User manual VAISALA DM500

[. . . ] USER'S GUIDE Vaisala DEWCAP Precision SAW Hygrometer DM500 ® M210205EN-D PUBLISHED BY Vaisala Oyj P. O. Box 26 FIN-00421 Helsinki Finland Phone (int. ): +358 9 8949 1 Fax: +358 9 8949 2227 Visit our Internet pages at http://www. vaisala. com/ © Vaisala 2006 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. The contents are subject to change without prior notice. 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. ________________________________________________________________________________ Table of Contents CHAPTER 1 GENERAL INFORMATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] OK. Select ENABLED WHEN, press SELECT. Now you can select the measurement status that activates the alarm. STOP: alarm is enabled when dewpoint measuring status is STOP. ERR: alarm is enabled when dewpoint measuring status is ERR. OK: alarm is enabled when dewpoint measuring status is OK WAIT: alarm is enabled when dewpoint measuring status is WAIT All the modes selected: alarming is not dependent on any measurement status (only on numeric set points). None of the modes selected (never): alarming is disabled. You can select any combination of the measurement status to control the alarm. Press OK and EXIT to return to the main view. Alarming The display is beeping and blinking and the note sign message is shown in the display. Mute the alarming by pressing MUTE and OK. If the alarming condition is still valid a small note sign remains in the header of the display. The note sign disappears when the alarming condition is not valid anymore. VAISALA _______________________________________________________________________ 57 User's Guide ______________________________________________________________________ This page intentionally left blank. 58 __________________________________________________________________ M210205EN-D Chapter 11 _____________________________________________________ Measurement Settings CHAPTER 11 MEASUREMENT SETTINGS This chapter provides you with information about the measurement settings. Automatic Frost Detection The automatic dew/frost sensing procedure senses if the condensation on the sensor is water (dew) or ice (frost). If the sensing is turned off, the Td/f value can be either dewpoint or frostpoint, depending on the sensor state. Then the other water content quantities are disabled. If the sensing is on (default), the Td/f value below temperature of 0 ºC/32 ºF is always frostpoint. Open MENU: press . Select Measuring, press Select Measurement settings, press Select Autom. frost detection. To enable the sensing, press To disable the sensing, press Press ON. OFF. . EXIT to return to the main view. NOTE Cleanliness of the sensor is essential for the proper operation of frost detection. VAISALA _______________________________________________________________________ 59 User's Guide ______________________________________________________________________ Forced Freezing In some measurement conditions there may be formation of a two phase system, ice-dew, on the sensor. This situation is dynamic and the time needed to reach an equilibrium may be rather long. To avoid an unstable phase transition, the DM500 has a function for generating a stable layer of frost on the sensor right from the beginning of the measurement. When turned on, the forced freezing procedure is automatically enabled when measurement is started. However, the forced freezing procedure may also be turned off by the user, if so desired. The automatic forced freezing procedure recognizes the temperature at which condensation begins to form on the sensor surface. The control of the forced freezing procedure is based on this temperature, and therefore the dewpoint of the measured gas should be stable during the freezing procedure. [. . . ] Other parameters, such as relative humidity, require knowledge of additional information, such as the temperature of the gas. Saturation Vapor Pressure Saturation vapor pressure is the maximum pressure of water vapor that can exist at a given temperature. This quantity is expressed in pressure units such as Pascals or millibars, and is often represented by the symbol "e. " There is a unique saturation vapor pressure for any temperature. Thus, if a gas is cooled until condensation forms (the dewpoint temperature), it is possible to determine the saturation vapor by measuring the temperature at which condensation forms or remains in equilibrium. Dewpoint Temperature (Td) Dewpoint is the temperature at which condensation begins to form when a gas is cooled. An object or surface is said to be at the dewpoint temperature when condensation is maintained in an equilibrium condition (amount of condensation is neither shrinking nor growing). [. . . ]