Data Acquisition

• Use different data formats so that the data transmitted to the host PC issuitable for a computer program (i.e. spreadsheet package) or a humanoperator• Store sensor measurements within the device or onto memory cards for latertransmission to the host PC• Transmit measurements back to the PC as soon as they are taken. This can beby direct connection over the RS-232 interface, by modem through thetelephone network, or by radio modem over a radio link• Control equipment external to the stand-alone deviceThis section outlines the basic software protocol (command formats, data formats anderror formats) required to program stand-alone logger/controllers as well as detailing thetype of commands required to perform some of the tasks outlined above.It is not our purpose here to detail the exact software structure of a particular standalonelogger/controller, as this will vary between manufacturers. However, to provide anexample, the most important commands, and their use in a program to control theDatataker range of loggers/controllers, by Data Electronics Australia Pty Ltd, is shown inAppendix H.Irrespective of whether commands are sent to stand-alone devices via the serialcommunications interface or using memory cards, the format of the commands is thesame. The PC always generates the command sequence. Programming the operation ofthe remote devices or reading data from them usually requires the user to enter ASCIIcommand strings only. Commands are sent one at time by using a command terminatingcharacter after each command. For terminal emulation packages, this is typically thecarriage-return (ASCII 0D). Multiple commands can be included on one line byseparating them with a delimiter, typically a tab or space character, then terminating thecommand string with the command-terminating character.Although the command format is not standardized between manufacturers of differentstand-alone devices, several formats are commonly used. These are:These are entered as continuous ASCII text, most commonly in upper case characters andalso contain one or more command options that specify the functions the command isrequired to perform. Although they vary between different manufacturers, commandoptions are typically enclosed in brackets, separated by commas (no spaces), and can berandom.Sometimes command options are referred to as command parameters since the user isrequired to append parameters that specify particular values associated with a command.These should not be confused with parameter commands.These are used as an on/off control function that either enables or disables a particularfeature or function of a stand-alone device, thereby controlling its operation. The feature‘X’ is enabled/disabled by sending the following switches:/X feature enabled/x feature disabled