User manual VAISALA HMM213

[. . . ] USER'S GUIDE Vaisala HUMICAP Humidity and Temperature Module HMM213 ® U339EN-1. 3 PUBLISHED BY Vaisala Oyj P. O. Box 26 FI-00421 Helsinki Finland Phone (int. ): +358 9 8949 1 Fax: +358 9 8949 2227 Visit our Internet pages at http://www. vaisala. com/ © Vaisala 2009 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. ________________________________________________________________________________ Table of Contents CHAPTER 1 GENERAL INFORMATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] These versatile modules incorporate the HUMICAP®180R humidity sensor, which uses an operating principle based on changes in the capacitance of a thin polymer film as it absorbs water molecules. The HMM213 modules measure temperature with the reliable Pt 100 sensor. If the module is ordered with chemical purge option, it incorporates a composite sensor. 16 ____________________________________________________________________ U339EN-1. 3 Chapter 3 ________________________________________ To Be Noted When Measuring Humidity CHAPTER 3 TO BE NOTED WHEN MEASURING HUMIDITY This chapter describes issues that need to be noted in the measurement of humidity. In the measurement of relative humidity and especially in calibration, it is essential that the temperature equilibrium is reached. Even a slight difference in the temperature between the measured object and the sensor causes an error. For example, at +20 °C (+ 68 °F) and 50 %RH, a temperature difference of ±1 °C between the measured object and the sensor causes an error of ±3 %RH. A graph of the measurement error at 100 %RH when the temperature difference between ambient air and the sensor is 1 °C is presented in Figure 1 on page 18. The error is at its greatest when the temperature of the sensor differs from that of the surroundings and the humidity is high. A difference of a few degrees in temperature may cause water to condense on the sensor surface. Efficient ventilation accelerates the evaporation of the condensed water whereas in an unventilated space, it may take hours. The HUMICAP®180R sensor returns to its normal functioning as soon as water has evaporated. Contaminated water condensing on the sensor may shorten its life span and alter the calibration. VAISALA _______________________________________________________________________ 17 USER'S GUIDE____________________________________________________________________ 10 9 8 7 dRH (%RH) 6 5 4 3 2 1 0 -40 -20 0 20 40 60 80 100 Temperature (°C) Figure 1 Measurement Error at 100 %RH when the Temperature Difference between the Ambient Air and the Sensor is 1 °C NOTE With a dewpoint module, the temperature equilibrium is not a problem as the temperature of the sensor head changes continuously and the sensor head has a fast humidity response. 18 ____________________________________________________________________ U339EN-1. 3 Chapter 4 _______________________________________________________________ Installation CHAPTER 4 INSTALLATION This chapter provides you with information that is intended to help you install this product. Selecting Location Finding a suitable site for HMM213 is important for getting representative ambient measurements Select a place that gives a true picture of the environment or process and is as clean as possible. Install the sensor head to a sufficient distance from the duct or chamber walls. Make sure to insert enough cable to the same space with the probe in order to prevent heat conduction. If an additional temperature probe is used, install it so that the warmed sensor head does not interfere with the measurement. Electrical Connections The HMM213 module is connected to a process control system with screw terminals. The wiring diagram is shown in Figure 2 below. X1 TX RX GND TX Us GND Terminal GND RX 12-35VDC + Figure 2 Electrical Connections VAISALA _______________________________________________________________________ 19 USER'S GUIDE____________________________________________________________________ Dimensions 1 (0. 4) 2 1. 0 6( 2) ~6 5 (2 . 56 ) Figure 3 Dimensions in mm (inches) Serial Bus Settings The serial communication parameters set at factory are: Parameter Baud Parity Data bits Stop bits Value 1200 None 8 1 20 ____________________________________________________________________ U339EN-1. 3 Chapter 5 __________________________________________________________ Serial Commands CHAPTER 5 SERIAL COMMANDS This chapter contains information that is needed to use the serial commands for this product. Output via the Serial Bus R Starting the Measurement Output R <cr> Starts output of measurements to the peripheral devices (PC display or printer); output interval is set with command INTV. The output format depends on the transmitter configuration and parameters in use. The order, however, is always the same: relative humidity, temperature, and dewpoint. An example: RH 43. 0 %RH T 21. 0 'C Tdp 8. 0 'C <cr><lf> When the transmitter sends out the readings, the serial interface does not echo any commands; the only command that can be used is S (stop). S Stopping the Measurement Output S<cr> Ends the RUN state; after this command all other commands can be used. VAISALA _______________________________________________________________________ 21 USER'S GUIDE____________________________________________________________________ SEND Outputting a Reading Once SEND <cr> in STOP state or SEND aa <cr> in POLL state aa = address of the transmitter when more than one transmitter is connected to a serial bus (0 . . . 99; set with command ADDR) Outputs the current measurement readings via the serial line. The output format depends on which parameters the transmitter can output. [. . . ] In some applications, the sensor gain may decrease gradually due to interference caused by some chemical present in the ambient air (see Figure 5 below). The sensor polymer absorbs the interfering chemical; this reduces its water absorption ability and so decreases the sensor gain. In chemical purge, the interfering chemical is evaporated by heating the humidity sensor to a temperature level of approximately +160 °C. Automatic chemical purge takes place at startup. Calibration values Chemical purge Output signal Measured values after chemical exposure Humidity Figure 5 Decrease of the Sensor Gain Due to an Interfering Chemical and the Effect of the Chemical Purge Process The sensor with chemical purge option is a composite sensor in which the HUMICAP® and Pt 100 temperature sensors are attached to each other. [. . . ]