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Help needed for my project

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joe7:
Hi, I'm preparing my project report for my diploma, and I need some help regarding the technical information.
the project,  Load Monitoring System Over IoT:



Do you guys have an idea how the circuit measured the power/current used by the lamp/load connected to it?  usually, this kind of project uses the voltage sensor and current sensor, but this kind of project doesn't have it.

Thanks in advance

moffy:
It is a dangerous setup! The lady though barely legible calls one of the transformers a CT so that is how current is being measured.

ledtester:
There is an Atmel/Microchip app note on designing a single phase power meter:

https://ww1.microchip.com/downloads/en/AppNotes/Atmel-2566-Single-Phase-Power-Energy-Meter-with-Tamper-Detection_Ap-Notes_AVR465.pdf

In particular, it talks about how it measures RMS current using a current transformer.


--- Quote from: moffy on June 27, 2022, 11:29:45 pm ---It is a dangerous setup! ...

--- End quote ---

Well, here's a block diagram of the circuit (found at https://www.electrosal.com/product/load-monitoring-system-over-iot/ )



It is mains powered, but it looks like it is isolated and possibly only measures current (after all, it only displays current on the LCD). It could very well have the voltage hard coded.

(Based on the video I'm sure the "Load" block in the diagram is misplaced.)

The AVR design measures both current and voltage and is a more dangerous circuit. See the caveat at the beginning of the app note.

Terry Bites:
The transformer X2 look like it might be connected as a current transformer. Indeed, the narrator of the video identifies it as such. It’s just a regular transformer configured as a CT. It probably not a very linear CT but it will work. The output of the CT is rectified and smoothed to get a DC value proportional to the current. You need some transient protection on A0. Maybe a 5V Zener. There is no circuitry for voltage measurement. It appears that they are assuming a fixed mains voltage and a unity power factor. P=IV cos ϕ . The mains voltage and current are isolated by the two transformers. It won’t be very accurate but it's good enough for a demo. What is the +12V for? It looks like IC117 etc is mislabelled, does is provide 3.3V for another module, maybe Wi-Fi? Don’t forget to install fuses!

In a real life meter, you would measure the current, voltage, frequency and the time offset of the zero crossing points to determine the phase angle.
Take care.

Kleinstein:
The requirements for a current transformer are not that high - so usually no big problem using the more normal transformer for this. The problem is more in having too high a winding resistance and thus extra loss in the test circuit.
The more tricky part is measuring the voltage though a normal transformer. Especially small transformers are not that ideal.

A Diploma work at the university should be done one you own - so outside help is normally not allowed, especially not on the main topic ( things like grammar and spell checking may be OK).

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