Intrinsic Safety Testingby

• Gail Nicola, Electrical Engineering Technician

• Ed Vensko, Electrical Engineering Technician

Battery Flash Current Testing

• Purpose: To determine the maximum short circuit current of a battery.

• Pass/Fail Criteria: None. The data is used to determine the intrinsic safety of a particular circuit.

• Samples: 3 fresh or fully charged batteries for each battery manufacturer specified.

• Recommendations: – Submit samples with the application package, if possible.

– Individual cells should be submitted instead of a complete battery pack that may contain polyswitches or fuses.

– Verify that manufacturer & part number of samples agree with documentation.

Cap Lamp Bulb Life

• Purpose: To determine compliance with 30 CFR 19.9(b) and 19.9( c)2.

• Pass/Fail Criteria:

– 19.9(b) Average life of the bulb shall not be less than 200 hours and 92% shall have a life of 150 hours.

– 19.9(c)(2) Current consumption of at least 94% of the bulbs shall not exceed the average current by more than 6%. The candlepower of at least 90% shall not fall short of the average candlepower by more than 30%.

Cap Lamp Bulb Life

• Samples: 50 marked bulbs, discharge rack capable of testing 10 bulbs max.

• Recommendations: – Submit samples with application package

Accuracy of Methane Detectors

• Purpose: To determine compliance with 30 CFR Part 22 within the limits of error specified in 22.7(d)(2).

• Pass/Fail Criteria: When more than 2 readings for each percentage or the average of all 10 readings of any of the four samples exceeds the limits of error.

• Samples: 4 representative samples, calibration kit and calibration procedures, probes, maximum length specified sampling lines, batteries and/or battery chargers.

Allowable Variations in Scale Reading (In Percent)

METHANE IN AIRMIXTURES

MINIMUM INDICATION

MAXIMUMINDICATION

0.25 0.10 0.40

0.50 0.35 0.65

1.00 0.80 1.20

2.00 1.80 2.20

3.00 2.70 3.30

4.00 3.70 4.30

Accuracy of Methane Detectors

• Problems: – Sensors have not been burned in.

– Calibration gas is not accurate.

– All specified battery packs have not been submitted.

– How detectors react with low battery voltage

– No low flow pump alarms

– Flow rate, gas concentration, and pump calibration procedures not adequately specified.

• Recommendations: – Check performance of detectors before submitting

– Verify concentration of calibration gas.

- 4 instruments (2 with pumps, 2 without pumps)- calibration gas and instruction manual- regulators- probes- sampling tubing , specify length- battery chargers

Surface Temperature Test

• Purpose: To determine the maximum surface temperature of a component.

• Pass/Fail Criteria: The temperature of the external surfaces of components shall not exceed 150 °C if exposed to coal dust or 530 °C if exposed to a methane-in-air atmosphere.

• Samples:

– 10 samples of the component under test.

– 10 samples of the current-interrupting device (if applicable).

Surface Temperature Test

• Recommendations: – Position the surface mount components on a PCB with 2” leads.

– Use adequately rated components.

– Use dust tight enclosures.

– Submit 10 samples of components likely to overheat (e.g. low value/rated resistor and zener diodes, etc.) with your application package.

– Submit fuse manufacturer’s time versus current characteristic curves.

Coal Dust Blanketing Test

• Purpose: If a small component exceeds 150 °C during surface temperature testing then the component is subjected to the Dust Blanketing Test.

• Pass/Fail Criteria: The component fails the test if there is evidence of smoldering or ignition of the coal dust.

• Samples: 10 samples of each component

• Recommendations:

– Design circuitry with fuses to prevent overheating of components.

Hot Wire Calibration and Small Component Ignition

• Purpose: To determine if the heated element will ignite a methane-in-air mixture.

• Pass/Fail: The component must not ignite the test gas.

• Samples: 10 samples of each component specified

• Problems: Sensors are submitted without the elements exposed (sintered metal screen removed)

• Recommendations:

– Submit samples with the application package.

– Submit samples with elements exposed.

Current-Limiting Resistor Tests

• Purpose: To determine if the resistor decreases in resistance by more than 10 %.

• Pass/Fail Criteria: The resistor shall not decrease in resistance by more than 10% of its pre-test value, flame, or deform such that it would be short-circuited by an adjacent conductor.

