Note: Descriptions are shown in the official language in which they were submitted.
12~871
This invention relates to a device for measuring a
physical quantity and particularly to a measuring device
which measures a single physical quantity by a plurality Of
measuring means and utilizes the results as information.
The present invention will be illustrated by way
of the accompanying drawings, in which:-
Fig. 1 is a block diagram showing an embodiment of
the measuring device according to the present invention;
Fig. 2 is a block diagram of the comparison circuit;
Fig. 3 is a time chart which shows the output
voltage from the microcomputer;
Fig. 4 is a diagram for explaining the comparison
method by the comparator; and
Fig. 5 is a block diagram showing a prior art
device.
Temperature sensors, gas density sensors and
liquid level sensors measure physical quantities from the
change in the resistance of a resistor which varies accord-
in to its external environment. Measured resistance of
such a resistor is not used directly but is taken out after
it is electrically converted into voltage, current or ire-
quench by a measuring means at a later stage within the device and the information in the form of a physical van-
able into which it has been converted is subjected to van-
ions controls and then displayed by a display means.
There is no problem if the structure of the device
is such that only one physical quantity is measured as in-
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formation by one measuring means and then displayed. With
the application of modern electronics, for example, to the
display panels of automobiles, however, there are now devil
cues capable of displaying more than one type of information
on the basis of only one physical variable but by carrying
out various computational operations thereon. There is desk
cried in So Patent No. 4,061,023, for example, a device
which measures the momentary amount of fuel consumed by a
running vehicle and obtains not only the total amount of the
fuel consumed by integrating it but at the same time also
the momentary rate of fuel consumption by carrying out a
computational operation. In order to obtain two or more
types of information from one measured physical quantity as
in this example, the device may be so designed that this
physical quantity is transmitted to a plurality of
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measuring means where different operations are performed,
displays being made thereafter by display means connected to
the measuring means. For example, the voltage corresponding
to the amount of the fuel remaining in a running vehicle may
be transmitted to both first and second measuring means
where the first measuring means is only for measuring the
remaining amount of the fuel while the second measuring
means also receives information such as running time and
traveled distance and measures not only the remaining
amount of the fuel but also the total amount of the fuel
consumed and the rate of fuel consumption per unit time, the
display being made by display means connected to them. sty
this design, however, measurement errors may be caused by
the power sources of the individual measuring means.
Referring to FIG. 5, a rheostat Rx as a sensor is connected
in series with a pulp resistor Row to a power source 2 in a
first measuring means 1 which also includes a comparison
circuit 3 for obtaining information by converting the
physical quantity measured by sensor Rx into an electrical
quantity and a control circuit 5 for outputting this
information at a display means 4 at a later stage. The
comparison and control circuits 3 and 5 are powered by the
source I, and the comparison circuit 3 measures the physical
quantity by comparing the voltage between the terminals of
the rheostat Rx and the comparison voltage from the source
voltage ODD. The second measuring means 7 is for measuring
the physical quantity by the same sensor and making an
output at another display means 6 and is also provided with
a power source 8, a comparison circuit 9 and a control
circuit 10. Sensors 11 are connected to this control
circuit 10 and output electrical signals in accordance with
the conditions of other physical quantities. The comparison
circuit 9 and the control circuit 10 are powered by the
voltage ODD of the source 8.
In the case of a prior art device thus constructed,
voltage RXVDD/(Rx + Row appears at the input ends of the
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comparison circuits 3 and 9. If resistance Row is now
assumed to be known, RX/(Rx + Row becomes a fixed curve.
Thus, resistance Rx can be obtained by both measuring means
1 and 7 by comparing RxVDD/(~x + Row and the comparison
voltage from source voltage ED in comparison circuit 3 and
y p no RXVDD/(Rx + Row and the comparison voltage from
source voltage ED in comparison circuit 9.
Source voltages, however, fluctuate mostly within 10%.
This presents no problem to the comparison circuit 3 of the
first measuring means 1 because this applies ODD to the
rheostat Rx so that, if ODD fluctuates, what is being
compared also fluctuates at the same ratio. In the case of
the comparison circuit 9 of the second measuring means 7,
the output will be the same as that from the comparison
circuit 3 if source voltage ODD is the same as or
maintained at a fixed ratio with respect to ODD because what
is being compared will then again fluctuate at the same
ratio. Since source voltages may fluctuate by up to 10%,
however, a maximum measurement error of about 20% will
result in the comparison circuit 9 if the fluctuation in
source voltage ODD is I 0% and that in source voltage ODD
is -10%. Although this problem of measurement error can be
resolved by preliminarily adjusting the source voltage ODD
of source 8 to the source voltage ODD of source 2, it is
extremely cumbersome to make such an adjustment before each
measurement especially if there is a large number of
measuring means. Moreover, such adjustments cannot be
effective for sudden fluctuations in a source voltage. In
the past, therefore, different measured values were often
obtained due to the fluctuations of source voltages if two
or more measuring means were used for one physical quantity.
