CN106324047B - Device and method for evaluating service life of catalytic combustion sensor - Google Patents
Device and method for evaluating service life of catalytic combustion sensor Download PDFInfo
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- CN106324047B CN106324047B CN201510388821.1A CN201510388821A CN106324047B CN 106324047 B CN106324047 B CN 106324047B CN 201510388821 A CN201510388821 A CN 201510388821A CN 106324047 B CN106324047 B CN 106324047B
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Abstract
The invention discloses a device and a method for evaluating the service life of a catalytic combustion sensor, wherein the device comprises a gas concentration control unit, an accelerated aging test unit, a sensor signal processing unit and a service life evaluation unit; the gas concentration control unit is connected with the accelerated aging test unit, the sensor signal processing unit is installed in the accelerated aging test unit and connected with the service life evaluation unit, and the service life evaluation unit is located outside the accelerated aging test unit and connected with the accelerated aging test unit. The device and the method for evaluating the service life of the catalytic combustion sensor can accurately evaluate the service life of the catalytic combustion sensor.
Description
Technical Field
The invention relates to a device and a method for evaluating the service life of a catalytic combustion sensor, in particular to the service life evaluation of the catalytic combustion sensor for detecting combustible gas on an industrial site.
Background
Catalytic combustion sensors used in industrial fields mainly detect the concentration of combustible gases. The output signal of the product has a linear relationship with the concentration of the combustible gas to be detected, and the detection range is generally within 0-100% LEL (low explosion limit). Because the catalytic combustion mode is adopted, the catalytic activity of the catalyst is gradually reduced along with the prolonging of the service time in the industrial environment, which is shown in that the output signal is gradually reduced on the product under the condition of the same gas concentration. The ratio of the product output signal to the concentration of the gas to be measured is called the sensitivity, and the sensitivity of the catalytic combustion sensor decreases with the increase of the service time. To ensure the necessary signal-to-noise ratio of the sensor output signal, a minimum sensitivity threshold is typically set (referred to as S2) below which a new sensor may be replaced. The sensor is decreased from the initial sensitivity (called S1) to the service time corresponding to S2, called the sensor service life (called T). The catalytic combustion sensor of any model, strictly speaking, products of the same model and different batches must be reliably evaluated for the service life before being used in an industrial field, so that the sensor can be replaced in time, and the safety of personnel and equipment is ensured. The invention provides a device and a method for evaluating the working life of a catalytic combustion sensor, aiming at the working life of the catalytic combustion sensor.
Disclosure of Invention
The invention aims to provide a device and a method for evaluating the service life of a catalytic combustion sensor, which can accurately evaluate the service life of the catalytic combustion sensor.
The invention discloses a device and a method for evaluating the service life of a catalytic combustion sensor, which adopt the following technical scheme:
the device comprises a gas concentration control unit, an accelerated aging test unit, a sensor signal processing unit and a service life evaluation unit: the gas concentration control unit is connected with the accelerated aging test unit, the sensor signal processing unit is installed in the accelerated aging test unit and connected with the service life evaluation unit, the service life evaluation unit is located outside the accelerated aging test unit and connected with the accelerated aging test unit, and the overall structure schematic diagram is shown in fig. 1.
The gas concentration control unit includes: the device comprises a bottle of 100% concentration combustible gas with a pressure reducing valve, a float flowmeter with adjustable flow, a two-position two-way direct-acting normally-closed electromagnetic valve, a fixed combustible gas detector and a power module.
Fixed combustible gas detector includes: the explosion-proof probe is structurally separated from the detector head and electrically connected with the detector head, the detector head supplies power to the explosion-proof probe, and the explosion-proof probe and the detector head are communicated through a bus. An infrared sensor is arranged in the explosion-proof probe, the measuring range of the infrared sensor is from 0-100% of the concentration of the combustible gas, the measuring accuracy is higher than that of the catalytic combustion sensor by one order of magnitude, the stability of output signals in air and the combustible gas is at least 10 times better than that of the catalytic combustion sensor, and preferably, British Dyname infrared combustible gas Premier series infrared sensors are used. The explosion-proof probe is arranged in the accelerated aging test unit, and the detector gauge head is arranged outside the accelerated aging test unit.
The detector head comprises an ARM singlechip and a relay, two Alarm concentrations can be set in the instrument firmware, wherein one Alarm concentration is Low (called Alarm Low, AL) and the other Alarm concentration is High (called Alarm High, AH), when the fixed combustible gas detector detects that the gas concentration reaches the Alarm concentration, the relay can act or the relay can be switched on in an attraction mode or is switched off in a separation mode;
the explosion-proof probe of the fixed combustible gas detector comprises an infrared sensor of the Premier series of British Dynament and an analog signal conditioning PCB (printed circuit board), wherein the PCB comprises a Mixed signal processor MSP430(Mixed Signal processor), an A/D (analog/digital) conversion channel converts a voltage signal which is generated by the infrared sensor and represents gas concentration into a digital signal which is linearly proportional to the gas concentration, and the digital signal is concentrated on an ARM single chip microcomputer of a detector head through a bus.
The power module inputs 220V 50Hz alternating current and outputs 24V 1A direct current to respectively supply power to the fixed combustible gas detector and the electromagnetic valve. The flow of the float flowmeter with adjustable flow can be set to 50 ml/min when the volume of the box body is 24 liters.
