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Description  |
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TECHNICAL FIELD
This invention relates to multifunction measurement devices, and more
specifically to devices provided with a single measurement circuit for
time-shared use in performing a plurality of diverse measurements, and
further provided with a plurality of displays for simultaneously
displaying results of the plural diverse measurements.
BACKGROUND ART
In the measurement art it is known to use a single meter for performing any
one of a number of different measurement functions. Such meters are known
as multimeters, and encompass volt-ohm meters (VOM) and vacuum-tube
voltmeters (VTVM) as illustrative examples. Multimeters which are
digitally controlled, or have digital output displays, are known as
digital multimeters (DMM). DMM's, similarly to other multimeters, include
a single metering device which, under control of a programmed controller,
is capable of performing at any one time a single measurement function of
a single parameter. The resultant function is displayed to a predetermined
accuracy on a single, multidigit, display.
The meters of the prior art, particularly DMM's, thus include sensitive
measurement circuitry as well as sophisticated control circuitry. In a
DMM, for example, a programmed microprocessor may be used as the
controller, together with an external keyboard or other device for
inputting control signals and user commands to set a desired measurement
function. Because a microprocessor controller is used, the number of
measurement functions which may be performed by the meter is significantly
increased. DMM's are thus expensive devices capable of sophisticated
individual measurements.
A typical measurement meter utilizes a set of input leads which include
probes for contacting circuit nodes at which desired parameters are to be
measured. As is known in the art, typically two such input leads are
required to measure an electrical parameter such as current or voltage. A
DMM controller is capable of causing the measuring device to perform
various functions for determining a number of characteristics of a
measured electrical signal parameter, such as determining current or
voltage frequency, peak or RMS AC values, DC values, impedance ratios, and
the like.
In many instances it is desirable or necessary to measure several different
circuit parameters, or to obtain several characteristics of one or more
measured parameters, at one or more circuit points. For example, it may be
necessary to determine the current or voltage at two separate circuit
points, or to determine both current and voltage at a single circuit
location. Alternatively, it may be necessary to measure frequency and
amplitude of a signal at a particular circuit location in order to
determine a frequency response of the circuit. Still further, it may be
necessary to determine the impedance of one circuit parameter and to
determine a voltage thereacross or a voltage or current at a different
circuit location.
In each of the above illustrations, in the prior art it is necessary to use
two prior art DMM's or other measurement devices for performing the
necessary measurements and for providing output displays indicative of the
measurement results. However, as noted above, the use of plural meters is
expensive because of complete duplication of an entire measurement system.
Thus, in some situations, a user may be tempted or required to use a
single meter in order to reduce expenses. In such an arrangement, the user
will provide a first input command to the controller (as by providing a
first setting for a measurement function key) to obtain a first
measurement, and thereafter will provide a second input command to the
controller (as by providing a second setting for the measurement function
key) to obtain the second measurement.
However, under these circumstances the measurements, which are performed by
a single instrument, are separated by a significant time lapse, which is
necessary for a user to enter two commands to the meter and/or to
reconnect the meter input leads to different circuit points. Moreover,
since only a single meter is used, the user is required to rely on his or
her memory to recall both measurements.
Clearly, measurements performed in such a manner may provide erroneous
results, in that values of two parameters are obtained only after
substantial time separation and in that one or both of the measured
parameters may be forgotten by the user or may be incorrectly recalled. In
those instances where substantially simultaneous readings are necessary,
and where it is necessary for a user to be provided with concurrent
displays of two or more measurement results, an expensive arrangement is
required in which plural meters are used.
There is thus a need in the prior art for an inexpensive device capable of
performing a plurality of measurements and of providing substantially
simultaneous and concurrent displays of the measurement results.
SUMMARY OF THE INVENTION
It is accordingly an objective of the invention to overcome the
difficulties of the prior art and to provide a single measurement
apparatus for measurement of a plurality of parameters or characteristics
thereof, and for concurrent display of a plurality of separate measurement
results.
It is a more specific object of the invention to provide an inexpensive
measurement apparatus, in which a single measurement circuit is used in a
time-shared fashion to measure a plurality of parameters or
characteristics, and in which the measurement results are concurrently
displayed on a plurality of displays.
It is yet another object of the invention to provide a measurement
apparatus in which a programmable microprocessor controller controls a
single measurement circuit to perform a sequence of measurements of
separate parameters provided thereto by one or more sets of input leads,
and in which the results of each of the measurements are displayed
substantially concurrently and simultaneously on predetermined, separate,
plural displays.