Summary of the Invention
It is an object of this invention to provide a
measuring device which, having a plurality of measuring
means for one physical quantity, is capable of yielding the
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same measured value by each of these measuring means.
According to the present invention there is
provided a measuring device adapted to supply a detection
voltage corresponding to a condition of a physical quantity
to a plurality of measuring means and to make displays
related to said physical quantity at display means connected
to said measuring means, said measuring device being char-
acterized in that each of said measuring means includes a
comparison circuit for measuring said physical quantity by
entering said detection voltage and comparing said detection
voltage with a comparison voltage and that said comparison
voltage is supplied from a common source which generates
said detection voltage. Suitably said comparison voltage is
generated by a ladder-type resistor circuit for analog-
digital conversion.
Referring now to Fig. 1, a first measuring means
21 is provided with a power source 22, a comparison circuit
23 and a control circuit 24, and there is a display means 25
connected at a later stage. A rheostat R as a sensor in
series with a pull-up resistor R is connected to the source
22, and the comparison circuit 23 and the control circuit 24
are powered by the source voltage ODD of -the source 22. A
second measuring means 26 is similarly provided with a power
source 27 r a comparison circuit 28 and a control circuit 29.
Sensors 30 which output electrical signals in accordance
with the conditions of other physical quantities are con-
netted to the control circuit 29 and a display means 31 is
connected at a later stage. The comparison circuit 28, how-
ever, is powered by the source 22 of the first measuring
means 21 while the control circuit 29 is powered by the
g DUD source 27.
Fig. 2 is a block diagram which shows an embody-
mint of comparison circuits 23 and 28 wherein No. 32 is a
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comparator and No. 33 is a microcomputer. Since resistors
Al, R2 and R3 are connected respectively to three output
terminals A, B and C of the microcomputer 33, while parallel
resistors R4, R5 and R6 are connected respectively between
them and the ground so as to form a ladder-type resistor
network for
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analog-digital conversion. The values of resistance of
these resistors R1 - R6 are such that R1 = R2 = R3 = R6 =
2R4 = 2R5, and the junction point between resistors R1 and
R4 is connected to the non-inversion input terminal D of the
comparator 32 while the inversion input terminal E of the
comparator 32 is connected to the junction point of the
pulp resistor Row and the rheostat Rx. Its output terminal
F is connected to the control circuit 24 or 29 through the
microcomputer 33.
In operation, the source voltage ED of source 22 is
applied to the rheostat Rx and this generates a detection
voltage RXVDD/(~X + Row which becomes an input to the
comparator 32. In the meantime, the voltage output at the
output terminals A, B and C of the microcomputer 33 is
either "H" (high) or "L" (low, or ODD = O) as shown in FIG.
3 so that a total of 8 different comparison voltages ranging
in value between O and 7VDD/8 can be output by combining the
three output voltages at terminals A, B and C. The
comparison voltage in this range is repeatedly output either
periodically or periodically and enters the comparator 32.
The comparator 32 then compares the voltage between the
terminals of the rheostat Rx with the output voltage from
the output terminals A, B and C of the microcomputer 33 and,
when their magnitude relationship changes, an output
inverted from the previous output is transmitted to the
microcomputer 33. The microcomputer 33 then performs
computational operations on the value of variable resistance
Rx in accordance with the signals output from the terminals
A, I and C and makes an output to the control circuit 24 or
29.
Since, as explained above, the same source voltage ODD
is applied to the comparison circuits 23 and 28 of the first
and second measuring means 21 and 26, the same comparison
can be effected by the comparator 32 regarding the rheostat
Rx and the same measured value can be obtained from the
different measuring means. FIG. 4 shows the comparison with
WOW
the voltage RXVDD/(Rx + Row between the terminals of the
rheostat Rx when the source voltage ODD is divided into 8
steps. While the source voltage which should be 7VDD/8 due
to fluctuation would become 7V'DD/8 if different power
sources were used for comparison circuits of different
measuring means as in the case of prior art devices and this
would result in different measured values from different
measurement sections, such inconvenience is obviated by a
device of the present invention described above.
Although the control circuits 24 and 29 are shown to be
powered by different sources, there is no problem because
source voltages do not relate directly to the measured
values.
As shown above, when two or more measuring means are
used to measure one variable resistance Rx, the present
invention teaches to supply source voltage from the same
source to the comparison circuits for comparing the
individual voltages so that the same measured value can be
obtained for Rx, independently of the voltage fluctuations
at the individual measuring means. This contributes to
increase the accuracy of measurement.
Although only one embodiment has been shown and
described herein, it should be understood that many changes
and modifications may be made therein without departing from
the scope of the appended claims. For example, there may be
more than two measuring means. Likewise, the number of
output terminals A, B and C of the microcomputer 33 is not
limited to 3. If this number is increased, resolution of
the measured value can be increased and accuracy of
measurement is improved.
In summary, the present invention provides a measuring
device which, with plurality of measurement sections
connected for one physical quantity, allows to obtain the
same measured value at each of the measuring means.
