4 PIDs for MFLI 500 kHz / 5 MHz Lock-in Amplifier

By Zurich Instruments

Zurich Instruments offers PID controllers exclusively as upgrade options for lock-in amplifiers, impedance analyzers and boxcar averagers. Consequently, a number of different inputs can be chosen for the PIDs: the set of choices includes amplitude, phase, quadrature and in-phase components of demodulated signals, boxcar outputs, as well as auxiliary inputs and outputs. Integrated digital signal processing guarantees maximum signal-to-noise ratio, minimal feedback loop latency and closed-loop operation with high stability. Even tiny signals can be located in a noisy and spurious-rich background and used as reliable inputs. The feedback signal is then available as an analog output and can also be directly applied to an internal frequency generator output to control its amplitude, frequency, offset and phase. 50 kHz max. loop filter bandwidth PID Advisor and Auto Tune PID PLL capability Phase unwrap for demodulator phase data The PID options for the MFLI Lock-in Amplifier and the UHFLI Lock-in Amplifier are also equipped with a D-gain low-pass filter and the phase unwrap functionality. In many cases, introducing a D-gain offers the potential to speed up the loop's response. However, this often leads to instability because it introduces increasing gains towards high frequencies. Introducing an adjustable low-pass filter in the D-branch helps take advantage of the D-gain without running into instabilities. Phase detection facilitated by a lock-in amplifier is usually limited by the arct2(y/x) function to the value range ±π. In turn, this limits the 'capture range' of the PID as well as the stability of operation in the presence of external noise. In the digital domain, this limitation can be overcome thanks to a 'phase unwrap' functionality that detects instances where phase detection exceeds its limits and keeps track of this behaviour accordingly. Zurich Instruments' PIDs support a 'capture range' that extends up to ±1024π.