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2.4.2. Resetting statistics (restarting measurement)
When the instrument measures the dose rate it displays the average
value of several readings over time to improve accuracy. Therefore, the
dose rate displayed on the LCD will change very slowly when there are
small changes in background radiation. It is possible to reset the
statistics manually in order to make the instrument acquire new
measurements.
To do this press and hold the SELECT button until the Measurement
mode menu appears on the display and then select “RESET STAT” by
pressing the MODE/SET button. Doing so restarts measurement of the
dose rate, which leads to a sharp increase of the coefficient of variation
displayed in Measurement mode.
When value of the coefficient of variation drops below 10% the readings
displayed by the unit are considered statistically acceptable and can be
used.
2.5. Acquiring gamma-scintillation spectra
PM1704A is designed to allow the user to acquire
gamma-scintillation spectra and perform express
radioisotope identification. This is a critical feature
that helps to distinguish between real threats and
false positives, thus saving critical time from the
moment the source is detected and aiding in decision-making on how to
proceed. It also allows the operator to send collected spectra to a remote
fusion center or reachback system for advanced processing and
identification.
To begin spectra collection, press the MODE/SET button until the unit
displays the message “SPECTRUM”, then press the SELECT button to enter
the Spectra Accumulation menu and select “START”. The LCD will display
the average count rate of the gamma radiation and ask the user to set the
optimum value for correct spectra accumulation.
2.5.1. Establishing proper count rate
For PM1704A, as for the majority of SPRDs, it is very important to have
count rate readings on the display within a certain interval, between 100
cps and 500 cps (marked on the analog scale at the bottom of the screen
by “
”) to acquire good quality spectra.