The schematic structure of the gas concentration control unit is shown in fig. 2: the circuit is a loop formed by a power supply module, a relay and an electromagnetic valve, when the ARM single chip microcomputer controls the relay to be attracted, the relay is conducted, the whole loop is conducted, the power supply module powers on the electromagnetic valve, and an air path switch controlled by the electromagnetic valve is conducted. The gas path is combustible gas in the gas cylinder, is limited by the float flowmeter, passes through the electromagnetic valve, and enters the accelerated aging test unit.
The accelerated aging test unit includes: an airtight organic glass test box, two fans, a hygrothermograph, a digital display manometer, a pressure is lost circulation mouthful, an aviation plug, a gas concentration control unit air inlet, a life-span evaluation unit air inlet.
The organic glass test box of ageing testing unit accelerates, organic glass wall thickness more than 15 millimeters adopts the cuboid structure, and the upper cover plate can be dismantled. The upper cover plate and the box body are sealed by a polytetrafluoroethylene sealing gasket, the screw holes are uniformly distributed on the organic glass wall, and the screw holes are compressed and sealed by screws penetrating through the upper cover plate. The volume of the box body is determined by the number of sensors to be tested, 8 sensors are preferably tested simultaneously, and the internal dimension of the box body is 400 multiplied by 300 multiplied by 200 mm. The schematic plan structure of the accelerated aging test box is shown in FIG. 3.
Two fans in the accelerated aging test box adopt an intrinsic safety explosion-proof type, are oppositely arranged on the side wall of the box body, are parallel in working direction, are staggered by a distance as much as possible, are perpendicular to air inlets of the gas concentration control unit and the service life evaluation unit, and quickly mix combustible gas and air.
The hygrothermograph in the accelerated aging test box adopts an intrinsically safe explosion-proof type, has small volume and size, is powered by a battery, and has a measurement temperature range of-30-100 ℃ and a measurement humidity range of 0-100% RH.
A digital display pressure gauge in the accelerated aging test box is of an intrinsically safe explosion-proof type, small in size and powered by a battery, and the pressure measuring range is 0-0.05 MPa.
A spring type pressure relief valve is arranged at a pressure air leakage opening in the accelerated aging test box, the pressure relief pressure is preferably 0.1MPa, and the pressure relief can be automatically carried out to ensure safety.
The aviation plug in the accelerated weathering test box supplies power to all components in the box and provides electrical connections to the components that need to communicate with external data. The aviation plug ensures the airtightness and explosion suppression of the electric connection joint, the number of the cores is determined by the number of the sensors to be detected, and a 24-core straight plug and a socket four-hole flange are preferably adopted for installation. Two air inlets in the accelerated aging test box are preferably ferrule type straight-through plate pipe joints made of stainless steel 316, and the air path is a stainless steel pipe or a Teflon hard pipe with the diameter of 4 mm.
The schematic circuit diagram of the sensor signal processing unit is shown in fig. 4, which includes: the sensor analog signal extraction circuit board comprises a sensor analog signal extraction circuit board and a sensor analog signal processing circuit. Sensor analog signal draws circuit board, can install 8 catalytic combustion sensors simultaneously, and sensor analog signal draws circuit board has three parts: (1) the 8 sensors are uniformly distributed around the sensor analog signal extraction circuit board in a circular shape, the center of the sensor analog signal extraction circuit board is provided with a sensor signal processing circuit, and a power supply chip in the circuit provides fixed working voltage for each sensor; (2) two resistors of the same value form one arm of the wheatstone bridge, and the catalytic (black) and reference (white) elements of the sensor form the other arm. The black and white elements of the 8 sensors are respectively a bridge arm, share a resistance bridge arm, and form 8 Wheatstone bridges. The current passes through the white element and then passes through the black element to be connected to the ground; (3) in the Wheatstone bridge, the midpoint voltage of the black and white element bridge arm is recorded as VC, the midpoint voltage of the resistance bridge arm is recorded as VR, and the output signal of the sensor is calculated according to VC-VR;
the sensor signal processing circuit comprises two parts: (1) a power supply part of a power supply chip TPS76333, which converts external power supply into working voltage of the sensor and simultaneously supplies power to an operational amplifier of the signal amplification part; (2) and the operational amplifier TLV2461 differentially amplifies the Wheatstone bridge input signal, and the amplified analog signal is transmitted to the service life evaluation unit.
The life evaluation unit includes: the system comprises two bottles of standard gas with a pressure reducing valve, one bottle of high-purity air, one bottle of combustible gas with the concentration of 50% LEL, a manual T-shaped three-way ball valve, a flow-adjustable float flowmeter, a desktop computer with an I/O expansion slot, a PCI interface data acquisition card and a set of data acquisition/storage/display software. The manual T-shaped three-way ball valve in the service life evaluation unit is made of 316 stainless steel, and can realize switching between high-purity air and 50% LEL combustible gas within 1 second. The flow rate of the float flowmeter in the life evaluation unit is adjustable, and the flow rate of the float flowmeter can be set to be 5 liters/minute when the tank volume is 24 liters.
The data acquisition card in the service life evaluation unit is inserted into an I/O expansion slot of a PC mainboard and is accessed in a PCI bus mode to acquire the voltage analog signal input by the sensor signal processing unit. Preferably, the number of channels of the data acquisition card is 16 single ends/8 differential channels, the sampling frequency is 1M, the resolution is 16 bits, the precision is 0.05% of a full range, and the range is 0-5V. The data acquisition/storage/display software in the life evaluation unit is preferably capable of setting data acquisition conditions, when to start and end sampling/sampling frequency/recording time/channel number, etc., capable of realizing data recording of the voltage analog input signal for more than 12 hours, and the data export function supports a plurality of file formats, such as: microsoft Excel, NI LabVIEW and MathWorks MATLAB etc. A schematic diagram of the life evaluation unit is shown in fig. 5.
