Xylem H-4280 - Manual (Page 22)

3-10 SDI-12 Command and Response Protocol H-4280
3.9 Extended Read Channel_Config and Write Channel_Config
Each of the 8-input channels can be configured to make Unipolar/Bipolar and Single/Differential
measurements. Use the “aXRC!” and “aXWC!” extended commands to monitor or change the
configuration for each input channel. The Slope, Offset and SDI_Digits for each channel can also
be configured with these commands.
The H-4280 always makes 8-measurements, even if one or more of the channels is configured for
a differential measurement. For example: if Channel 0 is configured for a differential
measurement, the Channel 0 measurement is determined by the input voltage on both Channel 0 &
1. Subsequently a measurement is made for Channel 1, with the results determined separately by
the settings of Channel 1. Normally if Channel 0 is configured for a differential measurement, the
results of the adjacent channel measurement (Channel 1) is ignored by the data logger (and vice
versa).
Differential Channel Selection
Chan 0 1 2 3 4 5 6 7
0 + -
1 - +
2 + -
3 - +
4 + -
5 - +
6 + -
7 - +
For differential measurements; if the (+) input will always more positive than the (-) input, set the
channel to “unipolar”. The unipolar setting has the best resolution. If the (+) can be less positive
than the (-) input, set the channel to “bipolar”. The bipolar setting allows the measurement to go
negative but has the shortcoming of 1-bit less resolution.