Test Gas And Reference Air Connections; Restrictors; Connection Types; Test Gas Inlet - ABB Endura AZ25 Series User Manual

Endura AZ25 series probe
Combustion oxygen monitor

4.4 Test gas and reference air connections

The probe has one test gas inlet and one reference air inlet
(continuous supplies required). The AutoCal unit has two test
gas inlets and one test gas outlet marked VENT (the Ref. Air
connection at the AutoCal unit is not used with the AZ25 probe).
Caution. Only use clean dry instrument air free from
hydrocarbons,* or traceable certified bottled test gas
mixtures of O / N .
2 2

4.4.1 Restrictors

Systems can be ordered with or without restrictors – refer to
Section 3.5, page 9 for schematics of all configuration options.
Where restrictors are not fitted, flowmeters must be fitted to the
test gas and reference air lines to restrict / regulate the flow:

on systems with restrictors:
the reference air supply is set to 1 bar (15 psi) which gives
0.3 to 0.5 l / min (0.6 to 1.0 scfh) preset flow
the test gas supply is set to 1 bar (15 psi) which gives
1 l / min (2.118 scfh) preset flow

on systems without restrictors:
pressure is still set to 1 bar (15 psi) then flow is restricted
by valves on flowmeters

4.4.2 Connection types

Note. Refer to Section 3.5.1, page 9 for pneumatic entry types.
4.4.3 Test gas and reference air connections
Fig. 4.7 shows the test gas and reference air inlets at the probe.
Endura AZ25 probe
Reference air in
Endura AZ25 AutoCal unit
Test gas in
Test gas
2 in
Fig. 4.7 Endura AZ25 probe – test gas and reference air
connections
*ABB recommend our 5 µm / Oil Coalescing Filter Regulator – see
A 32
Appendix , page .
OI/AZ25P–EN Rev. E

4.4.4 Test gas inlet

The probe test gas (calibration) inlet is provided for in situ probe
testing using a test gas.
If AutoCal is not fitted, Test Gas 1 connection is used for Test
Gases 1 and 2. The gas connections are switched manually, as
requested by the calibration sequencing in the transmitter.
If the probe is connected permanently to the test gas supply
pipework:

fit a high quality, corrosion-resistant (stainless steel),
solenoid valve, manually operated valve or non-return
valve (that is leak-tight even at zero back-pressure) in the
pipework, as close to the test gas inlet valve as possible

keep the valve closed when the calibration system is not in
use
Caution. If the test gas connection is not sealed when not
in use, air leaking into the probe via the connection causes
measurement errors. In a pressurized flue, gases venting to
atmosphere through the connection cause corrosion of, and
/ or block, the test gas tube. In a negative pressure flue, air
leakage causes high O
Note. It is preferable to use air (20.95 % O
test gases as this is the sensor's zero point. Alternative
representative gases can be used according to local
environmental conditions.
To ensure better accuracy, use 2 test gases that represent
the top and bottom limits of the known operating range.
Due to resolution accuracies, do not calibrate the system
with gases of less than 1 % O
Refer to Section 3.5, page 9 for schematics of all configuration
options

4.4.5 Vent (AutoCal unit)

The vent is used to route the test gas(es) from the AutoCal unit
to the Test Gas inlet at the probe.
Ensure the vent and the tube from the vent do not become
blocked during probe use.
Test gas
1 in
Fig. 4.8 Vent connection at AutoCal unit
4 Electrical connections
reading errors.
2
.
2
Endura AZ25 AutoCal unit
Vent
) as one of the
2
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