Oxymitter 4000

Instruction Manual

IB-106-340 Rev. 3.0 December 2003

SECTION 8

TROUBLESHOOTING

8-1 OVERVIEW

While the Oxymitter 4000 electronics provides a significant number of diagnostic alarms to assist in troubleshooting potential problems, it’s good to place these alarms in perspective with respect to the instrument’s operating principles:

a.When the Zirconium Oxide sensing cell is heated to its setpoint [1357°F (736°C)], the cell will generate a voltage that represents the

difference between the process O2% and the reference O2% inside the probe (20.95% O2 ambient air).

b.Test points are provided to read the raw milli- volt value generated by the thermocouple that controls both the cell temperature and the raw cell signal.

c.The cell temperature at test points 3 and 4 should always be stable at approximately 29 to 30 millivolts, which represents the 736°C setpoint temperature.

d.When flowing calibration gasses, the raw cell millivolt value at test points 1 and 2 should represent the levels on the chart in Figure

8-1.Note that the raw cell millivolt value in-

creases logarithmically as the O2 concentra- tion decreases.

EMF (mV)

200

O2 Sensor Performance at 736OC

150

100

50

0 0

0.01

0.1

1

10

100

 

 

Concentration O2 (%)

 

37260043

O2

%

100

20

15

10

9

8

7

6

5

4

EMF(mV)

-34

1.0

7.25

16.1

18.4

21.1

23.8

27.2

31.2

36.0

O2

%

3

2

1

0.8

0.6

0.5

0.4

0.2

0.1

0.01

EMF(mV)

42.3

51.1

66.1

71.0

77.5

81.5

86.3

101.4

116.6

166.8

Figure 8-1. O2 Sensor mV Reading vs. % O2 at 736ºC (Reference Air, 20.9% O2)

Rosemount Analytical Inc. A Division of Emerson Process Management

Troubleshooting 8-1