User manual VAISALA GMP343

[. . . ] USER'S GUIDE Vaisala CARBOCAP® Carbon Dioxide Probe GMP343 M210514EN-C PUBLISHED BY Vaisala Oyj P. O. Box 26 FIN-00421 Helsinki Finland Visit our Internet pages at http://www. vaisala. com/ © Vaisala 2007 No part of this manual may be reproduced in any form or by any means, electronic or mechanical (including photocopying), nor may its contents be communicated to a third party without prior written permission of the copyright holder. Please observe that this manual does not create any legally binding obligations for Vaisala towards the customer or end user. All legally binding commitments and agreements are included exclusively in the applicable supply contract or Conditions of Sale. [. . . ] Note that if the noise distribution is somewhat uniform the median filter does not give any additional value. The default value is 0 (meaning that the median filter is disabled). Averaging Filter The averaging filter calculates a moving average over the user-set period of time. The longer the averaging time is the lower the noise at the measurement signal. For example, if the averaging is set to 30 seconds, the most recent average filter output is the average of the last 15 measurements (2 seconds measurement interval). The default value is 10 seconds, and the maximum filter length is 60 seconds. Table 6 on page 43 presents the measurement noise as a function of averaging time at 370 ppm CO2: Table 6 0s 10 s 30 s Averaging Times Noise 3 ppm 2 ppm 1 ppm Averaging Time VAISALA _______________________________________________________________________ 43 User's Guide ______________________________________________________________________ Smoothing Filter The smoothing filter calculates the running average by weighting the most recent measurement by the user-set proportion of the preceding measurement. By using the smoothing filter, averaging up to even 15 minute periods can be accomplished. The smoothing filter is feasible for the background measurement where fast changes in the CO2 concentration are not common. See the next section to find the difference between smoothing and averaging in regard to response time. The smoothing factor is set by the SMOOTH command, where the range of the factor is 0 . . . The relationship between averaging and smoothing from the noise reducing point of view is like follows: (SMOOTHING FACTOR × 4) = approx. AVERAGING TIME (s) The default value is 0 (meaning that the smoothing filter is disabled). How the Filtering Affects the Response Time The following figure illustrates the difference of the two filters in regard to time response. The averaging time is set to 40 seconds while the smoothing factor is set to 10 to have about equal noise rejection properties. See also the response time tables presented in Specifications, Response time (90 %), on page 80. Figure 9 The Difference of the Two Filters in Time Response 44 __________________________________________________________________ M210514EN-C Chapter 4 ________________________________________________________________ Operation Setting the Median Filter Use the median filter to remove random peak values caused by possible external interference. MEDIAN x <cr> SAVE <cr> x=0. . . 13 (default=0) >median 3 MEDIAN : 3 >save EEPROM saved successfully (829 ms). > Setting the Averaging Filter Use the averaging filter to reduce the noise of the measurement. AVERAGE x <cr> SAVE <cr> x=0. . . 60 seconds (default =10 s) >average 20 AVERAGING (s) : 20 >save EEPROM saved successfully (829 ms). > Setting the Smoothing Filter Use the smoothing filter to reduce the noise of the measurement for long averaging periods. SMOOTH x <cr> SAVE <cr> x=0. . . 255 (default =0) VAISALA _______________________________________________________________________ 45 User's Guide ______________________________________________________________________ >smooth 10 SMOOTH : 10 >save EEPROM saved successfully (829 ms). > Flushing the Filters (Resynchronization) With this command you can flush the filters to get rid of the effect of the past measurements. RESYNC <cr> >resync > Linearization Due to the principle of the CO2 absorption, the sensor of GMP343 produces a signal which is not linear in relation to the CO2 concentration. However, the output signal is linearized with the internal linearization function. [. . . ] Vaisala Service Centers perform calibrations and adjustments as well as repair and spare part services. Vaisala Service Centers also offer accredited calibrations, maintenance contracts, and a calibration reminder program. Do not hesitate to contact them to get further information. NORTH AMERICAN SERVICE CENTER Vaisala Inc. , 10-D Gill Street, Woburn, MA 01801-1068, USA. Phone: +1 781 933 4500, Fax: +1 781 933 8029 E-mail: us-customersupport@vaisala. com EUROPEAN SERVICE CENTER Vaisala Instruments Service, Vanha Nurmijärventie 21 FIN-01670 Vantaa, FINLAND. [. . . ]