Abstrict A method of obtaining a measure of flow from an electromagnetic
flow meter is disclosed. A shaped excitation waveform is applied
to the flow meter and an output is received from the meter. The
sampled output data from the meter is then resolved into a non-flow
waveform component and a flow waveform component to derive a measure
of flow. Resolving the data into expected waveform components rather
than correlating each frequency component of the sampled output
data with a sine wave may allow readings to be obtained without
processing each frequency component separately. Also, the method
may allow more accurate removal of the non-flow component from the
output signal, and may decrease the time delay before the initial
reading and allow the use of a greater reading repetition rate.
Claims What is claimed is:
1. A method of obtaining a measure of flow from an electromagnetic
flow meter, comprising: applying a shaped excitation waveform to
a coil of an electromagnetic flow meter; receiving and sampling
an output signal from the meter in response to the application of
the shaped excitation waveform; and resolving sampled output data
from the meter into a non-flow waveform component and a flow waveform
component so as to derive a measure of flow.
2. A method according to claim 1 wherein the shaped excitation
waveform comprises a pulsed waveform.
3. A method according to claim 1 wherein the shaped excitation
waveform includes a first pulse rise section of a first polarity.
4. A method according to claim 1 wherein the shaped excitation
waveform includes a substantially constant section of a first polarity.
5. A method according to claim 1 wherein the shaped excitation
waveform includes a pulse decay section.
6. A method according to claim 3 wherein the shaped excitation
waveform includes a second pulse rise section.
7. A method according to claim 3 wherein the shaped excitation
waveform includes a second substantially constant section.
8. A method according to claim 3 wherein the shaped excitation
waveform includes a second pulse decay section.
9. A method according to claim 6 wherein the second pulse rise,
substantially constant, and pulse decay sections are of the opposite
polarity to the first pulse rise section, substantially constant,
and pulse decay sections.
10. A method according to claim 1 wherein the shaped excitation
waveform comprises at least one substantially constant section.
11. A method according to claim 10 wherein the constant section
of the shaped excitation waveform is used to determine background
interference.
12. A method according to claim 11 wherein the background interference
is subtracted from the sampled output data.
13. A method according to claim 1 wherein the shaped excitation
waveform comprises a plurality of pulse rise sections, substantially
constant sections, and pulse decay sections.
14. A method according to claim 13 wherein alternate substantially
constant sections are of alternate opposing polarities.
15. A method according to claim 1 wherein the shaped excitation
waveform is a substantially square wave waveform.
16. A method according to claim 15 wherein alternate pulses of
the square wave are of opposing polarities.
17. A method according to claim 1 wherein resolving comprises
performing a weighted least squares fit between the sampled output
data and a model of the expected waveform.
18. A method according to claim 1 wherein the non-flow waveform
component is represented in the form z.Vz(t).
19. A method according to claim 18 wherein Vz(t) is based on the
differential of the current input to produce the excitation waveform
(dI/dt).
20. A method according to claim 18 wherein Vz(t) is based on a
zero signal captured empirically.
21. A method according to claim 20 wherein Vz(t) is based on an
average of a plurality of captured zero signals.
22. A method according to claim 18 wherein z is a scalar multiplier
term, and wherein resolving includes determining the value of z.
23. A method according to claim 1 wherein the flow waveform component
is represented in the form f.Vf(t).
24. A method according to claim 23 wherein Vf(t) is determined
empirically.
25. A method according to claim 24 wherein Vf(t) is determined
empirically and is based on an average of a plurality of captured
flow signals.
26. A method according to claim 23 wherein Vf(t) is modelled by
a mathematical function.
27. A method according to claim 23 wherein f is a scalar multiplier
term, and wherein resolving comprises determining the value of the
scalar multiplier term f.
28. A method according to claim 1 further comprising determining
a measure of a trend within the sampled output data.
29. A method according to claim 28 wherein the measure of a trend
is subtracted from the sampled output data.
30. A method according to claim 1 wherein correlating is performed
over a window that does not contain an integer number of periods
of all frequency components.
31. A method according to claim 30 wherein the window is shorter
than the period of the lowest frequency component.
32. A method of determining a measure of a non-flow signal from
an electromagnetic flow meter comprising: applying a shaped excitation
waveform to an electromagnetic flow meter; receiving an output from
the meter in response to application of the shaped excitation waveform;
resolving sampled output data from the meter into a non-flow waveform
component and a flow waveform component; and determining a measure
of the non-flow waveform component based at least in part on the
resolved sampled output data.
