Bicron Surveyor 50 Geiger Counter
© Brooke Clarke 2006
This is a modern (solid state) type
counter that has a removable probe. The Bicron PGM probe is
called a "pancake" probe and has a much larger capture area for
particles than the conventional "hot dog" type probes.
When the two clasps are opened the
bottom box can be removed from the chassis giving access to the 9
battery attachment clips. There is provision for storing a
Controls & Indicators
The rotary switch has positions:
off - power off
bat. - the top of the meter scale is marked bat. ok
HV - about 1/3 up from meter zero is a narrow band marked HV ok
87 DMM shows 695 volts)
x100 - 50 mR/h or 60,000 cpm
x10 - 5 mR/h or 6,000 cpm
x1 - 0.5 mR/h or 600 cpm (maybe 66 counts in 1 minute background)
Of all the pancake probes shown on
the LND, Inc. web page only the 7311
correct voltage rating and physical configuration that will fit
housing and is rated for 900 volt operation. The PGM pancake
probe housing has a 55 mm window opening which has a window
screen covering and the GM tube is rated as having an effective
of 44.5 mm.
When the probe is disconnected and a Fluke model 87 DMM (specified
have 1 volt accuracy on the 0 - 1000 VDC range) is used to measure
meter HV the result is 695 Volts, not the 900 volts mentioned in
sales literature for this model. This is a measurement
since the Fluke 87 has an input impedance of 10 M and the
the Bicron 50 shows 3 M of resistance after the HV sampling
resistors. When a 10 M meter is used to measure 900 volts
source resistance of 3 M the voltage should be about 692 volts
very close the the observed 695 volts. Using the voltage
in reverse an indicated voltage of 695 corresponds to a source
of 695 * 13/10 =) 903.5 volts.
If the meter is in one of the counting range positions (x100, x10
x1) and the Digital Multi Meter is used to measure the voltage the
meter indicates full scale. I'm sure that this is caused by
digital signals coming out of the DMM and triggering the counting
circuits of the GC.
type BNC connectors
on the cable are marked UG-932/U on one
end and KV-59-37
pat 3195098 on the other end.
The PGM probe connector is marked Kings KV-79-15
and the Bicron 50 HV connector is marked Kings KV-79-15.
Coaxial Cable Connector, July 13, 1965, H.E. Miller et al, 439/454
174/75C assigned to Douglas Aircraft. - traps the center pin.
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