The working life evaluation method of the whole catalytic combustion sensor comprises the following primary reference operation steps:
1. the whole system device is installed in a strong ventilation environment, such as a fume hood, and the temperature and the humidity of the environment are constant between 20-25 ℃ and 40-60% RH;
2. installing a catalytic combustion sensor to be subjected to life evaluation on a sensor analog signal extraction circuit board;
3. powering on all units of the whole system;
4. calibrating an infrared sensor of a gas concentration control unit;
5. preheating the catalytic combustion sensor for 10 minutes, and then covering an upper cover of the accelerated aging test box without screw pressing;
6. opening a high-purity air cylinder pressure reducing valve of a service life evaluation unit, manually switching a three-way valve to high-purity air, introducing the high-purity air into an accelerated aging test box, adjusting the flow rate by a float flowmeter to be 5 liters/minute, observing a digital display pressure gauge in the accelerated aging test box, and ensuring that the air pressure in a box body is within the normal working pressure range of a catalytic combustion sensor;
7. observing the data measured by an infrared sensor of the gas concentration control unit to ensure that the concentration of the combustible gas in the box body is zero;
8. starting data acquisition/storage/display software in the service life evaluation unit, and starting to record data after the catalytic combustion sensor outputs stable signals in the air;
9. opening a 50% LEL combustible gas cylinder pressure reducing valve of a service life evaluation unit, manually switching a three-way valve to 50% LEL combustible gas after recording for 1 minute by software, and continuously recording/storing a sensor output signal by the software until the signal is stably recorded for times of infrared sensor concentration reading;
10. ending the software in the life evaluation unit;
11. manually switching the three-way valve to high-purity air, introducing the high-purity air into the accelerated aging test box, enabling the flow rate to be 5 liters/minute, observing the measurement data of an infrared sensor of the gas concentration control unit, and ensuring that the concentration of combustible gas in the box body is recovered to zero;
12. closing the pressure reducing valves of the two gas cylinders of the service life evaluation unit, and then closing the float flowmeter of the service life evaluation unit;
13. compressing the upper cover of the accelerated aging test box by using screws;
14. opening a 100% concentration combustible gas cylinder pressure reducing valve of the gas concentration control unit;
15. turning on a float flowmeter of the gas concentration control unit, and adjusting the gas inflow rate to 50 ml/min when the relay is switched on and the solenoid valve action gas circuit is switched on;
when the current sensitivity of the catalytic combustion sensor needs to be measured, the operation steps are as follows:
1. closing a 100% concentration combustible gas cylinder pressure reducing valve of the gas concentration control unit;
2. turning off the float flowmeter of the gas concentration control unit;
3. loosening screws of the upper cover of the service life evaluation test box;
operating the 6 th to 15 th steps in the primary reference operation step;
the principle of the gas concentration control unit for controlling the concentration of the combustible gas in the accelerated aging test box is as follows:
the service life of the sensor is estimated, accelerated aging test time is designed, the accelerated aging concentration coefficient is determined by dividing the former by the latter α, and the concentration of the combustible gas in the accelerated aging test is determined according to the actual industrial environment, the common concentration C1 of the combustible gas (the average value of alarm concentration recorded by a detector) and the corresponding relation between α and the accelerated aging test concentration (determined by the test and detailed later).
In principle, the concentration of combustible gas in the accelerated aging test box does not need to exceed 70 percent LEL, and in addition to ensuring the test safety, the concentration overload under special conditions needs to be prevented from damaging the sensor. The accelerated aging concentration of 50% LEL is described below as an example.
In the combustible gas detector, a Low concentration Alarm point (called Alarm Low, AL) is set to 49% LEL, and a High concentration Alarm point (called Alarm High, AH) is set to 50% LEL. The working conditions of the detector relay are as follows: less than 49% LEL is on and more than 50% LEL is off.
When the concentration of the combustible gas in the service life evaluation test box is lower than 49% LEL, the relay is switched on, the electromagnetic valve is electrified, the gas circuit is conducted, the combustible gas with the concentration of 100% is introduced into the test box at a small flow of 50 ml/min, and the combustible gas is quickly and uniformly mixed by the fan. When the concentration of the combustible gas in the test box reaches 50% LEL, the relay is disconnected, the circuit is broken, the electromagnetic valve is powered off, and the gas circuit is cut off. At the moment, the concentration of the combustible gas in the test box still rises slightly due to the gas path hysteresis effect, and the highest concentration value can be controlled within 51 percent LEL by adjusting the flow of the flowmeter. In the whole concentration control process, the concentration of the combustible gas is in the range of 49-51% LEL and is changed in an oscillating mode in a sine wave mode.
There must be a range between C1 and C2, otherwise the relay is frequently operated and the concentration cannot be effectively controlled. According to the national standard GB15322.1 combustible gas detector 1 st part industry and commercial use combustible gas detector, the measuring range is in the gas detector of 3 ~ 100% LEL, and the range indication deviation is at 5% LEL, and the fluctuation range of combustible gas concentration 1% LEL in this life evaluation system is acceptable.
