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Operation Instructions
3
3-15
Figure 3-20. The Air Density Screen With Air Density Corrections Disabled
Air density correction is only applied to dose or dose rate measurements such as, Roentgens, rads,
Grays, Sieverts, etc. These measures are dependent on correctly compensating for the mass of air in the
ion chamber. Electrical units (coulombs and amperes) are, by definition, insensitive to the mass of air in
the ion chamber.
3.9.10 Using the UNITS SELECT Button
Pressing the UNITS SELECT button displays the Units Select screen, see Figure 3-21. The radiological
units shown on the Units Select screen appear on the Measurement screens when displaying dose, dose
rate, accumulated dose, and average dose rate. This screen allows the radiological rate divisor (hr, min,
s) to be specified. The “f” cursor points to the radiological rate measurement unit. Press the UP arrow to
increase the rate divisor, and press the DOWN arrow to decrease the rate divisor.
Figure 3-21. The Units Select Screen for an Ion Chamber Calibrated for Dose Measurements
Ion chambers having dose rate calibration units will not have a rate divisor, e.g. Curies (Ci), becquerles
(Bq), or kerma (Sk). The dose rate units will be multiplied by seconds to produce an equivalent dose unit,
see Figure 3-22.
Figure 3-22. The Units Select Screen for an Ion Chamber Calibrated for Dose Rate Measurements
3.9.11 Using the BIAS SELECT Button
Pressing the BIAS SELECT button displays the Bias Select screen, see Figures 3-23 through 3-24. This
screen displays the bias setting and the bias voltage measured by the Model 35040 Therapy Dosimeter.
The “f” cursor points to the bias setting, expressed both as a voltage and as a percent of the maximum
voltage setting. The line below the bias setting indicates the bias polarity. The bottom line displays the
bias voltage measured by the instrument, and three letters to signify the bias polarity. When the central
electrode is positive, CEP is displayed to the right of the measured voltage. When the central electrode is
negative, CEN is displayed to the right of the measured voltage. (NOTE:
The bias settings are user
customizable; see Section 3-10.)
22.5 C 760 mmHg
ADCF = 1.000
OFF
dose unit: R
ADC
rate unit: R/min
ADC
dose unit: Ci·s
rate unit: Ci