Are your temperature sensors safe?

"When it comes to installing temperature sensors such as thermocouples or resistance thermometers [RTDs] in hazardous areas, many companies are still making mistakes with regard to equipment certification requirements. Some of our customers, for example, do not fully understand or are not aware of product certification requirements based on their Zone and classification choice. Also they are unaware of the new ATEX harmonised standards and how these standards affect equipment being sourced," says Chris Chant, Business Development Manager at Okazaki Manufacturing Company (OMC). He continues: "It is crucial that these companies understand the ATEX harmonised standards, and which supplier equipment is properly certified for the selected hazardous area and protection concept that they have selected, otherwise safety of installations cannot be guaranteed."

According to Chant, companies that use temperature measurement products such as thermocouples and RTDs installed in potentially explosive atmospheres need to ensure that the sensor assembly (sensor, enclosure and terminal glands) actually meets the overall area classification requirements for each specific installation. In Europe, this is covered by the ATEX Directives, including the new ATEX harmonised standards.

Directive 94/9/EC covers equipment that is intended for use in potentially explosive atmospheres. The CE mark on equipment such as this represents the manufacturer's declaration of compliance to this directive and to the EN standards that are harmonised to it. All equipment should be supplied with a declaration of conformity stating compliance with these standards and issued with product certification provided by a notified body such as BASEEFA or SIRA here in the UK.

If the chosen certification classification is Exia for use in zone 0, 1 or 2 then there is no need for product certification in the case of thermocouples or RTD sensors, but care must be taken to ensure the correct installation, with selection of an appropriate barrier, and to ensure that the IP rating of the termination is correct and that there is appropriate terminal clearance.

Of more concern is when thermocouples or RTD sensors are designated Exd (flameproof). In this case product certification is 100% required. Care should be taken when using a terminal housing - the sensor should be terminated in a suitable Exd-certified enclosure. As Chant explains: "A standard temperature assembly such as this normally requires a spring-loaded sensor to ensure good contact is made with the tip of the thermowell. The base of the housing is therefore fitted with a flame path-controlled bore or collar that provides a flame path seal into the base of the housing, enabling free movement of the sensor via spring loading."

However, Chant warns that this can lead to certification problems. "Although the enclosure rating is not affected, the inclusion of the sensor introduces a possible fault condition, which requires additional certification."

OMC has overcome these challenges by having the complete assembly (sensor and enclosure) certified as Exde IIC T6, which provides Exd certification for the enclosure and Exe (increased safety) certification for the sensor. This means that the user can install the assembly in a Zone 1 hazardous area without requiring additional thermocouple or RTD IS safety barriers. If, for example, a head mounted, hockey puck style transmitter is installed, no extra certification is needed for the electronics module.

For many years, the EN50014 series of standards has been the backbone of ATEX compliance. However, by the end of 2008, most of the series was superseded by standards from the EN60079 series and has been withdrawn. This presents a potential problem for holders of ATEX EC type examination certificates to these withdrawn standards. To help customers, all OMC products have now been upgraded and are fully certified to the latest ATEX harmonised standards.

Other scenarios also require careful consideration. For example, if companies install the latest Hart and digital fieldbus transmitters (such as a Yokogawa YTA 110 and YTA 320 or an Emerson 3144P), care should be taken to ensure that approval of the complete assembly is certified, not just the transmitter. First, the integral transmitter and housing should carry its own certification, then the temperature sensor coupled to this transmitter should also carry its own certification or be glanded to the unit using an approved terminal gland.

To simplify installation, OMC has developed its FPN (flameproof nipple) range of thermocouple or RTD sensors. These units, which are pressure tested to 1,000psi, can be fitted to other manufacturers' temperature transmitters, while still maintaining the spring loading feature and an IP66/67 rating, without requiring any compression glands to be fitted that would restrict movement of the sensor. Again, by working with BASEEFA, OMC has achieved Exde IIC T6 certification for the FPN range.

When terminating mineral-insulated (MI) thermocouples and RTD sensors into suitably certified Exd or Exe enclosures, engineers also need to ensure that the terminal glands carry the appropriate certification. The glands themselves need to be approved for use with sensors rather than just for cables. As Chant explains: "This is because, unlike cables, a temperature sensor is not terminated at each end and so can have different fault conditions. We offer a comprehensive range of thermocouples and RTDs that are certified as combined units with their own range of termination glands, giving an overall certification of Exde IIC T6. This greatly simplifies the whole compliance process for the customer."

