Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Reexamination Certificate
2001-03-29
2003-08-19
Oda, Christine K. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
C324S076620
Reexamination Certificate
active
06608474
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-098871, filed Mar. 31, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a frequency change measuring device that measures changes in frequency to measure changes in a physical quantity.
Conventional methods for measuring a change in a physical quantity in terms of a frequency change involve using a variable-capacitance displacement sensor whose electrical capacitance is varied by a change in the physical quantity and measuring a change in an oscillator frequency caused by that sensor.
There are two such methods. The first method involves dividing the output frequency of the sensor which varies with a change of the physical quantity to define gating times and counting reference clock pulses within the interval between each gating time. The second method involves dividing a reference clock frequency within the measuring device to define gating times and counting the output frequency of the sensor within the interval between each gating time.
The first and second methods are common to each other in that a change in the sensor output frequency is measured in terms of a change in count value and an operation is performed on the count value to thereby determine a change in the physical quantity. Usually, the precise frequency measurements by those known methods require the reference clock frequency to be stabilized using a thermostatic oven or the like.
In
FIG. 1
there is illustrated an example of a frequency change measuring device which implements such methods as described above. The measuring device is composed of a displacement detector
80
and an operations unit
70
. The displacement detector comprises a variable-capacitance displacement sensor
81
which detects a change in a physical quantity as a change in its electrical capacitance and an oscillator
82
using the sensor as its frequency determining component. The operations unit
70
comprises a reference clock generator
71
which generates a clock signal as reference of measurement timing, a frequency divider
72
for dividing the output frequency of the reference clock generator, a gate circuit
73
for defining gating times from the output signal from the frequency divider, a counter
74
for counting the output frequency of the displacement sensor
80
in the interval between each gating time, a latch circuit
75
for holding the count in the counter, and an operations circuit
76
for performing operations on the count read from the latch circuit to determine the change in the physical quantity.
In the arrangement of
FIG. 1
in which the oscillating frequency is varied in sympathy with a physical quantity, the resolution of frequency is improved by increasing the gating interval (window) between gating times, making it easy to detect variations in the physical quantity. However, as the gating interval becomes longer, it becomes more susceptible to variations and the magnitude of errors in frequency measurement increases. To decrease the magnitude of measurement errors, the gating interval is simply stabilized. To stabilize the gating interval, the reference clock generator is used put in a thermostatic oven. Power must be continuously applied to the operations unit
70
including the thermostatic oven during frequency measurement. The thermostatic oven needs large consumptive electrical power. In the field where a battery must be used as a power supply, therefore, measurements cannot be made over a long period of time.
In the above arrangement, if a cable used to send a signal from the displacement detector
80
to the operations unit
70
is long, then the signal will suffer attenuation within the cable. That is, since an oscillator output signal of the detector
80
is sent as it is to the operations unit
70
as the measuring signal, the signal is subject to attenuation. In particular, when the frequency of the measuring signal is high, the amount of attenuation is great and the distance over which the signal can be transmitted is short.
With the conventional frequency measuring device, as described above, when the gating interval is made long to increase the frequency resolution, it is susceptible to variation and hence the frequency measurement error increases in magnitude. The power must be applied continuously to the device which includes the thermostatic oven requiring large consumptive power during measurement. When the cable between the detector and the operations unit is long, the measured signal sent over the cable suffers considerable attenuation.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a frequency change measuring device which has no requirement for a thermostatic oven for stabilizing the frequency output of a reference clock generator.
According to a first aspect of the present invention, there is provided a frequency change measuring device including at least one frequency divider for frequency dividing a measuring signal whose frequency is varied by a change in a physical quantity to produce frequency-divided signals; at least one counter for counting the frequency-divided signals to calculate frequency-division numbers; at least one frequency division numbers transmitter for transmitting the frequency division numbers in synchronism with the frequency-divided signals; a frequency division numbers receiver for receiving the frequency division numbers receiver for receiving the frequency division numbers transmitted from the frequency division numbers transmitter to output the frequency division numbers; a reference clock generator for generating reference clocks; and an operations unit for determining a change in the frequency of the measuring signal on the basis of the frequency outputs of the reference clock generator and the frequency division numbers.
According to a second embodiment of the present invention, there is provided a frequency change measuring device including at least one frequency divider for frequency dividing a measuring signal whose frequency is varied by a change in a physical quantity to produce frequency-divided signals; at least one first counter for counting the frequency-divided signals to calculate frequency-division numbers; at least one frequency division numbers transmitter for transmitting the frequency division numbers in synchronism with the frequency-divided signals; a frequency division numbers receiver for receiving the frequency division numbers transmitted from the frequency division numbers transmitter to output the frequency division numbers; a second counter for counting an output of a reference clock generator which generates reference clocks; a latch unit for latching a count of the second counter on the basis of signals synchronous with the frequency division numbers from the frequency division numbers receiver; and an operations unit for determining a change in the frequency of the measuring signal on the basis of the count latched by the latch unit and the frequency division numbers.
The frequency change measuring device preferably further comprises a power supply for driving the frequency division numbers receiver, the second counter, the latch unit, and the operations unit, the power supply being turned on intermittently.
There may exist a plurality of measuring signals, the frequency divider, the first counter and the frequency division numbers transmitter each correspond in number to the measuring signals, and the frequency division numbers calculated from the measuring signals are received by at least one frequency division numbers receiver.
Preferably, the frequency divider, the first counter and the frequency division numbers transmitter are packed together as a frequency dividing unit, and the frequency division numbers receiver, the second counter, the latch unit and the operations unit are packed together as a frequency operations unit, and the transmission
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Oda Christine K.
President of Nagoya University
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