Abstract: A variable color digital measuring instrument sequentially exhibits measured values in a color in accordance with the relation of the present measured value to a past measured value. A memory, controlled by a timer, is provided for storing data representing the past measured value. A comparator compares the present measured value with the data stored in the memory and develops a comparison signal accordingly, which is then used to control the color of the presently exhibited measured value.

Abstract: A rapid low voltage testing apparatus for detecting sequentially a plurality of electrical components of an electrical circuitry device for at least one of a plurality of predetermined low voltage levels. The rapid low voltage testing apparatus comprises a first multi-position switch having an output for sequentially outputting one of a plurality of input voltages; and a second multi-position switch having an output for sequentially outputting one of a plurality of predetermined output voltage levels which adjusts the sensitivity of a voltage detection circuit to the one of the plurality of predetermined output voltage levels. Upon a detection of a match between the first multi-position switch output and the second multi-position switch output, an indicator notifies the operator of the testing apparatus that one of the plurality of low voltage levels has been detected.

Abstract: An ultra high accuracy voltage measurement system utilizes a Josephson junction voltage generator whose voltage is controlled by a high precision frequency.

Abstract: A digital multimeter is provided with a highly reliable seal at a connection interface between an upper and lower enclosure forming an enclosure. The multimeter also has a highly reliable seal at peripheral boundaries of operating elements disposed on a surface of the enclosure thereby providing a highly-reliable, water-proof and dust-proof mechanism at a low cost. A packing serves as an elastic sealing material and is disposed at the connection interface between the upper enclosure and the lower enclosure. The packing is pressed and crushed in a slant direction relative to the direction of the thickness of the enclosure thereby providing a sealing mechanism at the connection interface. The periphery of a rubber key serving as an operating element is sealed by a double sealing mechanism comprising an uneven face formed on a peripheral side and an even face formed on the upper enclosure.

Abstract: A digital tester includes structure for: automatically effecting AC/DC determination of an input signal and subsequent AC/DC switch-over of a measurement system, enabling high-response measurement; measuring a pulse width using a simple construction and having high reliability, by handling changes in an input potential as changes in potential zones; and storing the probes and test leads so that the digital tester is easier to handle for a higher degree of convenience in use.

Abstract: A system for determining a property, such as conductivity, of a material in which a sensor provides a square wave sensor output signal the value if which is selected to the proper in response to a square wave driver signal. The sensor output signal is compared with a feedback signal to produce an error signal. A forward circuit responds to the error signal and provides an in-phase component thereof which is integrated to provide an integrated DC output signal. A feedback signal provides an in-phase square wave feedback signal the peak-to-peak amplitude of which has a precisely selected relationship with the integrated DC output signal for comparison with the square wave sensor output signal to reduce the error signal to zero. The integrated DC output signal can be digitized and suitably processed to provide a signal which represents the property of the material to a high degree of accuracy.

Abstract: An analog-to-digital converter utilizes low-resolution and high-resolution conversion paths for precision voltage measurements. A first conversion made using a comparatively low resolution ADC is used to predict the reference voltage to one input of a null detector that receives the input voltage on another input, and effectively magnifies the voltage difference between its inputs. In a preferred embodiment, the duty cycle of a pulse-width modulator is adjusted to precisely adjust the reference voltage to provide a nulled (or near null) reading from the null detector. A low resolution ADC then converts the voltage from the null detector, which when added to the reference voltage, yields a final reading with 18-bit to 22-bit accuracy. The preferred embodiment is implemented to read the output from a pressure transducer and employs a binary search technique to rapidly adjust the duty cycle of the pulse-width modulator.

Abstract: A digital multimeter includes a microprocessor control and a keyboard input. The microprocessor functions to control the display of parameters measured by the meter and displays such measured parameters. The keyboard includes switches to allow the user to select a parameter which is desired to be measured as well as a range of values for that parameter for use in measuring parameters of a device under test connected to the multimeter. The microprocessor communicates with the keyboard and functions to control a resistor and switch network to configure the multimeter to test selected parameters within selected ranges. The multimeter incorporates an overload protection function which compensates for an over-large voltage on the input leads of the multimeter, thus preventing damage to the circuit and to the multimeter.

