Compressed Air Best Practices - March 2008 - (Page 43)

Focus Industry FOOD PROCESSING | 03/08 | changes in dewpoint. The auto calibration changes the sensor output to relative humidity, which changes when temperature changes. This allows it to evaluate if the low humidity reading at 0% RH is correct and then to compensate for any dry end drift. The initial cost of these sensors is in the low to moderate range. Recommended calibration intervals are from one to two years. The thin film polymer sensor has a very fast response time to changing dewpoint, because of the conductivity of the polymer and the temperature probe. Most manufacturers recommend the thin film polymer type of probe for use in the production facilities with refrigerated dryer systems only. This is not usually recommended for general use in desiccant dryers due to marginal accuracy in the lower pressure dewpoint ranges. Calibration All manufacturers recommend factory calibration of the sensor at least once a year. We recommend having a spare probe to install and run while the other probe is being calibrated. The newly installed probe then can be used until the next calibration date. This practice will allow for constant monitoring of the dewpoint, without several days or weeks of down time to the dewpoint monitor. Some manufacturers offer a handheld Monitor/Calibration Unit for field calibration with the probe/electronics being sent back to the factory for calibration. There are also units available with automatic calibration feature built into the unit that will automatically calibrate the sensor while the unit is on line and running. Installation Guidelines: Sample Air The sample air line for the dewpoint monitor should be taken from the top of the main compressed air line leading to the main plant or to any part of the production area to be monitored. This will help protect the probe and sampling system from liquid water that may condense in the pipeline and may saturate the probe. The sample line should be made of stainless steel and be approximately ¼" in diameter. Actual flow rate depends on each individual unit. This is the typical sample system available; some have a filtering system either outside or inside the assembly. If a flow meter is not standard, consider installing one inside the case to set the proper flow over the probe: p p Side mount sample system The air sample from the pipeline should be measured at full line pressure not at atmospheric pressure. The dewpoint changes at lower pressures. The lower pressure will cause the unit to report false readings. The sample system should always be installed with a pressure gauge. This will allow the operator to verify that the sample air is at full line pressure. These can be either digital or analog The sample system should be located as close as possible to the sample point (from the main pipeline) www.airbestpractices.com p p 43 http://www.airbestpractices.com

Table of Contents Feed for the Digital Edition of Compressed Air Best Practices - March 2008

Compressed Air Best Practices - March 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month: Saving Energy with Blowers in Canada Do You Provide World-Class Service? Managing Rotary Screw Air Compressors at Midwest Bakery The Difference Between Acfm and Scfm for Proper Vacuum Sizing Best Practices — Multi-Module Process Air Dryers The Vacuum Formation Process in Building Compressed Air Filter Elements Solberg Manufacturing Real World Best Practices: Measuring Pressure Dewpoint in a Compressed Air System Resources for Energy Engineers: Training Calendar & Product Picks Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - March 2008

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