Super Systems Gold Probe - Manual (Page 9)

8
SSi Gold Probe Manual Rev C
TROUBLE SHOOTING
When trouble arises with a furnace control
system, it is important to establish where the
problem is located; the probe, signal
transmission lines, the control instrument, or
the furnace itself. Several simple tests can help
to isolate the problem quickly. It is most
important to first understand the nature of the
fault. Aside from erratic behavior like cycling,
or failure to stabilize at the set point, the most
common symptom is non-conformity of the
work pieces to quality assurance specifications.
To evaluate most faults, the recommended
tools are:
1. a good 3 ½ digit millivolt meter with at
least 10 meg  input impedance and 0 to
1999 mV range,
2. a temperature calibrator and,
3. a simulator to output 0 to 1300 millivolts
at less than 50 megohms output
impedance.
Probe troubleshooting: In order to establish
the source of problems in your installation, first
resist the temptation to remove the Gold
Probe from the furnace.
All of the following
meaningful questions must be answered while
your Gold Probe (or any other carbon sensor) is
in the furnace, at temperature, and exposed to
a normal atmosphere under manual control:
1. Does an Alnor dew point reading (or
shim stock analysis) verify the indicated
value from the probe? If there is reasonable
correlation, the problem is NOT the probe.
2. Are the connections from the T/C extension
wire and sensor cable clean and firmly
attached at the correct probe and control
instrument terminals? Note that the shield
wire in the sensor cable should be
connected to ground at the control
instrument end only!
SYMPTOM POSSIBLE CAUSE
High % C
 Low reading due to:
 High probe resistance
 Cracked zirconia
 Dirty reference air
 Faulty cable insulation
 Instrument calib./ calc.
 Air leak to burnoff fitting
 Furnace air leak at probe
 Oily parts or sooted furnace
 Wrong recipe time/temp
Low % C  High Reading due to
 Probe plugged with soot
 Instrument calib./calc.
 Wrong recipe time/ temp
Erratic  Faulty signal due to
 Bad sensor connections
 Electrical noise source
 Radiant tube leak
 Bad Endo
 Mixing valve setting
 Instrument setting
Sooted fce  Endo not cracked (temp too
Low in generator or
Catalyst inactive)
3. Is the control instrument CO or H
2
factor set to
the appropriate value? This “factor” is referred
to by various manufacturers as Zone Factor,
Process Factor, Gas, Furnace Factor, CO
Factor, Calibration Factor, etc. This factor may
require adjustment in order to make the
calculated %C or dew point agree with other
measurements.
4. Do the actual Gold Probe temperature and O
2
mV signal, as measure by the temperature
calibrator, and digital voltmeter, agree with the
displayed values on the control instrument? If
not, and instrument calibration problem is
likely.