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If you are not sure whether M3 measures voltage or something else, you can read the configuration
for M3 by using the XG3! command. Refer appendix A for a description of the XGm command.
Ratiometric Measurement
The module can measure ratio of voltages between any two of the 6 inputs: AN1, AN2, AN3, AN4, Vref and
ground. The measurement is done using high precision delta-sigma, Analog-to-Digital (A/D) converter, which
can be programmed for following parameters:
Input Channels
Digital Filter for different data-output rate (averaging time) to get different line rejection frequencies
Buffered or Non-Buffered input
Input Gain of 1,2,4,8,16,32,64 or 128
In addition to this, you can specify
Slope: A multiplier to convert ratio to a different engineering unit
Offset: A constant value to be added to the result after adjusting it with Slope
Vref Warm-up Time: Time Vref should be turned on before taking a measurement
Switched Voltage: This can be set to 5volts or 12volts if sensor requires an external excitation
voltage
Switched Voltage Warm-up time: Time switched voltage should be present before taking a
measurement.
SDI-12 set-up command
To set-up a Ratio measurement or change a parameter (other than default), you can use the SDI command
aXRm+p+n+s+o+t+v+w+x+i+g!
Where,
a: SDI-address of module
m: Measurement number (M command number : 1…9)
p: Measurement channel (1:AN1, 2:AN2, 3:AN3 4:AN4 and V:Vref)
n: Reference channel. Default is Vref (2.5volts)
s: Slope. Default is 1.00
o: Offset. Default is 0.00
t: Averaging time (less than 0.09 for 15Hz, greater than 0.09 and less than 0.19 for 7.5Hz, greater than 0.19
for 3.75Hz). Default is 0.067.
v: Vref warm-up time. Default is 0.010, i.e. 10mS
w: Switched voltage during measurement ( = 0, 5 or 12). Default is 0
x: Switched voltage warm-up time in sec. Default is 0.1, i.e.100mS
i: U=Un-buffered, B=Buffered. Default is U
g: Gain = 0, 1, 2, 4, 8, 16, 32, 64, 128. Default is 0, which means auto-gain
You can do a quick set up by only specifying the measurement channel. To ensure that unspecified
parameters are at factory defaults, suffix the measurement channel with “+FD”.