In Part 2, I discussed using Exic for Zone 2 applications ‘Intrinsic safety in normal operation’ i.e. with no safety factor required.
To repeat, firstly and importantly, there is a misconception that the Co values are defined by the design of barrier/isolator. The Co value is actually defined in IEC/SANS60079-11: 2012 Table A.2 page 96.
So, any barrier/isolator with 28 V safety description will have Co = 83 nF (Zone 0/1; IIC). In practice, Co will define the maximum allowable cable length for most cases. However, as explained in Part 2, using Exic where applicable is one method to have longer cable lengths.
Gas Group classification impacts Co parameter as per Figure 1.
Figure 1: Co values.
Figure 2 shows an Exia loop with Co = 83 nF. The max cable capacitance Cc = 63 nF. With a typical cable capacitance of 95 nF/km, this would equate to maximum cable length of 660 m.
Figure 2: IIC IS loop for Zone 0/1 (Co 83 nF).
If the loop was Exic, then Co = 272 nF, so Cc = 252 nF would theoretically allow 2,5 km of cable i.e. no longer a limiting factor. (The limiting factor in this system is likely to be operating voltage at the end of the cable being high enough for the transmitter to work.)
If the Gas Group were IIB then Co = 650 nF, which eliminates capacitance as a limiting factor.
Conclusions
1. For installations requiring long cable runs, classifying the area as Zone 2 offers significant benefit.
2. Alternatively, a IIB (or IIA) classification is another way of allowing longer cables lengths.
Certified safe power for hazardous industrial environments Conical Technologies
IS & Ex
When working in high-risk environments like oil and gas, petrochemical plants or other hazardous industrial zones, safety isn’t just important, it’s essential. That’s why Traco Power developed the TIB-EX series of DIN rail power supplies, purpose-built to deliver reliable power even in the toughest conditions.
Read more...Parker strengthens explosion safety
IS & Ex
Parker Hannifin has announced that its 37 mm Ex d m coils have attained new ATEX and IECEx Type Examination Certificates according to the latest explosion protection standards.
Read more...Stopping the sparks from flying
IS & Ex
Whenever electrical equipment is required for use in hazardous environments they must be designed with intrinsic safety in mind. Darren Barratt, product sales manager at alarm and event management specialist, Omniflex outlines the importance and key aspects of intrinsic safety design.
Read more...Control and monitoring with only one device Pepperl+Fuchs
IS & Ex
Pepperl+Fuchs has expanded its portfolio of K-System isolated barriers for DIN rail mounting (power rail) with the KCD2-SCS interface module. As the first 2-channel AI/AO intrinsic safety barrier with dual function, the module can be configured individually for analogue input or output control signals.
Read more...Hazardous area solutions Extech Safety Systems
IS & Ex
SEW-EURODRIVE is revolutionising industrial automation with advanced gear units, decentralised drives and the energy-efficient MOVIGEAR system.
Read more...Inspection system for leak detection in valves in hazardous areas Extech Safety Systems
Valves, Actuators & Pump Control
Leaking valves in industrial plants not only lead to loss, safety risks and possible contamination and pollution, but also result in high economic costs. Therefore, valves in hazardous areas require regular proper inspection and preventive maintenance to ensure their functionality.
Read more...Field service regime key for effective PDS/CPS operation
IS & Ex
While their primary objective is to ensure the safety of people, proximity detection system and collision prevention system installations also have a direct bearing on other critical parameters such as equipment availability and productivity.
Read more...World’s first 5G smartphone for ATEX and IECEx zone 1/21 Extech Safety Systems
IS & Ex
i.safe MOBILE has launched the world’s first 5G smartphone for ATEX and IECEx zone 1/21. The intrinsically safe mobile device, which was also developed for use in 5G campus networks, offers companies great flexibility thanks to its wide range of possible applications, especially in the automation sector.
While every effort has been made to ensure the accuracy of the information contained herein, the publisher and its agents cannot be held responsible for any errors contained, or any loss incurred as a result. Articles published do not necessarily reflect the views of the publishers. The editor reserves the right to alter or cut copy. Articles submitted are deemed to have been cleared for publication. Advertisements and company contact details are published as provided by the advertiser. Technews Publishing (Pty) Ltd cannot be held responsible for the accuracy or veracity of supplied material.
printer friendly version