Xylem SDI-12 Data Logger iRIS 220, iRIS 320, iRIS 350, iRIS 150, iRIS 300 - Manual (Page 17)

11 iQuest (NZ) Ltd - PO Box 15169, Hamilton, New Zealand Tel: +64 7 857-0810 Fax: +64 7 857-0811 Email: [email protected]
3.5.5 Digital I/O
On the iRIS 220/iRIS 320 the I/O functions are fixed in hardware as two inputs and two outputs. The iRIS
350 has four digital I/O channels which can each be potentially configured as either an input or output. When
set as an output, the channel can either supply switched 12V or else act as a pull-down switch for loads with
a different supply voltage.
iRIS 350. The I/O channels have been fixed in modes that make the iRIS 350 emulate the
earlier iRIS 220/320 model. Future versions will enable all the I/O features built into the
hardware. For the emulated mode, these are the channel allocations:
DIO1 = DI1, DIO2 = DI2, DIO3=DOUT1, DIO4=DOUT2
Digital Inputs
The digital inputs are selectable for either mechanical or electronic operation. In either case it is necessary
to pull the input down to 0Vdc to activate it. Inputs will handle up to 30Vdc in the off state for parallel
connection across existing equipment. The “debounce” is enabled by a jumper link, which if fitted enables a
longer time constant circuit to eliminate multiple pulses caused by contact bounce. The debounce jumpers
are positioned in the centre of the PCB on the iRIS 350 and the right hand eedge on the iRIS 220/320.
iRIS 220/320 - The top jumper is Digital Input #2 and the bottom jumper is Digital Input #1.
iRIS 350 - The top jumper is Digital I/O #4 and the bottom jumper is Digital I/O #1.
Fit the jumper for mechanical switching at up to 20Hz. In this mode the input is normally pulled up to 12V
through a 10K resistor providing a wetting current of approximately 1.2mA. A 100nF capacitor is also fitted
across the input to provide limited hardware debounce, preventing false triggering due to contact bounce.
For installations that do not have an external power source it is important that the input is not held low for a
prolonged period of time, as this will increase the current drawn from the internal battery.
Remove the appropriate jumper for electronic switching at up to 5kHz. In this mode the input is normally
pulled up to 5V through a 57K resistance, providing a wetting current of approximately 100A.
Figure 5 - Digital Input Circuit
IMPORTANT NOTE!
In almost all installations where an iRIS is connected in parallel with other equipment to share a
common pulse input (e.g. from a flow meter), there has not been a detrimental effect, as the iRIS
inputs present a relatively high impedance to the circuit. However, in the event that connecting an
iRIS does cause pulse failure, iQuest recommend removing the debounce selection link for the
appropriate input. This sets the input to electronic switching mode, even if the actual pulse source is
a clean contact (reed switch or similar).
The debounce jumpers are located on the right edge of the PCB (iRIS 220/320) or in the centre of the
PCB (iRIS 350) and can be accessed once the front cover is opened.
Hint: When removing a jumper, simply fit it to one pin only of the connector to avoid it being
lost.
DIOx
DGND
100nF
JPx
1K
10K
+12V 5V
1nF
47K
To internal logic circuitry