Fluke Biomedical 10100AT - Manual (Page 27)

Operation
Basic Measurement Techniques
2
2-9
2.6.2 Making Exposure Measurements
Select Exposure Unit
The following integral exposure units are available for selection:
Exposure: Roentgens or Coulombs/kg air
Absorbed Dose: Grays (in air)
Dose Equivalent: Sieverts (x, gamma, or electron source and N=1 for air)
Charge: Coulombs (for the unlisted ion chamber)
Press UNITS SELECT button and use UP or DOWN buttons until the cursor is on the desired unit.
Taking the Exposure
Press RESET/MEASURE just before the exposure. Make the exposure. The exposure value will be
displayed.
Automatic / Manual Reset & Hold
When the Exposure Reset option is set to Automatic Reset, the electrometer is reset once the instrument
senses the exposure is over. The final calculated value of the exposure is held on the display until either
another above threshold exposure occurs, in which case the old value is discarded and the new value is
displayed; or there is function change or power down. The instrument treats exposures separated by less
than two seconds as single exposures.
When the Exposure Reset option is set to Manual Reset, the electrometer is only reset when the
Reset/Measure button is depressed. The final calculated value of the exposure is held on the display until
Reset/Measure button is depressed, in which case the old value is discarded and the display is reset to
zero. When the Manual Reset option is active, the symbol appears in the upper right corner of the
display.
Resetting of the electrometer takes approximately 100 ms to complete. If an exposure starts while the
electrometer is being reset, the result is an erroneous measurement. Instead of displaying the erroneous
measurement, the display would read:
Simply repeat the exposure to clear the message and display a new measurement result.
2.6.3 Making Exposure Rate Measurements
For selection of ion chamber, verification of ion chamber with the instrument, minimum radiological
quantities, and general considerations please refer to the discussions in section 2.6.1, as they apply here
equally well. In addition, there are some aspects that are unique to exposure rate measurements.
Nonlinear Filter
Incorporated in the instrument's firmware is a digital nonlinear filter that responds quickly to significant
changes in exposure rate, but possesses a much larger time constant for small changes, such as
measurement system noise.
Realtime Display
While operating in the exposure rate mode, the display is updated at an approximate rate of once per
second. Each new display value corresponds to the average exposure rate present since the previous