Guru
Joined: 13/10/2014
Location: AustraliaPosts: 1625
| Posted: 09:16am 06 Jun 2023 |
The P-detector follows the peaks of the rectified waveform, it's normally preceded by a Precision Full-wave rectifier, the P-rectifier @ 50 Hz would produce the 100Hz 1/2 wave waves that you normally see from any full wave rectifier, but without typical Diode non-linearity.
Which is why I thought the Peak-detector would be ideal for this task as the unidirectional Hall sensor output is not unlike a rectified AC signal.
The waveform on the DC input cable to these inverters will always have a 100hz waveform when the inverter is running, that is produced by the FETS drawing current to make a 50Hz "AC" waveform from a DC input.
The waveform on the DC input is not an AC waveform, it's not alternating current or voltage, it's more like 100hz DC pulses shaped like a sinewave, there is no zero crossing. The zero current point is at the base of the waveform.
As far as the peak detector is concerned, this waveform looks the same as 100Hz full wave rectified 50Hz AC without any filtering. Not that the frequency matters.
So trying to calibrate it with a straight DC signal is not going to work. Trying to use an sinewave generator is not going to work, it's not the same thing.
You really need the waveform shape from the Hall Sensor that is on the DC input of your Inverter, whatever wave shape comes out of the sensor from the Current flowing into your Inverter should stay relatively the same at all power levels, unless you have an unknown problem in the inverter.
However there is a way to calibrate the meter and get accurate information from the Hall Sensor. I mentioned a low cost (relative I guess) handheld Digital Oscilloscope / DSO a few pages back.
I managed to figure how to get it to grab the waveform on trigger, I got the end of the startup waveform before it wound down to running current. It was spot on in the values returned and the waveform is exactly the same as my big TEC DSO. That was on my second go having never played with the Mini digital CRO before, it's not a true DSO with scroll-able memory, but you can grab the waveform and view it, and it will tell you the correct values.
I need to test it bit more tomorrow, to see if it can reliably trigger and capture the part of the startup waveforms we need, but it looks good so far. BTW it displays the Inverter AC and DC current waveforms perfectly when running as a straight Digital CRO.
It might be something to consider, I think around $75 for this one, likely lower cost units are around, just check the spec as some are nasty, this one was on spec at 500kHz bandwidth and only slightly down at 1Mhz.
Link to CRO
You want Color Set 2, it has the CRO Probe and Adapter $78.
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Edited 2023-06-06 20:17 by KeepIS