Manual Operation
44
4.2.4 Cutoff
As mentioned above, a mass flow meter has no natural zero and the rough data are noisy. Consequently with
now flow a meter would indicate and give out continuously a small fluctuating flow.
The parameter CUTOFF is used to provide a clear zero. If the calculated and filtered flow is below cutoff, the
meter indicates zero, the total values remain unchanged and the outputs show zero flow as well.
The value for CUTOFF must be above the noise floor in the given application and well below the minimum flow to
be measured.
As a good compromise the default value for CUTOFF is 0.5% of the full scale range of the meter.
For setting CUTOFF refer to chapter 4.5.6.3.
4.2.5 Step
response
Sometimes it is necessary to react fast to a fast changing flow, but also to have a stable output, if the flow is
(mostly) constant. This cannot be achieved by adjusting the flow filter.
The parameter STEP RESPONSE provides a fast reaction at fast changing flow, also the filter constant is high.
If the difference between the measured flow and the filtered flow is smaller than the step response value, the flow
filter remains active. If the difference is higher than step response, the filter is cleared and filled with the new
value.
The recommended value for constant or slowly changing flow is 99% (the default value ex work). If the unit has to
react to fast changing flow, the optimum value depends on the individual situation. For ON / OFF operation a
value of half the ON flow is recommended.
If STEP RESPONSE is set too low, even small changes in flow or even the internal noise will activate the step
response function and partially or all the time deactivate the filter, leading to noisy readings and noisy output
signals.
For setting CUTOFF refer to chapter 4.5.6.4.
4.2.6 Interaction of the parameters
As each of the 3 parameters affects the calculation of the flow in a different way, a bad combination of different
parameters can lead to systematical errors.
FLOW FILTER and CUTOFF
If the filter constant is set to a high value, the calculated flow is delayed compared to the actual flow. In ON-OFF
operation this leads to the fact that it takes a long time until the calculated flow settles to the ON or OFF value.
The total value remains correct if the unit measures long enough after the flow got switched off. If cutoff is set to a
high value, the meters stops measuring too early and consequently the calculated total is too low. Also the
number of pulses at the frequency output is too low. The error is systematic.
NOTE
In ON-OFF operation high values for the flow filter combined with high values for cutoff must be avoided!
Jumps of the flow not going down to zero are not affected by cutoff.
FLOW FILTER and STEP RESPONSE
As described above, a linear filter just delays the flow reading and consequently the total but does not alter the
final total.
If the step response is activated, a nonlinear term is added to the filter. The indicated flow will follow more closely
the total flow, but the remaining deviation depends on the values for the filter and for step response, but also on
the slope of the flow change and on the size of a step.
If the flow changes slowly or a jump is smaller than step response, the step response function will not be activated
and remains linear all the time, producing the normal delay.
If the flow changes fast and the step is higher than step response, the filter will be made faster, the indicated flow
follows more closely the actual flow and the delay will be smaller.
Summary of Contents for TRICOR TCE80 -E Series
Page 1: ...Certified according to DIN ISO 9001 Manual TRICOR Coriolis Mass Flow Meter ...
Page 2: ...SW Version Main V2 0x Display V2 0x Manual Revision 2 1 ...
Page 93: ...Listings 93 Fig 26 Dimensions TCE8000 E except A Fig 27 Dimensions TCE8000 E A ...
Page 98: ...Contact Copyright KEM Subject to change without notice ES Rev 002 23 01 2012 ...
