Flow Control - Jan 2012
reader feedback Are Coriolis Flowmeters Aptly Named I found the article on the naming of Coriolis flowmeters by Yoder in the November issue especially enlightening pages 14 18 Many of the explanations of the effect discuss the appearance of a force not an actual force Then what twists the tubes Heres a better explanation IMHO If you stand near the earths axis say the north pole you travel a small rotational distance as the earth turns for 24 hours say 240 miles in a day or 10 mph As you walk south away from the axis your rotational speed increases At the equator your rotational distance is about 25000 miles in 24 hours or more than 1000 mph youve accelerated Acceleration requires a force In these flowmeters the fluid moves away from and back towards the rotational axis accelerating and decelerating the fluid in Analog vs Digital Pressure Gauges requirements of our distributors and their customers around the world Analog gauges provide one major advantage over digital and that is in the quick visual recognition that a process is in optimal pressure this is given by the position of the pointer on the dial news notes Analog vs Digital Pressure Gauges A nalog dial gauge technology has been around for more than 150 years dating back to the Industrial Revolution when steam processes emerged in machine age factories and locomotives Accidents resulting from over pressure werent uncommon and as a result instruments like pressure gauges and safety relief valves came into play to protect workers and everyday citizens from hazardous application scenarios Up until about 30 years ago analog pressure gauges remained relatively unchanged in their basic components with a Bourdon tube originally designed by Eugene Bourdon of France at the heart of the technology Around this same time the digital wristwatch came into fashion and soon afterward a new digital option for pressure gauges was introduced The digital gauge has been on the rise ever since but its analog predecessor remains a leading presence in the pressure measurement space Both have improved over the last 15 years as new materials of construction have become available and new manufacturing techniques and technologies have been introduced such as laser welding and helium leak testing This has resulted in mechanical gauges that are more reliable last longer provide a more consistent reading and are less expensive Regarding digital gauges specifically the evolving technology has allowed new more stable sensing elements to be developed Higher accuracy measurement can now be made and effects such as temperature drift can now be calibrated allowing the sensor to remain accurate over a wide range of operating temperatures Choosing the Right Gauge From backyard swimming pools to hightech laboratories pressure gauges are found in a wide range of applications Some of the common uses for pressure gauges are tire pressures calibration tank refill leak detection process monitoring and line testing just to name a few Can a case be made for using one gauge versus the other According to the experts that question is directly related to what application it will be used for It acceleration and the other direction at the outlet deceleration An analog dial pressure gauge is used on an oil head in Alaska Photo courtesy of Ashcroft Inc Digital gauges are more resistant over their analog counterparts to withstanding over pressure spikes without sustaining damage Photo courtesy of Automation Products Group is very important that end users select a pressure gauge that is going to operate the best for them and give them the best results based on what they want to use it for says Gene Urbinati global product line director for Mechanical Products at Ashcroft ashcroft com Gordon W Greathouse applications engineer for Automation Products Group apgsensors com says the best way to determine whether to use analog or digital gauges is to decide what kind of accuracy is needed for the reading How much are you willing to spend he asks Do you need any type of outputs and where is this gauge going to be installed If an accuracy of 05 percent and greater will suffice and you have a static application and want the least expensive option an analog gauge would work well He says digital gauges on the other hand will provide a precise accurate reading no interpretation is needed and microprocessor technology will allow for several additional programmable functions By Amy W Richardson 8 September 2011 Flow Control FC 0911 DA 1 indd 8 8 26 11 11 31 AM Circle 9 or Request Info Instantly at www FlowControlNetwork com I enjoyed reading your article on analog digital pressure gauges in the September issue of Flow Control and wholeheartedly agree that analog gauges will not be displaced with digital gauges While Winters Instruments manufactures both digital and analog pressure and temperature instruments our core business remains in the analog game and this is supported by the the rotational directions Acceleration requires a force F MA which is where the fluids mass makes its appearance The force on the fluid transfers to the tube twisting it in one direction at the inlet Jim Talbot JET Publicity a pointer at the mid range 12 oclock should mean that pressure is good A digital gauge showing a number will not always provide facilitate such quick verification Desmond Khor Winters Instruments When considering the modern technology available today there are some common application issues end users can more adeptly address with modern day digital pressure gauges than they could with previous generations of analog devices Accurate precise readings of lowpressure applications of less than 5 PSI are possible with digital gauges because of microprocessing in digital gauges says Greathouse Leak detection is also more precise with digital gauges He says resolutions of up to 01 or 001 are common with digital gauges while pressure changes of such small increments are virtually impossible to detect with analog gauges Urbinati says digital gauges are more resistant to withstanding over pressure spikes without sustaining damage typically 200 percent of the rated pressure range compared to 130 percent for analog gauges although analog gauges now have improved features to prevent wear from vibration and pulsation Digital gauges may also be more suitable for applications where there is constant pressure pulsation which could cause an analog gauge to wear out moving parts and the operator to see a constantly moving indicator says Urbinati Digital gauges sample at various rates typically 100 or 250 milliseconds to average out small pulsations and display a constant value Further he says a digital gauge is desirable when the end user wants both a local and remote pressure indication or when an automated process control uses pressure as an input to the control system For all the modern advantages of the digital gauge there are some times when the simplicity of the analog gauge would work best and be more cost effective For instance when only a general reading is required high medium low an analog gauge would be the best choice Analog gauges are offered in many different display sizes as well And one major advantage is that they require no power or batteries Common Pitfalls Negative Impacts Not being aware of the gauges datasheet specifications unfamiliarity with the www FlowControlNetwork com January 2012 13
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