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Introduction to spark ignition test for intrinsic safety and explosion-proof certification testing method

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| 2020-11-26|Return

With the rapid development of China's economic construction and the increasing scale of industrial production, explosion-proof issues have 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 of national explosion-proof standards.

belowZhongnuo TestingThis article 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, as shown in FigureA1~FigureA6Among the various forms corresponding to the reference curve, short-circuit test is the most unfavorable. For more complex circuits, due to different conditions, short-circuit tests are requiredZhongnuo TestingPerhaps not the most unfavorable condition. The most unfavorable condition for a stable voltage and 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 combined circuit of capacitors and inductors should be evaluated and tested. If the total inductance or capacitance evaluated is compared to the AppendixAThe ignition curve or data table allows for small values1%(Refers to the capacitance corresponding to voltage or inductance corresponding to current, which does not exceed the ignition critical value)1%When, The maximum allowable capacitance or inductance can be taken from the ignition curve or the values allowed in the data table, respectively.


2. Component tolerance

1)During the experiment, consideration should be given to component tolerances and variations in power supply voltage. The spark test device should be connected to each test point in the test circuit identified in the technical review, where it is believed that an open or short circuit may occur.

2)The test should be based on the equipment protection level, recognized faults, and the maximum external capacitance considered in the product design(Co)And maximum external inductance(Lo)Or inductance to resistance ratio(Lo/Ro)Under certain circumstances.

3)The test should be conducted on samples that have been tested and are consistent with the approved drawings and prototypes; After actual inspection, the drawing data can be modified to meet this requirement for the type inspection.

4)According to the intrinsic safety circuit evaluation criteria, if the product circuit is a simple circuit, according to theGB 3836.4-2010appendixAThe method and diagram describedA1~FigureA6Reference curve or table providedA1A2When the provided data can determine its intrinsic safety performance, spark testing may not be conducted; But there should be evaluation records and safety factors provided.

5)When there is no specified applicable range for voltage, it is usually calculated as ±1%Value;

6)Testers are usually2People, one person operates, one person records. Testers must hold a certificate to work, and interns are not allowed to operate independently(7)During the internship period, personnel should receive guidance from formal testing personnel and are not allowed to operate equipment without authorization.

8(The experiment strictly follows theGB3836.4-2010in10.1Request to proceed; During the experiment, the data should be recorded in a formal record form in a timely manner. The record form should be filled out according to regulations and there should be no 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 mixtures and spark testing devices

1)The table should be used according to the category specified by the tested equipment11.0Double safety factor or table21.5Explosive test mixture given by multiple safety factors.

2)During the gas distribution process, explosive or high-pressure gases should be operated strictly in accordance with relevant operating procedures.

3)Priority TableThe safety factor of the specified test mixture can be obtained by increasing the voltage or current. If this situation is not applicable, the tableThe composition of the explosive test mixture given has the requirements specified in this standard1.5 A safety factor of times.

4)The purity of the test gas should not be lower than95%.

5)Before conducting spark ignition tests of the same class, calibration should be carried out. 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 a ammeter (see table)And the table2)Confirmation conducted.

4. Safety factor

A safety factor of 1.5 times should be obtained using one of the following methods:

① Parametric method

1) For inductive and resistive circuits, increase the current to1.5Multiple times the fault current. If it cannot be achieved1.5Double the safety factor, which can further increase the power supply voltage; For devices using batteries, the voltage can be increased by increasing the number of batteries.

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, the capacitor can be regarded as a battery, and the circuit can be regarded as a resistive circuit.

