In an electromagnetic flow meter converter comprising a deviation
amplifier for amplifying the deviation between a feedback signal
and an input signal from a flow rate detector, and a converter circuit
for converting the amplified output of the deviation amplifier into
a frequency signal, the improvement comprising a frequency divider
for frequency dividing the frequency signal, a digital setting unit
for setting the frequency dividing factor of the frequency divider,
and a multiplier for multiplying the output of the frequency divider
by a comparison voltage which is proportional to the current applied
to the coil of the flow rate detector to provide the feedback signal,
whereby the span is set digitally and whereby the compatibility
between the converter and the flow rate detector is obtained by
setting the product of the meter constant of the flow rate detector
and a predetermined maximum flow velocity. A second embodiment uses
an oscillator, frequency dividers and multipliers to adjust and
expand the range of zero adjustment to a value lower than 0% and
to prevent mutual interference between the zero adjustment and span
What is claimed is:
1. An electromagnetic flow meter converter comprising
a deviation amplifier for taking from a flow rate detector an input
signal representing flow rate and a feedback signal and then amplifying
a deviation between said feedback signal and said input signal and
for providing an amplified output;
a converter circuit for converting said amplified output of said
deviation amplifier into a frequency signal;
a first frequency divider for frequency dividing said frequency
signal and for providing a frequency divided output;
a digital setting unit for setting a frequency dividing factor
for said first frequency divider; and
a first multiplying means for multiplying said frequency divided
output of said first frequency divider by a comparison voltage which
is proportional to current applied to a coil in said flow rate detector,
to provide said feedback signal; wherein
the product of a meter constant of said flow rate detector and
a predetermined maximum velocity of flow is set in said digital
2. The converter of claim 1 wherein said first frequency divider
is a decimal frequency divider.
3. The converter of claim 1 wherein further comprising a frequency
dividing means for converting said frequency divided output of said
first frequency divider, into a train of pulses having a substantially
uniform pulse duration, and for supplying said pulse train to said
first multiplying means.
4. An electromagnetic flow meter converter comprising
a deviation amplifier for taking from a flow rate detector an input
signal representing flow rate and for amplifying a deviation between
said feedback signal and said input signal for producing an amplified
a converting circuit for converting said amplified output of said
deviation amplifier into a frequency signal;
a first frequency divider for frequency dividing said frequency
signal and for producing a first frequency divided output;
a first multiplying means for multiplying said first frequency
divided output of said first frequency divider by a comparison voltage
which is proportional to current applied to a coil in said flow
rate detector to provide said feedback signal;
an oscillator for generating a referency frequency;
a second frequency divider for frequency dividing said reference
frequency and for providing a second frequency divided output;
a second multiplying means for multiplying said second frequency
divided output of said second frequency divider by a zero point
voltage relating to said comparison voltage to provide an output
to be added to said feedback signal; and
a digital setting unit for setting the same frequency dividing
factor in said first frequency divider and in said second frequency
5. The converter of claim 4 wherein said first and second frequency
dividers include decimal frequency dividers.
6. The converter of claim 4 further comprising a pair of frequency
dividing means for converting each output of said first and second
frequency dividers into a train of pulses having a substantially
uniform pulse duration and for supplying each pulse train to said
corresonding first and second multiplying means.
7. The converter of claim 4 wherein the product of a meter constant
of a flow rate detector for detecting a flow rate and a predetermined
maximum velocity of flow, is set in said digital setting unit.
8. The converter of claim 4 wherein a pulse output is obtained
through a subtraction circuit by subtracting a certain value from
the output pulse of said voltage to frequency converting circuit.
BACKGROUND OF THE INVENTION.
1. Field of Invention.
This invention relates to an electromagnetic flow meter converter
(hereinafter called "converter") which amplifies and converts
a deviation of a feedback signal from an input signal, into a frequency
signal, and further converts the frequency signal into the feedback
signal; and more particularly, to improvements in the span setting
portion of the converter.
