CMD140 n
sets the IOUT Pressure Range HI
CMD142 n
sets the IOUT Pressure Range LO IOUT
Pressure Range HI must be greater than IOUT
Pressure Range LO
CMD144 n
sets the IOUT Scale:
1 = 0 to 20mA, or 4 = 4 to 20 mA.
CMD150 c
sets the poll address character for ASCII and
SDI-12 modes. Any ASCII character from ‘0’
(ASCII 48) to ‘z’ (ASCII 122) may be used. For
SDI-12 limit the characters from 0 to 9.
CMD160 n
sets the baud rate. Acceptable values are
38400, 9600, 4800, 2400, and 1200. Note
that the baud rate change occurs immediately
after the command is received. Therefore, in
order to continue communicating, the serial
communication program that issued the
command must also change to match.
CMD300 n
c a u s e s t h e s e n s o r t o p a u s e o r r e s u m e
measurement. 1 = Stop, 2 = Run.
CMD400 n
c auses the sensor to issue a repor t
summar izing parameter set tings.
1 = Tex t (parameter values and labels)
2 = C ode O nly (parameter values only).
CMD420
burns the current parameter settings to flash
memory. This step
must
take place to retain
changes to settings otherwise parameters will
revert to previous values at the next power up.
4.4 SDI-12 COMMANDS
SDI-12 stands for serial data interface at 1200 baud. It is
often used to interface battery powered data recorders with
microprocessor based devices designed for environmental
data acquisition. SDI-12 is used typically when low power
is a concern. The SDI-12 device normally remains in a
low power, standby state until it is polled at which time
a measurement is sent. SDI-12 can effectively address
multiple sensors on the same cable.
Model 61402L uses the SDI-12 (V1.4) serial communication
protocol to initiate measurements and set sensor operation
parameters. The default sensor address is 0 (zero), and
can be changed to any valid single-character value if
needed. Additional details about the SDI-12 protocol may
be found at www.sdi-12.org.
After initial power-up with 12 VDC, the sensor is in a low-
power standby state with a quiescent current of 1.60 mA. A
valid and properly addressed SDI-12 command wakes the
sensor to initiate a measurement, set or check operating
parameters. After command processing has finished, the
sensor returns to the low-power standby state.
SDI-12 ‘M’ or ‘C’ commands initiate a measurement. The
sensor response message indicates the maximum time
needed before the measurement is ready, and data values
will be available. The maximum time ranges from 1 to 5
seconds depending on the Sample Count.
If an ‘M’ command initiates a measurement, the sensor
sends a Service Request when the measurement is ready
to be retrieved. When the polling device receives the
Service Request it then sends a ‘D’ command to request
measurement results from the sensor. With ‘C’ commands,
no Service Request is sent, and the polling device must
wait the full delay time before sending the ‘D’ command to
request the measurement.
SDI-12 Measurement commands and responses:
COMMAND
RESPONSE
DESCRIPTION
aM!
attts<CR><LF>
Take a measurement
aMC!
attts<CR><LF>
Take a measurement with CRC
checksum
aC!
atttss<CR><LF>
Take a concurrent measurement
aCC!
atttss<CR><LF>
Take a concurrent measurement
with CRC checksum
aD0!
a+tttt.t+bbbb.b<CRC><CR><LF>
where:
a
= Sensor address
ttt
= Delay time (seconds)
s/ss
= Number of samples to collect
ttt.t
= Temperature (selected units)
bbbb.b
= Barometric Pressure (selected units)
<CRC>
= CRC checksum (only where requested)
<CR><LF>
= Carriage return, line feed (ASCII 13, 10)
SDI-12 NON-MEASUREMENT COMMANDS:
The SDI-12 protocol includes standard commands for
identifying the sensor and changing its address.
CMD
RESPONSE
DESCRIPTION
?!
a<CR><LF>
Address Query
a!
a<CR><LF>
Acknowledge Active
aI!
a13 YOUNG C092000 vvvnnnnnn<CR><LF>
Send Identification: vvv = Firmware Version
nnnnnn = Serial Number
aAb!
b<CR><LF>
Change Address:
a = Sensor address
b = New sensor address
aV!
a0000<CR><LF>
Start Verification
EXTENDED COMMANDS:
The SDI-12 command set may be customized with
Extended Commands to accommodate manufacturer
settings and other functions. Extended Commands are
listed below. Where two responses are shown, one is for a
valid command, the other is for an invalid (ERR) command.
COMMAND
RESPONSE
DESCRIPTION
aXB!
aXB, OK<CR><LF>
Save parameter settings to flash.
Cycle power after saving parameters.
aXP!
aXP, V=v, OP=o, ASC=s, MP=m, OS=op, SC=sc<CR><LF>
v = voltage (120 = 12.0 volts)
o =
s =
m =
op = offset (hPa x 10)
sc = sea level correction (hPa x 10)
aXC±nnnn! aXC, SC=±nnnn<CR><LF>
Sea Level Correction (-5000 to +5000 hPa)
aXF±nnnn! aXF, OP=±nnnn<CR><LF>
Offset (-5000 to +5000 hPa)
aXM
aXM, M=nnnnn<CR><LF>
Multiplier (10000 = 1.0000)
aXO
aXO, O=nn<CR><LF>
Output Period (0 – 60)
aXS
aXS, S=nn<CR><LF>
Sample Count (1 – 32)
5.0 MAINTENANCE
The MODEL 61402L barometer requires no regular
maintenance. Periodic calibration certification, if required,
is available from the factory.
6.0 WARRANTY
This product is warranted to be free of defects in materials
and construction for a period of 12 months from date of
initial purchase. Liability is limited to repair or replacement
of defective item. A copy of the warranty policy may be
obtained from R. M. Young Company.
