Hybrid AC/DC current probes
Alternating current probes

As transformers may be used, alternating currents are reasonably simple to calculate. For calculating alternating currents, a current transformer is widely used. The current to be determined is pushed through the primary winding (often a single turn), and by calculating the voltage through a current-sense resistor, the current through the secondary winding is found (or “burden resistor”). There is a load resistor for the secondary winding to set the current scale. A transformer’s properties give many advantages. The current transformer refuses typical voltages in the mode, so it is possible to reliably quantify single-ended voltage on a grounded secondary. The efficient series resistance R s of the primary winding {\displaystyle R {s}} is set by the secondary winding load resistor R {\displaystyle R} and the transformer transforms the ratio N {\displaystyle N}, where:

Additional probe features

Both scope probes have any facility for grounding (earthing) the probe to the reference voltage of the circuit. Typically, this is done by attaching a rather short pigtail wire from the head of the probe to the ground. Inductance in the ground wire will result in the detected signal being skewed, so this wire is held as small as possible. Instead of some cable, some probes use a tiny ground foot, enabling the ground connection to be as small as 10 mm.

Board Test Fixture Probes

In order to satisfy the research needs, Smiths Interconnect provides a full variety of regular spring touch probes and has long been regarded as the world’s largest producer of probes. With over 60 separate series of probes varying from 0.02″ (0.51 mm) to 0.187″ (4.75 mm) pitch with various length, travel, ICT, lead free and rotator options, we have a comprehensive portfolio of bare boards, equipped printed circuit boards and surface mount assemblies built for general purpose research.

Active scope probes
Simple test leads

A standard voltmeter probe is a single wire test lead that has a connector fitting the voltmeter on one end and a rigid, tubular plastic portion with both a handle and a probe body on the other end. Without disrupting the test (by being part of the electrical circuit) or being subjected to harmful voltages that could trigger electrical shock, the handle enables an individual to retain and direct the probe. The wire is attached inside the probe body to a stiff, pointed metal tip that touches the DUT. Some probes allow the tip to be connected to an alligator clip, thereby causing the probe to be attached to the DUT such that it does not need to be fixed in position.

Lo Z probes

Z probes are a specialized form of passive low-capacitance probe used in very-high-frequency, low-impedance circuits. In design, they are identical to 10 passive probes, except at far lower levels of impedance. Typically the probe cables have a characteristic impedance of 50 ohms and are attached to oscilloscopes with a matched input impedance of 50 ohms (rather than 1 megohm). On the traditional 1 megohm oscilloscope, high-impedance scope probes are expected, however the 1 megohm input impedance is only at a low level; the input impedance is not a constant 1 megohm around the bandwidth of the probe, but rather decreases with frequency. A Tektronix P6139A input impedance, for instance, begins to collapse above 10 kHz and is around 100 ohms at 100 MHz.