iRIS 350FX Reference Manual V1.50
62
HyQuest Solutions (NZ) Ltd
- PO Box 9466, Hamilton, New Zealand Tel: +64 7 857-0810 Email: [email protected]
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 analogue sensor signal.
However, these 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 current sink 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 analogue
input. See Section
for details on the analogue input links.
The internal 100Ω current sink resistor generates a 0.4 to 2V signal (from the 4 to 20mA current), which is
then measured at the analogue input. The sensor should be configured for the correct channel, scaling and
logging regime as described in Section
. 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
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 (-)
Name: Water Lvl
Source: 1. Analogue In 1
Process Mode: Period Average
Multiplier: 6.2500
Offset: -2.5000
Log Rate: 15 mins
Summary of Contents for iRIS 350FX
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