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Claims  |
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What is claimed is:
1. A digital tester comprising:
analogue-to-digital converter means, operating at a high speed, for
converting an input signal into a digital signal and outputting said
digital signal as an AC/DC determination signal;
AC/DC determining means, receiving said AC/DC determination signal, for
comparing said AC/DC determination signal with a predetermined DC
determination range defined by positive and negative thresholds, and for
determining said input signal to be AC when said AC/DC determination
signal exceeds said DC determination range by exceeding both the positive
and negative thresholds for a predetermined comparison period, said AC/DC
determining means outputting a determining signal based on whether said
input signal is determined to be AC;
a measurement system having an AC side and DC side, and
switching means coupled to said measurement system and determining means
for switching said measurement system between said AC side and said DC
side in response to said determining signal.
2. A digital tester according to claim 1, wherein said AC/DC determining
means compares said AC/DC determination signal with said DC determination
range at least twice during a predetermined time interval, and judges said
input signal to be AC when said AC/DC determination signal has exceeded
said DC determination range by exceeding both the positive and the
negative thresholds each time said AC/DC determination signal is compared
to said DC determination range during said predetermined time interval.
3. A digital tester according to claim 1, wherein said switching means
holds said measurement system to either one of the AC side and the DC side
as a normal state, and said AC/DC determining means issues, as said
determining signal, a switching command signal for switching over said
measurement system from said one of the AC side and the DC side as said
normal state to another off of the AC side and the DC side when said input
signal requires said measurement system to be set to the other side.
4. A digital tester according to claim 3, wherein said switching means sets
said measurement system to the DC side in said normal state and switches
over said measurement system to the AC side as the other side.
5. A digital tester according to claim 1, further comprising:
high-resolution analogue-to-digital converter means of double integral type
for converting said input signal into a digital measurement signal when
the measurement system is set to either one of the AC and DC sides; and
reset signal generator means for outputting a reset signal to said
high-resolution analogue-to-digital converter means when said input signal
is changed over between AC and DC by said AC/DC determining means.
6. A digital tester according to claim 1, wherein said measurement system
comprises:
a first circuit path extending between an input terminal of the digital
tester and a DC terminal and;
a second circuit path extending between said input terminal of the digital
tester and an AC terminal, said second circuit path including a
rectifying/smoothing circuit;
wherein said switching means is selectively movable between said DC
terminal and said AC terminal.
7. A digital tester including measuring terminals for attachment to a
circuit to be tested for carrying an input signal from the circuit to be
tested, and a measurement system coupled to said measuring terminals for
performing tests using the input signal, said measuring system having an
AC side and a DC side, said digital tester comprising:
an analogue-to-digital converter, coupled to said measurement terminals,
for converting the input signal into a digital AC/DC determination signal;
an AC/DC determining unit, receiving said AC/DC determination signal, said
AC/DC determining unit comparing said AC/DC determination signal with a
predetermined DC determination range defined by positive and negative
thresholds, and determining said input signal to be AC when said AC/DC
determination signal exceeds both the positive and the negative thresholds
during a predetermined comparison period, said AC/DC determining unit
outputting a determining signal based on whether said input signal is
determined to be AC; and
a switch, coupled between the measurement system and determining unit, said
switch receiving said determining signal so as to selectively supply the
input signal to one of the AC side and the DC side of the measurement
system in response to said determining signal.
8. A digital tester according to claim 7, wherein said AC/DC determining
unit compares said AC/DC determination signal with said DC determination
range at least twice during a predetermined time interval, and judges said
input signal to be AC when said AC/DC determination signal has exceeded
said DC determination range by exceeding both the positive and the
negative thresholds each time said AC/DC determination signal is compared
to said DC determination range during said predetermined time interval.
9. A digital tester according to claim 7, wherein said switch supplies said
input signal to either one of the AC side and the DC side in a normal
state, and said AC/DC determining unit issues, as said determining signal,
a switching command signal for causing said switch to switch over and
supply said input signal to an other side when said input signal requires
said measurement system to be set to the other side.
10. A digital tester according to claim 9, wherein said switch supplies the
input signal to the DC side in said normal state and switches over to
supply the input signal to the AC side as the other side.
