Valve Magazine - Summer 2009

INSTRUMENTATION

WIRELESS VALVE MONITORS

The benefits of using these alerts include:

; Mitigating common maintenance errors such as excessive packing friction; poor seat loading; and degraded elastomers

; Minimizing work time in hazardous areas

; Calibration assurance

; “As found/as left” documentation

; Consolidated maintenance documentation for quick review and reference

; Availability of proactive and predictive maintenance practices

; Increased efficiency of plant and maintenance operations

; Improved outage planning

PROVIDING CRITICAL
VALVE INFORMATION

Digital valve controllers, with their ability to monitor and report on valve health, have proven they improve

Reliability’s a Real Consideration

The reliability of wireless systems depends on having multiple paths of communication so that if one device fails or is blocked, another path can be taken. This is solved through the use of “mesh networks” that offer many different paths for transmissions to follow in order to reach the gateway (or receiver), which directs the communication to a control system or other appropriate locations in the plant. The mesh provides redundancy that yields a high level of communication reliability no matter what permanent or temporary obstacles may exist between the transmitting device and the gateway. This is not true of all wireless systems.

Another assurance of reliability is an electronic technique called “frequency hopping.” If one of the assigned frequencies is jammed or compromised by noise or other interference, the wireless transmitter senses the problem and

process reliability and reduce overall maintenance costs. The diagnostics collect and correlate data, establish the cause of a problem, and recommend specific corrective action. When they are integrated into the system, the operator and the maintenance staff have direct access to those recommended actions. This is information critical to keeping a valve in operation, rather than just statistics on how the valve is operating.

As this shows, it makes sense today to equip critical control valves with a digital valve controller capable of in-service diagnostics. It is also important to select a digital instrument with multiple sensors and analysis software that enables plant personnel to evaluate current valve operation and forecast future performance. Addressing both immediate and long-term control valve performance has a dramatic effect on process plant efficiency, overall profitability and control valve life-cycle costs. automatically uses another channel.

With multiple paths between devices and many frequencies available, the reliability of wireless networks is at least equal to wired systems, and they are not subject to power outages or inadvertent damage to cables. The mesh network concept and frequency hopping techniques are included in the already-approved WirelessHART standard to which the smart wireless system adheres, as well as the pending ISA100 standard.

Devices based on this technology have been proven in use to demonstrate greater than 99% data transfer reliability.

A large number of wireless transmitters rely on battery power with battery life typically running between 5 to 10 years, depending on how fast a given device updates. This is a distinguishing characteristic between wired and bat-tery-powered devices. Wired instruments send information almost con-

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Today’s digital diagnostic technology allows fault detection and analyses to be made while the control valve is in operation. And today’s valve instrumentation has multiple on-board sensors that combine with advanced analysis software to provide high levels of performance information.

The most advanced digital valve controllers now can detect and evaluate more than 200 different problems that impact control valve dynamic performance. These include instrument air leakage, valve assembly friction, instrument air quality, incorrect bench-set, travel deviation and process buildup on valve trim and much more. In addition, the appropriate digital controller can perform online, partial stroke testing of safety valves.

The best level of understanding is gained by implementing and consistently executing maintenance plans driven by, or at minimum augmented by, valve diagnostic tools. Maintenance plans should define what diagnostic tools should be used for each tag based on specific phases of plant operation such as: commissioning, normal operation, pre/post outage, and following valve repair.

CONCLUSION

While older technologies can be maintained that provide high performance, moving to new technologies provides capabilities that will improve your plant performance over a longer period of time by eliminating the cycles of degradation followed by maintenance. If your plant decides to keep using the older technologies, make sure that during turnarounds, the maintenance is thorough.

But if you choose newer technologies, you enable detection of problems before operations are significantly affected. VM

HARRY BURNS is Fisher FIELDVUE Product Manager, Emerson Process Management (www. emerson.com). He has worked with Fisher equipment for more than 30 years and is currently managing the development and introduction of the User Interface for setup and maintenance for the FIELDVUE Instruments. Reach him at 641.754.3055

stantly, whereas wireless devices may operate on a one-minute schedule, remaining at rest most of the time and coming to life just long enough to transmit an update. This can be done more often if required by the situation, but with a corresponding reduction of battery life. In addition, these devices provide an estimate of remaining power life that enables scheduled maintenance.

Serious About Security

A very real issue with all wireless transmissions is that some outsider might be interested in intercepting or altering the data. Security is taken very seriously by IT experts, who have identified several important elements to wireless transmission security.

The first of these is encryption, a method of seemingly random symbols that surround each transmission. Even if the message is intercepted, it takes too long to decode to be of use. Encryption keys are changed frequently so that anyone trying to read intercepted messages by comparing them will not be able to break the code before it is changed.

In addition, each transmission must be authenticated, meaning that the sending and receiving devices must recognize each other, or the transmission will be ignored. Another step is data verification by the receiving device. The authentication and verification rules are built into the devices, so no foreign device will be able to intercept a transmission or send bogus information to the receiving station.

The channel-hopping feature discussed earlier protects against jamming of channels by either intentional or non-intentional sources, which is the final key to secure wireless transmissions.