Fluke Biomedical TNT 12000 - Manual (Page 59)

Operation
How to Use the Dosimeter Detector (TNT 12000 DoseMate)
2
2-31
Measurement Mode Selection
The Dosimeter has three measurement modes. Table 2-5 shows the modes and their
definition.
Table 2-5. Dosimeter Measurement Modes
Measurement Mode Definition
Dose Automatic drift and offset compensation, and automatic post-exposure display
hold are done in this mode.
The display updates at the end of each exposure. Only the Dose value shows
along with the mAs measurements
[1] in the Measurement Screen.
When Automatic Reset is enabled, at the end of an exposure, the measurement is
held on the display and the meter is reset automatically. The exposure start and
end detection are based on the exposure rate level crossing a 0.25 pA threshold.
You can reset the exposure measurement anytime, by selecting Reset in the
measurement screen.
When the Automatic Reset option is disabled, exposure start detection is based on
the exposure rate level crossing a 0.25pA threshold but the exposure
measurement is only reset by selecting Reset in the measurement screen.
Dose Rate Automatic offset compensation and nonlinear digital filtering are performed in this
mode. Auto ranging provides five decades of sensitivity ranges.
The measurement range covers a span from low-level image intensifier inputs to
unattenuated direct beams.
Note: The display of the mAs values remain unaffected (if the mAs detector is
selected for measurement).
Differentiation between exposure on and off condition is based on 0.25 pA
threshold.
Low Rate This mode is only for making very low dose rate measurements. Nonlinear digital
filtering and auto ranging provide five decades of sensitivity ranges. In this mode,
automatic current offset and drift compensation is disabled. As a result, the system
leakage (includes dosimeter, cable and ion chamber) must be compensated for.
This option should only be used with ion chambers suitable for very low dose rate
measurements.
In the Measurement Screen, only the Dose Rate will be displayed along with the
mAs readings
[1] and the display updates once per second.
Note: The display of the mAs values remain unaffected (if the mAs detector is
selected for measurement).
[1] mAs units are only shown if the mAs Detector is setup for measurements.
To set the Dosimeter mode:
1. Use B or A to highlight the Mode button in the Dosimeter MEASUREMENT screen
and push E. The MODE SETUP screen shows in the Display.