Campbell SN500SS, Руководство по эксплуатации продукта

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Table C-3: Example aC! sequence
YD0!
Ten seconds later, after a total of 40 seconds have
passed, the data logger starts the process of data
from sensor Y by issuing the first
D command.
Y+1+2+3+4+5+6<CR><LF>
The sensor immediately responds with the sensor
address and the 6 values.
C.2.8 Start measurement commands with cyclic redund-
ancy check (aMC! and aCC!)
Error checking is done by using measurement commands with cyclic redundancy checks ( aMC!
or
aCC!
). This is most commonly implemented when long cable lengths or electronic noise may
impact measurement transmission to the data logger. When these commands are used, the data
returned in response to
D
or
R
commands must have a cyclic redundancy check (CRC) code
appended to it. The CRC code is a 16-bit value encoded within 3 characters appended before the
<CR><LF>. This code is not returned in the data table but checked by the data logger as it
comes. The code returned is based on the SDI-12 protocol. See the SDI-12 communication spe-
cification for version 1.3 available at
www.sdi-12.org to learn more about how the CRC code is
developed.
C.2.9 Stopping a measurement command
A measurement command (
M!
) is stopped if it detects a break signal. A break signal is sent by
the data logger before most commands.
A concurrent measurement command (
C!
) is aborted when another valid command is sent to the
sensor before the measurement time has elapsed.
C.2.10 Send data command (aD0! … aD9!)
The Send Data command requests data from the sensor. It is issued automatically with every type
of measurement command (
aM!
,
aMC!
,
aC!
,
aCC!
). When the measurement command is a
M!
or a
MC!
, the data logger issues the
aD0!
command once a service request has been received
from the sensor. When the data logger is issuing concurrent commands ( aC! or aCC! ), the Send
Data command is issued after the required time has elapsed (no service request will be sent by
the sensor). In transparent mode (
SDI-12 transparent mode (p. 25)), the user asserts this com-
mand to obtain data.
Depending on the type of data returned and the number of values a sensor returns, the data log-
ger may need to issue
aD0!
up to
aD9!
to retrieve all data. A sensor may return up to 35 char-
acters of data in response to a
D
command that follows an
M!
or
MC!
command. A sensor may
SN500SS Net Radiometer 24