Abstract: An analog isolation barrier data acquisition system comprises a plurality of satellite sampling modules which are referenced to remote grounds for sensing direct current (dc) voltages which are referenced to these remote grounds. The satellite sampling modules are capable of monitoring several signals which are referenced to its local ground system, and are comprised of three functional blocks: a signal selection block which allows proper selection of the dc voltage signal to be monitored; a modulation block which modulates the selected dc voltage signal to produce a modulated waveform; and a barrier coupling block which transfers waveform information contained in the modulated waveform from the local floating ground reference system to an analog ground reference system.

Abstract: A control system for RF (radio frequency) power measurements eliminates calibration requirements and compensates errors due to nonlinear detector characteristics and temperature drifts by using feedback to automatically adjust the power of a fixed frequency temperature stable reference signal to equal the power of the unknown incoming signal. Since the power of the reference can be precisely known, the power of the unknown signal is determined. The reference signal path has an identical electrical transfer function as the measurement input signal path so that nonlinearities and temperature variation in the measurement path are exactly offset by the corresponding variations in the feedback reference path.

Abstract: An AC input signal is sampled with a plurality of sets of equally spaced samples, but whose sample interval between the samples does not exactly divide the period of the input signal. Nevertheless, and error cancellation technique allows ultra accurate measurements to be made. The samples in each set of the plurality of sets are supplied to a computational process that extracts some parameter; e.g., RMS voltage. The extracted parameter is in error, owing to the non aliquot nature of the sampling. The size of the error is related to, among other things, where on the input waveform the associated set began. The error is a period AC function of that starting location. By arranging for n-many sets to start at phase differences of 1/n apart on the input waveform, a series of n-many parameter.sub.i are obtained that are each of the form [result.sub.i +error.sub.i ]. Thus, the error.sub.i are sampled at aliquot locations along an error function, and therefore sum to zero. Thus, averaging the parameter.sub.

Abstract: A method for measuring various measurable variables with a multimeter includes specifying one of a plurality of measurable variables to be determined through a position of a measurement range switch and/or through a selection between various input connections respectively assigned to the measurable variables. Input circuits are assigned to respective measurable variables. A preliminary test is performed for at least one of the measurable variables to check if an input circuit is suitable for picking up an applied test signal, before an actual main measurement is carried out. A given input circuit is enabled for picking up the test signal only if the preliminary test has shown that the test signal is suitable for the given input circuit. An error signal is issued if a test signal being unsuitable for the given input circuit ensues. A multimeter for measuring various measurable variables includes a measurement range switch and/or various input connections for specifying a measurable variable to be picked up.

Abstract: A voltage measuring instrument which generally includes signal conditioning circuitry coupled to input probes for protection against overvoltages and processing of input voltage signals. A VAC/VDC control circuit will determine whether AC or DC voltages are present, and will positively indicate when no voltage is present in a test circuit. The metering circuit of the invention will thereby automatically determine the proper mode of operation for the type of voltage present in a test circuit so as to eliminate user selection of operating parameters and possible errors. Further, the metering circuit is adapted to generate a proper reference voltage for the measured voltage automatically, to again eliminate selection of a voltage range by the user. A power supervision circuit is adapted to automatically shut off the measuring instrument after a predetermined amount of time has elapsed, and will automatically shut off power in the event that available battery power drops below a given level.

Abstract: A multi-function, multi-mode switch for an instrument that changes the instrument between primary and secondary functions and between first and second modes of operation within the primary and secondary functions. The instrument changes from the first mode of operation to the second mode of operation when the switch is actuated for a first period of time. The instrument changes from the second mode of operation to the first mode of operation when the switch is activated for a second period of time. The instrument changes between the primary and secondary functions when the switch is operated for a third period of time. The switch controls a program that instructs the instrument to perform the appropriate operations. The program also instructs the instrument to confirm that an operation has occurred via audible and visual feedback.