In accordance with the above and other objects of the invention there is
disclosed a measuring apparatus for measurement of a plurality of
characteristics of various parameters of a signal under test, provided to
the apparatus by a set of input leads. In the inventive measuring
apparatus a single measuring means is provided for shared use in measuring
the plural characteristics. The single measuring means measures only one
of the plural characteristics at any one time, and a control means is
provided for selecting the plurality of characteristics to be measured
sequentially by the single measuring means. The single measuring means
thus provides plural data representing the sequential measurements
performed under control of the control means. A plurality of displays are
provided for concurrent display of the data representing the plural
sequential measurements.
Preferably, the control means includes a programmable microprocessor which
is programmed to select at least first and second characteristics to be
measured by the single measuring means in sequence, so that the plural
displays indeed provide concurrent displays of the sequentially performed
measurements. The microprocessor may further be programmed to select at
least first and second functions to be performed by the single measuring
means on the electrical parameters provided to the single measuring means,
so that different characteristics of a single parameter may be measured
and displayed concurrently by the plural displays. The specific
characteristics or functions may be selected by a user through the use of
a keyboard or other input means to provide inputs to the programmed
microprocessor.
In accordance with another aspect of the invention, there is provided an
improvement to a measurement apparatus which includes a measurement
circuit, a microprocessor for the output signals therefrom, a display
driver, and a display. Pursuant to the invention, the measurement
apparatus includes a plurality of displays, and the microprocessor is
programmed to cause the measurement circuit to perform a sequence of
functions and to direct the results of specific functions to specific
displays.
In accordance with one form of the improvement, the microprocessor may be
programmed to cause the measurement circuit to perform a sequence of
functions on a sequence of input parameters provided thereto, and to
direct the results of specific functions to specific displays. Thus,
different measurements may be performed on different signals, and the
results may be concurrently displayed.
In accordance with another form of the invention, the microprocessor may be
programmed to cause the measurement circuit to perform a sequence of
functions on a single set of input parameters, and to direct the results
of specific functions to specific displays. Thus, different measurements
may be performed on the same signals, and the results may be concurrently
displayed.
These and other aspects, features and advantages of the invention will
become more readily apparent to one of ordinary skill in the art to which
the invention pertains upon reading the following description of the best
mode for carrying out the invention, together with the drawings
illustrating the same.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a block diagram of a prior art digital multimeter;
FIG. 2 discloses a flow chart for a microprocessor of the digital
multimeter of the prior art;
FIG. 3 shows a block diagram of a digital multimeter incorporating the
present invention;
FIG. 4 shows a flow chart for a microprocessor of the inventive multimeter;
and
FIG. 5 shows a front panel of a meter incorporating the features of the
invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to the illustration of FIG. 1, there is shown a block diagram
representation of a typical digita1 multimeter (DMM) of the prior art. As
is known to those of ordinary skill in the art, such meters operate by
providing an input signal on a set of input leads 10 to a measuring
circuit 12. The input signal may represent a voltage between two circuit
points, a current through a particular circuit element, or the like.
The measuring circuit 12 performs the appropriate function or functions on
the signal provided by input leads 10, generates a result, and converts
the result to a digital form for processing by a microprocessor 14. For
example, measuring circuit 12 may provide analogue-to-digital (AD)
conversion of the input signal, and may determine a peak value thereof.
One such conversion technique is described in U.S. Pat. No. 4,556,867,
assigned to the assignee hereof and incorporated herein by reference.
Alternatively, an RMS value of the input signal may be determined by
measuring circuit 12, or the number of zero crossings or polarity changes
in the signal may be measured to determine the frequency of the input
signal. Where current is to be measured, a voltage may be measured across
an appropriate internal impedance and where impedance is to be measured an
internally generated voltage may be applied to input leads 10 and the
resulting current determined therein.
The appropriate function may be performed by measuring circuit 12 on the
input signal parameters in response to a control signal provided by
microprocessor 14 to the measuring circuit 12. As hereinabove described, a
prior art DMM requires a manual function switch (not shown) to be changed
to an appropriate function setting, thereby to provide an appropriate
command to the microprocessor. Upon receipt of the appropriate command,
the microprocessor controls operation of the measuring circuit 12 to
perform the appropriate measurement on, or to obtain the appropriate
function of, the input signal.
Once the designated measurement has been made, or the desired function
performed, the desired characteristic of the signal (e.g., amplitude,
frequency, etc.) is provided by the measuring circuit in digital form to
microprocessor 14.
The microprocessor 14 is programmed to convert the settings of the manual
function switch to appropriate control signals for measuring circuit 12.