11. A digital tester according to claim 7, further comprising:
a high-resolution analogue-to-digital converter of double integral type,
coupled to said measuring terminals, for converting said input signal into
a digital measurement signal when the measurement system is set to either
one of the AC and DC sides; and
a reset signal generator, coupled to said AC/DC determining unit for
outputting a reset signal to said high-resolution analogue-to-digital
converter when said input signal is changed over between AC and DC by said
AC/DC determining unit.
12. A digital tester according to claim 7, wherein said AC/DC determining
unit includes a programmed microcomputer.
13. A digital tester according to claim 7, wherein said measurement system
comprises:
a first circuit path extending between an input terminal of the digital
tester and a DC terminal and;
a second circuit path extending between said input terminal of the digital
tester and an AC terminal, said second circuit path including a
rectifying/smoothing circuit;
wherein said switching means is selectively movable between said DC
terminal and said AC terminal.
14. A digital tester comprising:
an input terminal;
a first circuit path extending between said input terminal and a DC
terminal;
a second circuit path extending between said input terminal and an AC
terminal, and including a rectifying/smoothing circuit;
a switch having a switch input selectively engageable with said AC terminal
and said DC terminal, and a switch output;
a sequential comparison type analogue-to-digital converter, coupled to said
switch output, which converts an input signal received by said input
terminal into a digital AC/DC determination signal;
an AC/DC determining unit, coupled to said sequential comparison type
analogue-to-digital converter, which receives and compares said AC/DC
determination signal with a DC determination range defined by positive and
negative thresholds, said AC/DC determining unit determining said input
signal to be AC when said AC/DC determination signal exceeds both the
positive and the negative thresholds during a comparison period, said
AC/DC determining unit outputting a determining signal to said switch
based on whether the input signal is determined to be AC;
said switch selectively engaging one of said AC terminal and said DC
terminal in response to said determining signal.
15. A digital tester according to claim 14, wherein said AC/DC determining
unit compares said AC/DC determination signal with said DC determination
range at least twice during a predetermined time interval, and judges said
input signal to be AC when said AC/DC determination signal has exceeded
said DC determination range by exceeding both the positive and the
negative thresholds each time said AC/DC determination signal is compared
to said DC determination range during said predetermined time interval.
16. A digital tester according to claim 14, wherein said switch engages the
DC terminal unless said AC/DC determining unit has determined said input
signal to be AC.
17. A digital Lester according 14, further comprising:
a high-resolution analogue-to-digital converter of double integral type,
coupled to said switch output, which converts said input signal into a
digital measurement signal; and
a reset signal generator, coupled to said AC/DC determining unit, which
outputs a reset signal to said high-resolution analogue-to-digital
converter when said input signal is changed over between AC and DC by said
AC/DC determining unit.
18. A digital tester according to claim 14, wherein said AC/DC determining
unit includes a programmed microcomputer. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital tester, and more particularly to
techniques for determining whether an input signal to the digital tester
is AC or DC, for measuring a pulse width for an input potential to the
digital tester, and further to a construction of a body of the digital
tester.
2. Description of the Related Art
Digital testers as circuit meters have been popularly used in
fault-location and in the service of electric and electronic equipment.
Each tester incorporates a voltmeter, an ammeter, an ohmmeter, etc., has a
wide range of measurement, and is easy to handle.
A digital tester has a measurement system that is generally switched over
depending on whether an input signal is AC or DC. Therefore, digital
testers are provided with a mode change switch for externally switching
over the measurement system.
In use of digital testers, a pair of probes each provided with a measuring
terminal at one end are employed, and test leads connected to the other
ends of the probes are connected to a body of the digital tester. On the
other hand, when carrying digital testers, the digital tester body is
placed in a box case and the probes are stored by utilizing a gap left in
the box case.
SUMMARY OF THE INVENTION
In a conventional digital tester, however, switching over the measurement
system between the AC side and the DC side requires a user to recognize
whether an input voltage, or the like, is AC or DC, by making a judgment
from the circuit configuration and so on. This raises a first problem of
rendering the digital tester inconvenient to those persons who do not have
much electrical knowledge.
In view of the above first problem, a first object of the present invention
is to provide a digital tester that can automatically effect AC/DC
determination of an input signal and then switch over its measurement
system between the AC side and the DC side with high responsivity.