Compared with the prior art, the invention has the following beneficial effects:
the method for calculating the residual life of the catalytic combustion sensor based on the system comprises the following steps:
1. the catalytic combustion sensor sensitivity calculation method comprises the following steps:
output signal in air-V1
Output signal-V2 in combustible gas
Concentration of combustible gas-C
Sensor sensitivity-S
S＝(V2-V1)/C
2. The method for calculating the service life of the catalytic combustion sensor comprises the following steps:
2.1 confirmation of accelerated aging gas concentration coefficient α
Initial sensitivity of sensor-S1
Minimum sensitivity threshold of sensor-S2
In actual industrial environment, the common concentration of combustible gas is-C1
High concentration accelerated aging combustible gas concentration-C2
Experiment one: under the concentration of C1, the sensors of the same type and the same batch are continuously aged for 24 hours in the system, the time required for reducing the sensitivity from S1 to S2 is recorded as T1;
experiment two: under the concentration of C2, the sensors of the same type and the same batch are continuously aged for 24 hours in the system, the time required for reducing the sensitivity from S1 to S2 is recorded as T2;
the accelerated aging gas concentration coefficient α is T1/T2;
2.2 confirmation of accelerated aging Interval coefficient β
In actual industrial environment, the average frequency of combustible gas (alarm frequency of detector) -N appears within 24 hours
In actual industrial environment, the average time of occurrence of combustible gas (alarm duration of detector) -T3 in 24 hours
Then: in actual industrial environment, the time of exposing the detector to combustible gas within 24 hours-T4 ═ NxT 3
Experiment three: under the concentration of C2, the sensors of the same model and the same batch age for T4 time (the concentration of C2 is controlled by a gas concentration control unit, and the clean air atmosphere is ensured by a residual life evaluation unit) within 24 hours in the system, and the time required for reducing the sensitivity from S1 to S2 is recorded as T5;
the accelerated aging interval coefficient β is T5/T2;
2.3 validation of Life time T
T＝T2×α×β；
The actual industrial environment is often complex and harsh, and the gas type is more than one combustible gas and various toxic/interference gases are also available. If the type and concentration of the main poisonous/interference gas can be confirmed, the 100% concentration fuel gas of the gas concentration control unit and the 50% LEL concentration fuel gas of the service life evaluation unit in the system can be proportionally mixed in advance with the poisonous/interference gas, so that the service life evaluation can be more accurately carried out.
Drawings
Fig. 1 is a schematic overall structural diagram of a catalytic combustion sensor service life evaluation device provided by the invention.
Fig. 2 is a schematic structural view of a gas concentration control unit.
FIG. 3 is a schematic diagram of an accelerated weathering test unit.
Fig. 4 is a schematic circuit diagram of a sensor signal processing unit.
Fig. 5 is a schematic structural diagram of the life evaluation unit.
In the figure:
1 gas concentration control unit 2 accelerated aging test unit 3 sensor signal processing unit
4 life-span evaluation unit 11 detection appearance head 111 ARM singlechip
112 relay 12 alternating current power supply 121 circuit
13 flame-proof probe 131 mixed signal processor 132 infrared sensor
14 air connector 15 airtight connector 16 electromagnetic valve
17 power supply module 18 float flowmeter 19 combustible gas
191 gas path 21 gas concentration control unit gas inlet 22 aviation plug
23 pressure air release port 24 fan 25 screw
26 digital display pressure gauge 27 thermo-hygrometer 28 life assessment unit air inlet
31 sensor signal processing circuit 32 sensor 41 accelerated aging test box
42 high-purity air 43 combustible gas 44 display screen
45 machine box
Detailed Description
The invention is further described below with reference to the figures and examples.
The invention discloses a device and a method for evaluating the service life of a catalytic combustion sensor, which adopt the following technical scheme:
the device comprises a gas concentration control unit 1, an accelerated aging test unit 2, a sensor signal processing unit 3 and a service life evaluation unit 4: the gas concentration control unit 1 is connected with the accelerated aging test unit 2, the sensor signal processing unit 3 is installed in the accelerated aging test unit 2, the sensor signal processing unit 3 is connected with the service life evaluation unit 4, the service life evaluation unit 4 is located outside the accelerated aging test unit 2 and connected with the same, and the overall structural schematic diagram is shown in fig. 1.
The gas concentration control unit 1 includes: the gas detector comprises a bottle of 100% concentration combustible gas 43 with a pressure reducing valve, a float flowmeter 18 with adjustable flow, a two-position two-way direct-acting normally-closed electromagnetic valve 16, a fixed combustible gas detector and a power module 17.
Fixed combustible gas detector includes: the explosion-proof detector comprises a detector meter head 11 and an explosion-proof probe 13, wherein the explosion-proof probe 13 and the detector meter head 11 are separated in structure and are electrically connected, the detector meter head 11 supplies power to the explosion-proof probe 13, and the explosion-proof probe and the detector meter head are communicated through a bus. The infrared sensor 132 is installed in the explosion-proof probe 13, the measurement range of the infrared sensor 132 is from 0-100% of the combustible gas 19, the measurement accuracy is higher than that of the catalytic combustion sensor by one order of magnitude, the stability of output signals in air and combustible gas is at least 10 times better than that of the catalytic combustion sensor, and preferably, British Dynaiment infrared combustible gas Premier series infrared sensors are used. The explosion-proof probe 13 is arranged in the accelerated aging test unit 2, and the detection meter head 11 is arranged outside the accelerated aging test unit 2.
The detector head 11 comprises an ARM singlechip 111 and a relay 112, two Alarm concentrations can be set in the firmware of the detector, wherein one Alarm is Low concentration Alarm (called Alarm Low, AL) and the other Alarm is high concentration Alarm (called Alarm high, AH), when the fixed combustible gas detector detects that the gas concentration reaches the Alarm concentration, the relay 112 acts, or the relay is closed or disconnected;
the explosion-proof probe 13 of the fixed combustible gas detector comprises an infrared sensor of Premier series of British Dynament and an analog signal conditioning PCB (printed Circuit Board), wherein the PCB comprises a Mixed signal processor MSP430(Mixed Signal processor), an A/D (analog to digital) conversion channel converts a voltage signal which is generated by the infrared sensor and represents gas concentration into a digital signal which is linearly proportional to the gas concentration, and the digital signal is concentrated on an ARM singlechip 111 of a detector head 11 through a bus.
