SECTION 4
PREVENTIVE MAINTENANCE
4.6 Severe or Stubborn Contamination
If the Clean Test indicates residual contamination in
spite of a clean appearance:
1
Repeat the cleaning procedure. Calibrate the
instrument using the 290, 1000, and 100
mmol/kg standards. Then run a second Clean
Test. If there is significant improvement, conta-
mination can likely be removed by repeated
cleaning.
2
You can often successfully remove the contami-
nant simply by applying a droplet of purified
water to the thermocouple and allowing it to
stand for 30 to 60 minutes.
Causes of Unusual Contamination
While there are many potential causes of unusual
contamination, the following are the most common:
❑ A severely contaminated thermocouple with visi-
ble accumulations of organic matter or salt
deposits is evidence of incorrect or careless
loading procedures.
❑ Careless loading of greasy or waxy specimens.
❑ Failure to clean fingerprints or other deposits from
the sample holder.
❑ Oily residue from compressed air lines when an
air jet is used to blow water droplets from the
thermocouple after cleaning.
❑ Improper use of Blow Clean. Liquid discharged
from the can onto the thermocouple mount leaves
an oily deposit that is difficult to remove.
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