dataTaker DT80, Руководство пользователя

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UM-0085-B09 DT80 Range User Manual Page 346
RG
Other Considerations
Execution Time
In Measure on Demand mode, SDI12 channels may take a significant amount of time to execute – often 10 seconds or
more, depending on the sensor. During this time no other schedules or commands are executed.
Note however that the DT80 will only request a measurement of a given register set once per schedule. So the following
schedule:
RA1M 5SDI12(R1) 5SDI12(R3) 5SDI12(R201) 5SDI12(R4)
would execute as follows:
1.
DT80 requests a measurement of register set #0 (
0C!
), then waits until it is ready.
2.
DT80 reads values for registers 1, 3 and 4, which are all part of register set #0. It will probably be given values
for other registers (e.g. register 2), which it will discard because they are not referenced in the job
3.
DT80 can now evaluate (i.e. return/log values for) the first two channels.
4.
DT80 requests a measurement of register set #2 (
0C2!
), then waits until it is ready.
5.
DT80 reads value for register 1 (in register set #2) and discards any other values that it receives.
6.
DT80 can now evaluate the last two channels.
Notice that the DT80 waits for the sensor on two occasions, once for each register set.
Versions
The DT80 automatically determines the version of the SDI-12 specification that a given sensor supports, and tailors the
types of messages it sends accordingly. For example:
• Error check codes (CRCs) are used on data messages, but only if the sensor supports SDI-12 Version 1.3 or
later.
• Continuous Measurement mode is only available if the sensor supports SDI-12 Version 1.2 or later.
Unfortunately some sensors do not fully implement the SDI-12 version that they claim to support. In these situations the
VER
nn
option can be used to force the DT80 to assume a particular SDI-12 version.
Troubleshooting
There are two main areas where difficulties may arise when setting up an SDI-12 system
• the DT80 cannot communicate properly with the sensor
• the sensor does not support the request you are making of it
These will be discussed in the sections below.
Diagnostic Messages
When troubleshooting an SDI-12 connection, it can often be helpful to see the actual SDI-12 messages. The DT80
provides a special parameter setting for this purpose:
P56=2
If this parameter setting were used with the weather station example described above (Measure on Demand mode), you
might see something like:
7SDI12: [8] 3C1!300704
7SDI12: [25] 3D0!3+22.91+42.40+21.0+1013.9
Ext temp 42.4 degC
Pressure 1013.9 hPa
7SDI12: [8] 3C2!300603
7SDI12: [18] 3D0!3+4.29+31.43+012
Wind speed 4.3 km/h
which shows the measurement request message ( 3C1! or 3C2! ) and response, followed by the data retrieval message
( 3D0! ) and response, for each register set.
Set
P56=0
to turn off these messages.
Communications Problems
If the sensor does not reply at all to a request, the DT80 will output an error message, e.g.:
8SDI12(R3)
dataTaker 80 E80 - Serial device not responding (8SDI12:AD0:R3)
8SDI12 NotYetSet