Vol. 5 No. 6 Subject: Flow Measurement News Date: 10-1-03 From: McCrometer, "The Flow Measurement Specialists" ........ http://www.mccrometer.com ........ ******************************************* This newsletter is e-mailed by McCrometer monthly to subscribers worldwide. It consists of flow measurement information of interest for professionals in this field. For More information on our complete line of flowmeters go to: http://www.mccrometer.com ******************************************* McCrometer Newsletter - September 2003 Special Notice - McCrometer is pleased to announce the addition of guest authors for our monthly newsletter. This month we feature Walt Boyes and David W. Spitzer, PE. Walt has more than 25 years of experience in the controls and instrumentation industry both for process instruments and environmental controls, and David has over 25 years experience in many facets of instrumentation, process control, electrical, and utility engineering, including conceptualization, estimating, design, construction, startup, operation, troubleshooting, and teaching. Together, they own and operate Spitzer and Boyes LLC, serving both the profit and not-for-profit business sectors. The Flowmeter Start-Up Blues, Part Two By Walt Boyes and David W. Spitzer A start-up engineer’s nightmare is the flowmeter that is correctly specified, and appears to be installed at the correct location, but which does not appear to work properly. For example, a propeller meter, like other types of insertion flowmeters, might be installed sideways to the flow instead of in line with it. This is somewhat difficult to see, depending on the model of flowmeter, and causes erratic readings, or no readings at all. Other examples of installation problems are improper wiring of analog outputs, no power connection, pipe not full of fluid, and similar things that the start-up engineer has to watch out for. Often, you have to live without even a decent solution to the problem. In wastewater treatment plants, often the Palmer-Bowlus or Parshall flume is cast incorrectly into the concrete. Now the flume is really the flowmeter, and the “open channel flow transmitter” is merely a level sensor that determines automatically the height at the measurement point in the flume, and applies the correct algorithm to display flow. It is critical to the measurement that the flume be installed correctly; because the transmitter assumes that the level it is seeing is accurate. About the only thing you can do, other than to shut the plant down completely, is to dye test, or do velocimetric testing to determine an actual calibration curve for the flume, and reprogram the device. This holds true for closed pipe flowmeters as well. You may have to do this if your flowmeter is an insertion device and is located downstream of an elbow, or control valve. It isn’t all bleak, though. Typically, a flowmeter in building controls or process plants is used for control, rather than fiscal metering, and therefore, repeatability of the signal can be more important than absolute accuracy. So if you can get a repeatable signal you can live with, you can commission the flowmeter and make the system “work”, until the measurement is needed for heat and material balance calculations to improve the process. Calibration in-situ is usually impractical or impossible. Lots of flowmeters can be sold with “calibrators” and test and measurement instrumentation companies make “calibration” devices. Some of these devices simply allow you to adjust the current output of the flow transmitter. Others simulate the input from the sensor, and allow you to test the operation of the transmitter. You can use a “loop calibrator” to check the output of the flowmeter at arbitrary values. You can use a primary element simulator. These devices allow you to simulate the output of the transducer to the transmitter, but not to test the operation of the transducers themselves, or calibrate them. But there is usually no practical way to test the operation of most flow sensors in closed pipe applications. So you cannot use these “calibrators” to actually calibrate the flowmeter. The only way to calibrate a flowmeter is to pass a known quantity of fluid through the meter and determine the deviation of the flowmeter’s reading from the actual value of fluid flow. Unless you can run the output of the flowmeter to a calibrated volume, weigh tank, or to a tank truck and weigh the truck, you are stuck with comparing, rather than calibrating. And even if you can weigh the output of the meter, often the resolution of the scale is too coarse to determine if the flowmeter is living up to its, say, 0.5% of indicated flow rate specification or not. Of course, you can use a flow comparison device. The most popular of these is the clamp-on portable transit time ultrasonic flowmeter. These devices are quite accurate, but not accurate enough to be used as a calibrator in most applications. You can use these flowmeters to be a critical comparison. If the reading on the clamp-on portable transit time meter reads close to the reading of the installed flowmeter, the installed flowmeter is likely in good calibration. If they do not closely agree (within 5-10% of reading), something is likely wrong. ******************************************* About the Authors After receiving his MSEE in optimal control, David W. Spitzer PE obtained over 25 years experience in many facets of instrumentation, process control, electrical, and utility engineering, including conceptualization, estimating, design, construction, startup, operation, troubleshooting, and teaching. He has worked for United States Steel, Mobay Chemical, and Nepera Chemical and has consulted for numerous other companies worldwide. Walt Boyes has more than 25 years of experience in sales, sales management, marketing, and product development in the controls and instrumentation industry both for process instruments and environmental controls, including Executive Committee experience in three companies. He is an expert at business transformation for small to medium-sized companies. He provides strategic planning, organizational development, business re-organization and electronic business re-engineering services for companies from roughly $5 million to roughly $100 million in revenues per year. Spitzer and Boyes LLC serves both the profit and not-for-profit business sectors. To find out more about McCrometer's line of flow meters, including the V-Cone(r), Wafer-Cone(r), the V2-Municipal(tm), Water Specialties Propeller Meter(tm), Mc(r) Propeller, Ultra Mag(r), and SK(r) Variable Area Meters, please contact McCrometer at 951-652-6811 or visit our website at www.mccrometer.com ******************************************* Copyright 2003 McCrometer If you have comments or suggestions for newsletter topics you would like to see, please address them to: Bob Peters or Richard Steven mailto:newscomment@mccrometer.com ********************************************************************************* Know anyone looking for a steady dose of flow measurement information? ********************************************************************************* To subscribe send e-mail to mailto:news-request@mccrometer.com with a keyword SUBSCRIBE in the subject field. 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