33. A method according to claim 32 further comprising determining
a calibration measurement for the meter based on the measure of
the non-flow component.
34. A method according to claim 33 further comprising applying
a correction to flow measurements determined by the flow meter based
on the calibration measurement determined.
35. A method according to claim 32 further comprising detecting
a fault condition for the meter based on the measure of the non-flow
component.
36. A method according to claim 32 wherein the shaped excitation
waveform is a pulsed waveform.
37. A method according to claim 32 wherein the non-flow waveform
component is represented in the form z.Vz(t), and wherein Vz(t)
is a function of the current input to form the excitation waveform
and z is a scalar multiplier term.
38. A method according to claim 32 wherein the flow waveform component
is represented in the form f.Vf(t), wherein Vf(t) is a function
of the flow rate of a fluid through the flow meter, and wherein
f is a scalar multiplier term.
39. An apparatus for obtaining a measure of flow from an electromagnetic
flow meter comprising: means for applying a shaped excitation waveform
to the coil of an electromagnetic flow meter; means for receiving
an output from the meter; and means for processing the output from
the meter to resolve sampled output data from the meter into a non-flow
waveform component and a flow waveform component so as to derive
a measure of flow.
40. An apparatus for determining a measure of a non-flow signal
from an electromagnetic flow meter comprising: means for applying
a shaped excitation waveform to an electromagnetic flow meter; means
for receiving an output from the meter; means for resolving sampled
output data from the meter into a non-flow waveform component and
a flow waveform component; and means for determining a measure of
the non-flow waveform component.
41. A computer readable medium including a program for executing
a method of obtaining a measure of flow from an electromagnetic
flow meter, comprising: applying a shaped excitation waveform to
an electromagnetic flow meter; receiving an output from the meter;
and resolving sampled output data from the meter into a non-flow
waveform component and a flow waveform component to derive a measure
of flow.
Description CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. patent application Ser.
No. ______, Attorney Docket No. MATH2.002AUS, filed on the same
day as the present application, having the same inventor as the
present application, and entitled "ELECTROMAGNETIC FLOW METER".
The disclosure of the above-described filed application is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to electromagnetic flow meters.
However, aspects of signal processing techniques disclosed herein
may be more broadly applied. The operating principles of Electromagnetic
Flow Meters are well known, discussed for example in GB-A-2380798.
[0003] Where the sensing electrodes are in contact with the fluid,
due to electrochemical or other effects, a DC potential is usually
present across the electrodes even when there is no coil excitation,
i.e. no field. That component of the signal is independent of the
flow and is generally not static. For example, it may drift randomly
with time, flow and temperature. This inhibits the ability to determine
the flow in a static fashion. To overcome this some form of dynamic
excitation to the coils is typically provided in order to generate
a dynamic component at the electrodes that can be differentiated
from the background DC (or slowly varying) bias signal. This dynamic
signal is normally pulsed DC or an AC signal.
[0004] While using some kind of alternating signal to excite the
meter is usually necessary, it does introduce its own particular
problem, namely that electromagnetic coupling between the coil current
and the electrode wires typically creates a signal at the electrodes
when there is no fluid flow through the conduit. This signal is
completely independent of any flow-generated signal at the electrodes
and so the total signal received is the sum of the unwanted `zero`
term (the non-flow component) and the flow generated signal.
[0005] In a sinusoidally excited meter, this unwanted signal is
typically at nominally 90 degrees to the wanted signal and hence
is often termed the `quadrature` signal. The unwanted signal is
related to the rate of change of current in the coils and consequently
is often described as being due to the `transformer effect` where
the coil winding is the primary and the electrode wiring is the
secondary. In a perfectly symmetrical sensor, the signal created
in the electrode wiring in a typical sensor should be zero but manufacturing
tolerances mean that there is always some residual area in the electrode
wiring `loop` that picks up some of the primary current.
[0006] In a sinusoidally excited meter it is known to include some
kind of phase adjustment in the phase-sensitive detector to null
out this unwanted signal (this process can be performed in hardware,
manually or automatically or in software). Performance of the system
is often limited by the success of this zero removal system. In
many systems where the adjustment is only made at one operating
condition (factory calibration) then the system may exhibit errors
at other operating conditions, typically temperature or installation
related.
