Problems with current measurement (EmonLib)

[STest6905]

I want to measure current values using current transformer and library (EmonLib.h) in this example

#include "EmonLib.h"
EnergyMonitor emon1;
void setup()
{
  Serial.begin(9600);

  emon1.current(A0, 30);
}

void loop()
{
  double Irms = emon1.calcIrms(1480);
  Serial.println(Irms);
}

I use NodeMCU and SCT-013. I have succeeded. The values correspond to what the calibrated instrument shows but there is a problem. When the controller starts, it gives the first 3 values ​​not correct, but I need all the correct values.

2.88
0.67
0.16
0.06
0.04
0.04
0.04
0.04
0.05
0.04
0.03
0.02
0.02
0.03
0.02
0.01
0.01
0.01
0.01
0.01
0.01
0.02

scheme

What can be done in such a case?
Thank you.

[johnerrington]

@STest6905

Serial.begin(9600);

@STest6905

Serial.println(Irms);

Unless there is something in the emonlib library I see nothing here to control the rate at which measurements are taken - other than the very slow baud rate.

You havent explained how the ct is connected to the Node - so a schematic please?

How to make a schematic you can post.

When you submit a question on the forum you will usually need to add a schematic (circuit diagram). The tutorial that follows will explain some ways to create a useful image; however lets start by explaining how to add the image to your post. Its easy. Having created the image all you need to do is : Save the image somewhere convenient - maybe your desktop Start your post, and place the cursor (insertion point) where you want the image to be shown; [upload image to forum] 3: click th…

Is the current already established when you start making measurements?

[STest6905]

@johnerrington

You havent explained how the ct is connected to the Node - so a schematic please?

I have attached the wiring diagram for the transformer.

https://www.researchgate.net/profile/Viorel-Miron-Alexe/publication/312038242/figure/fig1/AS:465224521261060@1487929577727/Schematic-describing-the-interfacing-of-the-SCT-013-current-transformer-with-the-Arduino.png

[STest6905]

@johnerrington

Unless there is something in the emonlib library I see nothing here to control the rate at which measurements are taken - other than the very slow baud rate.

You can choose any of the available data transfer rates; it does not affect the values that are formed after a restart. The main problem is that the values jump when the controller is restarted...

[johnerrington]

The output from the current transformer is an AC signal, that is biased to 5V / 2 by R1, R2

Because C1 charges from a source reisitance of R1//R2 = 5k you have a time constant of about 2 sec.

there will be a period of about 5RC = 10 sec before the bias vboltage becomes stable.

So You MUST ignore the first 10 sec before you start taking readings.

[STest6905]

OK. The option to ignore is not entirely suitable ... Well, what if you connect the power not to + 5V, but to some output (pin 5) and turn it on in the setup?

#include "EmonLib.h"
EnergyMonitor emon1;

const int PowPin =  5;

void setup()
{
  Serial.begin(9600);
  pinMode(PowPin, OUTPUT);

  emon1.current(A0, 30);
  
  digitalWrite(PowPin, HIGH);
  delay (1000);
}

void loop()
{
  double Irms = emon1.calcIrms(1480);
  Serial.println(Irms);
}

[JohnLincoln]

@STest6905

OK. The option to ignore is not entirely suitable ... Well, what if you connect the power not to + 5V, but to some output (pin 5) and turn it on in the setup?

Surely that will make it worse.

The power coming on happens before you can turn on an output pin doesn't it?

[anon57585045]

@STest6905

The main problem is that the values jump when the controller is restarted...

So add a start up delay.

[johnerrington]

@STest6905

The option to ignore is not entirely suitable

I dont see why - the current doesnt know when ou connect the meter.

You can TRY adding a second cap from the 2.5V to the 5V rail.

Who was it said "ye cannae break the laws of Physics" ...