© 2010 SST Sensing Ltd 2 www.sstsensing.com
DS0074 Rev 7
DESCRIPTION
The O2I-FLEX Interface provides all necessary
electronics to power and control SST Sensing’s range of
dynamic Oxygen Sensors.
The O2I-FLEX Interface can be user configured to output
measuring ranges of 0-25% O
2
and 0-100% O
2
. The
entire measurement range is linear in both cases. Factory
default is 0-25% O
2.
When configured for 0-100% O
2
the
user can also customise the analogue output ranges to
suit their application.
The interface outputs the measured values
simultaneously via 4 output channels, 4-20mA, 0-10V
DC
and RS232 (Rx and Tx), all outputs are referenced to the
system GND.
A digital 3.3V
DC
logic output cycles at the same
frequency as the electrochemical pumping action of the
oxygen sensing cell during normal operation, thus
providing a real time sensor health check, if the output
ceases to cycle the sensor has entered a start-up or error
state. This provides fault proof operation. The digital
output is also used during the calibration process to
indicate the interface status.
A green on-board LED mirrors the CYCLE output and can
be used to visually determine the sensor status or during
the calibration process. A red LED indicates the unit has
power applied.
SST’s range of oxygen sensors do not directly measure
the oxygen concentration but instead measure the partial
pressure of oxygen within the measurement gas. In order
to output an oxygen concentration (%) the O2I-FLEX
must be calibrated, or more specifically, re-referenced in
a known gas concentration, typically normal air.
Calibration, or re-referencing, is achieved by connecting
the calibration input to GND or by pressing the on-board
calibration switch and monitoring the status of the digital
cycle output or by visually monitoring the on-board green
LED. During the calibration process the output will either
automatically calibrate to a fixed reference or can be
manually calibrated to any output by way of a PCB
mounted potentiometer. The fixed reference is factory set
to 20.7% O
2
for calibration in normal air though this value
may be altered via the RS232 interface for calibration
with a reference gas of any known oxygen concentration.
Calibration is stored on power loss.
The auto or manual calibrate function is user
configurable. Regular calibration removes the effects of
application and atmospheric pressure changes and also
eliminates any sensor drift that may occur during the first
few hundred hours of operation.
For more detailed information on the operation
of SST Sensing Oxygen Sensors please refer to
the following application note via our website:
AN0043 Operation Principle and Construction of
Zirconium Dioxide Oxygen Sensor.
O2I
-
Flex
Oxygen Interface
