Key progress in the integrators
Evidently, all these elements have evolved since the 19th century, but the greatest improvements lie with the integrators. The first major step was the transition to analog electronics, particularly op-amp based integrators. However, these have limited bandwidth, are subject to many different noise sources, and still require a digitizer.
Another approach converts the input voltage to a frequency, which is then measured with a high-precision counter. Inherently digital and with outstanding precision, this design – also used in Metrolab’s PDI5025 – has been the champion amongst precision integrators for the last 20 years. Its main limitation is the frequency range of the voltage-to-frequency converter (VFC), requiring relatively long integration times – at least on the order of a millisecond.
A third, more brute force approach is to digitize the input voltage and to compute the integral numerically. This approach depends critically on the performance of the analog digital converter (ADC): range, resolution, speed, linearity, noise – every conceivable ADC parameter influences the integrator performance.
Leveraging latest CERN developments
CERN and the University of Sannio have recently developed a new high-speed, high-precision integrator, based on the ADC approach. Coupled with a new high-speed rotating coil system, its purpose is to study dynamic effects such as eddy currents and the decay/snapback phenomena observed when ramping superconducting magnets.
The principle is simple, the implementation everything but. In addition to amplifying and digitizing the input voltage with great precision, the instrument must measure time very accurately. A high-resolution clock synchronizes the ADC with the arrival of trigger pulses, and a digital signal processor (DSP) interpolates the ADC values to determine the exact voltage at the time of the trigger. With the following ADC values, the DSP then computes a trapezoidal approximation of the integral until the next trigger. These partial integrals are output continuously on a PCI bus, interfaced directly to a computer.
The design has been licensed by Metrolab and will be commercialized as the Fast Digital Integrator FDI5026. Compared to the PDI5025, the FDI5026 offers 100x faster trigger rate and 100x better resolution, making it the new world champion amongst precision integrators.