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Four-point measurement of resistance between voltage sense connections 2 and 3. Current is supplied via force connections 1 and 4. In electrical engineering, four-terminal sensing (4T sensing), 4-wire sensing, or 4-point probes method is an electrical impedance measuring technique that uses separate pairs of current-carrying and voltage-sensing electrodes to make more accurate measurements ...
The van der Pauw Method is a technique commonly used to measure the resistivity and the Hall coefficient of a sample. Its strength lies in its ability to accurately measure the properties of a sample of any arbitrary shape, as long as the sample is approximately two-dimensional (i.e. it is much thinner than it is wide), solid (no holes), and the electrodes are placed on its perimeter.
In a four-terminal measurement, the current used to make the measurement is injected using a second, separate pair of leads, so the contact resistance of the measurement probes and their leads is not included in the measurement. Specific contact resistance can be obtained by multiplying by contact area.
This is the main advantage of the four-point measurement. Schematic of electrical measurements performed with a multi-tip STM. Each tip can be configured as current probe or as voltage probe. The simplest example of an electrical measurement is a classical four-point resistance measurement.
A four-point probe is used to avoid contact resistance, which can often have the same magnitude as the sheet resistance. Typically a constant current is applied to two probes, and the potential on the other two probes is measured with a high-impedance voltmeter. A geometry factor needs to be applied according to the shape of the four-point array.
The two outer probes induce the current to the specimen and the two inner electrodes measure the resulting potential drop. The probes are all applied to the same surface of the specimen and the method is consequently suitable for measuring the resistivity of bulk concrete in situ. [4] The resistivity is given by:
A high voltage probe allows an ordinary voltmeter to measure voltages that would otherwise be too high to measure or even destructive. It does this by reducing the input voltage to a safe, measurable level with a precision voltage divider circuit within the probe body.
Electrical resistance survey of an archaeological site using a twin probe system. In most systems, metal probes (electrodes) are inserted into the ground to obtain a reading of the local electrical resistance. A variety of probe configurations are used, most having four probes, often mounted on a rigid frame. In these systems, two of the probes ...