User manual VAISALA WMT50

[. . . ] USER'S GUIDE Vaisala WINDCAP® Ultrasonic Wind Sensor WMT50 M210736EN-B PUBLISHED BY Vaisala Oyj P. O. Box 26 FIN-00421 Helsinki Finland 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. [. . . ] Command format: aI! VAISALA _______________________________________________________________________ 61 User's Guide ______________________________________________________________________ where a I != = = Device address Send identification command Command terminator The response: a13ccccccccmmmmmmvvvxxxxxxxx<cr><lf> where a 13 = = Device address The SDI-12 version number, indicating SDI-12 version compatibility; for example, version 1. 3 is encoded as 13 8-character vendor identification Vaisala_ 6 characters specifying the sensor model number 3 characters specifying the firmware version 8-character serial number Response terminator cccccccc vvv xxxxxxxx <cr><lf> Example: = = = = mmmmmm = 0I!013VAISALA_WMT50103Y2630000<cr><lf> Start Measurement Command (aM) This command asks the device to make a measurement. The measured data are not sent automatically and should be requested with a separate Send data command aD. The host device is not allowed to send any commands to other devices on the bus until the measurement is completed. When several devices are connected to the same bus and simultaneous measurements from the different devices are needed, Start concurrent measurement aC or Start concurrent measurement with CRC aCC should be used, see the next sections. See Examples of aM, aC and aD Commands on page 67. 62 ___________________________________________________________________M210736EN-B Chapter 7 __________________________________________________ Getting the Data Messages Command format: aMx!where a M x = = = Device address Start measurement command The desired sensor to make the measurement 1 = Wind 5 = Supervisor If x is left out, the query refers to the combined data message used for requesting data from several sensors with just one command. See Examples of aM, aC and aD Commands on page 67. Command terminator ! = The response is sent in two parts: The response part one: atttn<cr><lf> The response part two (indicates that the data is ready to be requested): a<cr><lf> where a ttt n <cr><lf> = = = = Device address The measurement completing time in seconds The number of the measured parameters available (maximum number is 9) Response terminator NOTE For changing the message parameters, units and other settings, see Chapter 8, Sensor and Data Message Settings, on page 81. NOTE When the measurement takes less than one second, the response part two is not sent. VAISALA _______________________________________________________________________ 63 User's Guide ______________________________________________________________________ NOTE The maximum number of parameters that can be measured with aM and aMC commands is nine (9). If more parameters are to be measured, Start concurrent measurement commands aC and aCC should be used (for which the maximum number of parameters to be measured is 20), see the following sections. Start Measurement Command with CRC (aMC) Command format: aMCx!This command has the same function as the aM but a three-character CRC is added to the response data strings before <cr><lf>. In order to request the measured data, Send data command aD should be used, see the following sections. Start Concurrent Measurement (aC) This command is used when there are several devices on the same bus and simultaneous measurements are needed from the devices, or if more than nine (9) measurement parameters are requested from a single device. The measured data is not sent automatically and it should be requested with separate Send data command aD. See Examples of aM, aC and aD Commands on page 67. where a C x = = = Device address Start concurrent measurement command The desired measurement 1 = Wind 5 = Supervisor If x is left out, the query refers to combined data message in which the user can request data from several sensors with just one command. See the examples below. 64 ___________________________________________________________________M210736EN-B Chapter 7 __________________________________________________ Getting the Data Messages ! = Command terminator The response: atttnn<cr><lf> where a ttt nn <cr><lf> = = = = Device address The measurement completing time in seconds The number of the measured parameters available (maximum number is 20) Response terminator NOTE For changing the message parameters, units and other settings, see Chapter 8, Sensor and Data Message Settings, on page 81. Start Concurrent Measurement with CRC (aCC) Command format: aCCx!This command has the same function as aC but a three-character CRC is added to the response data strings before <cr><lf>. In order to request the measured data, Send data command aD should be used, see the following sections. Send Data Command (aD) This command is used to request the measured data from the device. See Examples of aM, aC and aD Commands on page 67. VAISALA _______________________________________________________________________ 65 User's Guide ______________________________________________________________________ NOTE Start measurement command tells the number of parameters available. However, the number of the parameters that can be included in a single message depends on the number of characters in the data fields. If all the parameters are not retrieved in a single response message, repeat the Send data commands until all the data is obtained. where a D x = = = Device address Send data command The order of consecutive Send data commands. [. . . ] After a sensor transmits the last character of a response, it must relinquish control of the data line within 7. 5 milliseconds (tolerance: +0. 40 milliseconds. ) No more than 1. 66 milliseconds of marking are allowed between the end of the stop bit and the start bit (for example between characters) on any characters in the command or the response (no tolerance. ) This permits a response to an M command to be sent within a 380-millisecond window. Sensors must return to a low-power standby mode after receiving an invalid address or after detecting a marking state on the data line for 100 milliseconds (tolerance: +0. 40 milliseconds). When a recorder addresses a different sensor, or if the data line has been in the marking state for more than 87 milliseconds, the next command must be preceded by a break. - - - - VAISALA ______________________________________________________________________ 115 User's Guide ______________________________________________________________________ NOTE The low-power standby mode, in addition to being a low-power consumption state, is a protocol state and a break is required to leave that state. 116 __________________________________________________________________M210736EN-B Appendix C ______________________________________________________ CRC-16 Computation APPENDIX C CRC-16 COMPUTATION The computation of the CRC is performed on the data response before parity is added. All operations are assumed to be on 16 bit unsigned integers. [. . . ]