You will need the following optional accessories for a radiological check:
Check source 6706 (nominal activity 333 kBq Cs-137) or equivalent source according to DIN 44427,
Source holder 761.1 (Other holder types are available for probes, see probe manual).
This equipment allows to expose the 6150AD’s internal tube to a well-defined dose rate. In the following
we shall call the indication obtained under these conditions a »check reading«. The absolute value of the
check reading already gives some information on measuring accuracy. However, the absolute value
contains uncertainties like the ±10% tolerance of source activity. But, if you always use the same source
and holder for repeated check readings, check readings will not vary by more than a standard deviation of
4%. Consequently, the most accurate method is: use the first check reading as a reference, compare
further check readings with that reference, and observe to use always the same source and holder. This
method will quickly reveal changes in the 6150AD’s accuracy, because it restricts errors to statistical
errors and avoids systematic errors like activity tolerance. Of course you should carry out the reference
measurement at a time when you know that the instrument is properly calibrated, for example directly
Follow this procedure to obtain a check reading:
Insert the 6150AD into the holder 761.1 with its front side towards the thread for the check source. Screw
the check source into the holder until it touches the marking spot on the front side of the 6150AD. Do not
exercise more force than is required just to keep the 6150AD in place. Then switch the 6150AD on and
move to dose rate mean value indication by pressing the function key. After a measuring time of at least
ten minutes (to ensure sufficient statistical accuracy), take the indicated mean value as the check reading.
Conditions have to be stable when measuring the mean value. Consequently, the check
the measurement starts! Since measurement starts when
the 6150AD is switched on, you have to switch it on after screwing the source into
place! If you did not, just switch the 6150AD off and on again to start the measurement
once again. With the 6150AD3/4/5/6 you may also clear the mean value using the
With a new source the check readings will be approximately:
6150AD1/3/5: 155 µSv/h, »/H« and »/E« models: 165 µSv/h
6150AD2/4/6: 85 µSv/h, »/H« and »/E« models: 90 µSv/h
You may wonder why the 6150AD1/3/5 values are much higher than the 6150AD2/4/6 values, although
in all models the centre of the tube is at the same position. The reason is that the source is very close to
the tube, and thus the radiation field across the tube’s size is not constant. Indication is a spatial average
of the radiation field across the tube’s volume, and for the larger tube of the 6150AD2/4/6 this average is
only about half of the average across the smaller tube of the 6150AD1/3/5.
The check readings just specified are typical values only. Small deviations from these
coarse values are normal and must not lead you to the conclusion that the instrument
When comparing two check readings performed at different dates, you have to consider the activity loss
of the check source caused by its decay. This is done by multiplying the check reading »R« with a
correction factor »c«. The result is the »corrected check reading Rc«. You may only compare check
readings corrected to the same reference date. As reference date you may take the date when the source
had its nominal activity (usually imprinted on the source), or the date when the reference measurement
was performed. In the latter case, the age of the source is irrelevant. The correction factor c depends on
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