the exhaust flow rate of positive pressure explosion-proof equipment needs to be monitored and measured in real time during the ventilation phase. The core purpose is to determine whether the hazardous gas in the positive pressure chamber has been adequately purged and replaced through flow data, thereby ensuring that the equipment meets explosion-proof performance standards.

[0003] However, the pressure at the exhaust port of positive pressure explosion-proof equipment and the air pressure inside the positive pressure chamber are both within the range of micro-positive pressure, with pressure values ​​of only 50–500 Pa. Existing explosion-proof flow transmitters have significant technical defects: when a small pressure airflow passes through, either the flow signal cannot be detected at all, or the detected signal is severely distorted, failing to meet the accuracy and reliability requirements of explosion-proof standards for exhaust port flow monitoring. This makes it impossible to accurately determine whether the hazardous gas in the positive pressure chamber has been completely discharged, posing a significant hidden danger to safe production in flammable and explosive environments.

[0004] Therefore, there is an urgent need for an explosion-proof flow transmitter that can operate stably in explosive hazardous environments and accurately detect the flow rate of slightly positive pressure gas to solve the existing technical problems. Summary of the Invention

[0005] This invention provides a micro-positive pressure explosion-proof flow transmitter and a flow detection method to solve the problems that existing explosion-proof flow transmitters cannot detect micro-positive pressure gas flow and cannot work directly in explosive environments. This invention enables accurate and real-time monitoring of 50-500Pa micro-positive pressure gas flow, while also possessing excellent explosion-proof performance and allowing direct operation in hazardous areas.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a micro-positive pressure explosion-proof flow transmitter, which consists of three parts: upper, middle and lower, wherein: The lower part includes a transmitter base, a thermal mass flow chip, and a housing connector cover. The transmitter base is a three-way base. The lower end of the thermal mass flow chip body is connected to the transmitter base. The thermal mass flow chip body is sealed with epoxy resin filler and is integrally cured on the housing connector cover with an embedded sealing ring. The part of the thermal mass flow chip exposed on the housing connector cover is sealed with ceramic material. One end of the thermal mass flow chip is a thermal mass flow sensor containing a heater and a temperature sensor, and the other end is provided with a heater pin, a temperature sensor pin, and a ground pin. The middle part includes an outer shell and a PCB board. The outer shell is connected to the lower threaded part through an outer shell connector cover and a sealing ring to form an explosion-proof cavity that encloses the PCB board. The PCB board is fixed in the explosion-proof cavity by a PCB board holder. The PCB board integrates an operational amplifier circuit and a signal conversion circuit. The PCB board input is electrically connected to the pins of the thermal mass flow chip, and the PCB board output is electrically connected to an external positive pressure controller. The upper part is a cable, one end of which is connected to the PCB board, and the other end of which passes through the transmitter. The cable is surrounded by an explosion-proof stuffing box.

[0007] The lead wires of the thermal mass flow meter chip are encapsulated with epoxy resin, with an encapsulation length ≥20.0mm.

[0008] The number of threaded engagements between the outer shell cylinder and the outer shell connector cover is ≥5, and the engagement length is ≥8mm.

[0009] The explosion-proof stuffing box is made of nickel-plated brass and is fitted onto the outside of the cable. The length of the stuffing inside the explosion-proof stuffing box is ≥20mm.

[0010] The flow detection method of the micro-positive pressure explosion-proof flow transmitter of the present invention includes the following steps: Step 1: Connect the transmitter to the exhaust port of the positive pressure explosion-proof chamber through the transmitter base. The slightly positive pressure gas flows through the thermal mass flow chip via the transmitter base. Step 2: The heater of the thermal mass flow chip is powered on to generate heat, and the temperature sensor detects the gas temperature on the surface of the thermal mass flow chip in real time to obtain the temperature difference ΔT when the gas flows through it. Step 3: The operational amplifier circuit on the PCB board amplifies the temperature difference ΔT signal, and the signal conversion circuit calculates the gas mass flow rate qm according to King's Law; P / ΔT=K1+K2f (qm) K3,P=Iheater²Rheater Where P is the heating power, Iheater is the heating current, Rheater is the heater resistance, and K1, K2, and K3 are constants related to the physical properties of the gas. Step 4: The signal conversion circuit converts qm into a 4-20mA current signal and outputs it to the display device and the positive pressure controller; the positive pressure controller judges the gas replacement status based on the signal, and triggers an alarm or power off when abnormal.

[0011] In step 3, when the gas flow rate increases, qm increases, and the control system automatically increases Iheater to compensate for heat loss. The change in Iheater reflects the change in qm.

