With the rapid development of China's economic construction and the increasing scale of industrial production, the issue of explosion prevention has become more important. Explosion proof electrical products with diverse functions and varieties are widely used in various industries such as petroleum, chemical, and coal. Whether explosion-proof electrical appliances can operate stably and safely in various hazardous explosive environments during use must pass relevant tests according to national explosion-proof standards.
Below, Zhongnuo Testing briefly introduces the spark ignition test method in intrinsic safety explosion-proof certification.
General Provisions
The spark ignition test should be conducted when the circuit is in the most easily ignited state. For simple circuits, the diagramA1~PictureA6Among the various forms corresponding to the reference curve, short-circuit testing is the most unfavorable. For more complex circuits, short-circuit testing may not be the most unfavorable condition due to varying conditions. The most unfavorable condition for a regulated current limiting power supply usually occurs when a resistor is connected in series in the output circuit of the power supply, and the current is adjusted to the maximum value without reducing the voltage.
1. A circuit with both inductance and capacitance
For circuits containing both energy storage capacitors and inductors, the combination circuit of capacitors and inductors should be evaluated and tested. If the total inductance or capacitance evaluated is greater than using the appendixAThe allowable values for the ignition curve or data table are small1 %When the capacitance corresponding to the voltage or the inductance corresponding to the current does not exceed the ignition critical value1%At that time, The maximum allowable capacitance or inductance can be taken as the values allowed by the ignition curve or data table, respectively.
2. Component tolerance
（1）During the experiment, component tolerances should be considered, and changes in the power supply voltage should also be taken into account. The spark test device should be connected to each test point in the tested circuit identified in the technical review, where it is believed that open and short circuits may occur.
（2）The test should be conducted according to the equipment protection level, based on recognized faults and considering the maximum external capacitance of the product design(Co)And the maximum external inductance(Lo)Or the ratio of inductance to resistance(Lo/Ro)Under the circumstances.
（3）The experiment should be conducted on samples that have been tested and found to be qualified according to the reviewed drawings and consistent with the drawings; The final inspection can be carried out according to the actual inspection, and the drawing data can be modified to meet this requirement.
（4）According to the intrinsic safety circuit assessment criteria, if the product circuit is a simple circuit, according toGB 3836.4－2010appendixAThe method and diagram describedA1~PictureA6The provided reference curve or tableA1, A2When the given data can be used to determine its intrinsic safety performance, spark testing may not be required; But there should be evaluation records and a safety factor provided.
（5）When there is no specified applicable range for voltage, it is usually followed by ±1%Value taking;
（6）Test personnel are usually2One person operates, one person records. Test personnel must hold certificates before taking up their posts, and interns are not allowed to operate alone, （7）During the internship period, personnel should receive guidance from formal testers and are not allowed to operate the equipment without authorization.
（8(The experiment strictly followsGB3836.4-2010in10.1Request to proceed; During the experiment, data should be recorded in a formal record form in a timely manner. The record form should be filled out according to regulations, without any blank spaces.
（9）Special attention must be paid to electrical safety and the safety of hazardous gases, and relevant safety regulations must be strictly implemented.
3. Calibration current of experimental gas mixture and spark testing device
（1）The table should be used according to the category specified for the tested equipment1（1.0Double safety factor) or table2（1.5Explosive test mixture with a safety factor of several times.
（2）During the gas distribution process, the operation of explosive gases or high-pressure gases should be strictly carried out in accordance with relevant operating procedures.
（3）Priority Table1 The safety factor of the specified test mixture can be obtained by increasing the voltage or current. If this situation is not applicable, table2 The composition of the explosive test mixture given has the requirements specified in this standard1.5 Double the safety factor.
（4）The purity of the test gas should not be lower than95%.
（5）Calibration should be carried out before the spark ignition test of the same class. Calibration should be carried out according to the calibration circuit on the spark test device. The sensitivity of the test device should be determined based on the number of ignition revolutions caused. If necessary, the calibration circuit parameters should be measured using a voltmeter and ammeter (see table)1 And table2）Confirmation conducted.
4. Safety factor
The 1.5 times safety factor should be obtained by one of the following methods:
① Parameter method
1) For inductance and resistance circuits, increase the current by reducing the resistance value in the test circuit1.5Double the fault current. If it cannot be achieved1.5Doubling the safety factor can further increase the power supply voltage; For devices that use batteries, increasing the number of batteries can increase the voltage.
2) For capacitive circuits, increase the voltage to1.5Double the fault voltage. Alternatively, when a reliable current limiting resistor is used in conjunction with a capacitor,When the time constant is large enough, capacitors can be regarded as batteries, and circuits can be regarded as resistive circuits.
