12-Bit 4-20 mA Input Adapter
Page 4 of 6
Connecting the Adapters to the Logger
To use the 12-Bit 4-20 mA Input Adapter, stop the logger and insert the adapter’s modular jack into an
available sensor connection port on the logger. If no port is available, use a 1-to-2 sensor connection
adapter (Onset part # S-ADAPT), which allows you to plug two sensors into one port (HOBO Weather
Station only).
The logger automatically detects the new input adapter the next time you launch it. Launch the logger and
verify that the input adapter is functioning correctly. Measurements are recorded in milliamps (mA). See
the
HOBO Weather Station User’s Guide
or the
HOBO Micro Station User’s Guide
for details.
Operation
The 12-Bit 4-20 mA Input Adapter uses digital filtering and optional measurement averaging to reduce
the effect of noise and improve accuracy.
Regardless of whether measurement averaging is used or not, each sample is comprised of a 300 ms
(± 3%) warmup period and a 16.6 ms (± 3%) sample period. During the sample period, digital filtering is
accomplished by taking 32 readings. These readings are then averaged to produce a single measurement,
as shown in the following diagram:
Figure 4: Measurement averaging (not to scale)
Optional measurement averaging can be selected at launch. Use measurement averaging if measurements
may fluctuate significantly within the logging interval. Measurement averaging helps to prevent the
sampling error known as aliasing.
To use measurement averaging, set the Sampling Interval to a rate that is faster than the logging interval.
When measurement averaging is selected in this way, the adapter takes several measurements during the
logging interval and averages them to produce a single logged data point. For example, if the logging
interval is 10 minutes and the sampling interval is 1 minute, each recorded data point is the average of 10
measurements.
Note that fast sampling intervals (less than one minute) significantly reduce battery life.
For more information about sampling intervals, refer to the
HOBO Weather Station User’s Guide
or the
HOBO Micro Station User’s Guide.
