Some time ago, I came across a circuit diagram for the commonly available ZMPT101B Module – this one with a ZMPT101B transformer, an op.amp and a calibration potentiometer on a small circuit board, which requires a d.c. supply to operate.
A number of users of this module have tried to use it as part of a project to measure power, and have faced difficulties. When I saw the circuit, the reason was quickly apparent: it includes filtering components which introduce a large phase shift, making it very difficult to process the measurements to calculate real (active) power.
I have found a research paper which totally independently has validated my conclusion. The paper considers a number of ways to obtain a voltage sample and evaluates their suitability. The ZPMT101B Module shows, according to their results, an 11.288% error in the active power. This corresponds to a phase error of ~ 27.5°, worse even than the 20° which my simulation predicted.
This emphasises my advice to not use the ZMPT101B Module as part of an energy monitor.
This is notwithstanding the serious concerns I and others have regarding the electrical safety of the module, which is another very good reason not to use it.
