Control Engineering May 2014-CE : P6

inside process Figure 6: High-end transmitters offer transient suppression options that can be integrally mounted within the housing. Before installing a sys-tem, it might be wise to review this guidance to veri-fy that the design you are going to install is the best choice for the intended application. Should any changes be required, it is less expensive to change it while still in the shop instead of in the field. Some of the more critical tips for ensuring the best accu-racy and performance of your temperature measurement sys-tem include: n For many applications a properly specified RTD sen-sor should be the first choice unless the temperature range exceeds 600 C. Up to 850 C, the choice is appli-cation driven; over 850 C, a thermocouple is the only practical choice. n Mount the sensor integrally with the transmitter when-Ensuring optimal performance and accuracy ever possible to minimize noise pickup on the sensor lead wires. n Use a transmitter in a dual compartment housing to minimize environmental influence on the transmitter. n Use a stepped thermowell for fastest response. n Perform a wake frequency analysis to ensure selection of a proper thermowell configuration that will with-stand the vibration caused by vortex shedding as the process fluid flows past the thermowell. n Specify sensor-transmitter matching wherein the trans-mitter is configured to use the sensor-specific CVD constants which characterize the sensor, thus providing outstanding measurement accuracy. n Consider use of dual element sensors or two separate sensors for redundancy and drift monitoring. n For installations in electrically noisy environments, specify transient protection. n Consider specifying and using transmitter intelligent filtering, diagnostics, and other options to enhance measurement integrity, reliability, and accuracy. As-designed meets as-installed New Technology Meters (NTM) It is often the case where design and instrumentation spec-ifications are done before P&IDs and other drawings are finalized. Therefore, it is always important for the installation team to verify that the system specified by a design engineer meets the actual final design requirements of the application. The more critical the measurement, the more attention that should be given to every installation detail. It is much easier and cost effective to do it right the first time instead of delaying a start-up or requiring an unsched-uled shutdown to make system changes or to correct instal-lation problems. ce -Ryan Leino is a senior marketing engineer for Rose-mount products in the temperature group at Emerson Pro-cess Management. Go Online This is the sixth part of this temperature series. Read the earlier installments at NTM -L • Loop, Signal or Externally Powered • 2.9” x 1.5” Plastic or Metal Housing • Auto Tri-Color Bargraph • Input Failure Indication • Lifetime Warranty (520)748-7900 input #23 at Make the right choice: RTD vs. TC, July 2013 Taking the mystery out of thermowell selection, September 2013 The long and short of connecting sensors to control rooms, November 2013 Keys to achieving high accuracy and reliability in temperature measurement, January 2014 Temperature diagnostics help prevent unplanned shutdowns, March 2014 To learn more about measuring temperature in process manufacturing applications, go to and order a free copy of “The Engineer’s Guide to Industrial Temperature Measurement.” Subscribe to the Process Instrumentation & Sensors Monthly eNewsletter at P6 ● MAY 2014 CONTROL ENGINEERING ●

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