[0007] AC meters excited with a sinusoidal waveform (or a plurality
of frequencies as we have previously shown) can be beneficial but
require substantially continuous excitation. To reduce power consumption,
for example in a battery-powered meter, intermittent excitation
is preferred, and pulsed DC meters are typically used.
[0008] In `pulse` or `square wave` driven meters, the approach
is usually to provide adequate settling time after the coil current
is changed for the transient quadrature signal to die away (since
it is related to the rate of change of coil current). These meters
work well because there is substantially no quadrature signal but
the need for the signal to die away has implications on the maximum
speed at which the meter can be operated.
[0009] Conversely, if a measurement is not taken sufficiently quickly,
there is a potential problem of zero drift. The "square wave"
will not normally be true square wave as the slew rate will be limited
by the apparatus and will often be deliberately limited to reduce
effects of the high rate of change of current.
SUMMARY OF CERTAIN INVENTIVE EMBODIMENTS
[0010] The system and method described herein may provide a novel
solution to at least some of the problems described above whereby
a pulsed or square wave excitation can be used but the meter can
be operated significantly faster than would normally be possible.
[0011] According to a first aspect the invention provides a method
of obtaining a measure of flow from an electromagnetic flow meter
comprising applying a shaped excitation waveform, receiving an output
from the meter and resolving sampled output data from the meter
into a non-flow waveform component and a flow waveform component
to derive a measure of flow.
[0012] By shaped, we mean a waveform having a non-sinusoidal shape.
The waveform can be considered as a shaped waveform comprising a
plurality of frequency components, although the components may not
be explicitly added as the signal may be directly generated in the
time domain, for example using a Digital Signal Processor (DSP).
[0013] In this method, by taking the novel step of resolving into
expected waveform components, rather than the conventional method
of correlating each frequency component of the sampled output data
with a sine wave, a number of advantages can be obtained. Although
the shaped excitation waveform will effectively contain multiple
frequency components, it has been found that it is not necessary
to process each component separately to obtain a measure of flow.
[0014] Preferably, the shaped excitation waveform comprises a pulsed
waveform. For a pulsed waveform, using the present method it may
not be necessary to wait for transient signals to decay before a
reading can be taken. This may provide the advantage over prior
art systems that the delay time before the initial reading is taken
can be reduced and the rate of repetition of reading of the meter
can be increased.
[0015] Preferably, the shaped excitation waveform includes a first
pulse rise section of a first polarity.
[0016] Preferably, the shaped excitation waveform includes a substantially
constant section of a first polarity.
[0017] Preferably, the shaped excitation waveform includes a pulse
decay section.
[0018] Preferably, the shaped excitation waveform includes a second
pulse rise section.
[0019] Preferably, the shaped excitation waveform includes a second
substantially constant section of the opposite polarity to the first
substantially constant section.
[0020] Preferably, the shaped excitation waveform includes a second
pulse decay section. Preferably, the second pulse rise, substantially
constant and pulse decay sections are of the opposite polarity to
the first pulse rise section, substantially constant and pulse decay
sections.
[0021] Preferably, the shaped excitation waveform includes at least
one substantially constant section. This may be, for example, at
the beginning and/or end of a group of pulses in a pulsed DC system
or it may be an inter-pulse constant section.
[0022] The constant section of the excitation waveform may advantageously
be used to determine background interference using correlation.
For example, the constant section may be used to determine 50 Hz
interference.
[0023] Preferably, the background interference is subtracted from
the sampled output data; this is preferable to simple filtering.
[0024] Preferably, the shaped excitation waveform includes a plurality
of pulse rise sections, substantially constant sections and pulse
decay sections.
[0025] Preferably, alternate substantially constant sections are
of alternate opposing polarities.
[0026] The features provided may allow a pulsed shaped excitation
waveform to be used. Preferably, a substantially square wave waveform
may be used (although the slew rate will normally be limited and
so it will not be a perfect square wave). Preferably wherein alternate
pulses of the square wave are of opposing polarities, although more
complex patterns having opposing polarities.
[0027] This technique may provide a number of advantages, for example,
resolving the output data into components may allow the method to
be used with a wide variety of input waveforms, since the method
is not dependent on the input waveform used.
