Section 4
OM6636-B-00
12 February 2015
4-1
4. MAINTENANCE
4.1.
PREVENTIVE MAINTENANCE
4.1.1.
Cleaning
The instrument requires very little maintenance other than periodic dusting of the outside
of the enclosure. Use alcohol to clean around the standard resistor terminals to avoid
formation of leakage paths.
4.1.2.
Temperature
Check the internal temperature with the imbedded PRT before using the resistors as
references and also periodically.
Compare the calculated temperature with the value given in the Report of Calibration.
4.1.3.
Resistor Stability
Resistor stability is determined by comparison against known reference resistors.
4.2.
CERTIFICATION OF RESISTANCES
If the resistance of the standard resistors is to be determined by direct comparison with a
standards laboratory, the comparison should be made with the resistors inside the enclosure at the
operating temperature. After transportation, or if the resistors’ temperature stabilized enclosure
has been allowed to cool, the resistors should be allowed to stabilize at the operating temperature
for at least 36 hours before measurement or before use.
4.3.
CORRECTIVE MAINTENANCE
Symptoms appear at the beginning of each of the following paragraphs as a guide to detailed
fault location. Refer to Section 5 of this manual for the PRINCIPLES OF OPERATION.
4.3.1.
Preliminary Checks
Check POWER indicator - This should be lit when the instrument is connected to the AC
line and the power ON/OFF switch in set to “ON”. If not, check that both of the other two
HEATER and OVERTEMP indicators are also not lit. If they are both not lit, then a
general loss of power is indicated. If either indicator is lit, then it indicates that only the
power indicator circuit is defective. In addition, check the power outlet. The fuse in the
Power Entry module may be blown. It may have been a defective fuse.
Check the HEATER indicator - It should indicate the cycling on and off of the heater.
Check the OVERTEMP indicator - If it is lit, then the temperature inside the enclosure
