Discussion Overview
The discussion revolves around constructing an analog front end for measuring current using either a current transformer (C.T.) or a sense resistor, with the goal of translating the measurements into a 0-5V signal for an MCU. The focus is on achieving a wide range of current measurements (0-10A at 50/60Hz AC) with a resolution of 5mA, and includes considerations for waveform graphing and RMS values.
Discussion Character
- Technical explanation
- Mathematical reasoning
- Debate/contested
Main Points Raised
- One participant suggests using a small resistor (0.1 ohms or less) with a differential op-amp to achieve the necessary scaling for the current measurement.
- Another participant emphasizes the need for a precision rectifier and a high-resolution A/D converter, noting that at least 11-bit resolution is required for the desired range and resolution.
- There is a mention of the need to measure both the direction and amplitude of the current, which raises concerns about using a rectifier that may not capture directionality.
- A participant questions the resolution of the A/D converter, pointing out that most microcontrollers have only 10-bit resolution, and suggests considering a logarithmic amplifier if 5mA resolution is not needed at 10A.
- Another participant confirms that a 12-bit A/D is necessary for measuring both direction and amplitude, but notes that logarithmic amplifiers do not handle negative values well.
Areas of Agreement / Disagreement
Participants express differing views on the best approach to achieve the desired current measurement, particularly regarding the use of rectifiers and logarithmic amplifiers. There is no consensus on a single solution, and multiple competing ideas are presented.
Contextual Notes
Participants have not fully resolved the implications of using rectifiers on direction measurement, nor have they clarified the specific requirements for the A/D converter in relation to the proposed methods.