Campbell CS451, Product Manual

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CS451/CS456 Submersible Pressure Transducer
19
TABLE 8-3. CS451/CS456 SDI-12 Commands
a
XCONFIG2=
nnn
!
Where,
nnn = number of samples used with the
a M8! or a C8! command.
Configures the number of
samples used with the
a M8! or a C8! command
?! Returns the SDI-12
Address
As measurement data is transferred between the probe and data logger
digitally, there are no offset errors incurred with increasing cable length as
seen with analog
ue
sensors. However, with increasing cable length, there is still
a point when digital communications break down, resulting in either no
response or excessive SDI-12 retries and incorrect data due to noise problems.
(Using SDI-12 commands like MC! , which adds a cyclic redundancy check
(CRC), can significantly improve incorrect data issues.)
8.3 Measuring Multiple SDI-12 Sensors
Campbell Scientific recommends using separate terminals when possible.
However, multiple CS451/CS456 sensors or other SDI-12 sensors can be
connected to a single data logger control or U terminal. Each SDI-12 device
must have a unique SDI-12 address. See Appendix D ,
SDI-12 Sensor Support
(p. D-1)
, for more information.
8.4 Unit Command
An extended SDI-12 command is used to select the temperature units (Celsius
or Fahrenheit), pressure/level units (psig, kPa, bar, feet, met
re
, inches,
millimet re , multiplier (slope), and offset. This command is in the form of
XCONFIG1= tt,pp,mmm.mm,ooo.oo ! , where a = the SDI-12 address of the
sensor, tt = temperature units, pp = measurement unit, mmm.mm = multiplier
(slope), and
ooo.oo
= offset;
Valid entries for tt (temperature) are:
0 = Celsius
1 = Fahrenheit
Valid entries for pp (pressure/level) are:
0 = psig
1 = kPa
2 = Bar
3 = Feet
4 = Met
re
5 = Inch
6 = Millimet re
The level units are for level of fresh water. The multiplier (slope) and offset are
used to correct for relative density of water. Only SDI-12 instructions
M!
,
M7! , M8! , C! , C7! , and C8! output the results obtained when using the
multiplier and offset. The offset and multiplier are only applied to the
pressure/level value, not to the temperature.