2. Description of Prior Art.
FIG. 1 shows an example of a conventional converter which employes
a scheme to attain compatibility between the converter and a detector
used therewith. In FIG. 1 to an input terminal 10 an input signal
e.sub.i relating to a flow rate, is applied, which input signal
is provided from an electrode of a detector (not shown). This input
signal e.sub.i is amplified by an amplifier 11. The amplifier 11
has a variable gain so that a meter constant for compensation of
variations of the characteristics of the detector can be set in
the converter. A deviation of a feedback signal e.sub.f produced
by a multiplier 12 from the output of amplifier 11 is amplified
by a deviation (i.e. differential)amplifier 13. The output of deviation
amplifier 13 is synchronous rectified by a synchronous rectifying
circuit 14 into a DC voltage. This DC voltage is converted by a
voltage-to-frequency converting circuit 15 into a frequency signal
which has a certain pulse duration and whose frequency corresponds
to the value of the DC voltage. This frequency signal is converted
by a frequency-to-current converting circuit 16 into a DC current,
which is outputted through an output terminal 17. The frequency
signal from circuit 15 is also concurrently supplied to a frequency
ratio converting circuit 18.
The frequency ratio converting circuit 18 comprises a delay circuit,
frequency ratio selecting switch, counter, gate, etc, such as shown,
for example, in Japanese Patent Publication 56-41944 "Signal
Converter". The frequency output of frequency ratio converting
circuit 18 is supplied to multiplier 12. A comparison signal e.sub.r,
which is proportional to an excitation current, is produced across
a resistor connected in series with an exciting coil of the detector
(not shown). This comparison signal e.sub.r is applied to multiplier
12 through a terminal 19. A multiplier 12 is formed, for example,
by switching elements having turn-on/off action which is controlled
according to the frequency output of frequency ratio converting
circuit 18 and provides feedback signal e.sub.f which is proportional
to the product of comparison signal e.sub.r and the frequency output.
The operation of the converter of FIG. 1 is as follows. Denoting
the input frequency of frequency ratio converting circuit 18 by
F.sub.i1 the output frequency by F.sub.o1 and a frequency dividing
factor (a ratio) by K.sub.1 the relation
is obtained. Because comparison signal e.sub.r is sampled by multiplier
12 in accordance with output frequency F.sub.o1 feedback signal
e.sub.f can be written as
with m.sub.f representing the meter constant, a coefficient 1/m.sub.f
for compensation of variations of a signal voltage relating to a
flow rate to be detected by the detector, has been set in amplifier
11 so that the output of the amplifier 11 becomes e.sub.i /m.sub.f.
Because the circuit loop is designed as a whole so that output
e.sub.i /m.sub.f of amplifier 11 coincides with the feedback signal
e.sub.f, the following is obtained ##EQU1##
Letting the relation between frequency F.sub.i1 and a current output
I.sub.o1 at the output terminal 17 be
wherein .alpha. is a conversion constant, the following is obtained
Accordingly, by setting, in the respective cases, a set of frequency
division factor K.sub.1 and meter constant m.sub.f, it is possible
to change the extent of the span, while preserving compatibility
between the converter and the detector.
FIG. 2 shows another example of a conventional converter which
uses a scheme for permitting zero adjustment. In FIG. 2 input signal
e.sub.i is amplified by an amplifier 20 and applied to an inverting
input end (-) of a deviation amplifier 22 through a resistor 21
for span adjustment. Between inverting input (-) and the output
end of deviation amplifier 22 a parallel circuit is connected,
comprising a condenser C.sub.1 and resistor R.sub.1 and functions
so as to smooth the input voltage. On the other hand, a noninverting
input end (+) of deviation amplifier 22 is connected to a common
potential COM. The output end of amplifier 22 is connected to a
synchronous rectifying circuit 23 so that a signal is synchronous
rectified in synchronous rectifying circuit 23 and applied to an
The output of integrator 24 is converted by a voltage-to-frequency
converting circuit 25 into a frequency signal F.sub.i2. This frequency
signal F.sub.i2 is applied to a pulse width circuit 26 by which
its pulse duration is made uniform, and serves to turn ON and OFF
a switch SW1.
The comparison voltage e.sub.r is applied to one end of switch
SW1 and switches ON and OFF in accordance with the output pulse
of pulse width circuit 26. The resultant output is fed back negatively
through a resistor 27 to inverting input (-) of deviation amplifier
22 so that the input voltage of deviation amplifier 22 will become
zero. Accordingly, there is obtained an output whose frequency F.sub.i2
corresponds to input signal e.sub.i. This frequency signal F.sub.i2
is converted into a current output I.sub.o2 by, for example, a frequency
to current converting circuit 28 and appears at output terminal
17. A zero point adjustment can be made with respect to a span being
set, by voltage dividing comparison voltage e.sub.r and applying
the obtained voltage through a resistor 29 for zero point adjustment
to the inverting input (-) of deviation amplifier 22.
