Fluke 35040 Operator's Manual page 20

35040
Operators Manual
Charge
QOffset
0
- Charge samples in Leakage.
X - Samples discarded.
- Charge samples in exposure.
- Extrapolated charge due to leakage current
Figure 2-2. Leakage Current and Start of Exposure
When automatic exposure detection is disabled (start and stop threshold set to 0.0 pA), there is no
correction for extrapolated charge due to leakage current. The dosimeter must be manually reset
between exposures and the leakage current kept as low as possible for best results.
Exposure Charge and Dose
The charge on the electrometer during an exposure is due to the incident radiation plus the charge that
was on the electrometer before the exposure plus the extrapolated charge due to any leakage currents in
the ion chamber, cables, or electrometer. To obtain only the charge due to the exposure, the instrument
employs the following equation:
= −
Q Q [C] Q
Exposure Offset
= ×
Dose Q [C] ICCF
Exposure
The exposure charge variable Q
pressing the RESET/MEASURE button or automatically if the start and stop thresholds are used. Over
the duration of the exposure, Q
measurement value (4-1/2 digit) is held following the exposure.
Timed Charge and Dose
This measurement accumulates charge only while the elapsed time is less than or equal to the timer
interval setting. The displayed value is held following the completion of the timer interval.
= − −
Q Q [C] Q [C]
Timed 2 1
= ×
Dose Q [C] ICCF
Timed Timed
2-6
TOffset
Start of Exposure
( (
− ×
[C] I [A] T [s]
Leakage
×
[Units/C] ADCF
is set to zero at the start of an exposure either manually by
Exposure
and Dose are updated about once a second. The displayed
Exposure
( (
× −
I [A] T [s] T [s]
Leakage 2 1
×
[Units/C] ADCF
X
X X
Time
TStart
) )
−
T [s]
Offset
) )