[0028] The method of resolving into a non-flow component and a
flow component may be more accurate and more flexible than subtracting
a constant predetermined zero signal from the sampled output data,
since the zero signal subtracted may not accurately represent the
zero signal at the time the reading was taken.
[0029] Preferably, the resolving step comprises performing a weighted
least squares fit between the sampled output data and a model of
the expected waveform, the expected waveform comprising a flow component
and a non-flow component. Other methods of resolving the output
data into components to fit the data to the model of the expected
waveform may also be used.
[0030] According to one embodiment, the non-flow waveform component
may be represented in the form z.Vz(t).
[0031] Vz(t) may be based on the differential of the current input
to produce the excitation waveform, that is dI/dt. This has been
found to provide a good model for the non-flow component term.
[0032] According to an alternative embodiment, Vz(t) may be based
on a zero signal captured empirically. In this embodiment, the non-flow
component is preferably based on an average of a plurality of captured
zero signals. This may provide a more accurate representation of
the non-flow component. The zero signals may be captured at a plurality
of different operating conditions, for example at a plurality of
different temperatures, and the non-flow component used may be varied
depending on the operating conditions when the sampled output data
is taken.
[0033] z is preferably a scalar multiplier term and may be designated
the non-flow co-efficient. The value of the co-efficient is preferably
determined during the resolving step. The co-efficient preferably
represents the relative amount of the non-flow component present
in the sampled output data.
[0034] According to one embodiment, the flow waveform component
may be represented in the form f.Vf(t).
[0035] In one embodiment, Vf(t) may be determined empirically.
For example, the component may be determined experimentally using
one or more flow rates at one or more sets of operating conditions.
Preferably, the component may be based on an average of a plurality
of captured flow signals. This may allow experimental errors in
the expected flow component to be reduced and may provide a more
accurate expected flow component.
[0036] According to an alternative embodiment, Vf(t) may be modelled
by a mathematical function. For example, Vf(t) may be expected to
be generally proportional to the magnetic field.
[0037] f is preferably a scalar multiplier term and may be designated
the flow co-efficient. The value of the co-efficient is preferably
determined during the resolving step. The co-efficient preferably
represents the relative amount of the flow component present in
the sampled output data.
[0038] According to a preferred embodiment, the method preferably
further comprises determining a measure of a trend within the sampled
output data. A trend may result, for example, from experimental
effects such as heating of the components of the flow meter. The
trend may be, for example, a linear trend or an exponential trend.
[0039] Preferably, the measure of a trend may be subtracted from
the sampled output data. This may allow a more accurate measurement
of the flow rate to be determined.
[0040] According to one embodiment, the correlating step is performed
over a window that does not contain an integer number of periods
of all frequency components. Hence the system described herein may
be more flexible and determination of the flow rate may not be dependent
on the input waveform used.
[0041] Preferably, the window may be shorter than the period of
the lowest frequency component. This may allow the measurement of
the flow rate to be obtained with a higher bandwidth than the lowest
frequency component.
[0042] According to a further aspect there is provided a method
of determining a measure of a non-flow signal from an electromagnetic
flow meter comprising:
[0043] applying a shaped excitation waveform to an electromagnetic
flow meter;
[0044] receiving an output from the meter;
[0045] resolving sampled output data from the meter into a non-flow
waveform component and a flow waveform component;
[0046] determining a measure of the non-flow component.
[0047] In prior art flow meters, a predetermined non-flow component
is subtracted from the sampled output data to remove the non-flow
effects from the output signal. For example, the part of the sampled
output data that is due to transformer effects within the meter
itself can be removed in this way. Determining the magnitude of
this non-flow component itself has not seemed particularly useful,
since it provides no indication of the flow rate of the fluid. However,
it has been appreciated by the inventors that, surprisingly, determining
the magnitude of this non-flow component itself can provide a useful
tool to improve the accuracy of flow readings. For example, determination
of the non-flow component can be used to check that the flow meter
is within calibration tolerance and is free from faults. This may
prevent systematic errors being introduced to flow rates that are
subsequently determined. If the flow meter is in an environment
with particularly high or low temperatures, or with highly fluctuating
temperatures, it may be particularly useful to ensure that the meter
remains within calibration tolerance and the present method may
allow this to be done while the flow meter is in situ and over an
extended period of time.