[0012] In step 4, the positive pressure controller's judgment criteria are as follows: when the current signal is 4mA, the flow rate is judged to be 0, indicating that the gas has not been replaced; when the current signal is in the range of 4-20mA and is stable, the replacement is judged to be normal; a sudden increase in the current signal indicates possible leakage.

[0013] The micro-positive pressure explosion-proof flow transmitter and flow detection method designed using the above-mentioned technical solution of this invention have the following advantages compared with the prior art: 1. Excellent explosion-proof performance: Through multiple explosion-proof designs such as ceramic sealing of the exposed part of the thermal mass flow chip, epoxy resin encapsulation of the thermal mass flow chip pins (≥20.0mm), explosion-proof cavity formed by the outer shell and the outer shell connector cover, and brass nickel-plated explosion-proof stuffing box for the cable, the transmitter can work stably in explosive hazardous areas and meet the explosion-proof standard requirements. 2. High detection accuracy: It adopts a thermal mass flow chip combined with the constant temperature difference principle and uses King's law to establish a mathematical relationship between heating power, temperature difference and flow rate. It can accurately detect the flow rate of gas under micro positive pressure of 50-500Pa, solving the problem of existing transmitters not being able to detect or having signal distortion. 3. Practical Functions: Outputs a 4-20mA standard current signal, which can be directly connected to display devices and positive pressure controllers to realize real-time flow monitoring, hazardous gas replacement judgment, and automatic fault alarm / power cut-off, ensuring the safety of equipment and personnel; 4. High stability: The thermal mass flow chip has excellent long-term stability and high temperature resistance. The epoxy resin sealing and ceramic protection design further enhances the equipment's ability to resist harsh environments and extends its service life. Attached Figure Description

[0014] Figure 1 This is a schematic diagram showing the overall structure of the present invention; Figure 2 This is a side view of the present invention. Figure 3 express Figure 1 A schematic diagram of the AA structure; Figure 4 express Figure 1 Schematic diagram of BB structure; Figure 5 This is a schematic diagram showing the disassembled structure of the present invention; Figure 6 A schematic diagram showing the external shape of the thermal mass flow rate chip of the present invention; Figure 7 A schematic diagram showing the structure of the present invention in use; Figure 8 This invention illustrates the constant temperature difference measurement principle of the flow meter. Figure 9 This is a schematic diagram illustrating the principle of the present invention.

[0015] In the diagram: 1-Transmitter base, 2-Thermal mass flow chip, 3-Epoxy resin, 4-Housing connector cover, 5-Sealing ring, 6-PCB board base, 7-PCB board, 8-Housing cylinder, 9-Explosion-proof stuffing box, 10-Cable, 11-Nameplate, 12-Grounding device, 13-Heater, 14-Temperature sensor, 15-Heater pin, 16-Temperature sensor pin, 17-Grounding pin, 18-Positive pressure controller, 19-Positive pressure equipment, 20-Explosion-proof flow transmitter, 21-Flame arrester, 22-Positive pressure explosion-proof cavity. Detailed Implementation

[0016] The micro-positive pressure explosion-proof flow transmitter and flow detection method of the present invention will be described in detail below with reference to the accompanying drawings.

[0017] The present invention relates to a micro-positive pressure explosion-proof flow transmitter and a flow detection method, which consists of three parts: upper, middle and lower.

[0018] The lower structure includes a transmitter base 1, a thermal mass flow chip 2, epoxy resin 3, a housing connector cover 4, and a sealing ring 5. The lower end of the thermal mass flow chip 2 is fixedly connected to the transmitter base 1. The body of the thermal mass flow chip 2 is sealed with epoxy resin 3 filler to ensure uniform filling and complete encapsulation of the chip body. The entire chip is then placed inside the housing connector cover 4, which is inlaid with the sealing ring 5. After the epoxy resin 3 cures, the lower structure assembly is complete. The transmitter base 1 is a three-way base for easy detection of flowing gas. The exposed portion of the thermal mass flow chip 2 is sealed with alumina ceramic material, utilizing the high-temperature resistance and strong resistance to harsh environments of ceramics to improve the transmitter's explosion-proof performance. One end of the thermal mass flow chip 2 integrates a thermal mass flow sensor, which includes a heater 13 and a temperature sensor 14. The other end of the thermal mass flow chip 2 has three pins, namely a heater pin 15, a temperature sensor pin 16, and a ground pin 17. The pin wires of the thermal mass flow chip 2 are encapsulated with epoxy resin with an encapsulation length ≥20.0mm to further enhance the sealing and explosion-proof effect.