Moreover, the microprocessor 14 is programmed to transform the digital
information output by the measuring circuit 12 to a format suitable for
display on a display 16. The appropriately transformed signals are
provided to a display driver 18 in order properly to drive display 16.
Referring now to FIG. 2, there is shown a flow chart illustrating operation
of microprocessor 14. As described therein, after the instrument is
powered-up at step 20, at step 22 the microprocessor initiates the
measurement circuit to an appropriate measurement mode determined by the
setting of the manual function selecting switch (not shown). The measuring
circuit 12 is set to the proper mode in step 22 to perform the desired
function or to obtain the desired characteristic of the input signal. At
this point the microprocessor 14 enters the main measurement loop of the
DMM.
Thereafter, at step 24, the microprocessor 14 reads the output data
provided by the measuring circuit 12. At step 26 microprocessor 14
converts the data from measuring circuit 12 to suitable format for
display, and transfers the same to the display driver 18 at step 28. The
above sequence of operations is repeated until the microprocessor 14 is
instructed externally to change measurement mode. As seen at step 30,
microprocessor 14 determines whether or not an external mode change
command has been provided. If the result of the determination at step 30
is negative, operation resumes at step 24, and measurement of the same
characteristic of the input signal continues.
If the result of step 30 is affirmative, i.e., if an external mode change
command has been given, such as by changing the setting of the manual
function setting switch, operation of microprocessor 14 returns to step
22, wherein the new mode is set. Thus, the microprocessor 14 outputs
appropriate control signals for measuring circuit 12 to perform the
function newly set by the user. Thereafter, operation in the revised mode
continues in a loop, as described, until a further external mode change
command is detected at step 30.
Thus, the prior art DMM will repeatedly perform a single type of
measurement, will determine a single characteristic of an input signal,
and will provide a substantially continuous display of the single
measurement until input of an external mode change command.
Such operation may be alternately described by the Program Description
Language (PDL) or pseudo-code ilustration which follows:
power-up
loop
set measurement mode
repeat
get reading from measuring circuit
convert reading to display format
output reading for display
until different measurement mode selected
endloop.
In the present invention both the structure and operation of the prior art
are modified in order to provide automatic handling by a single instrument
of plural measurements which previously required multiple instruments.
More specifically, as previously summarized herein, a single measuring
circuit of a single DMM is used to perform at least two functions in
sequence, and at least two displays are provided on the single DMM to
display the plural results. Thus, by modifying the control program of the
microprocessor, by adding a display and by modifying the display driver,
there results a DMM which fully simulates operation of two or more DMM's
of the prior art.
Referring now to FIG. 3 there is shown an illustration of a preferred
embodiment of the present invention in which a single DMM provides
automatic performance of two functions and further provides displays of
the results of two measurements.
More specifically, a measuring circuit 32 receives input signals provided
on inputs 33. As noted from the Figure, the number of input leads is
increased, thereby to permit input of a plurality of different signals or
parameters to the measuring circuit. It should be understood, however,
that the inventive concept provides a plurality of characteristics for
display. The characteristics may be different functions of a single signal
or parameter, or may be one or more functions of different signals or
parameters input to the measuring circuit.
Thus, the three input leads 33 shown in FIG. 3 are only illustrative of one
type of operation, in which voltage signals from two circuit points are
input to the single measuring circuit, and in which a common reference
potential is similarly input. When it is desired to know the values of the
two voltages on two of the input leads relative to the common reference
value on the third lead, microprocessor 34 provides control signals to
measuring circuit 32 first to measure and determine the voltage value on
one of the input leads and thereafter to measure and determine the voltage
value on the other of the input leads.
The microprocessor 34 transforms the two output signals to a proper format
for display, and provides the same for display on a primary display 36a
and on a secondary display 36b. Display driver 38 receives the signals
from the microprocessor 34 and, under control thereof, passes the
appropriate signal to the appropriate display.
As is apparent from the foregoing, the number of input leads to measuring
circuit 32 may be increased over the prior art. However, such a
modification does not necessarily increase the complexity of the measuring
circuit. Rather, a simple controllable switching circuit (not shown) may
be provided at the input to measuring circuit 32. In response to control
signals from microprocessor 34 the switching circuit may provide inputs
from one or another of a plurality of sets of input leads to the measuring
circuit. The same control signals may be provided to the display driver in
order to activate the primary or secondary display, 36a or 36b, to display
the results of the measurement. Of course, the number of displays provided
in the inventive meter need not be limited to two.
