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

Multipoint assemblies enable 3D temperature profiling of process reactors

A range of multipoint temperature assemblies is now available from Okazaki Manufacturing Company (OMC), which is suitable for all types of process applications, including crude oil storage tanks, hydrocarbon cracking units, chemical reactors and desulphurisation catalyst bed reactors.
 
Most catalyst bed reactors operate at very high pressures and temperatures, making the vapour generated potentially very dangerous. The design of the reactor and multipoint temperature assemblies are therefore critical to safe plant operation. The reactors are between 3m and 6m in diameter, and are between 10m and 40m high.

For optimal process operation, the temperature needs to be controlled and monitored accurately and fast, as well as three-dimensionally at multiple pre-set levels within the reactor catalyst filling. It is therefore preferable to have a minimum number of entry nozzles, or to utilise existing nozzles when upgrading.

For chemical reactors and desulphurisation catalyst bed reactors, OMC's AerOradial range of multipoint temperature assemblies is ideal. This assembly offers the maximum number of temperature measurement points through a single process connection or entry nozzle. OMC utilises its own AerOpak mineral insulated cables, providing single tip measurement or multiple sensing points within a single stem. This enables full, three-dimensional temperature profiling, which ensures safe control of the process with a fast thermal response.
 
Assemblies can be positioned through the side, top or bottom of the reactor vessel, with adjustable spacers for catalyst tubes or with an optional mounting system for fitting to the reactor.
 
To ensure the pressure seal is maintained on the assembly, OMC uses a special welding technique known as 'orbital seal welding'. Here, the sensors are welded into custom-designed pressure containment chambers. These chambers can be fitted with pressure gauges or transmitters, which indicate any safety problems such as a primary seal failure.
 
 Chris Chant, Business Development Manager at Okazaki Manufacturing Company comments: "Our range of multipoint temperature assemblies is comprehensive and all designed and manufactured in our Japanese plants. Most of the units we supply are in stainless steel, but we also offer assemblies in exotic materials such as Alloy 600, 625, 825 or Hastelloy X. Some of our designs are fitted with smaller diameter sensors or a thin-walled guide tube and machined tips, to enable the sensor to be replaced while the process is still running, minimising production downtime for the customer. We even offer full site supervision of the installation if the customer requires this."
 
OMC multipoint temperature sensors and termination glands are fully certified as a combined pair to Exde IIC T6 standards, for termination into a suitable enclosure, which can be mounted directly on top of the assembly or remotely at a more suitable attachment point.
 
OMC's range of multipoint temperature assemblies also includes standard multipoint assemblies for storage tanks and vessels. Depending on the customer application, multiple special features can be added to the standard unit to improve the safety, interchangeability, response times and accuracy of the assembly. Typical assemblies include guide tube systems and heat transfer blocks. Flexible versions are also available for installation around bends and can be fitted from the underside of tanks.
 
For further information, view website: www.okazaki-mfg.co.uk or email: info@okazaki-mfg.co.uk   Refer to page 41

Insertion probe flow meter displays new feature

The HydriNs 2 electromagnetic insertion probe from Hydreka, on offer from  Halma Water Management, builds on the functionality, proven success and recognised accuracy of the original flowmeter. Chief  among the new features is support for an optional LCD screen that gives readouts of all measurements.

As with Hydreka's original HydriNs, this product is a portable, easy deployable and remote-monitoring ready method of measuring bi-directional flow rates, using a highly accurate electromagnetic sensor suitable for a wide range of pipe sizes. 'Hot tap' installation means that the supply is not interrupted, and in addition to the direct output to datalogging devices for result recording and wireless telemetry, the HydriNs 2 also supports an optional LCD display for local (within 200m) viewing of readings, results and alarms. The battery life for both the probe and the display is up to 10 years, depending on the setup settings, and both units are watertight - rated to IP68.

The HydriNs 2can be effectively used throughout the water distribution network, measuring accurate flow rates at reservoirs, treatment works, pumping stations, water pipes and DMA zones. Velocity profiling at the point of measurement validates the enhanced accuracy provided by the stainless steel elestrodes. The flow data is easily downloaded and interpreted with the tailor-made Winfluid software (PC or PDA), which can also be used to program the device. Aids to help the physical installation include a reinforced stem, anti-ejection, locking nut and insertion point clamp. This product is also easily linkable to other HWM products. For further information, view website: www.halma-water.com   Refer to page 176