[0019] The middle structure includes a PCB board holder 6, a PCB board 7, and an outer casing 8. The outer casing 8 is threadedly sealed to the lower structure via an outer casing connector cover 4 and a sealing ring 5, forming a closed explosion-proof cavity. The threaded engagement surface must ensure a engagement of 6 turns (≥5 turns) and an engagement length of 10mm (≥8mm). The PCB board 7 is fixed inside the explosion-proof cavity via the PCB board holder 6. The explosion-proof cavity effectively isolates the external explosive environment, protecting the safe operation of the PCB board 7. The PCB board 7 integrates an operational amplifier circuit and a signal conversion circuit (including a BC635 chip and resistors R1-R6). The input terminal of the PCB board 7 is electrically connected to the pins of the thermal mass flow chip 2, and the output terminal is electrically connected to an external positive pressure controller, used to process the signals collected by the thermal mass flow chip 2 and transmit them to the positive pressure controller 18.

[0020] Upper structure: Includes cable 10 and explosion-proof stuffing box 9. The upper end of the transmitter body is connected to the cable. One end of cable 10 is connected to PCB board 7, and the other end of cable 10 passes through the transmitter body. The cable is fitted with an explosion-proof stuffing box made of nickel-plated brass with a stuffing length ≥20mm. The explosion-proof stuffing box can prevent external explosive gases from entering the transmitter through the cable gaps, and at the same time fix the cable to ensure the safety of signal and power transmission.

[0021] Finally, a nameplate 11 is affixed to the surface of the outer casing 8, indicating the equipment model, explosion-proof rating, parameters, and other information, and a grounding device 12 is installed.

[0022] The flow detection method of the micro-positive pressure explosion-proof flow transmitter of the present invention is based on a thermodynamic mass flow chip, microelectronic circuits, and the constant temperature difference principle to perform real-time calculation and monitoring of the flow rate of gas under minute pressure. The specific steps are as follows: Step 1: Gas introduction. Connect the micro positive pressure explosion-proof flow transmitter 20 to the exhaust port of the positive pressure explosion-proof chamber 22 of the positive pressure equipment 19 through the transmitter base 1. The micro positive pressure gas (50~500Pa) in the positive pressure explosion-proof chamber 22 is introduced through the transmitter base 1 and flows through the thermal mass flow chip 2.

[0023] Step 2: Heat Exchange and Signal Acquisition. The heater 13 of the thermal mass flow meter 2 generates heat when energized, and the temperature sensor 14 measures the temperature of the micro-pressure gas on the surface of the thermal mass flow meter 2 in real time. When the micro-pressure gas flows through the thermal mass flow meter 2 at different flow rates, according to the principle of heat diffusion, different gas flow rates result in different rates of heat loss from the surface of the thermal mass flow meter 2, thus causing a change in the temperature difference ΔT between the heater 13 and the temperature sensor 14. Furthermore, the temperature difference ΔT is linearly related to the gas flow rate.

[0024] Step 3: Signal Processing and Calculation. The operational amplifier circuit within PCB board 7 amplifies the temperature difference signal acquired by the temperature sensor, and the signal conversion circuit performs calculations based on King's Law of thermal effects. The mathematical formula for King's Law is: P / ΔT=K1+K2f (qm) K3, Where P is the heating power of the heater (P=Iheater²Rheater, Iheater is the heating current, Rheater is the heater resistance), ΔT is the temperature difference of the low-pressure gas, qm is the gas mass flow rate, and K1, K2, and K3 are constants related to the physical properties of the low-pressure gas. As the gas flow rate increases, qm increases accordingly. The control system automatically increases the heating current Iheater to compensate for the heat carried away by the gas. The change in heating current Iheater directly reflects the change in gas flow rate.

[0025] Step 4: Signal Output and Application. The signal conversion circuit linearizes the calculated flow signal and outputs a 4-20mA standard current signal corresponding to the instantaneous flow rate. This signal can be used to display the instantaneous flow rate in real time and is also transmitted to the positive pressure controller 18. The positive pressure controller 18 determines whether the hazardous gas in the positive pressure explosion-proof chamber 22 has been completely discharged and whether the components of the positive pressure explosion-proof chamber 22 can start working based on the flow signal. If an abnormal flow is detected (such as a flow rate of 0 or below a set threshold, indicating insufficient gas replacement; a sudden increase in flow, indicating possible leakage), the positive pressure controller 18 automatically triggers an alarm or power-off protection mechanism. The detected gas is discharged from the positive pressure explosion-proof chamber 22 through the flame arrester 21.

