Retrotec DM32, Operation Manual

Page: 6 / 91

Page 6 of 91
© Retrotec 2017
8.8 Calculated Result will be wrong if the Range and Device installed on fan are different than those
selected on the gauge ................................................................................................................................. 60
8.9 Moving tubes might cause fluctuating pressure readings ............................................................. 60
8.10 Fans with a single tube have results adjusted by gauge ................................................................ 61
8.11 Pressure can overshoot when using the Set Pressure key ............................................................. 61
8.12 Check if large fixed errors are caused by pinched tubes ................................................................ 62
8.13 Check if large fixed errors are caused by water in the tube ........................................................... 63
8.14 Check if large fixed errors are caused by sun heating the tubes.................................................... 63
8.15 Check if wind is causing fluctuating pressure ................................................................................. 63
8.15.1. Use the [@ Pressure] key to reduce the effects of wind ....................................................... 64
8.15.2. Use Time Averaging feature to reduce the effects of wind ................................................... 64
8.15.3. Let Time Averaging take effect before making readings ....................................................... 64
8.15.4. Use Baseline feature to reduce the effects of a constant wind ............................................ 64
8.15.5. In extreme cases you can use a Wind Damping Kit designed to reduce wind-related
fluctuations ............................................................................................................................................. 65
9. Technical Specifications ................................................................................. 67
Appendix A: Understanding Pressures on the Gauge ........................................... 68
Differential Pressure .................................................................................................................................... 68
Positive vs. Negative Pressure ..................................................................................................................... 68
Why static and fluctuating pressures occur, causing bias ........................................................................... 69
Managing fluctuating pressures created by wind ....................................................................................... 69
Reduce uncertainty in results by taking lots of readings ............................................................................ 70
Appendix B: Flow Equations used with Devices ................................................... 71
Appendix C: Manually estimate Flow if required test pressure cannot be reached
............................................................................................................................ 76
Cannot Reach 50 Pa Factors ........................................................................................................................ 77
Cannot Reach 25 Pa Factors ........................................................................................................................ 78
Appendix D: Details about the @Pressure extrapolation function ....................... 79
“n value” for @Pressure extrapolation ....................................................................................................... 80
Errors occur in estimated flow if gauge and actual “n” don’t match .......................................................... 81
Appendix E: Tables to adjust Flow values for temperature difference ................. 84
Appendix F: Tables to correct Flow if range selected did not match the installed
range ................................................................................................................... 86
Appendix G: Measure Supply or Exhaust flow with a gauge and box .................. 87