The power module 17 inputs 220V 50Hz alternating current and outputs 24V 1A direct current to respectively supply power to the fixed combustible gas detector and the electromagnetic valve 16. The flow rate of the float flowmeter 18 with adjustable flow rate can be set to 50 ml/min when the tank volume is 24 liters and the flow rate of the float flowmeter 18 is set to 50 ml/min.
The structure of the gas concentration control unit 1 is schematically shown in fig. 2: the circuit is a loop formed by the power module 17, the relay 112 and the electromagnetic valve 16, when the ARM single chip microcomputer 111 controls the relay 16 to be sucked, the relay 16 is conducted, the whole loop is conducted, the power module 117 powers on the electromagnetic valve 16, and the air path switch controlled by the electromagnetic valve 16 is conducted. The gas path is combustible gas 19 in a gas cylinder, is limited by a float flowmeter 18, passes through an electromagnetic valve 16 and enters the accelerated aging test unit 2.
The accelerated aging test unit 2 includes: the device comprises an airtight organic glass test box, two fans 24, a hygrothermograph, a digital display pressure gauge 26, a pressure air leakage port 23, an aviation plug 22, a gas concentration control unit air inlet 21 and a service life evaluation unit air inlet 28.
The organic glass test box of the accelerated aging test unit 2 has an organic glass wall thickness of more than 15 mm, and adopts a cuboid structure, and an upper cover plate can be detached. The upper cover plate and the box body are sealed by a polytetrafluoroethylene sealing gasket, the screw holes are uniformly distributed on the organic glass wall, and the screw holes are compressed and sealed by screws penetrating through the upper cover plate. The volume of the box body is determined by the number of sensors to be tested, 8 sensors are preferably tested simultaneously, and the internal dimension of the box body is 400 multiplied by 300 multiplied by 200 mm. The schematic plan structure of the accelerated aging test box is shown in FIG. 3.
The two fans 24 in the accelerated aging test box 41 are of intrinsic safety explosion-proof type, are oppositely arranged on the side wall of the box body, are parallel in working direction, are staggered in distance as far as possible, are perpendicular to the gas concentration control unit 1 and the service life evaluation unit gas inlet 28, and quickly mix combustible gas and air.
The hygrothermograph in the accelerated aging test box 41 is of an intrinsically safe explosion-proof type, has small volume and size, is powered by a battery, and has a measurement temperature range of-30 ℃ to 100 ℃ and a measurement humidity range of 0-100% RH.
The digital display pressure gauge 26 in the accelerated aging test box 41 adopts an intrinsically safe explosion-proof type, has small volume and size, is powered by a battery, and has a pressure measurement range of 0-0.05 MPa.
A spring type pressure relief valve is arranged at a pressure air release port in the accelerated aging test box 41, the pressure relief pressure is preferably 0.1MPa, and the pressure relief can be automatically carried out to ensure safety.
The aviation plug 22 in the accelerated weathering test chamber 41 provides power to all components in the chamber and provides electrical connections to components that need to communicate external data. The aviation plug 22 ensures the airtight and explosion-proof of the electric connection joint, the number of cores is determined by the number of sensors to be tested, and a 24-core straight plug and a socket four-hole flange are preferably adopted for installation. Two air inlets in the accelerated aging test box 41 are preferably ferrule type straight-through plate pipe joints made of stainless steel 316, and the air path is made of stainless steel pipes with the diameter of 4 mm or Teflon hard pipes.
The schematic circuit diagram of the sensor signal processing unit 3 is shown in fig. 4, which includes: a sensor analog signal extraction circuit board, and a sensor analog signal processing circuit 31. Sensor analog signal draws circuit board, can install 8 catalytic combustion sensors simultaneously, and sensor analog signal draws circuit board has three parts: (1) the 8 sensors are uniformly distributed around the sensor analog signal extraction circuit board in a circular shape, the center of the sensor analog signal extraction circuit board is provided with a sensor signal processing circuit 31, and a power supply chip in the circuit provides fixed working voltage for each sensor 32; (2) two resistors of the same value form one leg of the wheatstone bridge and the catalytic (black) and reference (white) elements of sensor 32 form the other leg. The black and white elements of the 8 sensors 32 are each one arm, and share a resistive arm, thereby forming 8 wheatstone bridges. The sensor 32 is a black-white element bridge arm, and the current firstly passes through a white element and then passes through a black element to be connected to the ground; (3) in the Wheatstone bridge, the midpoint voltage of the black and white element bridge arm is recorded as VC, the midpoint voltage of the resistance bridge arm is recorded as VR, and the output signal of the sensor is calculated according to VC-VR;
the sensor signal processing circuit 31 includes two parts: (1) a power supply part of a power supply chip TPS76333, which converts external power supply into working voltage of the sensor and simultaneously supplies power to an operational amplifier of the signal amplification part; (2) and the operational amplifier TLV2461 differentially amplifies the Wheatstone bridge input signal, and the amplified analog signal is transmitted to the service life evaluation unit.
