Oxigraf O2iM NEMA 4X Oxygen Analyzer
February 13, 2007 08-0427-B0, Manual, O2iM.doc Page 17
4.4.2 Autocalibration
The O2iM analyzer is equipped with autocal, which enables automatic calibration at a programmable
interval or on activation of alarm detector B. Autocal requires an external calibration gas connected
to the calibration gas input port. If pressurized, the gas must be pressure regulated to a pressure from
5 to 15 psi. The oxygen concentration value must equal the CAL1 setup value.
Three parameters in the setup menu control autocal operation. The Autocal Period enables autocal
if it is non-zero and sets the time between autocal cycles with 0.1-hour resolution. The Cal Valve
Delay parameter sets the delay time from activation of the cal gas valve to the start of the calibration
cycle. It compensates for the time to completely fill the oxygen measurement cell with the
calibration gas. Autocal Level B option triggers an autocal if the level B detector is active. The first
autocal cycle will start five seconds after any change to the Autocal Period parameter on return to O2
mode.
Calibration gas for both manual and autocal modes must be supplied via the cal gas input port. The
autocal gas valve switches from sample input to the calibration gas source when the CAL1 is selected
using the keypad. Multiple presses of the FLOW key cycles through the sample, low cal, and high
cal sources to allow display of cal gas flow and pump drive level.
The cal gas flow rate should be regulated to the sample gas flow setpoint by the flow control servo.
In some cases the internal cal gas regulator may need adjustment to enable flow regulation. Use the
following procedure to adjust the cal gas regulator inside the O2iM enclosure:
a) With the instrument operating normally press the FLOW key and note the sample flow rate and
pump drive level for the sample input stream.
b) Press the FLOW key again to turn on the low cal gas valve and note the pump drive level.
c) Adjust the low cal gas regulator with a screwdriver to get the cal gas pump drive level equal to
the sample mode drive level.
d) If the O2iM application does not use the sample pump then adjust the regulator for a cal gas
flow rate of 100 to 200 ml/min.
e) Press the O2 key to return to an oxygen reading. If desired, press the FLOW key again to
advance to the high calibration settings. Normally, field calibration of the high setting is not
required for this application. Should the user wish to perform this operation, note that external
pressure regulation of the 100% O2 cal gas is required.
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