Keithley Instruments, Inc.

John G Banaska

Gregory Roberts, Ii

Wayne C Goeke

Gregory Sobolewski

Michael P Minneman

Kenneth A Reindel

Gary K Bish

David J Howarth

Ks Bhaskar

Bob Spinks

Andy J Creque

Michael Atwell

A method for compensating for a dielectric absorption effect in a measurement configuration during measurements by an instrument having measurement terminals includes providing a feedback loop in the instrument, the loop having a gain adjustment and a simulation impedance and being adapted to provide a signal counter to the dielectric absorption at the measurement terminals; applying a transient calibration signal to the test terminals for at least two values of the gain adjustment; measuring a response to the calibration signal for each of the at least two values; and determining an operating value of the gain adjustment based on the measured responses. The operating value is used for subsequent measurements by the instrument, the simulation impedance modeling the dielectric absorption characteristics of the measurement configuration.

Dielectric absorption compensation for a measurement instrument

An electronic instrument having in its circuitry a specific solid state switch that exhibits detrimental current leakage at elevated temperatures, a variable voltage device in the instrument connected to the specific switch, the variable voltage device being capable, at an experimentally determined voltage setting, of zeroing out the leakage current in the specific switch, the variable voltage device being set at a voltage setting determined experimentally using said specific switch at an elevated temperature thereby temperature compensating said specific switch.

Output leakage compensation and method for implementing the same

A circuit for controlling a voltage across a device and permitting measurement of a current through the device includes a sense impedance in series combination with, the device, a sensed voltage measured across the sense impedance being representative of the current through the device; a capacitive stability element in parallel combination with the sense resistance, the capacitive stability element being virtually absent by connection to a virtual version of the sensed voltage when the device has a first capacitance and being present when the device has a second capacitance, the second capacitance being larger than the first capacitance.

High capacitance load testing

A range-changing circuit includes an array of graduated impedances in serial relationship, and a voltage sensing and limiting switch across one of said impedances. The switch limits the voltage across said one of the impedances in response to a voltage sensed by the switch.

Automatic ranging current shunt

A circuit for alternatively controlling a current through a device and permitting measurement of a voltage across the device or controlling a voltage across the device and permitting measurement of a current through the device includes a sense impedance in series combination with the device, an error amplifier selectable to control the controlled current or voltage, the error amplifier providing an error signal for the control, and a floating buffer driving the series combination in response to the error signal.

Source measure circuit

A low leakage solid state switch for range-changing uses a pair of low leakage diodes switched to a reference voltage to block leakage through the switch when it is in the 'off' state.

Low leakage solid state switch

An integrated modular measurement system includes a universal module which is operable to receive measurement data from one or more measurement sensors, convert the measurement data into a value that represents a characteristic being measured and indicate the value to a user in a plurality of signal formats. An input module is coupled to the universal module and is operable to house one or more measurement sensors. The universal module and input module together operate to provide versatile measurement acquisition. A custom calibrated sensor module includes one or more sensors and a memory associated with and local to the one or more sensors. The memory contains calibration information which is uniquely associated with the sensors. In taking a measurement, the calibration information associated with the sensor taking the measurement is accessible for conversion instructions to thereby improve conversion accuracy. A method of interfacing a universal module to a plurality of measurement sensors includes coupling one of the measurement sensors to the universal module and identifying the measurement sensor being used. In addition, the universal module is configured in response to the identification of the measurement sensor to thereby facilitate accurate and versatile measurement acquisition for a plurality of measurement sensors.

Integrated modular measurement system having configurable firmware

A current in a circuit is measured without breaking the circuit. A relatively low resistance element in the circuit such as a component lead is chosen. A current is forced through the element and the voltage drop measured. Another current is forced through the element and the voltage drop measured. The values of these currents and voltages are used to determine the original current in the circuit.

In-circuit current measurement

Two enhancement mode MOSFETs in series are used to provide a solid-state switch. The MOSFETs are turned on by a photovoltaic array. Resistors in series with the MOSFETs serve to provide a control voltage to current-limit the circuit. An additional photovoltaic array is used to supply drain to gate bias when the switch is off to minimize device capacitance. The circuits can be cascaded to raise the voltage-handling limits.

High voltage solid-state switch with current limit

A range selecting impedance is switched into or out of a parallel range-selecting network by connecting the impedance across the network through an n-channel and a p-channel FET connected in parallel output configuration. The n-channel FET does the switching if the drains are negative with respect to the sources. The p-channel FET does the switching if the drains are positive with respect to the sources. Each FET is controlled by a gate drive whose output waveform is varied to select the rate at which the FETs switch. In cases of several different switched range impedances, the FETs are used to switch the smallest impedance into the network, another range impedance is selected, and then the FETs used to switch the smallest impedance out of the network. In this way, fast glitch-free range switching is achieved.

Range changing using N and P channel FETS

An apparatus capable of acting as a current-limited voltage source or a voltage-limited current source is disclosed. The output of the apparatus is provided by a differential amplifier. The current and voltage outputs are compared to positive and negative current and voltage limits. Depending on whether the apparatus is in the voltage mode or the current mode, the inverting input of the differential amplifier is clamped to the appropriate voltage or current comparison signal, respectively, to provide an error signal to the differential amplifier. This clamping is current limited so that if the output current limits are exceeded while in the voltage source mode, a clamp to one of the current comparison signals occurs and dominates the voltage clamp. Similarly, if the output voltage limits are exceeded while in the current source mode, a clamp to one of the voltage comparison signals occurs and dominates the current clamp. To enable a voltage or current source limit to be set at zero, the opposite polarity limit is offset slightly to avoid contention should it also be set near zero.

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Wadsworth, OH, United States of America

John G Banaska