Fluke Biomedical 10100AT - Manual (Page 26)

10100AT
Operators Manual
2-8
temperature of the Model 35050AT, TRIAD TnT Dosimeter. This temperature may not be the same
temperature as the Ion Chamber that is in use. In normal use, the internal operating temperature of the
35050AT may be 1 to 2°C above ambient temperature. This operating temperature is normally achieved
within 15 minutes of turn on.
Adequate time must be allowed for the Dosimeter and Ion Chamber to reach thermal equilibrium before
automatic temperature sensing is used. For a large temperature differential, the thermal equilibrium time
of the 35050AT may be up to 2 hours. If it is not possible to allow the instrument to reach thermal
equilibrium, manual entry of temperature and pressure is recommended. A 3°C change in temperature
results in approximately a 1% change in air density correction factor (ADC).
The housing of the Model 35050AT Dosimeter and its ion chambers are vented to atmospheric pressure;
as a result, there should be no difference between the atmospheric pressure measured by Model
35050AT Dosimeter and the actual atmospheric pressure of the ion chamber.
A 3°C change in temperature results in approximately a 1% change in air density correction factor (ADC);
an 8-mmHg change in barometric pressure results in approximately a 1% change in ADC.
In the event that the temperature/pressure sensor becomes non functional, an error message, “Temp &
Press Error Use Manual Entry” is displayed and only the manual temperature and pressure entry mode is
available.
kV Measurement Delay
A kV measurement delay may be used to postpone the start of data analysis in order to skip over
waveform anomalies (such as overshoots or filament preheat effects), which may occur at the beginning
of an exposure. This feature is only active in the Tri-measurement Exposure mode (when the 35080 is
used).
When a delay is used, the 35050AT waits for the specified delay time after the beginning of an exposure
before starting data analysis. If no radiation is detected after the delay time has elapsed, data analysis is
delayed for up to one second after the delay time has elapsed. If no radiation is detected within one
second after the delay time has elapsed, the 35050AT assumes that no exposure has occurred and
displays the "-delay" message.
The delay range is from -999 to +999 milliseconds, and the polarity of the measurement delay only affects
how exposure time measurements are performed.
When a negative measurement delay is specified, the 35050AT does not include the delay time in the
measured exposure time. A negative measurement delay should be used in cases when x-ray generator
filament preheat pulses or other waveform anomalies should be excluded from kV and exposure time
measurements.
When the measurement delay is positive, the 35050AT includes the delay time in its measured exposure
time. A positive measurement delay should be used in cases when the kV waveform contains leading
edge overshoot anomalies that should be excluded from kV measurements but included in the exposure
time measurement.
Exposure Time Units
When seconds are selected as exposure time units, the measurement method is based on a kV threshold
crossing. The threshold is set at 75% of the kVp, or the minimum kVp for the filter pack in use, whichever
is greater. The maximum exposure time is six seconds and the measurement resolution is 0.2 ms.
Exposure time is displayed in milliseconds (ms) or seconds (s).
When Pulses are selected as exposure time units, the 35050AT counts the number of x-ray pulses in a
pulsed or single-phase radiographic exposure. Pulses are counted by detecting each passage through a
threshold on the rising and falling edges each pulse in the output waveform. Exposure time is displayed in
pulses (P). This is primarily for use with single-phase full and half-wave rectified generators. Pulse
counting will not function properly on single-phase generators employing output filter capacitors to smooth
the generator's output because the generator's output does not drop to zero between pulses.