Xylem SDI-12 Data Logger iRIS 220, iRIS 320, iRIS 350, iRIS 150, iRIS 300 - Manual (Page 58)

iRIS Datalogger User Guide V1.50
52 iQuest (NZ) Ltd - PO Box 15169, Hamilton, New Zealand Tel: +64 7 857-0810 Fax: +64 7 857-0811 Email: [email protected]
6.4 Connecting a 2-Wire Loop-Powered 4-20mA Sensor
The iRIS also supports the connection of many types of industry standard 4-20mA current loop instruments
such as ultrasonic or radar level sensors. A very common configuration used with these devices is known as
two-wire or loop-powered mode. This requires only two wires to the sensor and the 4-20mA loop current
provides power for the sensor as well as being the proportional analog sensor signal.
However, theses sensors often require a minimum voltage across them that may not be reliably achieved
with a 12V supply, taking into account the voltage drop across the sense resistor. In such cases, a separate
12-24V boosted sensor supply is recommended.
The diagram below shows the recommended connection diagram for such an installation. It assumes the
use of AI1 as the desired input channel. The current sink resistor should be enabled for the appropriate
analog input. On the iRIS 350 this is provided on-board. The iRIS 220/320 an external resistor needs to be
fitted. See Section 3.5.4 for details on the analog input links.
On the iRIS 350 the internal 100 sense resistor generates a 0.4-2V signal (from the 4-20mA current), which
is then measured at the analog input. The sensor should be configured for the correct channel, scaling and
logging regime as described in section 4.4.8. An offset value will be required as part of the configuration, as
the 4mA (0.4V) offset needs to be eliminated.
TOP iRIS I/O Connector
BOTTOM
A typical sensor configuration example for this type of installation is
shown here. The instrument is a 10 metre, 4-20mA output ultrasonic
transducer. The level is averaged and the result logged every 15
minutes.
If power consumption is an issue, the sensor can be controlled by a digital output on a timed
basis. See the description in Section 6.3 above.
* Sensor 1 Cfg
(Now: 6.1200 [1.3792V]
0 Exit
1 Source [1: Analog1]
2 Name [Water Lvl]
3 Mode [Period Avg]
4 Multiplier [ 6.2500]
5 Offset [ -2.5000]
6 Log Multiplier [1000]
7 Log Rate [15min]
8 Alarms
9 Data
Isolated
12V – 24V
DC- DC
Converter
- +
24V
12V
- +
Charging source
E.g. solar panel
- +
External
12V Battery
(Required)
-
Signal 4-20mA Sensor
+
AI4
AI3
AI2
AI1
AGND
AOUT
DIO4
DIO3
DIO2
DIO1
SDI-12
DGND
12V+
GND (-)
VIN+
GND (-)