Trim Point Selection - Number And Position; Max-Min Calibration Procedure - Flow vision FC01-Ex User Handbook Manual

Flow Meter | FC01- Ex

4 .2 .2 Trim point selection - number and position

Between 2 and 20 trim points can be set.
They are addressed in a "downward" sequence to ensure the user can recognize the trim points still
available by the trim point index indicated.
A reasonable distribution on the characteristic curve depends on the desired accuracy, the required
measuring range or continuity criteria such as differentiating criteria. These issues are addressed
in chap. 9 (Examples).
Generally, there are fewer trim points needed in the upper characteristic curve range than in the lower
range, the reason for this being the flattening characteristic curve (see chap. 9).
Depending on the medium and the measuring range, it is possible to use different procedures in
selecting the trim points.
A linear preselection of the trim points has been provided for in the FC01-Ex. With the appropri-
ate number of trim points set, this procedure achieves good results over the entire velocity range
(5 m/s with water, 25 m/s with air).
A trim point distribution which significantly reduces the measuring error when compared to a
linear distribution, can be determined by the following formula (see 9.2 - Example 2).
AB - trim value [m/s]
MA - lower measuring range value [m/s]
ME - upper measuring range value [m/s]
MB - measuring range [m/s]

4 .2 .3 MAX-MIN Calibration procedure

The MAX/MIN calibration procedure has been selected because the critical parameter (max. heating power)
is determined in the computer background after the first calibration step (max. flow velocity).
If too high a temperature differential has been selected for the heater control to indicate, this is dis-
played as "error 30". It is then immediately possible to reduce the temperature differential to a value
the controller is able to indicate (see chap. 4.2.1, Selection of CTD value).
It is thus verified and ensured when starting the calibration that the flow characteristics can be dis-
played, eliminating that a curve must be dropped because its last trim point(s) cannot be indicated.
34
TECHNICAL IMPLEMENTATION
of customer calibration
MB = ME - MA
AB = MA + (MB x (1 - e
g = 2,5 x (SP - 1)/SG
SP -
SG -
g -
-(((SP-1) x g)/SG)
))
trim point No. SP = 1 ... SG
overall number of trim points
distribution coefficient