With circuit configurations of more and more various equipment being
designed in digital form, there increases the need for measuring a pulse
width to check those circuit configurations. Nonetheless, a conventional
digital tester is provided with no circuit for measuring a pulse width,
which results in a second problem of rendering the digital tester
inconvenient to those persons who are engaged in the design of digital
circuits. The reason is in that measuring a pulse width requires a circuit
for time-sharing an input signal, comparing changes in the input signal
with each other from time to time, and detecting the rise and fall of a
pulse, as well as a relay circuit. These circuits, however, could not be
mounted in a circuit meter such as a small-sized digital tester.
In view of the above second problem, a second object of the present
invention is to provide a digital tester that can measure a pulse width
with simple construction and high reliability, by determining changes in
an input potential as change-over of potential zones.
Furthermore, a conventional digital tester has a third problem in that the
digital tester is not handy to use because probes are required to be
stored along with a body of the digital tester in a box case whenever
carried, or probes must be stored separately in spite of the digital
tester body having a reduced size. Additionally, when probes are stored in
a box case, they are often stored such that test leads are wrapped over
probe grips. This condition of the stored test leads gives rise to another
inconvenience in that the test leads must be unwrapped prior to using the
digital tester.
In view of the above third problem, a third object of the present invention
is to provide a digital tester in which the structure of a body of the
digital tester is improved to ensure a higher degree of convenience in
such a point of making probes easier to handle.
To solve the above first problem, one embodiment of a digital tester
according to the present invention includes a high-speed A/D converter
able to operate at a high speed for converting an input signal into
digital form and outputting it as an AC/DC determination signal. The
digital tester also includes an AC/DC determining unit for comparing a
level of the input signal with a DC determination range defined by
positive and negative thresholds based on the AC/DC determination signal.
The AC/DC determining unit determines the input signal to be AC when the
level of the input signal has exceeded the DC determination range on both
the positive and negative sides for a predetermined comparison period, and
issues determination signals corresponding to AC and DC based on this
determination. The digital tester further includes a switching unit for
switching over a measurement system between the AC side and the DC side in
response to the determination signals.
In the above digital tester, preferably, the AC/DC determining unit
compares the level of the input signal with the DC determination range at
least twice at a predetermined time interval, judges the input signal to
be AC when the level of the input signal has exceeded the DC determination
range on both the positive and negative sides in each of the comparison
periods, and then issues the determination signals.
Preferably, the switching unit holds the measurement system set to either
one of the AC side (the side of a rectifying/smoothing circuit) or the DC
side (the side of an input path) in a normal state, and the AC/DC
determining unit issues, as the determination signal, a switching command
signal for switching over the measurement system from one normal side to
the other side when that input signal, which requires the measurement
system to be set to the other side, is applied. In this case, the
switching unit preferably sets the measurement system to the DC side as
one side in a normal state and switches over the measurement system to the
AC side as the other side when appropriate.
In the case that a high-resolution A/D converter of the double integral
type is used as the A/D converter for converting the input signal into
digital form and outputting it as the measurement signal in a state that
the measurement system is set to the AC or DC side corresponding to the
input signal, a reset signal generator is preferably provided for
outputting a reset signal to the high-resolution A/D converter when the
input signal is changed over between AC and DC.
To solve the above second problem, a digital tester according to the
present invention includes a potential zone determining unit for
determining to which one of a plurality of potential zones (potential
zones A, B and C) an input potential VIN belongs. The potential zones are
defined by at least two reference potentials, e.g., +1V and -1V. The
potential zone determining unit outputs a result of the determination as
potential zone signals Sa. A start signal generator is included, and
detects, based on the potential zone signals Sa output from the potential
zone determining unit, that the input potential VIN has exceeded any one
of the reference potentials and whether VIN has changed from one to
another different potential zone. The start signal generator outputs a
start signal S1 for instructing the start of pulse width measurement. A
stop signal generator is also included, and detects, based on the
potential zone signals Sa output from the potential zone determining unit,
that after output of the start signal S1 from the start signal generator
unit, the input potential VIN has changed over in the potential zone again
by exceeding at least the reference potential which was exceeded for the
first time, i.e., at the time of the start signal S1 being output. The
stop signal generator outputs a stop signal S2 for instructing the end of
the pulse width measurement. A time counting unit counts a time period
from the output of the start signal S1 to the output of the stop signal
S2.
Preferably, the above digital tester further comprises a forced stop
command signal generator for outputting, upon being operated externally, a
forced stop command signal St for commanding the stop signal generator to
forcibly output the stop signal S2.