The life evaluation unit 4 includes: two bottles of standard gas with pressure reducing valves, one bottle of high-purity air 42, one bottle of combustible gas 43 with the concentration of 50% LEL, a manual T-shaped three-way ball valve, a float flowmeter 18 with adjustable flow, a desktop computer with an I/O expansion slot, a data acquisition card with a PCI interface and a set of data acquisition/storage/display software. The manual T-shaped three-way ball valve in the service life evaluation unit 4 is made of 316 stainless steel, and can realize switching between high-purity air and 50% LEL combustible gas within 1 second. The flow rate of the float flowmeter 18 in the life evaluating unit 4 is adjustable, and the flow rate of the float flowmeter 18 can be set to 5 liters/minute when the tank volume is 24 liters.
The data acquisition card in the life evaluation unit 4 is inserted into an I/O expansion slot of a PC mainboard, is accessed in a PCI bus mode, and acquires voltage analog signals input by the sensor signal processing unit. Preferably, the number of channels of the data acquisition card is 16 single ends/8 differential channels, the sampling frequency is 1M, the resolution is 16 bits, the precision is 0.05% of a full range, and the range is 0-5V. The data acquisition/storage/display software in the life evaluation unit 4 is preferably capable of setting data acquisition conditions, when to start and end sampling/sampling frequency/recording time/number of channels, etc., capable of realizing data recording of the voltage analog input signal for more than 12 hours, and the data export function supports a plurality of file formats, such as: microsoft Excel, NI LabVIEW and MathWorks MATLAB etc. A schematic diagram of the life evaluation unit is shown in fig. 5.
The working life evaluation method of the whole catalytic combustion sensor comprises the following primary reference operation steps:
1. the whole system device is installed in a strong ventilation environment, such as a fume hood, and the temperature and the humidity of the environment are constant between 20-25 ℃ and 40-60% RH;
2. installing a catalytic combustion sensor to be subjected to life evaluation on a sensor analog signal extraction circuit board;
3. powering on all units of the whole system;
4. calibrating an infrared sensor of a gas concentration control unit;
5. preheating the catalytic combustion sensor for 10 minutes, and then covering an upper cover of the accelerated aging test box without screw pressing;
6. opening a high-purity air cylinder pressure reducing valve of the service life evaluation unit 4, manually switching a three-way valve to high-purity air 42, introducing the high-purity air 42 into the accelerated aging test box 41, regulating the flow rate by a float flowmeter 18 for 5 liters/minute, observing a digital pressure gauge 26 in the accelerated aging test box 41, and ensuring that the air pressure in the box body is within the normal working pressure range of the catalytic combustion sensor;
7. observing the data measured by the infrared sensor 132 of the gas concentration control unit 1 to ensure that the concentration of the combustible gas in the box body is zero;
8. starting data acquisition/storage/display software in the service life evaluation unit 4, and starting to record data after the catalytic combustion sensor outputs stable signals in the air;
9. opening a 50% LEL combustible gas cylinder pressure reducing valve of the service life evaluation unit 4, after recording for 1 minute with software, manually switching a three-way valve to 50% LEL combustible gas, and continuously recording/storing a sensor output signal by the software until the signal is stably recorded for times of infrared sensor concentration reading;
10. software in the end life evaluation unit 4;
11. manually switching the three-way valve to high-purity air, introducing the high-purity air 42 into the accelerated aging test box 41 at a flow rate of 5 liters/minute, observing the measurement data of the infrared sensor of the gas concentration control unit 1, and ensuring that the concentration of the combustible gas 43 in the box body is recovered to zero;
12. closing the pressure reducing valves of the two gas cylinders of the life evaluation unit 4, and then closing the float flow meter of the life evaluation unit 4;
13. compressing the upper cover of the accelerated aging test box 41 by using screws;
14. opening a 100% concentration combustible gas 43 cylinder pressure reducing valve of the gas concentration control unit;
15. turning on the float flowmeter 18 of the gas concentration control unit 1, and adjusting the gas inlet flow by 50 ml/min when the relay is switched on and the electromagnetic valve action gas circuit is switched on;
when the current sensitivity of the catalytic combustion sensor needs to be measured, the operation steps are as follows:
1. closing a 100% concentration combustible gas cylinder pressure reducing valve of the gas concentration control unit 1;
2. turning off the float flow meter 18 of the gas concentration control unit 1;
3. loosening screws of the upper cover of the service life evaluation test box;
operating the 6 th to 15 th steps in the primary reference operation step;
the principle of the gas concentration control unit 1 controlling the concentration of combustible gas in the accelerated aging test box 41 is as follows:
the service life of the sensor is estimated, accelerated aging test time is designed, the accelerated aging concentration coefficient is determined by dividing the former by the latter α, and the concentration of the combustible gas in the accelerated aging test is determined according to the actual industrial environment, the common concentration C1 of the combustible gas (the average value of alarm concentration recorded by a detector) and the corresponding relation between α and the accelerated aging test concentration (determined by the test and detailed later).
In principle, the concentration of the combustible gas 43 in the accelerated aging test box 41 does not exceed 70% LEL, and in addition to ensuring the test safety, the sensor is prevented from being damaged by concentration overload under special conditions. The accelerated aging concentration of 50% LEL is described below as an example.
In the combustible gas detector, a Low concentration Alarm point (called Alarm Low, AL) is set to 49% LEL, and a High concentration Alarm point (called Alarm High, AH) is set to 50% LEL. The working conditions of the detector relay are as follows: less than 49% LEL is on and more than 50% LEL is off.