Operation of the improved measurement apparatus of the invention is
illustrated in the pseudo-code below.
power-up
loop
determine primary and secondary measurement modes
repeat
set primary measurement mode
wait for measuring circuit to settle
obtain primary reading from measuring circuit
convert primary reading to display format
set secondary measurement mode
wait for measuring circuit to settle
obtain secondary reading from measuring circuit
convert secondary reading to display format
output primary and secondary readings to display
until different pair of measurement modes selected
endloop.
The same operation is illustrated in the flow chart of FIG. 4. As shown
therein, and as may be understood from the above pseudo-code,
modifications of the present invention from existing DMM control programs
are required in order to determine a sequence of measurement modes, in
response to an external input command. Thus, a single multi-function
selection keyboard may be provided, together with an input key identifying
a selected function as being a primary or secondary function. In response
thereto, at step 42 the microprocessor 34 identifies the specific displays
on which specific measured characteristics of the input parameters are to
be dispayed.
At step 44 begins a sequence of steps which result in a display output
indicating results of the primary measurement. Thus, at step 44a there is
provided a delay to permit the measuring circuit to settle. At step 44b
microprocessor 34 obtains from the measuring circuit the value of the
primary parameter or characteristic being measured, and at step 44c the
microprocessor converts this value to an output format suitable for
display. At step 46 begins a sequence of steps which result in a further
display output indicating results of the secondary measurement. Thus, at
step 46a there is provided a delay to permit the measuring circuit to
settle. At step 46b microprocessor 34 obtains from the measuring circuit
the value of the primary parameter or characteristic being measured, and
at step 46c the microprocessor converts this value to an output format
suitable for display. At step 48 both display outputs are provided to the
display driver 38 for output to, and display on, respective displays 36a
and 36b.
The following examples illustrate operation of the present invention. In
the several examples are provided settings for the primary and secondary
characteristics to be determined by the measuring circuit and to be
displayed on the primary and secondary displays of a dual function DMM.
The functions, as well as application of the particular dual measurement
arrangement, are also described.
______________________________________
Primary Secondary
Characteristic
Characteristic
Description
______________________________________
dBm Frequency Signal level (in dBm) on primary
display; frequency on secondary.
Used for frequency response mea-
surement.
Min/Max Continuous Show peak and/or null of signal,
while monitoring current signal.
Only one measurement needed for
two displays.
Touch/Hold
Continuous Capture and hold stable readings
on primary display, while showing
current input on secondary. One
measurement needed for two
displays.
V mA Measure voltage and current
simultaneously. Useful for power-
supply monitoring.
VDC VAC DC and AC volts, simultaneously.
Example use: supply voltage and
ripple.
VDC Ohms Alternate between ohms and volts
measurement. DC volts shown will
depend on how quickly the
measured circuit charges and
discharges during swapping of
modes; thus, capacitance of the
circuit may be inferred.
______________________________________
A meter incorporating the present invention is shown at 50 in FIG. 5.
Therein, inputs 33a and 33b are provided for the two sets of input leads.
The primary and secondary displays 36a and 36b generate the displays of
two characteristics, whether of the same electrical parameter or of two
different parameters, in accordance with a selection by keys 52. The
displays further provide identification of the characteristics being
displayed, as well as polarity signs therefor.
It should be understood that although operation in the illustrated
presently preferred embodiment provides for performance of both
measurement functions by measuring circuit 32 prior to output of display
signals, so that both displays are provided at a single operating step 48,
operation may be modified as follows. Specifically, the primary result may
be provided to display driver 38 in a separate step, which may be inserted
in the flow chart of FIG. 4 immediately preceding step 46. Similarly, the
secondary result may be provided alone, at step 48. Thus, the two displays
may be updated alternately, while the two measurements are nonetheless
concurrently displayed.
Further, although the sequence of measurements performed by the inventive
structure is illustrated by only two measurements described in the
foregoing illustration, it will be clear to one of ordinary skill that the
flow chart of FIG. 4 may be further modified to control measuring circuit
32 to perform any number of measurements on any number of parameters, and
to provide the appropriate displays. Moreover, although in the preferred
embodiment the number of displays and the number of measurements are
equal, it is possible that a lesser number of displays may be used for a
greater number of measurements, and that display indicators may be
provided for identifying the specific measurement results being displayed.
It is similarly possible to modify operation of the invention by using the
same for measurement of a smaller number of characteristics than the
number of displays provided.
It should thus be clear that the preferred embodiment of the invention is
provided for illustration and not limitation of the invention, which is
described by the claims appended hereto and which includes all the
variations and modifications to which the claims are legally and equitably
entitled.
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