fetch

Usage

>> fetch [ channels | sleepafter ]

Security

Description

Requests an 'on-demand' sample set from the logger. If a recent scheduled sample set is available, those values may be returned to satisfy the fetch request. 'Recent' in this context currently means less than 500ms old. Otherwise, a sample set is explicitly acquired for the benefit of the fetch. A sample set acquired only for fetch is never stored in memory.

The logger simply responds with the <sample-data>; depending on the configured settling time (or power-on settling delay) for the attached sensors, there may be a noticeable delay before the <sample-data> appears. Refer to the channels command for further discussion of settling time.

• channels [= <listofchannels>], is the list of channels to be acquired, using either indices or labels of channels (see channel). The output format of the <sample-data> is the channels samples in the same order. If this parameter is not provided, the output format of the <sample-data> is determined by the outputformat command.
  

  If a channel or one of its supporting channel has its status set to off, requesting that channel will return an Error-14 as sample data for this channel. See channel for details.

• sleepafter [= <sleepafter>], controls power strategy after the fetch is issued. <sleepafter> is either:
  1. false (default behavior), subsequent fetch commands may return data more quickly; after an initial fetch command, the sensors usually remain powered up in anticipation of another request. This behaviour is protected by an 8-second (default) timeout, after which the sensors are turned off again. Refer to the settings command for information on changing the default sensor power-off timeout.
  2. true causes the logger to power down when it has finished reporting the <sample-data>. This is equivalent to issuing two separate commands, fetch then sleep, except that after completing the fetch the logger goes to sleep silently; there is no "Ready" prompt following the <sample-data>, just as there is no "Ready" prompt following a sleep command. Note that the entire logger powers down if possible, not just the sensors; however if any normally scheduled samples are required immediately after the fetch, the power down action will be delayed until after those samples are complete.

Examples

Fetch a sample from all channels.

Fetch a sample from some specific channels.

Fetch command reporting error for channel 1 (timeout) and channel 3 (unable to compute value).  Channel 2 is not calibrated.  List of error code can be found in within Sample data standard format.