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35040
Operators Manual
1-4
Measurement Accuracy: Charge measurement accuracy is warranted to be better than ±
(0.20%rdg + 2
counts) over the operating temperature range of 18°C to 28°C for 1 year.
Field Calibration: Field calibrations may be performed via a restricted distribution MS-DOS Calibration
program. This program is available to the AAPM accredited calibration laboratories (or equivalent) and
may be used to adjust the current and charge scale factors from their nominal factory setting of 1.000.
Timed Charge Measurements
Range and Resolution: Same as charge measurements.
Measurement Method: The timed charge measurement is derived by monitoring the charge integrated
over a time interval that begins with the activation of the timer. The timer automatically stops when the
elapsed time is equal to the timer interval setting or the exposure is over. Interpolation is used to
determine the charge at an integral number of seconds.
Measurement Accuracy: Same as charge measurements assuming that the rate of charge delivery does
not dramatically change within the interpolation window interval.
Current Measurements
Range, Resolution, and Noise:
Full Scale Range Display Resolution
Noise
(± counts)
200.0 pA 0.1 pA 2
2.000 nA 0.001 nA 2
20.00 nA 0.01 nA 1
200.0 nA 0.1 nA 1
1.000 μA 0.001 μA
1
Measurement Method: The basic current measurement is derived by monitoring the change in the
integrated charge level over successive 1-second intervals. Dividing the change in integrated charge by
the 1-second integration period interval yields the current value.
Measurement Accuracy: Current measurement accuracy is ±
(0.20%rdg + 2 counts) over the operating
temperature range of 18°C to 28°C for 1 year. Since the current measurements are based directly upon
charge measurements, an independent current calibration is not required.
Measurement Noise: Current measurement noise is typically 1 to 4 counts peak to peak (depending
upon the range) when the input is supplied by a quiet DC current source. When using a 0.6 cc Farmer
Probe to measure the output of a typical
60
Co source, noise in the current measurement may be on the
order of 0.4 R/min peak to peak at 100 R/min. Normal variations in the output exposure rate produced by
a linear accelerator may result in excessive noise on the current measurement.
Response Speed: The display of current measurement values will begin within 1 second of the start of
the exposure and reach 99% of the final level within 2 seconds.
Average Current Measurements
Range and Resolution:
Full Scale Range Display Resolution
200.00 pA 0.01 pA
2.0000 nA 0.0001 nA
20.000 nA 0.001 nA
200.00 nA 0.01 nA