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iRIS 220 / iRIS 320, V1.19 User Guide
3.4.2 Internal / External 12V Battery Supply
For all models there are two terminals provided on the I/O connector designated +12V and GND (or –12V on
old models). These can be used to power the unit from an external 12V battery or regulated dc supply. For
the iRIS 320 / iRIS 320V models, the internal battery is effectively connected directly to these terminals. See
Section 3.4.1 for warnings on connecting external power supplies to them.
3.4.3 External (Charger) Power Supply
Although the iRIS 320 can operate solely from its internal battery for a few days, you will typically need to
connect an external supply to the unit so that the internal battery remains in a charged state. You can
connect any external dc power source ranging from 15 – 30Vdc, including a solar panel, without requiring an
additional solar regulator.
The battery charging circuitry utilises a switch mode regulator for maximum efficiency. The external power
supply is protected against over-voltage by ultra-fast acting protection devices and a self-resetting
semiconductor fuse.
It can also be used to charge an external battery connected to the GND and 12V+ terminals. In the event
that the external battery draws excessive current, the charger will enter a current limit mode (900mA) until
such time as the battery has been recharged sufficiently to deliver the full supply voltage. The charging
profile used by the charger depends on the selected mode. See the Power Management description in
Section 4.3.1.
3.4.4 Analog Inputs
The four analogue inputs are uni-polar 0-5Vdc with 12-bit resolution. Each input presents a load impedance
of 98KΩ to the input signal.
Scaling factors should be chosen to convert from a raw value of 0-5000, which reflects the input signal range
of 0-5V (0-5000mV). When current sources such as 0-20mA or 4-20mA are used, an external sink resistor
(typically 250Ω) must be fitted between the analogue input and AGND.
NOTE: As the analogue inputs have an input impedance of 98KΩ, the actual sink impedance will be slightly
lower than the value fitted. For example, a sink resistor of 250 ohms is installed. The actual impedance will
theoretically be 249.36Ω; therefore the voltage measured by the iRIS will also be slightly lower than
expected.
Figure 5 - Analog Input Circuit
100nF
47K
51K
AGND
AINx
To ADC