When the concentration of the combustible gas in the life evaluation test box is lower than 49% LEL, the relay is switched on, the electromagnetic valve is electrified, the gas circuit is conducted, the combustible gas with the concentration of 100% is introduced into the test box at a small flow of 50 ml/min, and the combustible gas is rapidly and uniformly mixed by the fan 24. When the concentration of the combustible gas in the test box reaches 50% LEL, the relay is disconnected, the circuit is broken, the electromagnetic valve is powered off, and the gas circuit is cut off. At the moment, the concentration of the combustible gas in the test box still rises slightly due to the gas path hysteresis effect, and the highest concentration value can be controlled within 51 percent LEL by adjusting the flow of the flowmeter. In the whole concentration control process, the concentration of the combustible gas is in the range of 49-51% LEL and is changed in an oscillating mode in a sine wave mode.
There must be a range between C1 and C2, otherwise the relay is frequently operated and the concentration cannot be effectively controlled. According to the national standard GB15322.1 combustible gas detector 1 st part industry and commercial use combustible gas detector, the measuring range is in the gas detector of 3 ~ 100% LEL, and the range indication deviation is at 5% LEL, and the fluctuation range of combustible gas concentration 1% LEL in this life evaluation system is acceptable.
Claims (10)
1. A catalytic combustion sensor operating life evaluation device characterized by: the device comprises a gas concentration control unit, an accelerated aging test unit, a sensor signal processing unit and a service life evaluation unit:
the gas concentration control unit comprises a bottle of combustible gas, the combustible gas is connected with a float flowmeter through a gas circuit, the float flowmeter is connected with an electromagnetic valve through a gas circuit, the electromagnetic valve is connected with an airtight joint through a gas circuit, the gas concentration control unit also comprises a fixed combustible gas detector and a power supply module, the fixed combustible gas detector comprises a detector gauge head and an explosion-proof probe, the detector gauge head is connected with the explosion-proof probe through a circuit, an aviation joint is arranged between the detector gauge head and the explosion-proof probe, the power supply module is powered by a 220V alternating current power supply, the power supply module is connected with the detector gauge head and the electromagnetic valve through a circuit, the explosion-proof probe comprises an infrared sensor and an analog signal conditioning PCB, the PCB comprises a mixed signal processor, and the detector gauge head comprises an ARM single chip microcomputer, a relay;
the accelerated aging test unit comprises an airtight organic glass test box, a fan, a hygrothermograph, a digital display pressure gauge, a pressure air leakage port, an aviation plug, a gas concentration control unit gas inlet and a service life evaluation unit gas inlet;
the sensor signal processing unit comprises a sensor analog signal extraction circuit board and a sensor signal processing circuit, sensors are distributed on the sensor analog signal extraction circuit board, two resistors with the same resistance form one bridge arm of a Wheatstone bridge, a catalytic black element and a reference white element of each sensor form the other bridge arm, a black and white element of each sensor is a bridge arm, the bridge arms share the resistors to form the Wheatstone bridge, the bridge arms of the black and white elements of each sensor are connected to the ground after the current passes through the white element and the black element, and the sensor signal processing circuit comprises two parts, namely a power supply part and a conditioning circuit part of a power chip TPS 76333;
the service life evaluation unit comprises two bottles of standard gas, one bottle of high-purity air and one bottle of combustible gas, a manual T-shaped three-way ball valve, a data acquisition card comprising a float flowmeter, a desktop computer and a PCI interface, and data acquisition, storage and display software.
2. The catalytic combustion sensor operating life evaluation device of claim 1, wherein: the gas concentration control unit is connected with the accelerated aging test unit, the sensor signal processing unit is installed in the accelerated aging test unit and connected with the service life evaluation unit, and the service life evaluation unit is located outside the accelerated aging test unit and connected with the accelerated aging test unit.
3. A catalytic combustion sensor operating life evaluating apparatus as set forth in claim 2, wherein: the circuit of the gas concentration control unit is a loop formed by a power supply module, a relay and an electromagnetic valve, when the ARM single chip microcomputer controls the relay to suck, the relay is switched on, the whole loop is switched on, the power supply module powers on the electromagnetic valve, a gas circuit switch controlled by the electromagnetic valve is switched on, the gas circuit is combustible gas in the gas cylinder, the combustible gas is limited by a float flowmeter, passes through the electromagnetic valve and enters the accelerated aging test unit.
4. A catalytic combustion sensor operating life evaluating apparatus as set forth in claim 3, wherein: the combustible gas of the gas concentration control unit is provided with a pressure reducing valve, the electromagnetic valve is of a two-position two-way direct-acting normally-closed type, and the flow meter of the floater is of a flow adjustable type.
5. The catalytic combustion sensor operation life evaluation device according to claim 4, wherein: the organic glass test box in the aging testing unit accelerates, organic glass wall thickness more than 15 millimeters adopts the cuboid structure, and the upper cover plate can be dismantled, and the upper cover plate adopts polytetrafluoroethylene seal gasket sealed with the box, and screw hole evenly distributed is sealed at the organic glass wall by the screw compress tightly that runs through the upper cover plate, and preferred 8 sensors of simultaneous testing, box internal dimension 400 x 300 x 200 millimeters.
6. The catalytic combustion sensor operation life evaluation device according to claim 5, wherein: the two fans are arranged in the accelerated aging test box, are of intrinsic safety explosion-proof type, are oppositely arranged on the side wall of the box body, are parallel to the working direction and are perpendicular to the air inlets of the gas concentration control unit and the service life evaluation unit; the hygrothermograph in the accelerated aging test box adopts an intrinsic safety explosion-proof type; a digital display pressure gauge in the accelerated aging test box adopts an intrinsically safe explosion-proof type; a spring type pressure relief valve is arranged at a pressure relief opening in the accelerated aging test box, and the pressure relief pressure is preferably 0.1 MPa.
