If your process includes hazardous locations, you can appreciate the extra care that must be taken with the wiring to instrumentation located in these areas. And ongoing testing of these transmitters and final control elements poses challenges as well.In a Control Engineering article, Inspecting instruments installed in hazardous locations, Emerson’s Ian MacDonald describes how wireless instrumentation helps avoid these wiring and ongoing testing challenges. Ian opens describing some of these installation challenges:
Field transmitter wiring requires wiring, conduits, cable trays, field junction boxes, and marshalling cabinets. If the instrument is 4-wire, it must have separate power wiring. All wiring systems must meet the requirements of IEC 60079 [Explosive Atmosphere Standards] for the type of protection that the circuit is certified for. This could be “EX ia” for intrinsically safe, “Ex d” for explosion-proof, or one of the other types of protection permitted.
He notes how this standard applies to installation and ongoing maintenance:
IEC 60079-14 requires that an initial inspection must be carried out when the equipment is first installed. IEC 60079-17 says the interval between inspections shall not exceed three years without seeking expert advice.
The standard describes four levels of inspectionsâ€”continuous, visual, close, and detailed for the electrical equipment located in hazardous areas. Based on the paths of the wiring back to the control system, inspections may be difficult to perform. This difficulty increases the costs of the inspections.
Ian shares some typical issues found when conducting these inspections:
- Incorrect or damaged cable gland
- Damaged cables
- Non-IS (intrinsically safe) circuits installed with IS circuits
- Incorrect segregation of IS and non-IS circuits
- Wrong zener barrier or galvanic isolator fitted
- No earth on zener barrier
- Non-IS earths connected to IS earth, and
- Equipment not as scheduled
He describes how wireless instrumentation can reduce these costs both in the project phase as well as the ongoing maintenance phase.
By removing the wires, conduit, cable tray, field junction boxes, and marshalling cabinets, equipment costs are reduced and savings are realized in creating drawings and equipment schedules. This also reduces space and weight requirements, which can be very important in some industries where space is limited and weight is a factor.
The cost of installation must also be considered, as not having to install equipment required for wired instruments reduces labor costs and can speed up installation and commissioning times. This also allows for a reduction of facilities required to support this type of work, such as cabins, access equipment, and more.
From an ongoing inspection perspective:
Only the instruments themselves have to be inspected, and possibly the wireless gateways if they are installed in the hazardous area. But in many instances, gateways can be installed outside the hazardous area. For the same reasonâ€”fewer pieces of supporting devices-the number of repairs will be reduced.
You’ll want to read the article to see Ian’s comparison of wired vs. wireless and the 15 points of inspection vs one.
You can also connect and interact with other wireless experts in the Wireless group in the Emerson Exchange 365 community.