Teledyne 9060 Operating Instructions Manual page 41

the cause of each alarm until no further alarms appear on the display. For details on the
operation of the alarm button and the alarm functions refer to Section 4.
3.21 PROBE OR SENSOR CALIBRATION
The zirconia sensor provides an absolute measurement of oxygen partial pressure. There
are no calibration adjustments, apart from 'SENSOR OFFSET', for the probe or sensor.
The zirconia sensor EMF is either correct or replacement is required. To check that the
probe or sensor is functioning correctly, firstly check that the high impedance alarm,
'SENSOR FAIL', is not active. The actual impedance can be displayed on the lower line. It
should be less than 9 KΩ at 720°C (1320°F).
Once it has been established that the impedance is normal, the offset may be set using
the millivolt level marked on the oxygen probe or sensor. Refer to Section 5.5.11. The
probe offset can be tested on site. A small flow of air must be admitted to both the 'REF'
and 'CAL' ports when testing the probe offset. If the probe is in the process, the air must
fully purge the probe sensor without interference from the process gas sample. Teledyne
probes can easily achieve this with or without a probe filter and a gas flow of only 1 to 5
litres/minute (120 to 600 scfm) for a 1231 probe and up to 20 litres/minute (2400scfm) for
an unheated probe.
3.22 FILTER PURGING
Purging probe filters is controlled from the 'PURGE' button on the transmitter when in
'RUN' mode. If 'AUTO PURGE' has been enabled in set-up 53, pressing the PURGE
button will start the automatic cycle. Pressing any other button will cancel the auto purge
cycle. If AUTO PURGE was not enabled, the purge solenoid will only stay open for as
long as the button is pressed. Gradually adjust the purge air supply regulator, increasing
the pressure until sufficient flow is obtained to clear the filter. This is best checked with a
dirty filter after a period of operation, by withdrawing the probe from service and watching
any build up on the filter being blown off at the set pressure. Normally 30 kPa (5 psi) is
adequate but the air pressure may be set as high as 100 kPa (15 psi).
3.23 CALIBRATION GAS CHECK
If the installation has a filter purge facility, set this up first. Refer to the previous
paragraph. Press the 'CAL 1 or 'CAL 2' button while in 'SET UP' mode to obtain a
reasonable flow through the calibration check gas flow meter. If air is being used as a
calibration check gas, use the air from the regulator for filter purge. Then, when setting up
a gas for calibration checking, set the pressure from the calibration gas cylinder so that it is
the same as the pressure set on the air regulator. Then the setting on the rotameter / flow
regulator will be the same as that for the airflow. The flow required is 1 to 5 litres/minute
(120 to 600 scfm) ) for a 1231 probe and up to 20 litres/minute (2400scfm) for an unheated
probe.
Air is not the best gas for calibration checking on a zirconia sensor. The output of a
zirconia sensor with air on both sides of the sensor is zero millivolts. It is better to choose
a gas value which provides a reasonable output from the sensor and which is near to the
process oxygen level. A cylinder with 2% oxygen in nitrogen is a commonly used
calibration gas. The maximum pressure on the calibration check gas cylinder regulators is
100 kPa (15 psi).
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9060-Zirconia Analyser
41