.
RESISTANCE CALISRATION OF AN=PDR=39's
The Tl-3 or PDR~39 instruments rely on the accuracy of their hi-meg or
chamber load resistances for scale decading.
A single calibration cmtrol
‘(meter series resistance) performscalibration of all scales at onces
It was felt that some method of assuring hi-meg accuracy should be used to
check all instruments before they met field usee
It was also felt that the
Victoreen deposited carbon hi-meg resistances might be highly voltage sensitive
and should be checked under circumstances approximating their actual operating
potentials.
Commercial hi-meg ohm meters often use potentials up to 1000 volts
making them unsuitable for this application.
An Applied Physics Corp. vibrating
reed electrometer was used to measure the potential across a 100 megohm standard
resistance (calibrated to value / .3%) in series with the unlmown hi-meg (in place
in the instrument).
All resistors varying more than 5% were replaced.
to calibrate the 0 to 5 mr. range was madee
No attempt
Supplied
The standard Bendix bridge and sub miniature tube tester'by the Army for use
with the instrumants uses a potential of 16 volts across the unknown resistances
It is felt that the Bendix unit serves the purpose well - better perhaps than the
electromter technique which is of a laboratory nature.
For most accurate results each instrument should be calibrated on the scale
representing the mean deviation (since each scale varies f a few percent).
was not available for this purpose.
Tim
Each Tl-B carries within it a card giving
the deviations for future usée
The PDR-39 schematic places the 5 mr and 50 mr scales in parallel.
This results
in a 10% deviation (low) it was noticed however that the 10% deviation was not
always forthcoming when the instruemnt was radiation calibrated.
Further study
should reveal use-ful characteristic information.
/'£0/p,
The deviation percentage given on the cards in the instruments pertains to
goals error when radiation is reade
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