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3.
4.
5.
Raise the high voltage in uniform steps of 50 volts. At each step note the
radiation intensity on the CPM/S range. Do not go above the maximum
voltage for the detector
detector.
Plot the High voltage vs. counts on a graph.
Adjust the high voltage in the instrument to the value that corresponds to midway on
the plateau. If there is no upswing, then adjust it above the knee.
SET HIGH
VOLTAGE TO
MIDPOINT
KNEE
1000
COUNTS
f)
The other way is to use the Custom Settings Menu which allows programming
into the locations in EEPROM. This is more complicated and involves looking up
the locations of each item in the list. We recommend using the Detector Setup
Menu. Remember that the Detector that is selected using the Function Menu will
be the detector whose parameters you are saving or changing. See the individual
sections on how to use these Menus.
If you have problems with the programming and the instrument is functioning in
an unpredictable manor, you can revert back to the factory settings under the
Setup Menu, however the values for the previous calibration will be lost.
g)
UPSWING
Programming the Setup Value
The values on the worksheet may be programmed into the instrument in either of
2 ways. The first and easiest way is to use the Detector Setup Menu. This is an
interactive mode that shows the count rate as well as the settings for each of the
above items.
Log Bargraph
If you have a Log Bargraph the Range Low Limit sets the low end of the bargraph.
Set the Range High Limit as you would if using a normal bargraph The with the
log bargraph, the digital display will change ranges at each decade.
PLATEAU
0
0
1050
HIGH VOLTAGE
GRAPH OF HIGH VOLTAGE VS COUNTS
(2)
Discriminator
The Discriminator is set by lowering the value to the point where the instrument
will count from noise, then raising it past the point where it stops counting. Check
for double counting at low count rates. Lower the gain or raise the discriminator
to correct this problem.
(3)
Saturation
The saturation detector if installed, is used to prevent a saturated detector from
reading 0 on the display. Set it to 0 to turn it off. To adjust the setting in Detector
Setup Mode:
1.
Reduce the Saturation to zero.
2.
Expose the detector to sufficient radiation so the reading is at the top of the
highest scale.
3.
Raise the saturation until the reading shows off scale.
4.
Lower the saturation by 10%.
e)
Other variables and settings
The bargraph type, display type, inverted or normal display, modes for each
detector, and range up and down times can be reviewed under the Custom
Settings section.
MODEL 5085 MERIDIAN
Health Physics Instruments
19