To solve the above third problem, which is present in digital testers
having a digital tester body and probes having measuring terminals on one
end and test leads connected to the other end for electrical conduction of
the measuring terminals to said digital tester body, according to the
invention, the digital tester body is provided in its side surfaces with a
probe storing groove that is able to store the probes, and a slip-off
preventive mechanism for engaging outer peripheral surfaces of the probes
stored in the probe storing groove to prevent slip-off of the probes from
the probe storing groove. In this digital tester, the slip-off preventive
mechanism can be provided by utilizing, for example, elastically
contacting engagement portions formed to inwardly project from opposite
side walls defining the probe storing groove therebetween for coming into
elastic contact with the outer peripheral surfaces of the probes in the
probe storing groove.
In the present invention, preferably, the digital tester body is formed in
each of its side surfaces with the probe storing groove or a test lead
storing groove that is continuous with the probe storing groove for
storing the test leads, so that the digital tester body can store the
probes in the probe storing groove after the test leads are wrapped over
the body side surfaces to be stored in the test lead storing groove and
the probe storing groove.
Preferably, in those portions of the opposite side walls defining the probe
storing groove therebetween, where the measuring terminals of the probes
stored in the probe storing groove are positioned, there are formed
measuring terminal exposure recesses extending inwardly from open wall
edges. Measuring terminals of the probes stored in the probe storing
groove extend through these exposure recesses so that they are exposed to
the exterior of the digital tester. The term "recess" as used in the
specification is meant to refer to a shape having outer contours located
inside the outermost contour; thus, recess is not always limited to a
largely recessed shape.
Also preferably, in those portions of the opposite side walls defining the
probe storing groove therebetween, where the grips of the probes stored in
the probe storing groove are positioned, there are formed probe take-out
recesses extending inwardly from open wall edges. The grips of the probes
stored in the probe storing groove are exposed through these probe
take-out recesses.
In the present invention, preferably a measurement mode select rotary
switch provided on an upper surface of the digital tester body may have
small bosses formed on the switch surface for improving grip and thereby
preventing finger slips. In this case, preferably, the small bosses are
formed in the circumferential direction near an outer peripheral edge of
the measurement mode select rotary switch with a predetermined pitch. The
predetermined pitch of the small bosses is different from a pitch at which
the measurement mode select marks are formed around and outwardly of a
circumference of the measurement mode select rotary switch.
Further preferably, on the upper surface of the digital tester body, there
may be formed an upper recess extending from one side of an area in which
the measurement mode select rotary switch is formed, to an upper side edge
of the digital tester body.
In the digital tester according to the present invention, when a signal is
input to the digital tester, the high-speed A/D converter first converts
the input signal into digital form and outputs it as an AC/DC
determination signal. Based on this AC/DC determination signal, the AC/DC
determining unit then determines whether a level of the input signal
exceeds the DC determination range defined by positive and negative
thresholds on both the positive and negative sides for a predetermined
time period. In this process, the AC/DC determining unit judges the input
signal to be AC when the level of the input signal has exceeded the DC
determination range on both the positive and negative sides for the
predetermined time period, and outputs the appropriate determination
signal. In response to the determination signal, the switching unit
switches over the measurement system between the AC side and the DC side.
Thus, the input signal is determined to be AC when its level has exceeded
the DC determination range on both the positive and negative sides for the
predetermined time period, and to be DC when its level has not exceeded
the DC determination range or has exceeded the DC determination range on
either the positive or negative side only, followed by switching over the
measurement system by the switching unit. With the digital tester
according to the present invention, therefore, the measurement system is
automatically switched over corresponding to the input signal, enabling
the measurement to be performed under conditions corresponding to the
input signal with no need that the user have knowledge about whether the
input signal is AC or DC. While an A/D converter for converting the input
signal into digital form for output of a measurement signal is required to
have a high resolution, a high-speed A/D converter is employed as the A/D
converter for outputting the AC/DC determination signal in pursuit of a
high operation speed only, leaving resolution out of account. This speeds
up change-over of the measurement system between the AC side and the DC
side, with the result of a high response for the input signal.
On the other hand, when a signal is input to the digital tester according
to the present invention in a pulse width measuring mode, the potential
zone determining unit first determines to which one of the potential zones
(the potential zones A, B and C) the input potential VIN belongs, and then
outputs a result of the determination as the potential zone signals Sa.