Okazaki Manufacturing Company (OMC) in profile
Okazaki Manufacturing Company (OMC) was founded in 1954 and started the design and manufacture of temperature-related products in Kobe, Japan. The company has always been at the forefront of product design and the use of innovative technology. In 1963, OMC developed Resiopak, a metal-sheathed MgO insulated resistance thermometer now used for temperature measurement within the petrochemicals industry globally.

Today, OMC designs and manufactures a wide range of reliable, high quality, high accuracy temperature measurement products. With a turnover in excess of 110 million USD, OMC is one of the largest manufacturers of mineral insulated (MI) thermocouple and RTD cable, which is the first building block of industrial temperature sensors. OMC operates from a series of specialist sales support offices worldwide, backed up by a team of local representative companies all with specialist instrumentation departments. OMC has manufacturing sites in Japan, USA and Taiwan.

All OMC's temperature products can be fully certified for use in potentially explosive atmospheres to International Standards and to country-specific variations. OMC temperature assemblies are certified by FM for NEC (USA) standards, BASEEFA for IECEx Product Approval and for type approval in compliance with EU ATEX directives. Country-specific approvals include GOST K, GOST R, NEPSI (China) and KOSHA (Korea).

For further information, view website: www.okazaki-mfg.co.uk or email: info@okazaki-mfg.co.uk   Refer to page 41

New controls can reduce compressed air costs by 30%

Atlas Copco Compressors has introduced the next generation in compressor controls across its oil-injected screw compressors range 11-90 kW GA/GA⁺/GA VSD. The new Elektronikon graphical display controller and the integrated Energy Saving (ES) Systems ES4/6i, are significant contributors to further increasing compressed air efficiency, resulting in lower operating costs. In addition, free online visualization enables remote monitoring, allowing for anticipation of operating and maintenance needs.

Atlas Copco has combined its expertise and knowledge to launch the fifth generation Elektronikon graphical display controller (installed as standard on the GA⁺/GA VSD) while expanding the Energy Saving (ES) System to control, with the ES6i, up to six variable speed drive or fixed speed compressors simultaneously. 

Control and Save
The Elektronikon graphical display controller is a colour display, housed on the compressor, that shows several compressor and dryer parameters while built-in algorithms automatically implement energy saving cycles for both fan and dryer. Additional features such as dual pressure band and timer-based controls enable Atlas Copco to maximize energy savings by matching the operating pressure to air demand.

The optionally integrated Energy Saving Control System, ES6i, is capable of regulating and sequencing up to six variable or fixed speed compressors; while optimizing the customer's installation by reducing the overall working pressure band of each compressor to meet the varying air demand.  The possibility to manage up to six variable speed compressors with one integrated controller (up to four compressors with the ES4i) reduces installation costs while minimizing energy and maintenance costs through reduced pressure band. Depending on the compressor configuration and air demand, the improved ES control system can reduce yearly running costs up to 30%.
 
Communicate and Anticipate
Developing the fifth generation Elektronikon Graphical display controller, Atlas Copco's engineers focused on the importance of a user friendly interface.  Clear and easy communication keeps the user informed about the operating condition of the unit therefore reducing operation and maintenance cost.

The hardware innovations include a new human machine interface with durable keyboard and a user-friendly navigation system.  The Elektronikon® graphical display controller has a high quality 3,5" colour display.  The built-in web-server technology is a standard feature with no additional cost providing, through Ethernet communication, instant online compressor status visualization.  The graphic visualization provides service intervals in real time and displays a graphical service plan assisting in preventive maintenance.  Customers can select one of 32 languages while all registered data is stored for later use.  The optional AIRConnect allows for remote or local monitoring (through the phone or wireless internet connection) for additional on- or offline readings. 

Conclusion
The Atlas Copco oil-injected screw compressor with its highly efficient components (compressor element, coolers, motor), provides premium performance both in free air delivery and specific energy requirement.  Coupled with superior controls, overall efficiency is increased further by complete system optimization which results in reduced operating costs.

For further information, e-mail: gba.info@uk.atlascopco.com or view website: www.atlascopco.co.uk   Refer to page 43