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Installation
2.5.6 Connecting SDI-12 Instruments
SDI-12 instruments should be connected as shown in the diagram below. See Section SDI-12 Devices for information
on using the SDI-12 terminal mode to access SDI-12 instruments directly. Also, refer to Appendix – SDI-12 for detail on
the SDI-12 specification.
TOP iRIS I/O Connector
The instrument is a standard SDI-12 compatible water level sensor, set to
address 0. The level is the first value in the SDI-12 response obtained from the
sensor and is read in metres. The offset of 6.177 is the hypothetical offset at
the site to correct the readings to true RL. The corrected level is averaged and
the result logged every 15 minutes. The logging multiplier of 1000 is necessary
to maintain resolution for the logged data which is stored in millimetres.
Name: Water Lvl
Source: 12. SDI-12
Variable: 1
Process Mode: Period
Average
Multiplier: 1.000
Offset: 6.17
Log Rate: 15 mins
Note: The SDI-12 measurements are taken at a rate determined by the mode of the FIRST SDI-12 sensor that is
defined in the iRIS. If its mode is Instant, then a measurement is initiated for all SDI-12 instruments one
minute before logging will occur (e.g. on the 14th, 29th, 44th and 59th minute of each hour if the log rate is
15 mins. If the mode is Period Avg, then measurements are initiated at a rate of 10 seconds (plus time for
measurement to be ready). If a user is logged in via the LCD/keypad, then measurements are taken at the
faster rate no matter what the mode of the first SDI-12 sensor is set to. This allows easy calibration and checks
to be performed.
To cater for unusual situations where the combined time to take a measurement from all the SDI-12
instruments will exceed one minute, a compromise mode is provided. In this case, the SDI-12 instrument
measurement cycle can be set to start two minutes before logging. This is done by setting the address of the
first SDI-12 instrument to 5 or greater.
2.5.7 Connecting an Up/Down Water Level Instrument
A relatively common type of digital water level instrument is one that provides two pulse outputs. One output generates
a pulse for each increment and the other for each decrement in level. The iRIS maintains a record of these steps and
therefore the relative level.
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