② Gas method
Use Table1 The prescribed explosive test mixture. Using shunt short circuit(Sudden short circuit)The test for protecting circuits should evaluate circuits with shunt short circuit (sharp short circuit) protection separately, including maximum output power, voltage and current, and short circuit status. Circuits with equipment specified protection levels should not cause ignition after stable output voltage. When the explosion-proof type is related to sudden short circuits caused by other circuit faults, the allowable passing energy at the moment of sudden short circuits should not exceed the specified values of the corresponding equipment categories as follows:
–ⅡCClass equipment20μJ
–ⅡBClass equipment80μJ
–ⅡAClass equipment160μJ
–ⅠClass equipment260μJ
It is not suitable to use a spark test device to conduct ignition tests on rapid short-circuit circuits that allow the passage of energy. To evaluate the allowable passage of energy in rapid short-circuit circuits, transient oscilloscopes should be used for measurement.
5. Testing method for rapid short-circuit energy
according tow＝ivtMeasure separatelyiandvCurve, and then use the formulaW=∫_0^T?〖i*VdtCalculate the output energy. The measurement should be taken at any load that may be between the open circuit and short circuit limits, which can be achieved by simulating the load. According to the power supply voltage during open circuitUoValue, and there is a series of connected current limiting devices for the current ofIoAction corresponding to the level,So the circuit should be connected to approximatelyUo-0.5VWhen there is a left or right load, a greater thanIoThe transient current should be calculated to be greater thanIoThe energy of the time period. Other loads with voltages lower than this value should also be considered for testing. The application of the experiment is to measure the expected voltage and current with a digital oscilloscope recording as shown in the figure1 and2 As shown.
For example, if the power supply voltage is15 VAnd there is a series current limiting switch when the current is1 ATime action,So it can be anticipated that,When the circuit is connected to approximately13.5 VWhen the most unfavorable Zener load occurs, a greater than1 ATransient current. Zener loads with voltages below this value should also be considered for testing.
aboutIIBClass equipment, 13.5VWhat is the maximum current allowed by voltage3.76 A(As shown in the tableA.1 )Therefore,The experiment should be conducted when the current exceeds3.76 AMeasure voltage and current during this period. The configuration of the experiment, as well as the expected voltage and current, are recorded using a digital oscilloscope as shown in the figureE.1andE.2As shown. under these circumstances,Transient energy is measured by measuring the current of the Zener diode(Use a clamp ammeter)Calculate based on voltage. At the same time, a series of times corresponding to the current can be measured for each value of the Zener transistor, thereby obtaining a curve graph of voltage multiplied by current and corresponding time. Calculate the area of the curve before the current drops to the non ignition value, which is the transient energy obtained from the experiment.
In other cases,The most severe load may be a variable resistor. under these circumstances,Corresponding to each short circuit with a resistance value less thanUo/IoThe resistance load can draw a set of current time curves, and the transient power transmitted can be calculated by the power generated on the resistance and the corresponding time. This type of load can be a capacitor or an inductor, depending on the specific output parameters.
It should be noted that the voltage and current applications are less than1μs/Measure with a high-speed storage oscilloscope divided into grids. The selection of experimental equipment and the connection of experimental circuits should minimize the impact on the measured values. It is recommended to use clamp current measuring probes and high impedance voltage measuring equipment; It is recommended to use mercury contact tilt switches with bidirectional low contact resistance characteristics, but switches with equivalent characteristics can also be used.
6. Test with spark testing device
7. Sample preparation and processing
（1）The tested product should be fault set and handled according to its protection level. Usually, an open circuit is used to disconnect the circuit.
（2）Voltage or current, component tolerance, loose components.
（3）The voltage of the test circuit should be taken as the highest value, and the components should have an upper or lower limit according to their properties, with the principle that the circuit is in the most unfavorable situation.
（4）The spark test device should be connected to each test point in the tested circuit where open and short circuits are believed to occur,These points were confirmed after technical review and prototype testing.
8. Fault setting
The experiment should be conducted according to the5The protection level of the equipment specified in the chapter refers to the maximum external capacitance considered in the design of the equipment, including normal operation of the circuit, one or two faults(Co)And the maximum external inductance(Lo)Or the ratio of inductance to resistance(Lo/Ro)Under the circumstances.
Each circuit should be tested at the following required revolutions per minute
a) For DC circuits,400turn(5 min), of each polarity200Turn;
b) For communication circuits,1000turn(12.5 min)；
c) For capacitive circuits,400turn(5 min), of each polarity200Turn around.
9. Capacitance time constant
It should be ensured that the charging time is not less than3The time constant is multiplied and the calculation method is listed. It is possible to reduce two or three metal wires(Tungsten wire)Or slow down the rotation speed of the spark test device to increase the charging time. When using the method of reducing metal wires, the number of revolutions should be increased to maintain the same number of sparks.
Criteria for determining the qualification of spark test
If there should be no ignition in each test of each test circuit, it is judged that the spark ignition of the circuit is compliant. After each experiment, the spark test device should be recalibrated to verify the validity of the test results. If the calibration is not qualified, the ignition test of the tested circuit is invalid.
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