APPENDIX
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5.3. Accuracy of Pirani Vacuum Gauge
The relationship between pressure and output of a Pirani vacuum gauge is nonlinear and its accuracy
range varies with pressure values. To express the outgoing inspection criterion for a Pirani vacuum
gauge, it is defined as "within ± 3% of 100% full scale as converted to the linear scale" and is given
in the instruction manual as measurement accuracy.
To express the error range by pressure values
The pressure and recorder output of the GP-1G is in proportion to the controller meter scale
graduations, as shown by the recorder output characteristic table (graph).
What is meant by "within ± 3% of 100% full scale as converted to the linear scale" is that an error of
± 3% of the linear scale is involved when the meter scale is replaced by a linear scale of 100% full
scale.
To express the error range at a reference pressure of 40 Pa (0.4Torr) by pressure value, it is 32 to 49
Pa (0.33 to 0.48Torr), which is ± 3% as converted to a linear scale, as shown in Fig. 5-2.
Fig. 5-2 Linear memory conversion
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