3 research outputs found
A simple microcontroller based digital lock-in amplifier for the detection of low level optical signals
Traditionally digital lock-in amplifiers sample the input signal at a rate much higher than the lock-in reference frequency and perform the lock-in algorithm with high-speed processors. We present a small and simple digital lock-in amplifier that uses a 20 bit current integrating analogue-to-digital converter interfaced to a microcontroller. The sample rate is set to twice the reference frequency placing the sampled lock-in signal at the Niquest frequency allowing the lock-in procedure to be performed with one simple algorithm. This algorithm consists of a spectral inversion technique integrated into a highly optimised low-pass filter. We demonstrate a system with a dynamic range of 103dB recovering signals up to 85dB below the interference
A High Stability Optical Shadow Sensor with Applications for Precision Accelerometers
Gravimeters are devices which measure changes in the value of the
gravitational acceleration, \textit{g}. This information is used to infer
changes in density under the ground allowing the detection of subsurface voids;
mineral, oil and gas reserves; and even the detection of the precursors of
volcanic eruptions. A micro-electro mechanical system (MEMS) gravimeter has
been fabricated completely in silicon allowing the possibility of cost
e-effective, lightweight and small gravimeters. To obtain a measurement of
gravity, a highly stable displacement measurement of the MEMS is required. This
requires the development of a portable electronics system that has a
displacement sensitivity of nm over a period of a day or more. The
portable electronics system presented here has a displacement sensitivity nm ( nm at s). The battery power
system used a modulated LED for measurements and required temperature control
of the system to 2 mK, monitoring of the tilt to 2 radians,
the storage of measured data and the transmission of the data to an external
server.Comment: 8 Pages, 12 figures, 5 equations, currently submitted and under
review at IEEE Sensors SIE