(f) Rate of change of temperature.
The rate of change of
temperature may introduce inaccuracies in calibration. For most secondary
reference standards, the rate of temperature change does not require special
consideration. The rate of effect is the significant element in determining
the temperature of standards and TMDE as prescribed in TB 750-117/TB 750-25.
(2) Humidity.
(a) High humidity influences the stability of the standards
through corrosion, electrical conductivity, and dielectric constants.
Low
humidity can affect measurements by the accumulation of static changes.
(b) If temperature and humidity out-of-control conditions exist
concurrently for short periods, the instrument or standard may be assumed to
follow the temperature recovery providing condensation has not occurred.
Should condensation be present, the laboratory chief will determine whether
or not to calibrate based on the following:
1
Can the condensation be wiped off?
2
Is the critical material porous or impervious?
3 Does the standard or instrument perform in a normal manner?
Is there drifting? Is it erratic? (A series of readings may be needed to
attain necessary assurance.)
4 An inspection Should be made to ascertain that no physical
deterioration has occurred. Inspection should be restricted to the obvious,
withopt physical disassembly for a detailed inspection.
(3) Vibration.
A delicate instrument installed according to the
technical manual requirements, or recognized good practice, is in itself an
adequate vibration sensing device. Vibrations transmitted through supports
may cause a balance, a pointer, or a mirror on a suspension galvanometer to
oscillate. By observing the indicating elements of instruments, a decision
can be made whether or not to continue calibration operations.
When
transient vibrations degrade accuracy or cause doubt regarding actual
readings, calibration operations using the affected instruments will be
suspended until the transient vibrations have ceased.
(4) Dust.
A dust particle count greater than the limits specified
will not automatically prevent calibration. Corrective measures are to be
taken immediately to bring the particle contamination to within the
specified limits.
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