② Gas method

Using TablesThe prescribed explosive test mixture. Using shunt short circuitSharp short circuitThe testing of protective circuits should be evaluated separately for circuits with shunt short circuit (sharp short circuit) protection, including maximum output power, voltage and current, and short circuit status, with equipmentZhongnuo TestingThe stable output voltage of the circuit with the specified protection level should not cause ignition. When the explosion-proof type is related to sharp short circuits caused by other circuit faults, the allowable passing energy at the moment of sharp short circuits should not exceed the specified values of the following corresponding equipment categories:

-IICClass devicestwenty μ J

-IIBClass deviceseighty μ J

-IIAClass devicesone hundred and sixty μ J

-IClass devicestwo hundred and sixty μ J

It is not suitable to use a spark test device to conduct ignition tests on sharp short-circuit circuits that allow energy to pass through. To measure and evaluate the allowable energy of sharp short-circuit circuits, a transient oscilloscope should be used for measurement.


5. Test method for rapid short-circuit energy testing

according toW==IvtMeasure separatelyIandVCurve, and then use the formulaW=Δ_ 0 ^ TI * VdtCalculate the output energy. The measurement should be carried out on 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 when the circuit is openUoValue, and there is a series of current limiting devices in placeZhongnuo TestingThe current isIoAction when corresponding to level,So the circuit should be connected to approximatelyUO-0.5VWhen subjected to left and right loads, a current greater thanIoThe transient current should be calculated to be greater thanIoThe energy of the time period. Other loads with voltage below this value should also be considered for testing. The application of the experiment is to measure the expected voltage and current using a digital oscilloscope, as shown in the figureandAs shown.

For example, if the power supply voltage is15 VAnd there is a series current limiting switch at a current of1 ATime action,So it can be expected that,When the circuit is connected to approximately13.5 VWhen the most unfavorable Zener load is applied, a current greater than will be generated before causing the current switch to operate1 ATransient current of. Zener loads with voltage below this value should also be considered for testing.


aboutIIBClass devices13.5VThe maximum allowable current for voltage is3.76 A(As shown in the tableA. 1). therefore,The test 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. In this situation,Transient energyZhongnuo TestingBy measuring the current of a Zener tubeUsing a clamp ammeterCalculate based on voltage. At the same time, a series of times corresponding to the current for each value of the Zener tube can be measured, thereby obtaining a curve 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. In this situation,Corresponding to each short circuit until the resistance value is less thanUo/IoA set of current time curves can be drawn for resistive loads, and the transient power transmitted can be calculated based on the power generated on the resistance and the corresponding time. This type of load can be a capacitor or an inductor, depending on specific output parameters.


It should be noted that voltage and current should be applied less thanone μ S/Use a high-speed storage oscilloscope with separate compartments for measurement. test equipmentZhongnuo TestingThe selection and connection of the test circuit should minimize the impact on the measured value. It is recommended to use clamp current measurement probes and high impedance voltage measurement 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 have its protection level for fault setting and handling. Usually, an open circuit is used by disconnecting 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 based on their properties. The principle is that the circuit is in the most unfavorable situation.

4)The spark test device should be connected to each test point in the test circuit that is considered to have the possibility of open and short circuits,These points were confirmed after technical review and prototype testing.


8. Fault setting

The test should be conducted in accordance with section5The equipment protection level specified in the chapter, under normal circuit operation, one or two faults, and considering the maximum external capacitance of the equipment design(Co)And maximum external inductance(Lo)Or inductance to resistance ratio(Lo/Ro)Under certain circumstances.

Each circuit should be tested at the following required revolutions

a) For DC circuits,400turn(5 minutes)Each polarity200Transfer;

b) For AC circuits,1000turn(12.5 min);

c) For capacitive circuits,400turn(5 minutes)Each polarity200Turn.


9. Capacitance time constant

Ensure that the charging time is not less than3Double the time constant and list the calculation method. Can be reduced by two or three metal wiresTungsten wireOr 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.

Spark test qualification criteria

If there should be no ignition in each test of each test circuit, it is judged that the spark ignition in that circuit is qualified. After each test, the spark testing 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.

The copyright of this article belongs to Zhongnuo Testing. The right to pursue plagiarism and theft will be reserved. Reproduction must indicate the source of the original text.

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