The conventional technique shown in FIG. 1 has the following deficiencies
1. Because the frequency ratio converting circuit used to set the
span of the converter comprises delay circuit, gate, and binary
or decimal counter, etc, its configuration is complicated. In particular,
since a high degree of accuracy is required increasingly in the
field of electromagnetic flow meters, the setting of the span with
a degree of precision not exceeding 0.1% is desired and a setting
circuit which can handle a four digit decimal number is now needed.
Thus, a span setting circuit becomes complicated if formed by use
of counters, as is done in the prior art.
2. In the electromagnetic flow meter, the output signal of the
detector varies in magnitude slightly from detector to detector.
Thus, in order to prevent a span error from arising in case any
detector and converter are paired, the meter constant representing
the extent of variation of the signal voltage given by the detector
is determined for each detector and the gain of the first stage
amplifier of the converter is adjusted according to the meter constant
peculiar to the incorporated detector. Under such circumstances,
to adjust the gain of the amplifier 11 an analog voltage dividing
circuit, such as a potentiometer is needed. Thus, it is difficult
to provide a degree of precision which does not exceed the desired
With respect to the conventional technique used in FIG. 2 other
deficiencies and disadvantages occur.
3. The span is changed by adjusting resistor 21. Thus, the degree
of accuracy in setting the span depends upon the degree of precision
of resistor 21. Accordingly, it is necessary to set the value of
resistance accurately. However, this procedure has a distinct limitation
in that it is an analog type of adjustment system.
4. Because of the foregoing procedure of setting the span, current
output I.sub.o2 is required to be adjusted and made 0% when frequency
F.sub.i2 is zero, and this current output I.sub.o2 does not decrease
beyond 0%, even if resistor 29 is adjusted and its value of resistance
is set to a value lower than that corresponding to 0%. Thus, it
is difficult, with the prior converter, to adjust the zero point.
Thus, it can be appreciated that the prior art has a variety of
deficiencies and disadvantages and leaves much to be improved upon.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to overcome the aforementioned
and other deficiencies and disadvantages of the prior art.
Another object is to provide a digital setting system by which
the span of the converter can be set with a high degree of precision.
A further object is to provide a system by which adjustment of
the zero point is achieved easily without causing interference between
the setting of the span and the adjustment of the zero point.
A still further object is to provide a converter which is compatible
with any detector which might be used therewith.
The foregoing and other objects and features are attained by the
invention which encompasses an electromagnetic flow meter converter
comprising a deviation amplifier for amplifying a deviation of a
feedback signal from an input signal, a converting circuit for converting
the output of the deviation amplifier into a frequency signal, a
first frequency divider for frequency dividing the frequency signal,
a digital setting unit for setting a frequency division factor of
the first frequency divider, and a first multiplying means for multiplying
the output of the first frequency divider by a comparison voltage,
to provide the feedback signal.
To adjust and expand the range of zero adjustment to a value which
is lower than 0% without causing mutual interference between zero
adjustment and span adjustment, the converter further includes an
oscillator, a second frequency divider for frequency dividing the
output frequency of the oscillator, and a second multiplying means
for multiplying the output of the second frequency divider by a
zero point voltage relating to the comparison voltage to add the
results to the feedback signal, with the digital setting unit setting
the same frequency division factor in the first and second frequency
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram depicting a conventional converter using
means for attaining compatibility between the converter and a detector
FIG. 2 is a block diagram depicting another conventional converter
using means for permitting zero adjustment.
FIG. 3 is a block diagram depicting an illustrative embodiment
of the invention, wherein a digital setting of a span is achieved.
FIG. 4 is a waveform diagram depicting input and output waveforms
of a span setting unit of the embodiment of FIG. 3.
FIG. 5 is a block diagram depicting another illustrative embodiment
wherein the embodiment of FIG. 3 is modified.
FIG. 6 is a waveform diagram depicting waveforms appearing at various
parts of the embodiment of FIG. 5.
FIG. 7 is a block diagram depicting another illustrative embodiment
wherein no interference between zero point adjustment and span setting
is achieved .
