Installing A New Probe Or Sensor; Test Equipment Required - Novatech 1635 User Manual

5.7

INSTALLING A NEW PROBE OR SENSOR

Whenever a new oxygen probe or sensor is installed, the millivolt offset(s) value should be entered. To achieve this,
refer to Section 4.5, 11 & 12.
The probe or sensor offset is noted on a tag or label attached to probe or sensor. To check an offset on site, the probe or
sensor must be sensing air with reference air connected and allowed to settle at the operating temperature for 30
minutes. Read the offset in 'RUN' mode in millivolts on the lower line. Offset errors can occur if the sensor does not
have some air passing over it. A gentle flow of air in the calibration check port can be provided by a reference air pump
or similar. If a probe is in a process with the process running, the air purge on the sensing side of the sensor will only
be successful if the probe has a filter or small sensing hole. Probes with open sensing ends or with large sensing holes
allow the process gas to mix with the calibration gas, giving a false reading.
For heated probes or sensors, if the combustion appliance is not operational and the probe or sensor heater is interlocked
with the 'FUEL ON' signal, the 'HEATER LOCKOUT BYPASS' switch should be set to 'BYPASS' to power the
probe or sensor heater after removing the probe from the flue. For unheated probes, the sensing tip must be raised to at
least 700°C with a portable furnace.
Return the 'HEATER LOCKOUT BYPASS' switch to normal before installing the probe or sensor in the dryer or oven.
5.8

TEST EQUIPMENT REQUIRED

All measurements are simplified if an analyser is connected to the probe or sensor. Readings can then be easily taken of
probe or sensor impedance, EMF, temperature and percent oxygen. The analyser also provides proper heater control for
heated probes and sensors.
The following tests are described using readily available workshop equipment where an analyser is not available. If an
analyser is available the same test procedures will apply. First check all alarms on the analyser, allowing time for the
probe or sensor to heat up after switch on.
An instrument to measure probe or sensor EMF and temperature is required. A 3 1/2 or 4 1/2 digit multimeter will
perform both measurements.
A separate temperature indicator to suit the probe or sensor thermocouple type is also useful, although not necessary.
A reference air pump is required and a cylinder of calibration check gas e.g. 8 % oxygen in nitrogen. The cylinder
should have a pressure and flow regulator. Both of these are inexpensive devices available from gas supply companies.
The calibration check gas should be chromatograph tested to an accuracy of 0.1 % oxygen.
A small test furnace capable of raising the probe tip temperature to 720 °C is required. The furnace should have a
uniform temperature for about 50mm either side of the sensor's tip.
If a 1635 analyser is available at the test location then no other equipment will be required. If not, then a controllable
power source for the heater is required. A Variac (variable transformer), set to approximately 100 volts will regulate
the probe or sensor temperature to 720°C approximately.
48
PROBE & SENSOR MAINTENANCE
CAUTION DANGER
UNHEATED PROBES
HEATED PROBES OR SENSORS
August 2009
1635 Water Vapour Analyser