Retrotec DM32 - Manual (Page 6)

Page 6 of 94
©Retrotec Inc. 2014
8.8 Calculated Result will be wrong if the Range and Device installed on fan are different than those
selected on the gauge ................................................................................................................................. 61
8.9 Moving tubes might cause fluctuating pressure readings ............................................................. 61
8.10 Fans with a single tube have results adjusted by gauge ................................................................ 62
8.11 Pressure can overshoot when using the Set Pressure key ............................................................. 62
8.12 Check if large fixed errors are caused by pinched tubes ................................................................ 63
8.13 Check if large fixed errors are caused by water in the tube ........................................................... 64
8.14 Check if large fixed errors are caused by sun heating the tubes.................................................... 65
8.15 Check if wind is causing fluctuating pressure ................................................................................. 65
8.15.1. Use the [@ Pressure] key to reduce the effects of wind ....................................................... 65
8.15.2. Use Time Averaging feature to reduce the effects of wind ................................................... 65
8.15.3. Let Time Averaging take effect before making readings ....................................................... 65
8.15.4. Use Baseline feature to reduce the effects of a constant wind ............................................ 66
8.15.5. In extreme cases you can use a Wind Damping Kit designed to reduce wind-related
fluctuations ............................................................................................................................................. 66
9. Technical Specifications ................................................................................. 68
Appendix A: Understanding Pressures on the Gauge ........................................... 70
Differential Pressure .................................................................................................................................... 70
Positive vs. Negative Pressure ..................................................................................................................... 70
Why static and fluctuating pressures occur, causing bias ........................................................................... 71
Managing fluctuating pressures created by wind ....................................................................................... 72
Reduce uncertainty in results by taking lots of readings ............................................................................ 72
Appendix B: Flow Equations used with Devices ................................................... 74
Appendix C: Manually estimate Flow if required test pressure cannot be reached
............................................................................................................................ 79
Cannot Reach 50 Pa Factors ........................................................................................................................ 80
Cannot Reach 25 Pa Factors ........................................................................................................................ 81
Appendix D: Details about the @Pressure extrapolation function ....................... 82
“n value” for @Pressure extrapolation ....................................................................................................... 83
Errors occur in estimated flow if gauge and actual “n” don’t match .......................................................... 84
Appendix E: Tables to adjust Flow values for temperature difference ................. 87
Appendix F: Tables to correct Flow if range selected did not match the installed
range ................................................................................................................... 89
Appendix G: Measure Supply or Exhaust flow with a gauge and box .................. 90