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4.17 Commissioning - Run Mode
When the transmitter is turned on it will go to RUN mode. The SET-UP/RUN button will toggle between the
two modes. The upper line of the display will now read '% OXYGEN'. If the probe or sensor temperature is
not above 650°C (1200°F), a "Probe Low Temperature" message is flashed on the lower line. The probe or
sensor temperature can be checked on the lower line of the display.
4.18 Probe or Sensor Calibration
The zirconia sensor provides an absolute measurement of oxygen partial pressure. There are no calibration
adjustments, apart from 'Probe 1 Offset', for the probe. The zirconia sensor EMF is either correct or it needs
to be replaced. To check that the probe is functioning correctly, first check that the high impedance alarm,
'Probe 1 (2) High Impedance', is not active. The actual impedance can be displayed on the lower line. It
should be less than 9 K at 720C (1320°F).
Once it has been established that the impedance is normal, the offset may be set using the millivolt value
marked on the oxygen probe. See chapter 6.4.1 Probe 1 Offset. 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. Novatech 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. When a stable oxygen reading has been achieved, read the 'Probe EMF'. Enter this value into the
set-up menu #1 for the probe 1 (set-up #2 for the second probe if it is installed).
4.19 Filter Purging
Purging probe filters is controlled from the 'GAS/PURGE' buttons on the transmitter when in 'RUN' mode. If
'Automatic' has been selected in either 'Sol. 1 Auto/Man' or 'Sol. 2 Auto/Man' in Commissioning Menus 21 or
30, pressing the GAS/PURGE button will start the automatic cycle. Pressing the button again will cancel the
auto purge cycle. If 'Automatic' was not enabled, the 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).
4.20 Calibration Gas Check
If the installation has a filter purge facility, set this up first. Refer to the previous paragraph. Press the
'GAS/PURGE 1 or 'GAS/PURGE 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).
Note: If 'Dual probe' was selected in commissioning menu 4, 'Cal Gas 2' must be connected to probe 2.
Technical Manual
August 2018
26
1732 Oxygen Transmitter
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