PM-7 Operating Manua.. - Voss Associates

General Description
Background Updating Routine
count cycle will resume. Otherwise, the portal will return to the
background update mode at the end of the alarm hold time.
2. If no contamination is detected at the end of the count cycle, the chime
will sound and the green light will be lit. The chime will sound
intermittently. When the portal is clear, the instrument will return to
updating background until another person enters it.
3. If contamination is detected, the yellow COUNT lamp is extinguished,
the red CONTAMINATED lamp is lit and the horn will sound
continuously for the selected alarm hold time or until the ACK button
is pressed. Although the alarm can be posted before the count cycle is
complete, the alarm hold time does not start until the count cycle is
complete. Therefore, if long count times are in effect, the horn may
sound for longer than the selected alarm PM-7 hold time. The location
of the alarming detector(s) will be displayed around the graphic image of
a man. If a sum channel alarm occurs, a separate SUM CHANNEL
lamp will be lit if no individual detector channels alarm. The sum
channel alarm indicates the presence of distributed contamination. A
recount may be initiated by exiting and then re-entering the portal.
Background Updating
Routine
When the PM-7 is first turned on it will execute a forced background count.
During the initial background count the blue Out-of- Service lamp will
flash. The count will continue until all channels have logged a minimum of
40,000 counts. The resulting counts are divided by the elapsed time to yield
a count rate with an error term of 1% at 95% confidence. Once this initial
background count rate is established, subsequent background averages are
computed using the larger of the following two criteria:
1. The length of time necessary to acquire 40,000 counts.
2. Ten times the current measurement cycle count time.
In order to implement the background updating routine, the PM-7
maintains a buffer of the 85 most recent 1 second background
measurements. Thus, the two criteria that determine the length of time used
for the computed background average are bounded by the 85 second
maximum limit.
Thermo Fisher Scientific
Personnel Monitor -7 Techical Guide_3-5_