Thies CLIMA Ultrasonic Anemometer 2D Operating Instructions Manual page 6

6.2 Definition of Checksum and Status byte
6.2.1 Forming of Checksum
The checksum is the result of the byte-wise EXOR-combination of the bytes output in the telegram.
The EXOR-combination comprises all bytes between the telegram start sign „STX", or "$" within the NMEA-
telegram, and the byte "*" as identifier for starting the checksum.
Thus, the bytes „STX" or. „$" and „* " will not be taken into consideration with the checksum calculation!
6.2.2 Definition of Status Byte
The status byte contains information about the current state of the system.
The information comprises:
•
error events with the measurement value acquisition
•
a possible de-calibration caused, e.g., by a change in the measurement path length
(due to mechanical deformation of the transducer carrying arms)
•
the operation state of the instrument heating.
Bit 0 0 = no error
Bit 1 0 = no error
Bit 2 reserved
Bit 3 0 = heating switched off
Bit 4 to 7 reserved
The error event reported by Bit 0 does not necessarily cause the output of an erroneous measurement value.
Certain weather conditions like extreme precipitation and snowfall may disturb the measurement acquisition
for a short time, caused by sonic burst-echoes at the precipitation particles.
Such an event, however, is realized by a plausibility-algorithm, which leads to an immediate re-measurement
of the instrument – until a correct value is available.
The output measurement value is generally correct, in spite of the reported error, and does not contain the
erroneous data.
If Bit 1 is continuously set during the operation, you should reckon on a de-calibration of the instrument due
to mechanical deformation of the measurement arms.
6.3 Telegram Output Format and Analogue Value Output in Case of Error Events
In the following cases the digital telegram outputs „F" as measurement value figure instead of numbers:
•
If the measurement acquisition is constantly disturbed for more than 10 seconds in spite of multiple
measurements
•
If the deviation of the virtual temperature between both measurement paths is > 8 K.
In this case the analogue outputs are set on the maximum voltage-/current value(10V, 20mA).
1 = general error event, measurement value probably
correct, measurement value acquisition disturbed
1 = error event, deviation of the virtual temperature
between both measurement paths is > 8 K.
1 = Heating switched on
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