Endress+Hauser Gammapilot M FMG60 - Calibration for Density and Concentration Measurements

Commissioning Gammapilot M FMG60 with FOUNDATION Fieldbus
78 Endress+Hauser
6.5 Calibration for density and concentration
measurements
6.5.1 Basic 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
For density and concentration measurements the Gammapilot M needs (apart from the length of the
irradiated measuring path) the following two parameters:
• The absorption coefficient μ of the material measured
• The reference pulse rate I
0
9)
.
It calculates these parameters automatically from the following calibration points:
• Background calibration (calibration with the radiation switched off)
• Up to nine calibration points for samples of various known densities.
!
Note!
With self-radiating media it is always necessary to perform the background calibration with a filled
pipe. A simulated calibration with an empty pipe is not possible in this case.
L00-FMG60xxx-05-00-00-xx-003
Calibration points for density and concentration measurements; 0: background calibration; 1 to 9: calibration points for
various densities
One-point calibration
For many applications a one-point calibration is sufficient. That means, that apart from the
background calibration only one further calibration point is used. This calibration point should be
located as near as possible to the operating point. Densities in the proximity of this operating point
are measured fairly precisely, whereas the precision may decrease with increasing distance to the
operating point.
In one-point calibration, the Gammapilot M only calculates the reference pulse rate I
0
. For the
absorption coefficient it uses the standard value μ = 7.7 mm
2
/g in this instance.
Multiple-point calibration
If high accuracy is required over the complete measuring range, two (or more - up to nine)
calibration points should be applied. The calibration points should be located as far from each other
as possible and should be uniformly distributed over the measuring range. After the calibration
points have been entered, the Gammapilot M automatically calculates the parameters I
0
and μ.
9) I
0
is the pulse rate for the tube being empty. The value is significantly higher than any real pulse rate occurring during the measurement.
OFF
ON
ON
0
1
9