Abstract: An electrometer capable of measuring small currents without the use of a feedback resistor which tends to contribute a large noise factor to the measured data. The electrometer eliminates the feedback resistor through the use of a feedback capacitor located across the electrometer amplifier. The signal from the electrometer amplifier is transferred to a electrometer buffer amplifier which serves to transfer the signal to several receptors. If the electrometer amplifier is approaching saturation, the buffer amplifier signals a reset discriminator which energizes a coil whose magnetic field closes a magnetic relay switch which in turn resets or zeros the feedback capacitor. In turn, a reset complete discriminator restarts the measurement process when the electrometer amplifier approaches its initial condition. The buffer amplifier also transmits the voltage signal from the electrometer amplifier to a voltage-to-frequency converter.

Abstract: A high voltage measuring system with very high input impedance. The system measures a high voltage source under test by developing a control signal which is proportional to the differential voltage between the high voltage source being tested and an adjustable high voltage reference. This control signal is fed back into a controller which adjusts the reference source so as to match the reference source with the source under test. When the controller detects that matching has occurred, it measures the reference source. By measuring the reference source, as opposed to measuring the source under test directly, the system avoids loading down the source under test.

Abstract: A test lead socket indicating device is used for a volt-ohm-milliammeter (VOM) having a select input which is operable to set the VOM in a voltage, current or resistance measuring mode, a common input socket, a voltage socket, a resistance socket and a current socket. The test lead socket indicating device includes an indicator unit provided on the VOM and having a voltage indicator lamp disposed adjacent to the voltage socket, a current indicator lamp disposed adjacent to the current socket and a resistance indicator lamp disposed adjacent to the resistance socket. A counter unit has an input terminal connected to the select input. The counter unit has a digital signal output which is incremented each time the select input is operated. A decoder unit receives the digital signal output from the counter unit. The decoder unit activates one of the voltage, current and resistance indicator lamps according to the digital signal output.

Abstract: The present invention relates to a measurement circuit for providing the digital value of an analog electrical signal. The digital measurement circuit for measuring an analog electrical signal produces a measurement signal (M) and includes an amplifier (1) which receives said electrical signal (I), followed by an analog-to-digital converter (2) which delivers digital data (N). The gain of the amplifier (1) is controlled by a control signal (C) and said gain can take up at least two values. The measurement circuit further includes a control unit (3) producing said control signal (C) and storing the digital data corresponding to different gain values, and includes means for producing the measurement signal (M) on the basis of said digital data (N).

Abstract: A cardiograph has a remote front end which is connected to a host via a cable. The front end includes a clock and an analog-to-digital converter. The converter periodically holds and samples patient ECG signals. Each conversion takes place within the same fixed length of time. A clock signal is transmitted to the host on one of the conductors in the cable while digital words, each of which represents a sampled value of the ECG signal, are serially transmitted on another conductor in the cable. The clock signal synchronizes ac voltages applied to several power supplies with the sampling rate of the converter so that the ECG signal is sampled at the same phase of each ac voltage applied to the power supplies. The sampling thus occurs at the same phase, and thus the same amplitude, of each periodic noise cycle induced by the power supply electromagnetic fields. The periodic noise is thus removed from the sampled signal while a dc offset equal to the amplitude of the periodic noise at the sampling phase is added.

Abstract: A scale is disclosed for a measuring instrument in which a plurality of display elements, specifically liquid crystal display elements which are energizable to a visible condition or an enhanced visible condition selectively to provide a linear scale or a logarithmic scale. The scale is divided into decades which specifically have twelve display elements of which ten are selectively energizable to provide the linear scale and then to provide the logarithmic scale.