[0048] The ability for the meter to provide a meaningful self-diagnosis
may be very beneficial--a dynamic estimate of the meter accuracy
may be provided. For example, it might be that under unfavourable
conditions, the meter is only 1% accurate but under good signal
conditions may be 0.05% accurate or better. The meter may determine
a measure of accuracy, preferably based on the non-flow signal,
and may report this with the measurement value. Downstream equipment
may use the dynamically reported figure, rather than having to assume
a worst case accuracy of 1%.
[0049] Preferably, the method further comprises determining a calibration
measurement for the meter based on the measure of the non-flow component.
[0050] Preferably, the method further comprises applying a correction
to flow measurements determined by the flow meter based on the calibration
measurement determined. Hence a non-flow component determined in
this way may also be input back into the system to be incorporated
into later readings that are taken in the presence of flowing fluid
to determine more accurately the flow rate.
[0051] According to a further embodiment, the method may further
comprise detecting a fault condition for the meter based on the
measure of the non-flow component. A fault with the meter may be
brought to the attention of the operator so that readings may be
adjusted accordingly or so that the fault may be corrected.
[0052] Preferably, the shaped excitation waveform is a pulsed waveform.
The waveform preferably has at least some of the features of the
waveform described for the previous aspect. Preferably, the waveform
is a generally square wave pulse waveform.
[0053] Preferably, the non-flow waveform component is represented
in the form z.Vz(t), wherein Vz(t) is a function of the current
input to form the excitation waveform and z is a scalar multiplier
term. The value of z is preferably determined as part of the present
method.
[0054] Preferably, the flow waveform component is represented in
the form f.Vf(t), wherein Vf(t) is a function of the flow rate of
a fluid through the flow meter and f is a scalar multiplier term.
[0055] Features of the first method may be applied to the second
method and corresponding advantages may be provided.
[0056] According to a further aspect, there is provided apparatus
for obtaining a measure of flow from an electromagnetic flow meter
comprising:
[0057] means for applying a shaped excitation waveform;
[0058] means for receiving an output from the meter; and
[0059] means for processing the output from the meter to resolve
sampled output data from the meter into a non-flow waveform component
and a flow waveform component to derive a measure of flow.
[0060] Features of the method aspect described above may be applied
to the apparatus aspect and may provide corresponding advantages.
[0061] According to a further aspect there is provided a computer
program or computer program product for carrying out a method according
to the method aspects described above or any of their preferred
features.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] Embodiments of the invention will now be described by way
of example with reference to the accompanying drawings in which:
[0063] FIG. 1 illustrates one possible coil excitation signal (current)
for a meter;
[0064] FIG. 2 shows an electrode signal produced by a sensor when
driven by the coil excitation signal illustrated in FIG. 1;
[0065] FIG. 3 shows the total signal, that is the zero signal and
the flow-induced signal for a particular flow rate;
[0066] FIG. 4 shows the electrode signal of FIG. 3 with the zero
signal of FIG. 2 subtracted;
[0067] FIG. 5 is a schematic diagram of one embodiment of the invention.
DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS
[0068] FIG. 1 illustrates one possible coil excitation signal for
a meter. The waveform illustrated may be created by a controlled
drive voltage, for example by a Central Processing Unit (CPU) and
a Digital-to-Analogue (D/A) converter. As described in more detail
below, in the present embodiment, the precise waveform is not important,
however features of the pulse may include that it is zero outside
the active pulse region 110 and that the pulse has some AC content,
i.e. it goes positive 112 and negative 114 at least once. In most
embodiments, drive voltages may be slew-rate limited, since this
may create signals which are less problematic for the equipment
as rapid changes make the relationship between field and applied
current less predictable.
[0069] FIG. 2 illustrates an electrode signal produced by a real
sensor in the absence of fluid flowing past the sensor when driven
by the coil current shown in FIG. 1. This signal may be known as
the zero signal.
[0070] This electrode signal has high frequency noise and a small
amount of mains interference and other corruption. The signals captured
here are from an unshielded sensor. Signals captured from production
sensors, which may have shields incorporated with them may not show
as much noise. However, the techniques described herein can preferably
operate in the presence of such distortions. In the present embodiment,
the electrode signal captured can be sufficiently accurately described
as a scaled rate of change of the current (I) with respect to the
time (t), that is a dI/dt of the coil excitation signal shown in
FIG. 1.