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The embodiments shown in FIGS. 3-7 have circuit element having
the same functions as those shown in FIGS. 12 and bear the same
reference numerals, which for convenience of description will not
be further described hereat.
In FIG. 3 block unit 30 indicates a span setting unit which can
digitally set a span. The setting unit 30 divides input frequency
F.sub.i3 obtained from a voltage to frequency converter circuit
31 in accordance with a setting value to provide an output frequency
Specifically, the span setting unit 30 comprises four decimal rate
multipliers (i.e. frequency dividers) RM11 to RM14 and four switches
SW11 to SW14 and can divide the input frequency F.sub.i3 by a four
digit frequency demultiplication (i.e. dividing factor or ratio
(1 to 9999). Namely, it can provide an output whose frequency ranges
from one ten-thousandths (1/10000) to ninety-nine hundred ninety
nine ten-thousandths (9999/10000) of the input frequency. To set
the frequency division factor in the setting unit 30 setting switches
SWll to SW14 functioning as digital setting elements, are coupled
to corresponding multipliers RM11 to RM14 by which each number
of four decimal digits 10.sup.4 10.sup.3 10.sup.2 and 10.sup.1
can be set.
To ensure compatibility between a detector (not shown) and the
converter, the embodiment of FIG. 3 permits setting of a value which
corresponds to the product of a given full scale velocity of flow
and a meter constant of the detector used with the converter, by
means of the setting switches SWll to SW14. That is, it is also
possible to digitally set the meter constant by means of the illustrative
FIG. 4 shows the input and output frequency waveforms of the span
setting unit 30. FIG. 4 line (A) shows the input frequency F.sub.i3
waveform. FIG. 4 line (B) shows the output frequency F.sub.o3 waveform.
If data input S to be set in the four digit rate multiplier is
selected, for example, as S=1234 in comparison with the input frequency
(F.sub.i3) waveform of FIG. 4 line (A) containing 10000 pulses
in a given interval, the output frequency F.sub.o3 contains 1234
pulses (i.e. F.sub.o3 =1234) and shows a train of pulses, as shown
in FIG. 4 line (B) which has empty tooth positions. Apparently,
because the output waveform of the frequency divider becomes a train
of pulses with some empty tooth positions, an ON and OFF ratio of
pulses after frequency division, decreases in comparison to the
before frequency division, in proportion to the number of empty
In this way, according to the embodiment of FIG. 3 a digital type
span setting unit which is simple in configuration, is low priced
and is settable to any desired frequency division factor, can be
obtained by suitably connecting decimal frequency divider segments
and corresponding setting switches, with the number of digits being
selected as desired.
FIG. 5 is a block diagram showing a modification of the converter
of FIG. 3 wherein an output frequency F.sub.o4 produced by dividing
an input frequency F.sub.i4 by means of the span setting unit 30
shown in FIG. 3 is further divided by means of a frequency dividing
circuit 32 in accordance with the number 1/N into F.sub.o5. This
output F.sub.o5 is converted into a train of pulses having a certain
duration, by a pulse width (in terms of duration) circuit 33 which
may be formed by a one shot multivibrator circuit, for example.
The resultant pulse train is multiplied by comparison signal e.sub.r
from terminal 19 in multiplier 12.
Although the embodiment of FIG. 3 which includes the frequency
divider as the span setting unit 30 produces the output frequency
shown in FIG. 4 line (B) which is a pulse train having discrete
and dense portions due to empty pulse positions, and results in
fluctuations in the output, the embodiment of FIG. 5 is improved
in the manner as discussed below on this point.
FIG. 6 is a waveform diagram illustrating the effects of the frequency
division process performed by the converter shown in FIG. 5. FIG.
6 line (A) shows output frequency F.sub.o4 of span setting unit
30. FIG. 6 line (B), line (C), line (D) show output frequency F.sub.o5
waveforms of the frequency dividing circuit 32. In particular, the
waveform of line (B) corresponds to the case of 1/2 frequency division.
The waveform of line (C) corresponds to the case of 1/2.sup.2 frequency
division. The waveform of line (D) corresponds to the case of 1/2.sup.3
frequency division. As is apparent from these waveforms, the output
assumes gradually a certain period with an increase of the frequency
dividing factor. Accordingly, fluctuations of the output decrease
with the use of the frequency dividing circuit.