Abstract: An apparatus (10) for transmitting a patient physiological signal is provided. A converter (12) includes a front end circuit (28) that receives and conditions a patient physiological signal, V.sub.P, and produces conditioned signal, V.sub.C. A magnitude of V.sub.C is proportional to an amplitude of V.sub.P offset by a negative DC voltage. A track and ramp circuit (30) receives V.sub.C and produces a tracking voltage, V.sub.T. A magnitude of V.sub.T is inversely proportional to the magnitude of V.sub.C when the track and ramp circuit is in a tracking mode. A controller (16) includes a clock that produces clock pulses, V.sub.CK and a divider (38) that divides the clock pulse frequency and produces a trigger pulse, V.sub.TRIG. A leading edge of the V.sub.TRIG pulse starts a counter (40) counting V.sub.CK pulses. The leading edge of an optically transmitted V.sub.TRIG pulse is applied to the latch circuit (32), which produces a ramp command voltage, V.sub.R. A high V.sub.

Abstract: Disclosed is apparatus and method for converting and displaying the total RMS and AC RMS values of a signal in a voltmeter. This conversion is accomplished in a system having a processor and a plurality of signal conversion stages. The first signal conversion stage comprises a low-pass filter to extract the DC component of the input signal followed by an analog-to-digital converter to convert the DC component into a digital value. The remaining signal conversion stages convert the AC component of the input signal to a series of smaller and smaller DC average values. Typically there are five of these AC conversion stages, each comprising a high-pass filter connected to a full-wave rectifier which is in turn connected to a low-pass filter followed by an analog-to-digital converter. The first AC stage high-pass filter is connected to the input signal and subsequent AC stage high-pass filters are connected to the output of the full-wave rectifier of the previous AC conversion stage.

Abstract: Test meters, particularly of the type employed for testing electrical circuits, e.g. multimeters, are improved in operational efficiency. In one aspect, remote selection of test and/or report format frees the operators hands for concentration on a test piece. In another test results or format information are conveyed as synthesized speech in any of a number of selectable formats. By combining both aspects in a hand-held multimeter, a high degree of interaction between the operator and the meter is achieved.

Abstract: A bipolar analog voltage is converted into a digital signal by sensing the polarity of the voltage and selectively supplying a bias voltage to an analog-to-digital converter, which can preferably be a charge balanced voltage to frequency converter, as a function of the sensed polarity. The voltage to frequency converter has a double valued variable frequency output with a discontinuity at zero volt such that the converter derives a maximum output frequency for a maximum positive voltage and also for a negative value slightly displaced from zero; the voltage to the frequency converter minimum output frequency is derived from positive voltages slightly greater than zero and for maximum negative voltages. The converter output frequency and the sensed polarity are supplied to a frequency to digital converter which derives an output signal having a bit representing the polarity of the analog voltage and additional bits indicative of the magnitude of the analog voltage.

Abstract: An improved type of vector impedance measuring instrument is disclosed. The vector impedance is a vector current relative to (or normalized to) a pertinent voltage. A transducer for converting the impedance to corresponding current and voltage includes a digital signal processing unit. The vector value of the current is derived from parameter values set in the digital signal processing unit. This configuration eliminates a conventional vector ratio detector, which conventionally followed the transducer, saves cost, reduces size, and achieves high performance. Also, algorithms implemented in the digital signal processing unit are easily modified for a variety of transfer functins phase compensation, and corrections.

Abstract: A digital voltmeter which converts an input signal having an amplitude to be measured into a digital signal from which a series of pulses is developed having a duty cycle which is proportional to the amplitude of the input signal. These pulses are supplied are supplied to a digital-to-analog converter which develops an analog signal having an amplitude proportional to the duty cycle of the pulses and is compared with the input signal to stabilize the digital signal at a value corresponding to the amplitude of the input signal.

Abstract: The invention provides an electronic gage amplifier which converts sinusoidal signals representing measurement data from a gage head into a visual display of measurement data. The measurement signals are received by the amplifier at the input of a mixer where they are combined with a coarse adjustment signal. The coarse adjustment signal, which is provided by a multiplying digital-to-analog converter (MDAC) which is controlled by a microcomputer, yields a fine adjustment signal when mixed with the measurement signal. The resulting fine adjustment signal is amplified by a preamplifier, translated into a steady-state voltage by a programmable-gain demodulate-and-hold circuit (D/H) and converted to a digital word by an analog-to-digital converter (ADC). The microcomputer further causes a known reference signal to be processed through the MDAC, mixer, preamplifier, D/H, and ADC.

