Software Based Lock-In Amplifier
This paper is classified in two parts: first one works with the commercial instrument MFLI and second one works with the National Instrument’s hardware which is based on FPGA (USB-R Series DAQ). In our electromagnetic flow meter development project the Software based Lock-in amplifier is required for measurement of flow rates. The transmitter is excited by a sinusoidal constant current source of 0Hz - 400Hz. The receiver coil receives the signal which consists of flow information which is buried in ambient noise. A dual phase lock-in amplifier is required for measurement of phase difference between two Secondary coils. In National Instrument’s hardware which is based on FPGA (USB-R Series DAQ) we have designed another Software Based Lock-In Amplifier, which helps to convert a data acquisition instrument into digital Lock-In Amplifier. Utilizing the power of FPGA (Field Programmable Gate Array) the software based lock-in amplifier can achieve high-speed data synchronous demodulation of signals as high as 100MSa/s (depending on target). Programming has to be carried out such that we simultaneously acquire the data, carry out digital filtering and display the corresponding magnitude and phase of the signal.
Keywords - Lock-in Amplifier, Electromagnetic Flowmeter, Magnitude, Phase.