FIG. 7 is a block diagram showing another illustrative embodiment
of the invention, wherein deviation amplifier 22 receives at its
inverting input (-) the sum of the input signal amplified in amplifier
20 and supplied through a resistor 34 a voltage for zero adjustment
produced by voltage dividing the comparison voltage e.sub.r and
supplied through resistor 29 and switch SW2 and the feedback voltage
supplied through switch SW1. The output of deviation amplifier 22
is converted into a DC voltage by synchronous rectifying circuit
23. This resultant DC voltage is converted into a frequency signal
F.sub.i5 through integrator 24 and subsequently by a voltage to
frequency converting circuit 35. A frequency divider unit RMA can
accommodate four digits, for example, and divides the input frequency
F.sub.i5 applied by V/F circuit 35 to apply the results to a pulse
width circuit 36. Pulse width circuit 36 makes uniform the pulse
duration of the output frequency F.sub.o6 of frequency divider unit
RMA, to provide a control signal for turning ON and OFF switch SW1.
There is provided another rate multiplier unit RMB, to which a
certain reference frequency F.sub.r is applied from an oscillator
37 for example. A frequency dividing factor for determination of
the span, which is identical to a frequency division factor K.sub.2
is set in by means of a digital setting unit 38. The divided frequency
signal given from RMB is changed to a pulse train through a pulse
width circuit 39 to turn ON and OFF switch SW2.
To one end of switch SW2 a voltage e.sub.z ' is applied for zero
adjustment which is produced by dividing the comparison voltage
From the embodiment of FIG. 7 a zero adjustment voltage e.sub.z
is given by K.sub.2 f.sub.r e.sub.z '. Assuming for simplicity that
the gain is 1 then, the following relation holds at the input end
of deviation amplifier 22.
Using the relation e.sub.z =K.sub.2 f.sub.r e.sub.z ', the following
is then obtained. ##EQU3## The first term on the right is one proportional
to the input signal e.sub.i, whereas the second term does not depend
on frequency division factor K.sub.2 but is determined by zero
adjustment voltage e.sub.z. As a result, interference between span
adjustment and zero adjustment is eliminated.
Furthermore, to permit expansion of a variable range of zero adjustment
toward a lower value than 0%, value e.sub.z is set so that frequency
F.sub.i5 assumes a given value f.sub.o when input signal e.sub.i
=0. That is, by setting e.sub.i =0 and F.sub.i5 =f.sub.o in equation
(7), the the following is obtained ##EQU4## This indicates that
the above relation does not depend on the frequency demultiplication
Accordingly, there is no interference between span adjustment and
zero adjustment. The span can be set digitally at a high degree
of precision. Also, accurate setting of the zero point can be achieved.
Output value f.sub.o corresponding to input signal e.sub.i =0 of
the voltage to frequency converting circuit 35 is deducted from
output value f corresponding to input signal e.sub.i .noteq.0 by
a deduction circuit 40. Then, at output terminal 41 there is provided
a pulse output corresponding to the input signal.
Furthermore, this embodiment shows that the exciting current is
stable. The comparison signal e.sub.r can be replaced by a fixed
voltage supplied from a voltage source independent of the exciting
The invention accordingly has many advantages. For example, because
the digital type span setting unit is included in the feedback circuit
of the converter, to frequency demultiply the frequency signal,
and the product of the meter constant of the detector and the full
scale velocity flow, is set in the digital setting unit, the scan
can be set at a high degree of precision, and the compatibility
can be secured between the detector and converter all with a single
circuit configuration. Furthermore, because there is no need to
use a combination of analog circuit and digital circuit. the configuration
of the inventive converter is considerablv simplified.
Moreover, advantageously, because the same group of switches permits
setting of the span and insures compatibility of the converter with
the detector, the invention is economical. Furthermore, advantageously,
because the two routes, each including the frequency divider unit,
are provided and the same frequency division factor is given from
the digital setting unit to the respective routes, through switching,
thereby changing relatively the feedback voltage and zero adjustment
voltage, the span can be altered by means of a digital system of
high precision, the range of zero adjustment can be adjusted and
expanded to a value which is lower than 0% and interference between
zero adjustment and span adjustment is prevented. These results
were not obtainable with the prior art arrangements.
The foregoing description is illustrative of the principles of
the invention. Numerous modifications and extensions would be apparent
to the worker skilled in the art. All such modifications and extensions
are to be considered to be within the spirit and scope of the invention.