Abstract: There is provided according to the invention a method and apparatus for eliminating or minimizing the error due to amplifier offset or drift error in an integrating dual slope analog-to-digital converter. The converter is provided with a switching and control arrangement whereby the integrating capacitor is charged for one-half of the predetermined charging time as a function of the sum of the levels of the unknown signal and the error signal. The integrating capacitor is charged for the remaining half of the predetermined time period as a function of the difference of the levels of the unknown signal and the error signal so that the capacitor reaches a level of charge which is a function of the level of the unknown signal substantially unaffected by the level of the error signal.

Abstract: A high resolution analog to digital (A/D) converter amplifies and filters a magnitude difference between a pulse width modulated offset voltage and an input voltage to produce an amplified filtered difference voltage, the duty cycle of offset voltage modulation being adjusted such that the magnitude of the difference voltage is within a narrow input voltage range of a recirculating remainder A/D converter. The amplified, filtered difference voltage is converted to representative digital data by the recirculating remainder A/D converter. A microprocessor, which controls the offset voltage, combines the result with the magnitude of the offset voltage to produce a comparatively high resolution digital representation of the input voltage.

Abstract: A variable electrical current in a first winding on a magnetizable core produces a magnetomotive force in the core. A second core winding produces an opposing magnetomotive force digitally adjustable periodically by a third core winding, a pair of switches and a flip-flop coupled to a center tap for alternately closing such switches when triggered to opposite states. The flip-flop is triggered between opposite states when the third winding current reaches a particular magnitude. In each cycle, the time differences for producing the particular magnitudes and the opposite polarities are dependent upon the remanent core flux. Such time differences are counted digitally upwardly and downwardly for opposite polarities. The second winding current is adjusted digitally in each cycle in a direction to minimize such count. The magnitudes of successive adjustments may be compared periodically by adaptive tracking techniques to control the magnitudes of subsequent adjustments.

Abstract: Apparatus for measuring current over a wide range generates an eight bit accurate, 16-bit dynamic range digital signal from a current transformer secondary. Two signals proportional to the rectified secondary current, one generated by a large burden resistor and the other by an amplifier with programmable gain and an overrange indication, are applied through a multiplexer to an eight bit analog to digital converter which has three selectable reference voltages. A microprocessor selects the input signal, converter reference voltage, and one of four levels of amplifier gain which provide the greatest resolution for the magnitude of the current being measured, and provides an appropriate scale factor, from 2.sup.0 to 2.sup.8, for the eight bit accurate digital signal generated by the analog to digital converter.

Abstract: A meter is provided which visually displays and audibly announces values which are detected. A switch is manually operated to maintain the visual representation until the audible announcement has been generated.

Abstract: A method for measuring the difference between two voltages with a time-controlled measuring cycle includes feeding two voltages with opposite polarity to one integrator, initially integrating up one of the voltages and subsequently integrating down the other of the voltages with the integrator in an integration cycle, and delivering a voltage corresponding to the mean valve of the difference between the voltage at an output at the conclusion of the integration cycle.

Abstract: A method and apparatus for fixing an instantaneous measured value performs the steps of creating measured values as a mean value of a set number of individual measurements, recording sequential measured values after initialization in a cycle determined by a flow control, checking with a control device if a new measured value exceeds a base value and if the difference between the two latest measured values lies within a given limit range, before fixing the respective new measured value, and checking with the control device if the difference between the individual values resulting from the latest two individual measurements lies within the given limit range and if a fixing of the last measured value and/or individual value takes place when the differences between the mean values and the differences between the individual values lie in the respective given limit range.

Abstract: A digital panel meter adapted for replacement of a standard analog panel meter and designed to selectively receive different ranges of input signals such as AC or DC input signals. The meter circuitry employs an analog-to-digital converter having multiple digits, an input circuit including a range circuit, an operational amplifier and filter circuitry. A relay is tripped for signaling the attaining of a trip point. An audible alarm is provided that may be enabled or disabled and that may be operated in either continuous or short term modes.

