Xylem H-4280 - Manual (Page 11)

H-4280
Installation And Maintenance 2-3
2.6 Slope & Offset
Each channel can be configured with a y=mX+b linear equation to convert the input voltage into user units
such as pressure, feet or meters. The linear equation has a slope (m) term and an offset (b) term. At the
factory the slope is set to 1.00 and the offset to 0.00, with these settings the measurement will be in units
of Volts. The linear equation will work for sensors such as potentiometers, position sensors and 4-20mA
transducers with linear outputs. The y=mX+b equation will not work with thermocouples, thermistors and
other sensors having a non-linear response. For these sensors, leave the slope = 1.0, offset = 0.0 and
perform the more complex math operations in your data logger. The slope and offset settings are
configured with the extended “aXROn!” & “aXWOn nn!”, “aXRSn!” & “aXWSn nn!” or the “aXRCn!”
& “aXWCn! commands. See Chapter 3 for details.
2.7 Data Format
The number of digits printed past the decimal point can be configured for each channel. For example if
Digits = 2 for a particular channel the respective data will have two digits beyond the decimal point (x.xx).
At the factory all 8-channels are set for 3-digits beyond the decimal point. These settings are configured
with the extended “aXRCn!” & “aXWCn! commands. See Chapter 3 for details.
2.8 Programming Your SDI-12 Data Recorder
You must prepare your data recorder to receive and record the H-4280 data. Since data recorders differ,
refer to your data recorder manufacturer's directions. In general, program the data recorder to input 8-
values via the SDI-12 port. All eight parameters do not need to be actually recorded. Your data recorder
must issue an “aM!” command, then collect the data with “aD0!" and “aD1!" commands, as explained in
Chapter 3. Four parameters are returned in response to the “aD0!” command and four more with the
“aD1!” command.
The H-4280 places eight parameters in its data buffer:
a+A.AAA+BB.BBB+C.CCC+D.DDD+E.EEE+F.FFF+G.GGG+H.HHH
Where: a = SDI-12 address 0-9, A-Z
A.AAA = Channel 0
B.BBB = Channel 1
C.CCC = Channel 2
D.DDD = Channel 3
E.EEE = Channel 4
F.FFF = Channel 5
G.GGG = Channel 6
H.HHH = Channel 7