The original DC isolation module, developed under my direction around 1999, used an unconventional custom off-line power supply and four Analog Devices AD204 isolation amplifiers, to provide isolated voltage and current input from DC to about 1 kHz. This opened up a new market for recording sensors and telemetry signals on the TESLA, as well as some unique DC-level-sensitive AC applications, such as internal levels in static VAR compensators (SVCs) and DC converters.
Modern applications are much more stringent, however, needing better performance than the AD204 can provide (accuracy, noise level, and isolation), and the power supply couldn’t meet today’s restrictive EMC requirements.
So, I was asked to develop a newer high-performance DC Isolation Module. The basic concepts had been established by Steve Peddle, but he was quite busy on other projects.
The original concept was to perform “intelligent” ADC conversion on isolated “islands”, encoding the data in a protocol, and transferring the multiple streams of this protocol using digital isolation devices back to a central location, where it would be converted back by multiple DAC conversion on a circuit not isolated from the TESLA recoreder (as is required by the TESLA analog front-end).
I came across a potential alternative in the form of isolated sigma-delta modulator converters like the Analog Devices AD7401, which could give a highly accurate, flexible solution. Using an evaluation board, I captured data and performed extensive data analysis in Python. I implemented the sinc3 filter in Python, demonstrated the trade-offs, and explored the possibilities of various configurations.
I evaluated the technologies against each other and wrote a report. After discussions with Steve and ERLPhase management, we decided to proceed with the sigma-delta modulator approach.
We obtained the evaluation kit for the Silicon Labs Universal Bee MCU EFM8UB20, and wrote the initial code as proof-of-concept and to bring up the system, handing it over to the firmware development team to implement the core functions.
I developed and documented the isolation plan, which included double 300V isolation gaps. After a design review, I created the schematic, and had two interconnected PCBs developed. I wrote a verification & validation document with guideline for the firmware implementation.