Development of an Alternative Electronic Spark Test Apparatus

In this phase of the project, CRCMining has further developed and demonstrated proof of concept for an electronic alternative to the Spark Test Apparatus (STA) currently used in intrinsic safety (IS) certification of power supplies for use in an explosive environment. The Electronic Spark Tester (EST) requires neither the creation of real sparks or explosions, and instead, measures the response of a power supply to an electronically simulated break spark at its terminals. This method has many significant advantages over the STA, including greater reliability, a proportional measure of safety, and a test procedure which does not require hazardous substances or a specialized laboratory.

An electronic method brings significant benefits to key stakeholders in intrinsic safety testing, including:

· Benefits for power supply designers and manufacturers include more informative test feedback along with the possibility of testing power supplies before IS testing is conducted;

· Benefits for testing agencies with reduced risk to test personnel, as well as a greater certainty and repeatability in test results;

· Benefits for the end user including the possibility of on site or pre-installation testing of power supplies to ensure continued compliance of the power supply to the intrinsic safety standard.

The first phase of research investigated the application of electronic spark testing to the most common types of IS power supplies in underground mines. Key findings from this research included:

· A computer controlled electronic load circuit can successfully simulate a spark at the terminals of these power supplies.

· A relatively simple moving average power calculation, applied to the voltage and current waveforms of the simulated spark, can be used as a "safety metric", i.e.: a proportional measurement of ignition safety.

· The electronic test can reliably subject a power supply under test to a worst case spark event, which may occur rarely, if at all, in the STA.

The Second Phase of Research further investigated the application of electronic spark testing. Key findings from this phase of research are:

· Methane mixture burned approximately 8 times slower than hydrogen mixture,

· The "threshold ignitability" (i.e.: minimum value for which ignitions were obtained) for hydrogen obtained during phase 2 was comparable to that proposed during phase one,

· Successful development of a static, empirical spark model for low voltage and current applications,

· Improvements made to the hardware and software reduced issues found during phase one and tests were conducted on commercially available off the shelf IS power supplies.

A proposed third phase of research will develop the electronic spark testing apparatus to a pre-commercial device and continue the research into the ignitability metric and spark model.