Start concurrent measurement commands (aC!)
A concurrent measurement (aC!) command follows the same pattern as the aM! command with the exception that it does not require the data logger to pause its operation, and other SDI-12 sensors may take measurements at the same time. The sensor will not issue a service request to notify the data logger the measurement is complete. The data logger will issue the aD0! command during the next scan after the measurement time reported by the sensor has expired. To use this command, the scan interval should be 10 seconds or less. The response to each command has the form atttn<CR><LF>, where
a = the sensor address
ttt = time, in seconds, until the measurement data is available
nn = the number of values to be returned when one or more subsequent D! commands are issued.
See the following example. A data logger has three sensors wired into terminal C1. The sensors are addresses X, Y, and Z. The data logger will issue the following commands and receive the following responses:
|
Example aC! sequence |
|
|---|---|
XC!
|
The data logger makes a request to sensor X to start a concurrent measurement. |
| X03005<CR><LF> | Sensor X immediately indicates it will have 5 (05) values ready for collection within the next 30 (030) seconds. |
YC!
|
The data logger makes a request to sensor Y to start a concurrent measurement. |
| Y04006<CR><LF> | Sensor Y immediately indicates it will have 6 (06) values ready for collection within the next 40 (040) seconds. |
ZC!
|
The data logger makes a request to sensor Z to start a concurrent measurement. |
| Z02010<CR><LF> | Sensor Z immediately indicates it will have 10 values ready for collection within the next 20 (020) seconds. |
ZD0!
|
After 20 seconds have passed, the data logger starts the process of collecting the data by issuing the first D command to sensor Z. |
| Z+1+2+3+4+5+6+7+8+9+10<CR><LF> | Sensor Z immediately responds with the sensor address and the 10 values. |
XD0!
|
10 seconds later, after a total of 30 seconds have passed, the data logger starts the process of collecting data from sensor X by issuing the first D command. |
| X+1+2+3+4+5<CR><LF> | The sensor immediately responds with the sensor address and the 5 values. |
YD0!
|
Ten seconds later, after a total of 40 seconds have passed, the data logger starts the process of collecting data from sensor Y by issuing the first D command.
|
| Y+1+2+3+4+5+6<CR><LF> | The sensor immediately responds with the sensor address and the 6 values. |