Abstract: An analog-to-digital converter is provided based on supplying various multiplexed inputs, including analog input signal samples, to a voltage-to-current converter charging and discharging an integrated capacitor. A comparator determines the status of this capacitor to a control counter to provide digital representations.

Abstract: A method of using a waveform to sound pattern converter that produces an audible image of a time dependent signal by digitizing the signal to produce a plurality of discrete level signals, and produces a different audible tone signal for each level of the discrete level signals. A speaker is provided for producing audible sounds and circuitry is provided for driving the speaker to produce an audibly perceptible reference frame indicative of a predetermined time duration and also for driving the speaker with the audible tone signals such that the audible tone signals have the same time orientation with respect to each other as the discrete level signals have in the time dependent signal. The sounds are provided to listener to enable the listener to distinguish the shape of the time dependent signal based on the position and time relation of the tone signals relative to the reference time frame signal.

Abstract: An electronic interface device is provided for use between a sensor and a display unit, including a controllable generator which delivers a signal to the display unit and is connected to an input of a comparator whose other input receives the output signal of the sensor. The output of the comparator controls the up counting or the down counting of an up-down counter of clock pulses. The sign output of the up-down counter controls the generator.

Abstract: Analog-to-digital conversion in which a coarse digital representation of an input analog signal is converted to a coarse analog representation, and the difference between the original analog signal and the coarse analog representation is determined. A ramp waveform signal is generated, and a change in that waveform by an amount substantially equal to the difference between the original analog signal and the coarse analog representation is sensed. A plural bit fine digital signal corresponding to the sensed change of the ramp waveform is produced. The combination of the coarse and fine digital signals constitute the digital representation of the input analog signal. In one embodiment, the ramp waveform is increased until it is equal to the difference between the analog signal and the coarse analog representation, whereupon the ramp waveform is digitized.

Abstract: A digital measuring method an apparatus for displaying quasi-analog measured values performs the steps of displaying a measurement scale and interconnected triggerable indicator segments on a display having a given indicator center distance, representing a measured value to be indicated by the position of the indicator segments, controlling the resolution of the quasi-analog measured value display in dependence of the number of indicator segments triggerable within a measurement period to be represented, setting the resolution substantially lower than a resolution with which an A/D converter connected to the display operates, and subjecting a control command for triggering an actual indicator segment to a hysteresis, which assures that a switchover from a previous indicator segment to an actual indicator segmet does not take place until the actual measured value has increased or decreased by substantially more than one-half the given indicator center distance.

Abstract: A multimeter with variable color digital display indicates measured values in digital format and in variable color. The multimeter includes a color control circuit for selectively controlling color of the digital display in accordance with the measurement quantity, method, unit, mode, function, range, location, modifier, control, limits, and the like. A color converter circuit is disclosed for converting analog voltage to variable color.

Abstract: Power from an alternating signal having a frequency variable in a wide and relatively high range such as approximately 10 megahertz to 40 gigahertz is indicated by a detector. To calibrate the detector, an alternating signal is introduced from a source to a bridge including a regulating member such as a thermistor. The bridge also receives a direct voltage. The thermistor is maintained at a particular impedance such as 400 ohms, regardless of the power provided by the alternating signal, by varying the magnitude of the direct voltage. The alternating signal, which is regulated in accordance with the dc voltage, is also introduced to the detector. The detector output is introduced to a data processing unit which processes the detector output to indicate the power from the alternating signal. The output from the data processing unit is converted to an analog signal which is combined with the signal from the bridge to produce a resultant signal.

Abstract: In order to display a measured value, a digital measuring instrument is provided with a digital display and an analog display. The display value emitted by the digital display is fixed during a predetermined holding time. The analog display displays the difference between the current measured value and the particular display value of the digital display at the time. The current measured value may be read off at the beginning of a new holding time on the digital display, or it can be ascertained as the sum of the values of the digital and analog displays.

