496 Digital Signal Processing Lock-in Amplifier

Digital signal processing lock-in amplifier
The 496 lock-in amplifier ADC is a key component of spectroradiometer systems operating in conditions where the optical signal to be measured may be confounded with a background optical signal, whether from ambient lighting, or, in the infrared, heat (or infrared radiation) emitted by instrumentation and the background.

To discriminate the two contributions, the optical signal to be measured is modulated on a known carrier wave by an optical chopper, the relative phase difference between these two waveforms must be taken account of.

In the 496, the input and reference are digitised prior to determination of the components in two orthogonal states in order to take the vector sum of the two. Phasing intervention, as is custom with traditional lock-in amplifier-based systems, is therefore not required.

The 496 module is housed within the 417/417T base unit.

Inputs 2, remotely/manually selected 
Frequency Range 10Hz to 2kHz 
Gain Ranges Binary gain, 2-6 to 214
Input Impedance 100MΩ/25pf, pseudo differential
Dynamic Reserve Not applicable - digital demodulation
Gain Accuracy ±0.15%
Gain Stability  200ppm/°C
Output Stability 5ppm/°C to 500ppm/°C depending on sensitivity
Time Constant 10ms to 10s
Display: Signal, frequency, phase and SNR displayed to two decimal points
ADC Resolution 16 bit
ADC Speed 52 kHz
Input Range 0 to 10V
Linearity < 0.025% departure from linearity from zero to full scale
Interface: USB (via 417/417T base unit)