ABB Endura AZ20 series

Combustion Oxygen Monitor
Endura AZ20 Series Probe 4 Troubleshooting – Functional Checks
IM/AZ20M–EN Rev. B 11
4.3.1 Cell Function Check
Referring to Fig. 4.1:
1. Remove the leads to the cell terminals B (Cell+ red; Cell–
black) and connect the digital multimeter (0 to 200 mV
range) directly across the leads.
2. If AutoCal is fitted, open the test gas valve manually. If
AutoCal is not fitted, apply the test gas directly to the test
gas inlet and control it externally – refer to the probe User
Guide (IM/AZ20P–EN).
3. Leave the test gas to run for a minimum of 3 minutes and
record the reading on the digital multimeter.
4. Switch the test gas off.
5. The measured voltage should correspond to the oxygen
volume percentage for the test gas used – refer to
Fig. 4.3, page 10.
6. If this check has resulted in:
a. satisfactory readings:
the cell, heater and thermocouple are functioning
correctly – incorrect readings at the transmitter may
be due to transmitter calibration faults – refer to the
transmitter User Guide (IM/AZ20E–EN)
b. unsatisfactory readings:
there is a difference of more than ±5 mV between
the measured cell output voltage and the graph –
refer to Fig. 4.3, page 10
the thermocouple / electrode assembly may be
faulty (check this first – refer to Section 4.2, page 9)
or the cell may be faulty – refer to Section 5.7, page
16.
4.3.2 Detailed Cell Accuracy Check
To perform this check, calculate the span mV value first then
calculate the % O
2 value from the span mV value.
1. For millivolt readings and test gas management, refer to
steps 1 to 4 from Section 4.3.1.
2. To calculate the span mV value:
a. allow the probe to settle in air, or with test gas air for
5 minutes minimum to stabilize – note the millivolt
reading which should be ±2 mV (if the cell is less
than 1 year old), but may be up to ±5 mV on older
cells
b. calculate the span mV value as the
sum of zero and
test gas mV, for example:
–1 mV zero + 62.77 test gas mV = 63.77 mV span
+1 mV zero + 62.77 mV test gas mV = 61.77 mV
span
3. Use the following formula to calculate the % O
2 from the
span mV value:
Cell mV = 0.0496 T (log10 P0 / P1) + C mV,
where:
T = cell temperature °K =
(700 °C + 273.16) for process temperatures < 700 °C
or
(process temperature + 273.16) for process
temperatures > 700 °C
P
0 = partial pressure ref. gas (20.95 % O2)
P
1 = partial pressure measured gas
C = cell constant
Note. This check uses 1 test gas. Note. This detailed check uses 2 test gases – checking the
isolated cell output voltage using 2 test gases provides the
most accurate result.
The 2 test gases are:
 air (20.95 % O2) to give a zero reading
 a second test gas not less than 1 % O2