In one implementation, a circuit can include a reference pin and an operational amplifier that can include an output pin, an inverting input pin and a non-inverting input pin. The inverting input pin can be electrically coupled to the output pin via a first impedance and to the reference pin via a second impedance. The non-inverting input pin can be electrically coupled to the reference pin via a third impedance and can be configured to receive a detection signal. The reference pin can be configured to receive a detection reference signal associated with the detection signal.

A circuit that outputs a current which is proportional to an input voltage includes input and output terminals, a comparator, first and second transistors, an inductor, a first resistor, and a differential amplifier. A first input terminal of the comparator is coupled to the input terminal of the circuit, and a second input terminal of the comparator is coupled to an output terminal of the comparator. The first and second transistors are coupled to the output terminal of the comparator. The inductor is coupled to the first and second transistors. The first resistor is coupled between the inductor and the output terminal of the circuit. The differential amplifier includes a first input terminal coupled to a first terminal of the first resistor, a second input terminal coupled to a second terminal to the first resistor, and an output terminal coupled to the first input terminal of the comparator.

A circuit that outputs a current which is proportional to an input voltage includes input and output terminals, a comparator, first and second transistors, an inductor, a first resistor, and a differential amplifier. A first input terminal of the comparator is coupled to the input terminal of the circuit, and a second input terminal of the comparator is coupled to an output terminal of the comparator. The first and second transistors are coupled to the output terminal of the comparator. The inductor is coupled to the first and second transistors. The first resistor is coupled between the inductor and the output terminal of the circuit. The differential amplifier includes a first input terminal coupled to a first terminal of the first resistor, a second input terminal coupled to a second terminal to the first resistor, and an output terminal coupled to the first input terminal of the comparator.

Systems and methods are provided for measuring electrical parameters in an insulated conductor without requiring a galvanic connection. A non-contact, electrical parameter sensor probe may be operative to measure both current and voltage in an insulated conductor. The sensor probe includes a body, a Rogowski coil coupled to the body, and a non-contact voltage sensor coupled to the body or the Rogowski coil. The size of the loop of the Rogowski coil is selectively adjustable, such that the loop may be tightened around the conductor under test until the conductor is positioned adjacent a portion of the body or Rogowski coil that includes the non-contact voltage sensor. Measured electrical parameters may be provided to a user, e.g., via a display, or may be transmitted to one or more external systems via a suitable wired or wireless connection.

A dual circuit current loading analysis apparatus enables the efficient testing of an electrical circuit, particularly those in vehicular applications. The apparatus electrically loads two circuits simultaneously and compares those readings to a battery or power source. Circuit input ports and ports to attach to the positive and negative sides of the battery are provided and attached to a microcontroller, voltage measurement device and load test device. The results of the test are indicated on a display and LEDs.

An electronic test measurement system can include a device under test (DUT) and an electronic test instrument that includes a signal input configured to receive an electrical signal from the DUT, a cooling mechanism, and a processor. The processor can be configured to determine a frequency at which the cooling mechanism should operate, cause the cooling mechanism to operate at the determined frequency, select a filter based on the determined frequency, and apply the filter to the electrical signal to reduce interference with the electrical signal resulting from mechanical vibrations of the cooling mechanism.

A test and measurement probe system (100,104), including an input (106) to receive an input signal, the input signal including a low frequency (LF) and/or direct current (DC) component and an alternating current (AC) component, an extractor circuit (110), such as an AC coupling circuit or a LF and/or DC rejection circuit, configured to receive the input signal and to separate the AC component and the LF and/or DC component from the input signal, a first output (118) to output the alternating current component to the test and measurement instrument, and a second output to output the direct current component to the test and measurement instrument. In some embodiments, the LF and/or DC component is digitized prior to being output by the second output.

A Rogowski coil in a sensor unit has voltage induced by a conductor surrounded by the Rogowski coil. The voltage is integrated to represent current which is converted to digital data representing current in the conductor and sent wirelessly to a multimeter. The sensor unit may receive control signals from the multimeter and a remote control apparatus. A plurality of sensor units may be networked and controlled by the remote control apparatus.

A reel device is a casing device for rollingly storing wire. The casing has a turnplate and is coupled with a measuring model. The measuring model has a function of testing the external circuit or power source plug and providing warning or presenting information regarding the external circuit or power source plug.

The invention relates to a measuring device such as a multimeter, comprising a retractable assembly, and including (i) a cable comprising a first end portion having a first probe and a second end portion having a second probe; (ii) a reel comprising a rotatable hub adapted to wind up and unwind said cable; and (iii) a circuit in connection with said cable, the circuit being adapted to wirelessly communicate a signal measured by the first probe or the second probe to a remote location; wherein the circuit is rotatable in conjunction with said rotatable hub.