[0071] When there is flow present, there will be an additional
component which is generally proportional to the flow rate and to
the magnetic field, the magnetic field being generally proportional
to the coil current (but not exactly because of factors such as
hysteresis and magnetic circuit eddy currents).
[0072] FIG. 3 shows the total signal for a particular flow rate,
that is the non-flow signal and the flow-induced signal. Points
310 and 312 (at about x=4400 and about x=9500) are the points where,
after a longer settling time, most prior art systems would choose
to derive the flow signal as, in principle, the flow rate can be
determined based on the result of calculating (Va-Vb)/2. Note further
that in this case, the signal at A and B is not settled before the
coil current is changed.
[0073] It will be appreciated that the non-flow signal could be
subtracted from this waveform and, if the non-flow signal can be
expected to remain completely constant, then this would be a useful
thing to do. FIG. 4 shows the waveform after FIG. 2 the non-flow
signal, has been subtracted.
[0074] It can be seen that the waveform is now closer to an ideal
signal. However, the technique described herein has more flexibility
than this, particularly when the non-flow signal might be expected
to change, for example for wide temperature applications.
[0075] According to the present embodiment, the technique is to
find coefficients z and f such that:
z.Vz(t)+f.Vf(t)
[0076] matches the measured shaped waveform as closely as possible.
[0077] Where Vz(t) is a captured non-flow signal and Vf(t) is the
expected flow component in the absence of a non-flow/quadrature
term.
[0078] In the present embodiment, z and f are scalar multipliers
that represent the amount of the non-flow and flow components present
in the sampled output data.
[0079] This approach may be more flexible and accurate than simply
subtracting a predefined non-flow signal, particularly if the non-flow
signal being subtracted does not accurately reflect the current
non-flow signal.
[0080] As will be appreciated, the technique is generic and does
not depend in any way upon the exact waveforms being used, though
it is useful for the waveforms to have certain characteristics (or
to not have certain characteristics), some of which are discussed
in more detail below.
[0081] An example of a fitting technique that may be used to determine
the co-efficients z and f is weighted least squares. The technique
has been found to fit the real data over all measured flow rates
with no systematic residual error, just random noise.
[0082] The flat, zero section outside the pulse 110 may be used
to determine 50 Hz (or other mains or other significant source e.g.
60 Hz) interference using correlation. The magnitude and phase of
the interference as derived from this section may then be subtracted
from the whole window. This is found to be more effective than trying
to filter out the interference as the waveform is less distorted.
[0083] The flat zero sections may also be used to identify and
remove any linear trend from the measured electrode signal prior
to further processing.
[0084] Multiple captures of the non-flow signal can be taken (offline)
and may then be averaged to create a very clean non-flow signal
prior to being used in a weighted least squares regression.
[0085] Similarly, multiple flow signals can be taken and may be
averaged to get the Vf(t) term prior to a weighted least squares
regression.
[0086] The technique may also be used to identify that zero is
drifting if z shows a systematic shift from the factory calibrated
or site calibrated value.
[0087] In one embodiment, the current waveform may be used as the
Vf(t) and/or dI/dt may be used as the Vz(t).
[0088] One embodiment of a practical system will now be described
in more detail with reference to FIG. 5. A microprocessor 10 may
be provided which may maintain a `time` variable to calculate drive
signals. The drive signals, for example a square wave signal, may
be applied to the drive coil in the sensor 3 via power amplifier
2. The electrode signals may then be amplified 4 and may be converted
into discrete samples by ADC 5. Software modules running on the
microprocessor 10 may be used to implement the methods described
herein. The amplified output of the flow meter may be resolved into
a flow component and a non-flow component 6 and a measure of the
non-flow component may be determined 8. This may allow a correction
term to be calculated 9 and fed back into the system 6 to allow
a more accurate flow rate to be determined 6 and output 7.
[0089] The length of the samples may be set, to a fixed period
(e.g. 25 ms is convenient) or may be adjustable, for example by
setting a parameter at the microprocessor 10.
[0090] In one embodiment, a confidence value may also be determined
for each flow reading output. This may be used, for example, to
"weight" the data for filtering purposes. A number of
different filtering and weighting algorithms may be used and the
choice may depend on the application.
[0091] Modifications of detail may be made to the method and system
described and features disclosed herein may be provided independently
or in other combinations. |