When the input potential VIN is changed but remains in the same potential
zone without exceeding any reference potentials, the potential zone
signals Sa output from the potential zone determining unit remain
unchanged and, therefore, the start signal generator does not output the
start signal S1. When the input potential VIN has exceeded the reference
potential and changed over from one to another potential zone, the
potential zone signals Sa output from the potential zone determining unit
are changed. Upon detecting such change-over in the potential zone, the
start signal generator outputs the start signal S1 for instructing the
start of the pulse width measurement. Subsequently, when the input
potential VIN has changed over in the potential zone again by exceeding
the reference potential that was exceeded for the first time, the
potential zone signals Sa output from the potential zone determining means
are changed. Upon detecting such change-over in the potential zone, the
stop signal generator outputs the stop signal S2 for instructing the stop
of the pulse width measurement. Then, the time counting unit counts, as a
pulse width, the period from output of the start signal S1 to output of
the stop signal S2.
In the digital tester according to the present invention, the test leads
are connected to the digital tester body for electrical conduction between
the digital tester body and the measuring terminals. Under this condition,
a value of the voltage, etc. developed between the measuring terminals is
measured based on information input through the measuring terminals. Also,
in the digital tester according to the present invention, when the probes
are stored in the probe storing groove formed in the side surfaces of the
digital tester body, the probes are prevented from slipping off from the
probe storing groove because of the slip-off preventive mechanism provided
in the probe storing groove by utilization of the elastically contacting
engagement portions. This enables the digital tester to be carried with
the probes kept in such a stored state. Accordingly, the probes are no
longer required to be stored in a box case or the like each time the
digital tester is carried with the user. Additionally, the digital tester
can be used immediately after removing the probes out of the probe storing
groove, thereby making the digital tester more handy to use.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in detail with reference to the following
drawings in which like reference numerals refer to like elements.
FIG. 1 is a perspective view showing a state in use of a digital tester
according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a state of the FIG. 1 digital tester
when being carried.
FIG. 3(a) is a front view of the digital tester shown in FIG. 1, FIG. 3(b)
is a left side view thereof, FIG. 3(c) is a right side view thereof, FIG.
3(d) is a top view thereof, and FIG. 3(a) is a rear view thereof.
FIG. 4 is a block diagram showing the inner configuration of the digital
tester of FIG. 1.
FIG. 5 is a flowchart showing an AC/DC determining operation in the digital
tester of FIG. 1.
FIG. 6 is a flowchart showing an operation of comparing an input signal and
thresholds in the digital tester of FIG. 1.
FIG. 7 is a chart showing a waveform of the input signal for explaining the
operation of comparing the input signal and the thresholds shown in FIG.
6.
FIGS. 8(a) and 8(b) are each a chart showing a waveform of the input
signal, for explaining the AC/DC determining operation shown in FIG. 5.
FIG. 9(a) is a block diagram showing the inner configuration of the digital
tester of FIG. 1, and FIG. 9(b) is an explanatory view showing potential
zones relating to a basic operation of the digital tester.
FIG. 10 is a circuit block diagram showing the configuration of a pulse
width measuring circuit in the digital tester of FIG. 1.
FIG. 11 is a timing chart for explaining a pulse width measuring operation
in the digital tester of FIG. 1.
FIGS 12(a) to 12(f) are explanatory views showing waveforms of those input
signals that may be input to the digital tester of FIG. 1.
FIG. 13 is a circuit block diagram showing the configuration of a pulse
width measuring circuit in the digital tester according to a modified
embodiment of the present invention.
FIG. 14(a) is a front view of a digital tester according to a modified
embodiment, for explaining an advantage of the configuration of a
measurement mode select switch of the digital tester of FIG. 1, and FIG.
14(b) is a right side view thereof.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
One embodiment of the present invention will be hereinafter described with
reference to the attached drawings.
A digital tester 1 of this embodiment includes, inside its body 10, a
measurement circuit such as a resistance measuring circuit provided with
buffer amplifiers and selectors for selecting a reference potential and a
reference resistance suitable for resistance measurement depending on each
of plural measurement modes. The measurement circuit corresponds to some
of the functions incorporated in NJU 9210 made by New Japan Radio Co.,
Ltd. The body 10 of digital tester 1 also holds an AC/DC determining and
switching unit for automatically determining whether an input signal is AC
or DC, and automatically switching over a measurement system between the
AC side and the DC side. After the switch-over of the measurement system
by the AC/DC determining and switching unit, a voltage value of the input
signal or the like is measured.
