Fluke Biomedical 440RF - Manual (Page 23)

Operation
Low Level Measurements
2
2-15
For example, in Figure 2-10, a portion of the meter scale is shown and a certain fluctuating indication is
represented.
UPPER LIMIT - 0.16 mR/h
LOWER LIMIT - 0.08 mR/h
0.24 mR/h = 0.12 mR/h average
2
Non-Zero Compensations
In the event that local background radiation becomes, or is, an objectionable percentage of the indicated
value, it should be subtracted out in order to maintain maximum accuracy at low intensities. The value
used for background can be stated as described in Obtaining Readings from Fluctuating Indications, as
well as the value of external radiation or the operational check source. The value used for background
should be measured regularly, as there can be short-term variations and possible strain charges included
in the readings. For example, an indicated and averaged reading of 0.80 mR/h, less an indicated and
averaged background of -0.03 mR/h is equal to a compensated reading of 0.77 - mR/h.
Figure 2-10. Interpreting Fluctuations
2.9 Operational Check Source
This built-in source enables the operator to verify instrument operational status. A hexagonal knob is
located on the front surface of the case, above and to one side of the magnesium window (refer to Figure
2-3).
To operate the check source, rotate the knob in the direction indicated by the arrows until a mechanical
stop is reached. This is the check source position. Place enough torque on the knob so that the return
spring does not return the check source to rest position during this procedure. Place the function/range
switch in the 3 mR/h position. The source supplied with this instrument will indicate in the range of 1.2 to
1.8 mR/h. Wait approximately 15 seconds for the final value indication.
To stop check source operation, return the check source knob to rest position; the return spring will retract
the source back into a shielded position.
.08 mR/h
.16 mR/h
80% Deflections Over a Half-Minute
Within These Limits
Meter Needle