The lock-in amplifier can in some ways be considered to be a narrowband AC voltmeter, where the measurement bandwidth can be set to be as low as a few milli- or even micro-hertz. As such it is capable of measuring very small signals in the presence of large interfering signals, as long as such interference is not at the same frequency as the signal of interest.
With a wide operating frequency range, a lock-in amplifier can be used to perform swept-frequency magnitude and phase measurements on electronic components and networks, to a much higher resolution than is typical using instruments based on FFT analysis. They are particularly useful for determining resonant frequencies of crystals and cantilevers.
Using two instruments, or one instrument and an input multiplexer, it is possible to measure the complex AC voltage and current in a network or device, and from this calculate the complex impedance. One advantage of the lock-in in this application is the fact that excitation signal levels can be very small, so that they do not dissipate significant power in the sample which could change its electrical properties. An example of an application where this is particularly important is in measuring the properties of superconducting samples, for which purpose we make a special instrument, the model 7124 precision lock-in, which uses an all-analog fiber-optically isolated signal channel to completely eliminate any unwanted power dissipation in the sample.
SIGNAL RECOVERY supplies one of the widest commercially available ranges of lock-in amplifiers, as well as associated products such as a range of preamplifiers and supporting software, such as the Acquire package that makes it particularly easy to use our instruments for single- and swept-frequency measurements in these types of applications. Typical instruments used:
- 7124 DSP Lock-in Amplifier with Analog Front End and Digital Main Unit
- 7270 DSP Lock-in Amplifier 250kHz
- 5182 Current Preamplifier