John Fluke Mfg. Co., Inc.

Fluke Corporation

Larry E Eccleston

Chris W Lagerberg

David J Gibson

David E Bezold

Daniel B Carson

Walter W Prue, Jr

John Renner, Iii

John C Emery

A reversible test probe and test probe tip. In one embodiment, a test probe tip is reversible relative to a test probe body. The reversible probe has a first probe tip at a first end and a second probe tip at a second end. The test probe body has an opening operable to receive the first probe tip and the second probe tip. When the first probe tip is positioned in the opening, the first probe tip is electrically coupled to a metal device in the test probe body. When the second probe tip is positioned in the opening, the second probe tip is electrically coupled to a metal device in the test probe body. In another embodiment, a test probe having two test probe tips is reversible relative to a test lead.

Reversible test probe and test probe tip

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. The system utilizes a single ADC which is multiplexed between the low-resolution, high-speed reading and high-resolution, low-speed reading of the fully settled output of the null detector.

Precision analog-to-digital converter with low-resolution and

A voltage and resistance synthesizer includes a pulse width modulator (PWM) for synthesizing voltage and resistance values at a pair of terminals. A selector switch selects between a resistance synthesis mode, in which resistance values are synthesized from a single reference resistor, and a voltage synthesis mode, in which voltage values are synthesized from a single reference voltage. The pulse width modulator permits digital control words to be received which govern the synthesized value with 16 bit resolution. A low pass filter blocks the switching frequency components and provides a d.c. voltage which is the product of the duty cycle and the reference value.

Voltage and resistance synthesizer using pulse width modulation

A calibrator supplying electric parameters (viz voltage, current and resistances) over plural ranges to a meter to be calibrated comprises internal components for deriving each parameter over the plural ranges, an internal voltage reference, a DAC, a memory, an analog comparator and analog-to-digital converter. The internal components are connected in circuit with the internal voltage reference, analog-to-digital converter, comparator and memory for writing data signals into the memory indicative of calibration correction factors for the internal components. The internal components are connected in circuit with the memory and DAC so the DAC responds to the stored data signals indicative of the calibration correction factors to enable the value of the parameter supplied to the device by the internal components to be modified and corrected in accordance with the calibration correction for the parameter.

Apparatus for and method of internally calibrating an electrical

Calibrating errors of a variable gain amplifier used in an AC calibrator or a meter for measuring AC are determined for a gamut of frequencies. The gain of the variable gain amplifier is varied by adjusting the value of a variable resistor in discrete steps. A variable amplitude signal is applied to the amplifier while the resistor is adjusted in discrete steps so the amplifier derives a gamut of variable amplitude signals that are supposed to have predetermined values. The amplitudes of the gamut of variable amplitude signals derived by the amplifier are detected and compared with the values that the signals are supposed to have to derive a calibrating error signal of the amplifier for each variable resistor value. A gamut of variable frequency, constant amplitude signals is applied to the amplifier while the amplifier gain is constant. The amplifier has a tendency to derive an AC output signal having a different amplitude in response to different ones of the frequencies. The amplitude of the amplifier output for each frequency in the gamut of frequencies applied to the amplifier is detected and compared with the output signal of the amplifier while each frequency in the gamut of frequencies is applied to the amplifier with the amplitude of the amplifier output for one frequency in the gamut to derive an amplitude versus frequency response indication of the amplifier. The amplitude versus frequency response indication is modified by the derived calibrating error signal. The calibrated amplifier is used in a voltmeter or AC calibration so that the amplifier output is modified as a function of input frequency and gain setting.

Digital AC meter

Calibrating errors of a variable gain amplifier used in an AC calibrator or a meter for measuring AC is determined for a gamut of frequencies. The gain of the variable gain amplifier is varied by adjusting the value of a variable resistor in discrete steps. A variable amplitude signal is applied to the amplifier while the resistor is adjusted in discrete steps so the amplifier derives a gamut of variable amplitude signals that are supposed to have predetermined values. The amplitudes of the gamut of variable amplitude signals derived by the amplifier are detected and compared with the values that the signals are supposed to have to derive a calibrating error signal of the amplifier for each variable resistor value. A gamut of variable frequency, constant amplitude signals is applied to the amplifier while the amplifier gain is constant. The amplifier has a tendency to derive an AC output signal having a different amplitude in response to different ones of the frequencies. The amplitude of the amplifier output for each frequency in the gamut of frequencies applied to the amplifier is detected and compared with the output signal of the amplifier while each frequency in the gamut of frequencies is applied to the amplifier with the amplitude of the amplifier output for one frequency in the gamut to derive an amplitude versus frequency response indication of the amplifier. The amplitude versus frequency response indication is modified by the derived calibrating error signal. The calibrated amplifier is used in a voltmeter or AC calibrator to that the amplifier output is modified as a function of input frequency and gain setting.

Method of and apparatus for determining AC calibration errors and

The calibrator of an ohmmeter is compensated to eliminate any error as a result of the resistance of leads interconnecting terminals of the ohmmeter and a reference resistance to which the ohmmeter is connected during calibration. In accordance with one aspect of the invention, ohmmeter current flowing through a buffer amplifier biased by a floating power supply bypasses the ohmmeter leads. In accordance with another aspect, a current equal in magnitude but opposite in direction to the ohmmeter current is applied to the leads.

Method of and circuit for ohmmeter calibration

A hybrid circuit structure includes an electrical circuit and a heating circuit therefor, both mounted on a single substrate. Valuable substrate space is saved by mounting the electrical circuit components on one surface of the substrate and the heating circuit elements on the opposite surface. A temperature control circuit is included, preferably mounted on the same surface as the electrical circuit components. Precision resistors for gain control and other functions may be provided on a separate substrate which may be mounted directly to the single substrate or to a separator therebetween. The precision resistors are in thermal contact with the temperature controlled heating circuit, thereby further increasing the stability of the circuit.

Temperature controlled hybrid assembly

In a circuit utilizing a digital to analog converter, an amplifier receives two voltage levels of a digitally modulated input signal via two different switching circuits. Linearity of output signals provided by the amplifier is significantly improved by a circuit for effectively matching the resistances provided by the two switching circuits to the amplifier. A feedback circuit from the output of the amplifier, including a feedback amplifier, is used to withdraw from a switching device any current passing therethrough when ON, thus eliminating any effect of resistance of the switching device from the amplifier.

Linearity control circuit for digital to analog converter

A regulated voltage supply (10) for delivering a substantially constant voltage to a load (12) having a regulator (24) for controlling a raw voltage supply (22) to deliver that constant potential, wherein the supply includes sense leads (28 and 30) between the load and the regulator for monitoring load voltage, provided with a sense current cancellation circuit (30) for nulling sense current and preventing it from flowing through the sense leads; in a preferred implementation, including voltage-to-current converters (42 and 44) bridging respectively the output terminals (14 and 16) and the sense terminals (32 and 34), it provides a cancellation current equal in magnitude and opposite in direction to the sense current.

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Edmonds, WA, United States of America

Larry E Eccleston