Ludlum Measurements 239605, Manual

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Model 3-IS & 3-IS-1 Technical Manual
Section 2
Ludlum Measurements, Inc. Page 2-4 October 2010
portion on the meter scale. If the meter does not respond, check to see if the
batteries have been correctly installed. Replace the batteries if necessary.
Instrument Test
After checking the batteries, turn the instrument range switch to the X100
position. Place the
AUD ON
-
OFF
switch in the
ON
position. Expose the detector
to a check source. The instrument speaker should emit “clicks” relative to the
rate of counts detected. The ˝
AUD ON
/
OFF
˝ switch will silence the audible
clicks if in the
OFF
position. It is recommended that the ˝
AUD ON
/
OFF
˝ switch
be kept in the
OFF
position when not needed in order to preserve battery life.
Rotate the range switch through the lower scales until a meter reading is
indicated. While observing the meter fluctuations, select between the fast and
slow response time ( ˝
F
/
S
˝ ) positions to observe variations in the display. The
˝
S
˝
position should respond approximately 5 times slower than the
˝
F
˝
position.
The detector cable (on the Model 3-IS only) can be a source of problems. Test
the detector cable by bending or flexing either end of the cable and checking
for an increase in the rate of counts detected. Replace the cable if increases in
the rate of counts are detected.
Check the meter reset function by depressing the ˝
RES
˝ pushbutton switch and
ensuring the meter needle drops to ˝ 0 ˝ .
Once this procedure has been completed, the instrument is ready for use.
Reading the Meter Face Dial
Reading the meter face is very important for consistent measurements. There
are, in general, three types of meter faces: 1) count rate (typically cpm – counts
per minute) 2) exposure rate (typically mR/hr) and 3) “combo” (typically cpm
and mR/hr.) The following examples are intended to help the user interpret
the correct reading.
The normal procedure is to turn the range selector switch to the highest range
and if no readings are seen on the meter, turn the selector switch down to the
lower scales until a reading is seen. The ranges on the instrument selector
switch are multipliers for the meter reading. A typical single scale (one arc)
meter face with a cpm (counts per minute) dial is shown on the next page.