Read analog sensors on SDI-12 USB + Analog adapter
November 18, 2016 Leave a comment
Reading analog sensors are easy. The adapter has SDI-12 address of ‘z’, lower case. So reading the analog sensor just involves querying the SDI-12 address ‘z’. There are two sensing modes: single-ended, and differential. If you have mixed single-ended and differential channels, read single-ended, then differential. Discard channels you don’t need. It won’t hurt the sensors or the adapter if you wire them in differential mode but read in single-ended mode. The reverse is also true.
The sensing commands are ‘zM!’ for single-ended readings, and ‘zM1!’ for differential readings.
In both modes, you use ‘zD01!’ zee-Dee-zero-!, to get data. Essentially, the adapter itself is an SDI-12 sensor that reports 2 or 4 values, depending on sensing mode. This makes it very easy to integrate analog sensors into your existing data logger that is based on the original SDI-12 USB adapter. It is still advantageous to keep the original SDI-12 USB adapter so it can split SDI-12 sensors with the SDI-12 + Analog adapter. In case one SDI-12 sensor gets broken and interferes with the rest of the sensors on that adapter, the SDI-12 sensors on the other adapter will be unaffected.
To make this complete, the SDI-12 USB + Analog adapter also responds to the following commands:
Response: ‘z\r\n’ This means that the adapter is responding to queries.
Response: ‘z13Liudr SDITRD130\r\n’ This indicates that the firmware is in version 1.3.0.
Response: ‘z0014\r\nz\r\n’ This means that the adapter needs 1 second to acquire 4 single-ended auto-scale analog values. The second ‘z’ indicates it completed the acquisition.
Response: ‘z0012\r\nz\r\n’ This means that the adapter needs 1 second to acquire 2 differential auto-scale analog values. The second ‘z’ indicates it completed the acquisition.
Response: ‘z+1.23456+2.34567+3.45678+4.56789\r\n’ or ‘z+1.23456+2.34567\r\n’ These are single-ended or differential channel readings, depending on whether M or M1 was issued before D0.