Gammapilot M FMG60 FOUNDATION Fieldbus
Commissioning
Hauser
73
7.5
Calibration for density and concentration
measurements
7.5.1
General principles
The calibration points for the measurement are entered in the
"Calibration" (*1)
function
group. Each calibration point consists of a density value and the associated pulse rate.
Calibration points for density and concentration measurements
Function of the calibration points
In addition to the length of the irradiated measuring path, the Gammapilot M also needs
the following two parameters for density and concentration measurements:
• The absorption coefficient µ of the material measured
• The reference pulse rate I
0
It calculates these parameters automatically from the pulse rates of the following
calibration points:
• Background calibration (calibration with radiation switched off)
• Up to nine calibration points for samples of various known densities
In the case of self-radiating media, the background calibration must always be
performed when the pipe is filled. A simulated calibration with an empty pipe is not
possible in this case.
OFF
ON
0
1
9
A0018128
0
Background calibration
1-9 Calibration points for various densities
Two-point calibration
Two-point calibration is the recommended calibration procedure to meet strict accuracy
requirements over the entire measuring range. Background calibration is performed first
of all. Afterwards, the two calibration points are entered. These points should be as far
apart as possible. Once the two calibration points have been entered, the Gammapilot M
calculates the I
0
and µ parameters on its own.
One-point calibration
A one-point calibration can be performed if a two-point calibration is not possible. This
means that apart from the background calibration only one additional calibration point is
used. This calibration point should be as close as possible to the operating point. Densities
in the proximity of this calibration point are measured quite accurately, but the accuracy
can decrease as the distance from the calibration point increases. In one-point calibration,
6)
I
0
is the pulse rate when the tube is empty. The value is significantly higher than any real pulse rates occurring during the measurement.