7. The catalytic combustion sensor operating life evaluation device of claim 6, wherein: the aviation plug in the accelerated aging test box is a 24-core straight plug, a socket is mounted with four-hole flanges, two air inlets in the accelerated aging test box are connected with a plate pipe joint through a ferrule, the material of the two air inlets is stainless steel 316, and a gas path adopts a stainless steel pipe or a Teflon hard pipe with the diameter of 4 mm.
8. The catalytic combustion sensor operating life evaluation device of claim 7, wherein: the data acquisition card in the service life evaluation unit is inserted into an I/O expansion slot of a PC mainboard and is accessed in a PCI bus mode to acquire voltage analog signals input by the sensor signal processing unit, the number of channels of the data acquisition card is 16 single-ended channels/8 differential channels, the sampling frequency is 1M, the resolution is 16 bits, the precision is 0.05% of a full range, and the range is 0-5V.
9. An evaluation method using the catalytic combustion sensor operation life evaluation device according to claim 1, characterized in that: the working life evaluation method of the whole catalytic combustion sensor comprises the following primary reference operation steps:
1) the whole system device is installed in a strong ventilation environment, and the temperature and the humidity of the environment are constant between 20-25 ℃ and 40-60% RH;
2) installing a catalytic combustion sensor to be subjected to life evaluation on a sensor analog signal extraction circuit board;
3) powering on all units of the whole system;
4) calibrating an infrared sensor of a gas concentration control unit;
5) preheating the catalytic combustion sensor for 10 minutes, and then covering an upper cover of the accelerated aging test box without screw pressing;
6) opening a high-purity air cylinder pressure reducing valve of a service life evaluation unit, manually switching a three-way valve to high-purity air, introducing the high-purity air into an accelerated aging test box, adjusting the flow rate by a float flowmeter to be 5 liters/minute, observing a digital display pressure gauge in the accelerated aging test box, and ensuring that the air pressure in a box body is within the normal working pressure range of a catalytic combustion sensor;
7) observing the data measured by an infrared sensor of the gas concentration control unit to ensure that the concentration of the combustible gas in the box body is zero;
8) starting data acquisition, storage and display software in the service life evaluation unit, and starting to record data after the catalytic combustion sensor outputs stable signals in the air;
9) opening a 50% LEL combustible gas cylinder pressure reducing valve of a service life evaluation unit, manually switching a three-way valve to 50% LEL combustible gas after recording for 1 minute by software, and continuously recording and storing a sensor output signal by the software until the signal is stably recorded and the infrared sensor concentration reading times;
10) ending the software in the life evaluation unit;
11) manually switching the three-way valve to high-purity air, introducing the high-purity air into the accelerated aging test box, enabling the flow rate to be 5 liters/minute, observing the measurement data of an infrared sensor of the gas concentration control unit, and ensuring that the concentration of combustible gas in the box body is recovered to zero;
12) closing the pressure reducing valves of the two gas cylinders of the service life evaluation unit, and then closing the float flowmeter of the service life evaluation unit;
13) compressing the upper cover of the accelerated aging test box by using screws;
14) opening a 100% concentration combustible gas cylinder pressure reducing valve of the gas concentration control unit;
15) and (3) turning on a float flowmeter of the gas concentration control unit, and adjusting the gas inflow rate to 50 kiloliters per minute when the relay is switched on and the electromagnetic valve action gas circuit is switched on.
10. The evaluation method using the catalytic combustion sensor operation life evaluation device according to claim 9, wherein:
when the current sensitivity of the catalytic combustion sensor needs to be measured, the operation steps are as follows:
1) closing a 100% concentration combustible gas cylinder pressure reducing valve of the gas concentration control unit;
2) turning off the float flowmeter of the gas concentration control unit;
3) loosening screws of the upper cover of the service life evaluation test box;
4) opening a high-purity air cylinder pressure reducing valve of a service life evaluation unit, manually switching a three-way valve to high-purity air, introducing the high-purity air into an accelerated aging test box, adjusting the flow rate by a float flowmeter to be 5 liters/minute, observing a digital display pressure gauge in the accelerated aging test box, and ensuring that the air pressure in a box body is within the normal working pressure range of a catalytic combustion sensor;
5) observing the data measured by an infrared sensor of the gas concentration control unit to ensure that the concentration of the combustible gas in the box body is zero;
6) starting data acquisition, storage and display software in the service life evaluation unit, and starting to record data after the catalytic combustion sensor outputs stable signals in the air;
7) opening a 50% LEL combustible gas cylinder pressure reducing valve of a service life evaluation unit, manually switching a three-way valve to 50% LEL combustible gas after recording for 1 minute by software, and continuously recording/storing a sensor output signal by the software until the signal is stably recorded for times of infrared sensor concentration reading;
8) ending the software in the life evaluation unit;
9) manually switching the three-way valve to high-purity air, introducing the high-purity air into the accelerated aging test box, enabling the flow rate to be 5 liters/minute, observing the measurement data of an infrared sensor of the gas concentration control unit, and ensuring that the concentration of combustible gas in the box body is recovered to zero;
10) closing the pressure reducing valves of the two gas cylinders of the service life evaluation unit, and then closing the float flowmeter of the service life evaluation unit;
11) compressing the upper cover of the accelerated aging test box by using screws;
12) opening a 100% concentration combustible gas cylinder pressure reducing valve of the gas concentration control unit;
13) and (3) turning on a float flowmeter of the gas concentration control unit, and adjusting the gas inflow rate to 50 kiloliters per minute when the relay is switched on and the electromagnetic valve action gas circuit is switched on.
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