More specifically, the digital tester 1 of this embodiment comprises, as
shown in a block diagram of FIG. 4, a pair of probes 20a, 20b, a pull-down
resistor 31 connected to the positive probe 20a, a switching unit 32
connected downstream of the pull-down resistor 31, and a
rectifying/smoothing circuit 34 connected in parallel to an input path 33
leading from the pull-down resistor 31 to the switching unit 32. The
rectifying/smoothing circuit 34 has a rectifying circuit for full-wave
rectifying an AC when it is applied, and a smoothing circuit for smoothing
the rectified current, and serves as an input stage (measurement system)
in the case of an input signal 90 being AC. On the other hand, the input
path 33 serves as an input stage (measurement system) in the case of the
input signal 90 being DC. The switching unit 32 is schematically shown as
a switch 323 capable of selectively contacting a DC terminal 321 connected
to the input path 33 and an AC terminal 322 connected to the
rectifying/smoothing circuit 34. In the switching unit 32, the switch 323
is kept turned for connection to the DC terminal 321, as indicated by a
solid line, in a normal state where no signals are applied. Downstream of
the switching unit 32, there is connected a high-resolution A/D converter
37 for converting the input signal 90 into digital form and outputting it
as a measurement signal 95 to a measurement unit (not shown). The
high-resolution A/D converter 37 is of a double-integral type A/D
converter with high resolution covering 3200 counts, and is used for
measurement of the input signal 90.
The digital tester 1 of this embodiment also includes a high-speed A/D
converter 35 downstream of the switching unit 32. The high-speed A/D
converter 35 is of a sequential comparison type A/D converter which has a
lower resolution, covering 64 counts, than the high-resolution A/D
converter 37, but can operate at a high speed. The high-speed A/D
converter 35 converts the input signal 90 into digital form at a high
speed and outputs it as an AC/DC determination signal 91 to an AC/DC
determining unit 36. The AC/DC determining unit 36 comprises a
microcomputer and operates, based on operation programs stored therein, to
determine whether the input signal 90 is AC or DC, from the AC/DC
determination signal 91 output from the high-speed A/D converter 35, and
to control the switching unit 32 in response to a result of the
determination. More specifically, when the input signal 90 is determined
to be DC, the AC/DC determining unit 36 outputs a determination signal 92
for holding the switch 323 connected to the DC terminal 321 (i.e., in the
state indicated by the solid line). On the other hand, when the input
signal 90 is determined to be AC, the AC/DC determining unit 36 outputs a
switching command signal (another determination signal 92) for turning the
switch 323 to be connected to the AC terminal 322 (i.e., into a state
indicated by a broken line). In practice, the AC/DC determining unit 36
determines the input signal 90 to be AC when it is judged that a level of
the input signal 90 has exceeded a DC determination range (+3 V to -3 V),
defined by a threshold of 3 V (+3 V, -3 V), on both the positive and
negative sides for a predetermined comparison period, and to be DC, even
though it is actually AC, when the input signal 90 has not exceeded even
only one of threshold voltages of +3 V and -3 V. The AC/DC determining
unit 36 compares a level of the input signal 90 with the DC determination
range (+3 V to -3 V) twice during a predetermined time interval and
determines the input signal 90 to be AC when the level of the input signal
90 has exceeded the DC determination range (+3 V to -3 V) on both the
positive and negative sides in each of the two comparison periods.
The digital tester 1 of this embodiment further includes a reset signal
generator 38 for outputting a reset signal 93 to the high-resolution A/D
converter 37 when the input signal is changed over between AC and DC. In
response to the reset signal 93 output from the reset signal generator 38,
the high-resolution A/D converter 37 stops its processing operation and
then returns to an initial state for starting processing of the new input
signal 90 as soon as possible.
The above-described digital tester can be realized by adding to a digital
tester IC having functions incorporated in NJU 9210 made by New Japan
Radio Co., Ltd. the following elements: a high-speed A/D converter means
(i.e., the high-speed A/D converter 35) capable of operating at a high
speed, switching means (i.e., the switching unit 32) for switching over a
measurement system between the AC side and the DC side, AC/DC determining
means (i.e., the AC/DC determining unit 36) for comparing a level of the
input signal with a DC determination range defined by positive and
negative thresholds based on the AC/DC determination signal 91, and for
judging the input signal to be AC when the level of the input signal has
exceeded the DC determination range on both the positive and negative
sides for a predetermined comparison period, and for issuing the
determination signals 92 corresponding to AC and DC.
