Campbell Scientific CR3000 CR3000 Micrologger - Page 181

Section 7. Installation Serial number = 101 Start Measurement Commands (aM! & aC!) A measurement is initiated with M! or C! commands. The response to each command has the form atttnn, where • a = sensor address • ttt = time, in seconds, until measurement data are available • nn = the number of values to be returned when one or more subsequent D! commands are issued. Start Measurement Command (aMv!) Qualifier v is a variable between 1 and 9. If supported by the sensor manufacturer, v requests variant data. Variants may include: • alternate units (for example, °C or °F) • additional values (e.g., level and temperature) • diagnostic of the sensor's internal battery Example: Command: 5M! Response: 500410 (atttnn, indicates address 5, data ready in 4 seconds, will report 10 values). Example: Command: 5M7! Response: 500201 (atttnn indicates address 5, data ready in 2 seconds, will report 1 value). v = 7 instructs the sensor to return the voltage of its internal battery. Start Concurrent Measurement Command (aC!) Concurrent measurement allows the CR3000 to request a measurement, continue program execution, and pick up the requested data on the next pass through the program. A measurement request is then sent again so data are ready on the next scan. The datalogger scan rate should be set such that the resulting skew between time of measurement and time of data collection does not compromise data integrity. Note This command is new to Version 1.2 or higher of the SDI-12 Specification. Older sensors, older loggers, or new sensors that do not meet v1.2 specifications will likely not support this command Aborting a Measurement Command A measurement command (M! or C!) is aborted when any other valid command is sent to the sensor. 181