[0026] This invention utilizes a thermal mass flow meter, microelectronic circuits, and the principle of constant temperature difference to monitor and calculate the flow rate of gases under minute pressure in real time. Specifically, the thermal mass flow meter generates heat as the gas at the exhaust port flows through it. By applying the principle of thermal diffusion, the temperature difference of the gas at different flow rates is linearly related to the flow rate. Microelectronic technology is then used to convert this relationship into a flow signal output, thus solving the problem in the explosion-proof industry where existing explosion-proof flow transmitters cannot detect gases at minute pressures in exhaust ports.

Claims

1. A micro-positive pressure explosion-proof flow transmitter, characterized in that: It consists of three parts: upper, middle, and lower. The lower part includes a transmitter base, a thermal mass flow chip, and a housing connector cover. The transmitter base is a three-way base. The lower end of the thermal mass flow chip body is connected to the transmitter base. The thermal mass flow chip body is sealed with epoxy resin filler and is integrally cured on the housing connector cover with an embedded sealing ring. The part of the thermal mass flow chip exposed on the housing connector cover is sealed with ceramic material. One end of the thermal mass flow chip is a thermal mass flow sensor containing a heater and a temperature sensor, and the other end is provided with a heater pin, a temperature sensor pin, and a ground pin. The middle part includes an outer shell and a PCB board. The outer shell is connected to the lower threaded part through an outer shell connector cover and a sealing ring to form an explosion-proof cavity that encloses the PCB board. The PCB board is fixed in the explosion-proof cavity by a PCB board holder. The PCB board integrates an operational amplifier circuit and a signal conversion circuit. The PCB board input is electrically connected to the pins of the thermal mass flow chip, and the PCB board output is electrically connected to an external positive pressure controller. The upper part is a cable, one end of which is connected to the PCB board, and the other end of which passes through the transmitter. The cable is surrounded by an explosion-proof stuffing box.

2. The micro-positive pressure explosion-proof flow transmitter according to claim 1, characterized in that: The lead wires of the thermal mass flow meter chip are encapsulated with epoxy resin, with an encapsulation length ≥20.0mm.

3. The micro-positive pressure explosion-proof flow transmitter according to claim 1, characterized in that: The number of threaded engagements between the outer shell cylinder and the outer shell connector cover is ≥5, and the engagement length is ≥8mm.

4. The micro-positive pressure explosion-proof flow transmitter according to claim 1, characterized in that: The explosion-proof stuffing box is made of nickel-plated brass and is fitted onto the outside of the cable. The length of the stuffing inside the explosion-proof stuffing box is ≥20mm.

5. A flow detection method for a micro-positive pressure explosion-proof flow transmitter, characterized in that... Includes the following steps: Step 1: Connect the transmitter to the exhaust port of the positive pressure explosion-proof chamber through the transmitter base. The slightly positive pressure gas flows through the thermal mass flow chip via the transmitter base. Step 2: The heater of the thermal mass flow chip is powered on to generate heat, and the temperature sensor detects the gas temperature on the surface of the thermal mass flow chip in real time to obtain the temperature difference ΔT when the gas flows through it. Step 3: The operational amplifier circuit on the PCB board amplifies the temperature difference ΔT signal, and the signal conversion circuit calculates the gas mass flow rate qm according to King's Law; P / ΔT=K1+K2f (qm) K3,P=Iheater²Rheater Where P is the heating power, Iheater is the heating current, Rheater is the heater resistance, and K1, K2, and K3 are constants related to the physical properties of the gas. Step 4: The signal conversion circuit converts qm into a 4-20mA current signal and outputs it to the display device and the positive pressure controller; the positive pressure controller judges the gas replacement status based on the signal, and triggers an alarm or power off when abnormal.

6. The flow detection method for the micro-positive pressure explosion-proof flow transmitter according to claim 5, characterized in that: In step 3, when the gas flow rate increases, qm increases, and the control system automatically increases Iheater to compensate for heat loss. The change in Iheater reflects the change in qm.

7. The flow detection method for the micro-positive pressure explosion-proof flow transmitter according to claim 5, characterized in that: In step 4, the positive pressure controller's judgment criteria are as follows: when the current signal is 4mA, the flow rate is judged to be 0, indicating that the gas has not been replaced; when the current signal is in the range of 4-20mA and is stable, the replacement is judged to be normal; a sudden increase in the current signal indicates possible leakage.

Images