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AC Resistance Bridge

From Lake Shore Cryotronics

By using alternating current (AC) measurement in tandem with a specially designed internal lock-in amplifier, the Model 372 can extract very small measurement signals from background noise. This allows for much lower excitation levels to be used when compared to traditional direct current (DC) systems, minimizing the amount of energy that is dissipated into the device under test.

The Model 372, originally designed as Lake Shore’s best temperature measurement and control bridge, is perfectly suited for highly precise resistance measurements. It covers an impressive resistance range, from Milli-Ohm to several dozens of Mega-Ohm

Features

Reduces measurement noise due to patented technology
Current source with integrated amplifier
Excitation current from 1 pA
Single channel AC resistance bridge with optional scanners
Benchtop unit with either front panel or remote control

Further information

Externally generated electronic noise can be a major cause of self-heating if it can couple into the device under test. Thankfully, multiple noise-rejection strategies have been implemented to reduce this effect substantially:

The patent (U.S. Patent #6,501,255, Dec., 2002, “Differential current source with active common mode reduction,” Lake Shore Cryotronics, Inc.) balanced noise-rejecting current source ensures that external signals have no path to ground through the measurement circuit, effectively making the Model 372 unaltered by these noise sources.

The measurement signal cables use a driven guard that reduces parasitic capacitance in the cables that connect a scanner to the Model 372. This helps to further balance the measurement network and bolster the integrity of the noise rejection circuitry.

All measurement circuitry is isolated from other instrument components, limiting the impact of any small electrical disturbances.

The AC frequency options used for the measurement signal are selected to be naturally resilient to the 50 Hz or 60 Hz line frequencies.

Model 372