OBS501 Smart Turbidity Meter with ClearSensor
®
Technology
23
TABLE 8-2. SDI-12 and RS-232 Measurement Commands
Commands
Process
Values Returned
aC8!
Raw Burst Data in Volts
Open
Measure 100 Times
Close
Send Data
bs median
bs mean
bs standard deviation
bs minimum
bs maximum
ss median
ss mean
ss standard deviation
ss minimum
ss maximum
aM9!
Wiper
Leave Open
total open/close count
open wiper position count
open max current count
open timeout count
close wiper position count
close max current count
close timeout count
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
aC1!
,
aC5!
, and
aC8!
commands since the
M
command is limited to
nine returned values.
As the measurement data is transferred between the probe and the 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.
In these circumstances, use the
aMC!
command to do a cyclic redundancy
check (CRC).
8.5.1.1 Measuring Multiple SDI-12 Sensors
Up to ten OBS501s or other SDI-12 sensors can be connected to a single
datalogger control port. Each SDI-12 device must have a unique SDI-12
address of 0 and 9, A to Z, or a to z. See Appendix
(p. D-1)
, for more information.
8.5.2 RS-232
RS-232 measurements of the OBS501 are typically made by a CR800, CR850,
CR1000, or CR3000 datalogger or an RTU device. The OBS500CBL-L Field
Cable is used and wired appropriately for the measurement device. See TABLE
, for settings. Measurement commands are the same for RS-232 and SDI-12
as shown in TABLE
SDI-12 and RS-232 Measurement Commands
(p. 21)
.
NOTE
