Campbell Scientific OBS500 Smart Turbidity Meter with ClearSensor Technology - Manual (Page 30)

OBS500 Smart Turbidity Meter with ClearSensor™ Technology
TABLE 7-7. SDI-12 and RS-232 Measurement Commands
Commands Process Values Returned
aM7!
aC7!
Close Wiper
Send Data
Close wiper position count
Close max current count
Close timeout count
Close current (ma)
aM8!
aC8!
Send Wiper Data Open close total count
Open wiper position count
Open max current count
Open timeout count
Close wiper position count
Close max current count
Close timeout count
aC9! Open Wiper
Measure 100 Times
Close
Send Data
obs median
obs mean
obs standard deviation
obs min
obs max
ss median
ss mean
ss standard deviation
ss min
ss max
With the SDI-12 concurrent measurements ( aCx!), the datalogger
does not request the data until the next interval hits. For example,
if you have a 30-minute interval, you will not see the data for 30
minutes. There is not an equivalent M command to the aC9!
command since the M command is limited to nine returned values.
As the measurement data is transferred between the probe and datalogger
digitally, there are no offset errors incurred with increasing cable length as seen
with analog sensors. However, with increasing cable length, there is still a
point when the digital communications will break down, resulting in either no
response or excessive SDI-12 retries and incorrect data due to noise problems.
Using SDI-12 commands which add a CRC check (e.g., aMC!), can
significantly improve incorrect data issues.
7.4.1.1 SDI-12 Addresses
The OBS500 SDI-12 address can be set to 0 to 9, A to Z, or a to z which allows
multiple sensors to be connected to a single digital I/O channel (control port) of
an SDI-12 datalogger. (Most Campbell Scientific dataloggers support SDI-12.)
The OBS500 is shipped from the factory with the address set to 0. When it is
necessary to measure more than one OBS500, it is easiest to use a different
control port for each OBS500 instead of changing the address. If additional
control ports are not available, the address will need to be changed.
The address on the OBS500 can be changed by sending the SDI-12 change
address command aAb!. The change address command can be issued from
most SDI-12 recorders. For example, to change the address of a sensor that has
a default address of 0 to the address of 1 the following command can be sent:
0A1!
NOTE
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