Theory of Operation | 2 |
Basic Operating Equations |
Charge
X X X X
T 1.33s
0
X X X X X X
X
Q
1.33s
TOffset
T1 | T2 |
Time
Start of Exposure Detected | End of Exposure Detected |
- Sampled charge data points in average current. - Charge data points for leakage.
Figure 2-3.Average Current and Exposure Time
2.3.3 Air Density Correction Factor
=⎛ 760 mmHg ADCF ⎜
⎝P
⎞ | ⎛ T | ⎞ | |
⎟ | × ⎜ |
| ⎟ |
| |||
⎠ | ⎝ T c ⎠ | ||
The air density correction factor is used to correct dose and dose rate measurements for a vented ion chamber.
where the pressure “P” is expressed in mmHg, the temperature “T” is in Kelvin, and the calibration temperature “Tc” is in Kelvin. The calibration temperature is either 20°C (293.15 K) or 22°C (295.15 K), depending on that used by the calibration agency when calibrating the ion chamber. The calibration temperature must be specified during customization. The ADCF is displayed on the bottom line of the Air Density screen.
When the user has customized the Model 35040 Therapy Dosimeter to use other temperature and pressure units, the corresponding values entered by the user at the instrument’s front panel are automatically converted to mmHg and K before use in calculating the ADCF. The equations used for these conversions are listed below. The abbreviation FSL stands for “from sea level.”
mm Hg = inch Hg x 25.4
mmHg = 760 x (54,041 - feet FSL) / (54,041 + feetFSL)
mmHg = 760 x (16,472 - metersFSL) / (16,472 + metersFSL)
mmHg = mbar x 0.75006
mmHg = hPa x 0.75006
K = (5 / 9) x (F - 32) + 273.15
K = C + 273.15