Production of testers that can operate in difficult and hazardous areas is a very difficult and time consuming process; the highest levels of protection must be added so that none of the working parts can be affected and more importantly, the test instruments cannot effect the environment.
All test equipment produced for hazardous environments has high Ingress Protection (IP). An IP rating is typically 2 numbers; the first refers to dust protection and the second is liquid ingress protection. The chart below explains both dust protection and liquid ingress:
|Level||Object Size Protected Against||Effective against|
|0||—||No protection against contact and ingress of objects|
|1||>50 mm||Any large surface of the body, such as the back of a hand, but no protection against deliberate contact with a body part|
|2||>12.5 mm||Fingers or similar objects|
|3||>2.5 mm||Tools, thick wires, etc.|
|4||>1 mm||Most wires, screws, etc.|
|5||Dust protected||Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact|
|6||Dust tight||No ingress of dust; complete protection against contact|
It is common for most test equipment to be rated a 5 for dust protection (although this will vary depending on its application).
|Level||Protected against||Testing for||Details|
|1||Dripping water||Dripping water (vertically falling drops) shall have no harmful effect.||Test duration: 10 minutes Water equivalent to 1mm rainfall per minute|
|2||Dripping water when tilted up to 15°||Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle up to 15° from its normal position.||Test duration: 10 minutesWater equivalent to 3mm rainfall per minute|
|3||Spraying water||Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect.||Test duration: 5 minutesWater volume: 0.7 litres per minute
Pressure: 80–100 kN/m²
|4||Splashing water||Water splashing against the enclosure from any direction shall have no harmful effect.||Test duration: 5 minutesWater volume: 10 litres per minute
Pressure: 80–100 kN/m²
|5||Water jets||Water projected by a nozzle (6.3mm) against enclosure from any direction shall have no harmful effects.||Test duration: at least 3 minutesWater volume: 12.5 litres per minute
Pressure: 30 kN/m² at distance of 3m
|6||Powerful water jets||Water projected in powerful jets (12.5mm nozzle) against the enclosure from any direction shall have no harmful effects.||Test duration: at least 3 minutesWater volume: 100 litres per minute
Pressure: 100 kN/m² at distance of 3m
|7||Immersion up to 1 m||Ingress of water in harmful quantity shall not be possiblewhen the enclosure is immersed in water under defined conditions of pressure and time(up to 1 m of submersion).||Test duration: 30 minutesImmersion at depth of 1m|
|8||Immersion beyond 1 m||The equipment is suitable for continuous immersion in waterunder conditions which shall be specified by the manufacturer. Normally, this will mean that the equipment ishermetically sealed. However, with certain types of equipment, it can mean thatwater can enterbut only in such a manner that it produces no harmful effects.||Test duration: continuous immersion in waterDepth specified by manufacturer|
Liquid protection ratings vary more widely then dust protection, though most testers are only protected to level 4 (against splashing water). This combines to make an average IP rating for most testers of 54.
Although a high ingress protection rating ensures that it will work in dusty or wet areas, these testers are not always intrinsically safe.
Intrinsically safe (IS) equipment is designed to drastically reduce the risk that the tester will produce heat or a spark. This feature means that the equipment is useable in very volatile conditions, such as those in oil processing. Lack of this feature can mean ignition of volatile chemicals that may be present in the workplace. The following industries are amongst those known to have hazardous locations:
- auto (paint spray booths)
The difficulty in producing intrinsically safe equipment for use with electricity is that as current increases the heat generated by the equipment increases as well; because of this strict control on a circuit is required in all testers that are intrinsically safe. These factors lead to not every piece of equipment being available as intrinsically safe.
In order to correctly identify the correct IS tester a range of gas groups has been identified; these gasses or dusts that could cause an explosion. The chemicals that share similar properties such as minimum ignition current and spontaneous ignition temperature are put in the same groups.
|Gas group||Example gasses|
|I||Methane, gasses from underground coal mining|
|IIA||Most industrial gasses and propane/petrol|
|IIB||Coke oven gas and ethylene|
|IIC||Carbon disulphide and hydrogen|
To further assist the creating on IS systems there is a range of temperature classifications that show what temperature the equipment will never exceed during operation.
One of the hardest parts of producing testers that meet high safety standards is making sure that they are rugged and strong enough to withstand day-to-day use whilst never losing its protection from the elements. To ensure that only thoroughly tested and safe instruments are sold, in Europe equipment that is intrinsically safe must bear the CE mark this is typically displayed as EEX before the gas group and temperature classification.
Commonly used equipment that can be intrinsically safe includes multimeters and IS cameras. Fluke, Cordex and Beamex produce a wide range of high quality safety equipment.
Written by Barry Atkins at www.tester.co.uk