Zmpt101b problem with measure ac voltage

Projects General Guidance
1

I have a autotransformer which gives 0- 250vac recently i bout a zmpt101b for measuring the voltage but here is some problem when i set the Autotransformer voltage above to 5v its give right value and then decrease from 5v its show 4.8 v mean below the 4.8 v its not measured properly and then i remove the connection of this sensor to autotransformer its show 0.0 V which is good but after connecting the wire from autransformer and turning on its show 4.8v any idea why this happen?
Am using this code

#include <ZMPT101B.h>

#define SENSITIVITY 500.0f
voltageSensor(A0, 50.0);

void setup() {
Serial.begin(115200);
// Change the sensitivity value based on value you got from the calibrate
// example.
voltageSensor.setSensitivity(SENSITIVITY);
}

void loop() {
// read the voltage and then print via Serial.
float voltage = voltageSensor.getRmsVoltage();
Serial.println(voltage);

delay(1000);
}

2

Did you read the Amazon reviews before you bought the device?

3

How are you measuring the voltage independent of the ZMPT101B?

5

Yes just connected the autotransformer output to zmpt101 Nutral and phase and vcc gnd out Arduino pin

6

Yess

7

I've kindly asked you in your other topic not to post in "Uncategorized". So why did you post in that category again?

Topic moved.

8

Ok, then you know the output is AC.

9

You are not going to get a 0.04% accuracy with a ZMPT101b

10

Yes i know also connected a multimeter in the output of autransformer

11

Then all the voltages you reported in your first post should have been identified as AC.

12

Yess

13

I understand but why the module show 4.8 volt when i connected the autotransformer to supply and connected to zmpt101 when i increase voltage 5.5 above its give correct results but below 4.8 volt its show 4.8 why?

14

Did you calibrate it correctly?
Does the library you are using work for small voltages?
Does the module you have work with small voltages?

15

How to calibrate it correctly
Yes i think the resolution is 0.1v

16

From your first post:

Did you do this?
If so, what was the result?
And no I don't have this sensor myself, I'm just reading instructions here.

17

Follow the instuctions in the user manual for the module you have.
You will also need to calibrate the Arduino ADC.
Which Arduino are you using?

18

I am using arduino uno

19

When i change sensitivity ex- 500 to 250 value is half like in 500 its give 4.8 and 250 2.4

20

Once you have it calibrated correctly you will know the value to use for sensitivity

21

Based on this answer I take it you didn't run the calibration sketch as suggested in the instructions. That way you're not going to get anywhere.