The digital tester 1 of this embodiment also includes a pulse width
measuring circuit for measuring a pulse width of the input signal inside
its body 10, in addition to a measurement circuit such as a resistance
measuring circuit provided with buffer amplifiers and selectors for
selecting a reference potential and a reference resistance suitable for
resistance measurement depending on each of measurement modes, the circuit
corresponding to some of the functions incorporated in NJU 9210 made by
New Japan Radio Co., Ltd. The pulse width measuring circuit is operated by
depressing a mode subselect button 12a under a condition that a
measurement mode select rotary switch 13 is set to a mark 14c for
selecting frequency measurement. The pulse width measuring circuit is
arranged, as schematically shown in a block diagram of FIG. 9(a) and an
explanatory view of FIG. 9(b) for explaining the operation principles,
such that a potential zone determining unit 40 is provided for determining
to which one of potential zones A, B, C an input potential VIN belongs.
These potential zones are defined by two reference potentials of +1 V and
-1 V. Unit 40 outputs a result of the determination as potential zone
signals Sa, and a pulse width is measured based on the potential zone
signals Sa output from the potential zone determining unit 40. More
specifically, the digital tester 1 of this embodiment comprises,
downstream of the potential zone determining unit 40, a start signal
generator 50 for detecting that the input potential VIN has exceeded one
of the reference potentials and changed from one to another potential
zone, and for outputting a start signal S1 for instructing the start of
the pulse width measurement. Also downstream of the start signal generator
50, a stop signal generator 60 for detecting, based on the potential zone
signals Sa output from the potential zone determining unit 40, that after
output of the start signal S1 from the start signal generator 50, the
input potential VIN has changed over in the potential zone again by
exceeding that reference potential that was exceeded for the first time,
and for outputting a stop signal S2 for instructing the end of the pulse
width measurement. Additionally, in a time counting unit 70, the number of
clock signals generated during the time from output of the start signal S1
to output of the stop signal S2 is counted by a counter 71 for measuring a
pulse width.
The circuit configurations and functions of the potential zone determining
unit 40, the start signal generator 50, the stop signal generator 60, etc.
will be described below in detail with reference to FIGS. 10 and 11.
FIG. 10 is a circuit block diagram showing the configuration of the pulse
width measuring circuit incorporated in the digital tester of this
embodiment, and FIG. 11 is a timing chart showing waveforms of respective
signals input to and output from the pulse width measuring circuit.
Referring to these figures, the potential zone determining unit 40 has a
first comparator 411 for comparing the input potential VIN with +1 V as a
first reference potential and outputting a signal "H" when the input
potential VIN is a positive potential larger than +1 V, and a second
comparator 412 for comparing the input potential VIN with -1 V as a second
reference potential and outputting a signal "H" when the input potential
VIN is a negative potential larger than -1 V. An output of the first
comparator 411 is applied, along with an output of the second comparator
412 after being inverted, to an AND circuit 421, which outputs a signal
"H" over a signal line 431 when the input potential VIN is a positive
potential larger than +1 V (i.e., belongs to the potential zone B). Also,
the output of the first comparator 411 and the output of the second
comparator 412 are both applied to a NOR circuit 422, which outputs a
signal "H" over a signal line 432 when the input potential VIN is in the
range of 1 V to -1 V (i.e., in the potential zone A). Further, the output
of the second comparator 412 is applied, along with the output of the
first comparator 411 after being inverted, to an AND circuit 423 which
outputs a signal "H" over a signal line 433 when the input potential VIN
is a negative potential larger than -1 V (i.e., belongs to the potential
zone C). Accordingly, to which of the potential zones A, B, C the input
potential VIN belongs at the present can be recognized by knowing over
which of the signal lines 431 to 433 the signal "H" is output from the
zone potential determining unit 40. Thus, the signals output over the
signal lines 431 to 433 become the aforesaid potential zone signals Sa.
The start signal generator 50 comprises a D latch circuit 51 to which the
signals transmitted over the signal lines 431 to 433 are applied, and a
start timing detecting unit 53 for detecting rise or fall of the input
potential VIN based on both the signals (reset timing zone signals Sb) of
which data are held by the D latch circuit 51 and the potential zone
signals Sa applied ov | | |
