Testing of low-current equipment in explosive atmospheres

00038


Introduction
When flammable substances are used in industry, there are explosion hazard zones in the proximal space of installations.Equipment which is installed and used in these hazardous areas must not ignite an explosive atmosphere.Group II electrical equipment is divided into IIA, IIB and IIC according to the potentially explosive atmosphere for which it is intended.Equipment marked IIB is therefore suitable for applications requiring Group IIA equipment.Similarly, IIC marked equipment is approved for applications requiring Group IIA or IIB equipment.[1-2] https://doi.org/10.1051/matecconf/202438900038SESAM 2023 All equipment in the installation handling flammable substances must comply with explosion protection requirements.They must also comply with the specific environmental conditions in which the equipment is used.It must be adequately protected against explosions.Maintain a level of protection against the conditions for which it was built.Withstand the (foreseeable) stresses to which it is subjected during storage, transport, installation and operation.The project equipment is placed in relation to the requirements of the equipment evaluation process.In this process the documentation of the specific equipment and standard is analyzed.
In the next stage of the assessment, one or more samples of equipment are tested according to the requirements of the specific standard.[3]

Types of explosion protection
The method of complying with the ATEX Directive [4] is based on the implementation of harmonized standards in the design and manufacture of equipment which is intended to operate in potentially explosive atmospheres.The manufacturer will use technical solutions concretized by types of protection through the implementation of harmonized standards of the EN 60079 series.There are a variety of different types of equipment protection due to different regulatory standards.There are different types of protection to suit gas, dust and non-electrical equipment.Explosion protection involves checking how the equipment is adapted for use in an explosive atmosphere.Explosion protection is confirmed by testing and evaluation.Type of protection refers to specific construction measures that are applied to equipment to prevent ignition of the surrounding explosive atmosphere.Protection of equipment by the intrinsically safe "i" protection system is protection based on limiting electrical energy in equipment and interconnecting circuits exposed to explosive atmosheres below levels that could cause ignition due to sparking or thermal effects.In terms of the safety factors implemented, intrinsically safe electrical equipment is divided into three levels of protection: Protection level "ia" Protection level "ib" Protection level "ic" For the protection level "ic" the maximum surface temperature is determined by testing the samples under normal operating conditions, whith all protection devices in place.[5] 2 The main factor is the maximum surface temperature In this paper I present the explosion hazard and a brief presentation of the classification of equipment intended for use in explosive atmospheres and the test methodology for measuring the maximum surface temperature and the results obtained according to the laboratory procedure for two sensors.
Consideration should be given to the situation where the hazardous atmosphere may be ignited by the maximum equipment surface temperature for low current equipment.
The maximum temperature reached during operation under the most adverse conditions by any part or surface of the equipment.This temperature may occur on an internal component or on the external surface of the enclosure for electrical equipment operating in explosive gas atmospheres, depending on the type of enclosure protection.This temperature occurs on an outer surface of the enclosure for electrical equipment in explosive dust atmospheres and includes a defined dust layer condition.
The tests are carried out on samples of electrical equipment, in our case on the intrinsically safe group II sensor.
The measurement of the maximum surface temperature of electrical equipment shall be carried out in a quiet ambient atmosphere with the equipment mounted in the normal operating position.
Auto-ignition temperature is the temperature at which the gas will spontaneously ignite without any other ignition source, in degrees Celsius.
There is no correlation between the ignition energy of a group of gases and the ignition temperature, hence the temperature codes.If the ambient temperature differs from this range, this should be indicated.Gases are divided into two groups according to their LEL and UEL values.Dusty areas are defined as Group III and refer to equipment intended for use in areas with explosive dust atmospheres other than the gritty mines.Group III electrical equipment is marked with the temperature prefix "T" and details the actual maximum temperature encountered on surfaces accessible to the potentially dust atmosphere.[6]

Stands description
The maximum surface temperature test stand is for testing the maximum temperature of the sensor.It is used to test the equipment for the maximum surface temperature of the equipment for its use in Ex atmospheres.The stand consists of: ASUS G752VS laptop with dedicated software for 34972A;  The test procedure involves several steps: checking the integrity of the test stand, conditioning the test sensor, testing, analyzing and recording the results.
Ensuring the validity of results by ensuring the maintenance of the stand: periodic calibration of the equipment intended for measurement: current, voltage, temperature and intermediate checks during the test.
Checking the stand: checking the integrity of the housing and accessories, checking for dust and dirt accumulation, checking the operation of the operating field.
Stand overhaul: replacement of evaluated electrical circuit components (tester, electrical plugs/ connectors, conductors), calibration/metrological check.[7] 4 The equipment tested To meet the strict requirements of the ATEX Directive 2014/34/UE [8], sensor have been tested to ensure that there is no risk of ignition when operating in potentially explosive areas.The sensors are tested using equipment in the authorized laboratory to ensure that they withstand severe impact and drop tests, harsh environmental exposures and meet minimum protection requirements (IP6X dust test is required for testing in potentially explosive dust environments).

Results obtained after measuring the maximum surface temperature
In the case of determining the maximum surface temperature of sensor for explosive atmospheres with combustible dusts, the expression of the results is done by: the maximum surface temperature correlated with the maximum ambient temperature specified in the nominal regime and the temperature at the hottest point for the encapsulation parts of the material plastic.

Conclusions
Increasing the quality of the tests performed cannot be achieved without a holistic approach to the factors affecting the validity of the results.
Several factors are involved in ensuring an adequate level of test quality, including quality systems, human resources and measurements.
Appreciation of maintenance activities can be considered an investment, as they improve the productivity and accuracy of equipment.
The importance of ensuring the quality of the test results to which the equipment has been subjected, which confirms not only the conformity of the tested equipment.
There are types of protection for gas, dust or non-electrical equipment.The use of equipment in areas where flammable substances may be released requires explosion protection for them.Explosion protection must be confirmed in the certification process, which, in addition to assessment, also requires testing.The tests that equipment must undergo to confirm explosion protection are regulated by specific standards, depending on the type of protection adopted.
In conclusion it is true that this type of sensor falls into the T5 temperature class specified on the manufacturer is marking label.
The temperature class is based on use at an ambient temperature of 20 0 C/-40 0 C. Temperature classes are T1 to T6.

Fig. 2 .
Fig. 2. Stand configuration for inductive sensor maximum surface temperature measurement