Abstract: Device for measuring voltage by sampling, including a voltage metering sampling means (2) driven by a pilot frequency generator (12), an amplifier (3) to amplify the sampled signal and a signal processing unit (6) to evaluate the amplified signal in accordance with the prescribed measuring task. The device, in accordance with the invention, contains an auxiliary oscillator (14) which produces an auxiliary signal, as well as an amplifier (3) with adjustable amplification, which is located between sampling unit (2) and signal processing unit (6), and a differential circuit (5). The auxiliary signal on one side, together with the voltage to be measured, is connected to signal input (17) of sampling unit (2), on the other side by means of a phase shifter (13) to an input (25) of differential circuit (5).

Abstract: A converter of the flash type includes means for amplifying and d.c. level shifting portions of the input analog waveform fed to each A to D converter unit to provide each converter unit with a full voltage input swing relative to the reference voltage for conversion, thereby producing a more accurate digital output.

Abstract: An analog to digital converting device which can convert analog input signals individually into digital values of accurately corresponding magnitudes even when there is some difference in the input signals. The device comprises an integrating circuit which includes an operational amplifier for receiving an analog signal, an integrating capacitor connected between an input terminal and an output terminal of the operational amplifier, and a reset switch connected in parallel to the integrating capacitor. The integrating circuit is controlled to first perform an integrating operation and then an inverse integrating operation. A comparator is connected to an output terminal of the integrating circuit. A diode or transistor is connected in parallel to the integrating capacitor for limiting an amount of charge to be accumulated in the integrating capacitor by an inverse integrating operation to below a predetermined value.

Abstract: A subranging A/D converter generates high and low voltages using first and second DACs. A voltage divider receives the high and low voltages to generate plural reference voltages. A bank of comparators compares the analog voltage which is to be converted to each of the reference voltages, and a clocked logic circuit generates an intermediate digital signal indicative of the analog value relative to the plural reference voltages. The intermediate signal is used to decrement the high voltage and increment the low voltage, so that the reference voltages produced by the voltage divider assume subrange values. The process is repeated for as many clock cycles as is required to converge the high and low voltages to equal the analog voltage.

Abstract: The direction of change of an analog signal which is digitally displayed on a digital display can be immediately determined at a glance by providing a change-display in the vicinity of the digital display, which digitally displays the analog signal value. The change-display displays whether the analog input signal is increasing or decreasing by comparing the present value of the input signal with a previous value thereof. This comparison may be effected by integrating the input signal and comparing the integrated input signal with the input signal or by differentiating the input signal or by using a sample and hold circuit to hold a previous input signal value which is then compared with the present input signal value.

Abstract: Analog-to-digital conversion in which a coarse digital representation of an input analog signal is converted to a coarse analog representation, and the difference between the original analog signal and the coarse analog representation is determined. A ramp waveform signal is generated, and a change in that waveform by an amount substantially equal to the difference between the original analog signal and the coarse analog representation is sensed. A plural bit fine digital signal corresponding to the sensed change of the ramp waveform is produced. The combination of the coarse and fine digital signals constitute the digital representation of the input analog signal. In one embodiment, the ramp waveform is increased until it is equal to the difference between the analog signal and the coarse analog representation, whereupon the ramp waveform is digitized.

Abstract: A bipolar analog voltage is converted into a digital signal by sensing the polarity of the voltage and selectively supplying a bias voltage to an analog-to-digital converter, which can preferably be a charge balanced voltage to frequency converter, as a function of the sensed polarity. The voltage to frequency converter has a double valued variable frequency output with a discontinuity at zero volt such that the converter derives a maximum output frequency for a maximum positive voltage and also for a negative value slightly displaced from zero; the voltage to the frequency converter minimum output frequency is derived from positive voltages slightly greater than zero and for maximum negative voltages. The converter output frequency and the sensed polarity are supplied to a frequency to digital converter which derives an output signal having a bit representing the polarity of the analog voltage and additional bits indicative of the magnitude of the analog voltage.