• Samples: 10 samples of each CLR specified on the documentation and 10 samples of the current-interrupting device (if applicable).

• Recommendations:

– Submit samples with the application package.

– Design circuitry with fuses to prevent overheating of components.

– Submit fuse time versus current curve (if applicable).

Spark Ignition Test

• Purpose: To determine whether the circuit is capable of releasing enough electrical energy to cause an ignition of a flammable mixture of methane and air at the most easily ignitable composition.

• Pass/Fail Criteria: An ignition occurs.

• Samples: 3 samples each of motors, inductors, speakers, etc.

• Problems: – Unable to obtain a pretest calibration due to environmental conditions.

– Inductive calibration with copper electrodes

• Recommendations:– Design circuits with adequate current limiting resistance so spark testing may

be waived. (Reference ignition curves.)

Optical Isolator Test

• Purpose: Each optically-coupled isolator shall withstand a minimum dielectric voltage of either 2500 volts (rms) or four times the maximum safe-area voltage (whichever is greater) between its input and output.

• Pass/Fail Criteria: No breakdown shall occur.

• Samples: 9 of each type of optical isolator specified on the submitted documentation.

Optical Isolator Test

• Problems:

– Verifying internal spacing between input and output circuitry.

– Specification ratings of the optical isolator are not submitted.

• Recommendations:

– Submit adequate specifications for the optical isolator so the device is accepted based on evaluation only and testing of the component is waived.

– Submit nine samples of each optical isolator of all manufacturers specified on the submitted documentation.

Protective Transformer Test

• Purpose: Transformers for direct connection to a supply voltage shall be evaluated for dielectric strength.

• Pass/Fail Criteria: There shall be no breakdown of the insulation between the test points during testing.

• Samples: 3 samples of each transformer specified in your application.

• Recommendations:

– Submit samples that are adequately marked with manufacturer and manufacturer part number.

– Submit samples with application package.

Drop Test

• Purpose: To determine whether portable apparatus continue to be intrinsically safe after being subjected to 6 drops from a height of 3 feet onto an oak plank.

• Pass/Fail Criteria: There shall be no separation or ejection of the battery or batteries from the apparatus, nor other fault that could affect intrinsic safety. For equipment requiring a dust-tight enclosure to exclude coal dust entry, the enclosure of the sample shall continue to be dust-tight after the drop test.

• Samples: 1 representative sample of the manufactured portable instrument.

Drop Test

• Recommendations:– Drop an instrument at your facility before submitting for approval.

Piezoelectric Component Impact Test

• Purpose: To determine the maximum output energy generated by the piezoelectric component when it is impacted with an energy of 20 joules (2 kg at 1 m).

• Pass/Fail Criteria: The maximum output energy generated by the piezoelectric component shall not exceed 1500 micro joules.

• Samples: 3 each of the apparatus containing the piezoelectric component of a quality, design, and construction consistent with that of the final manufactured product.

Piezoelectric Component Impact Tests

• Problems: – Capacitance of the crystal is not specified and/or doesn’t match submitted

drawing.

– Connection directly to the crystal is not possible; crystal is located in a potted assembly with other oscillating circuitry.

– 3 samples of the component were not submitted in a test mockup with the samples mounted in their normal position..

– Unable to obtain a second impact on the sample of the component since the first impact completely destroys the sample.

• Recommendations:– Submit three samples mounted in test mockups.

– Attach output leads directly to the crystal or to amplification circuitry.

– Submit specification data with regard to the maximum capacitance of the crystal.

Standard Test Procedures

• ASTP2002

• ASTP2004

• ASTP2008

• ASTP2009

• ASTP2010

• ASTP2012

• ASTP2022

• ASTP2026

• ASTP2030

• ASTP2036

• ASTP2040

Battery Flash Current Test

Accuracy of Methane-Indicating Detectors

Cap Lamp Bulb Life Test

Current Limiting Resistor/Surface Temperature Test

Dust Blanketing Temperature Test

Hot Wire Calibration and Small Component Ignition Test

Spark Ignition Test

Optical Isolator Test

Protective Transformer Test

Drop Test for Portable Instruments

Piezoelectric Component Impact Test