Technical data

Flow meter FC01-Ex Flow meter FC01-Ex
Examples 73 Examples 73
9.2 Example 2: Distribution of trim points
Task definition
The FC01-Ex with calorimetric sensor shall be used to measure air flowing at a max. velocity of
25 m/s.
The lower measuring range value is approx. 0 m/s. A calibrated calorimetric metering pipe is
used as a reference. The pertinent measuring instrument indicates the flow velocity in m/s.
The measuring range of the reference instrument is specified between 1 m/s and 40 m/s; the
measuring error shall be 1% of the value measured.
The resultant error shall be < 3% of the upper measuring range value.
Approach / Implementation
With a disturbance-free flow profile, the trim points can be calculated by the following formula:
AB = MA + (MB x (1 - e
-(((SP-1) x g)/SG)
))
g = 2.5 x (SP - 1)/SG
AB - trim value [m/s]
MA - lower measuring range value [m/s] = 0 m/s
ME - upper measuring range value [m/s] = 25 m/s
MB - measuring range [m/s]
MB = ME - MA = 25 m/s
SP - trim point no.
SG - total number of trim points = 16
g - distribution coefficient
Determine the trim points using the above formulas.
V
lin
shows the alternative linear trim point selection.
Verification
Projecting the suggested trim points on to the standard curve used by E-T-A will result in max.
error being 0.5% MBE. This is clearly below the required ± 3% MBE (0.75 m/s).
With a linear trim point distribution, max. error would be 2.4%. This would also be a satisfactory
solution, with the advantage that you needn’t calculate the trim points.
9.2 Example 2: Distribution of trim points
Task definition
The FC01-Ex with calorimetric sensor shall be used to measure air flowing at a max. velocity of
25 m/s.
The lower measuring range value is approx. 0 m/s. A calibrated calorimetric metering pipe is
used as a reference. The pertinent measuring instrument indicates the flow velocity in m/s.
The measuring range of the reference instrument is specified between 1 m/s and 40 m/s; the
measuring error shall be 1% of the value measured.
The resultant error shall be < 3% of the upper measuring range value.
Approach / Implementation
With a disturbance-free flow profile, the trim points can be calculated by the following formula:
AB = MA + (MB x (1 - e
-(((SP-1) x g)/SG)
))
g = 2.5 x (SP - 1)/SG
AB - trim value [m/s]
MA - lower measuring range value [m/s] = 0 m/s
ME - upper measuring range value [m/s] = 25 m/s
MB - measuring range [m/s]
MB = ME - MA = 25 m/s
SP - trim point no.
SG - total number of trim points = 16
g - distribution coefficient
Determine the trim points using the above formulas.
V
lin
shows the alternative linear trim point selection.
Verification
Projecting the suggested trim points on to the standard curve used by E-T-A will result in max.
error being 0.5% MBE. This is clearly below the required ± 3% MBE (0.75 m/s).
With a linear trim point distribution, max. error would be 2.4%. This would also be a satisfactory
solution, with the advantage that you needn’t calculate the trim points.