Grove - DC Current Sensor - Wrong Values

ccorrientes · April 19, 2020, 7:01pm

Deer Community, I hope you can help me out.

I have the given the job to measure the Voltage and Current of a lightbulb.

I like to use the Grove 2.5A and 10A DC Current sensors on an Arduino Uno Rev3 for this .
http://wiki.seeedstudio.com/Grove-2.5A-DC-Current-Sensor-ACS70331/#feature
http://wiki.seeedstudio.com/Grove-10A_DC_Current_Sensor-ACS725/

My DC Power-supply shows me 3.1 Voltage and 0.2 Ampere Current

My MultiMeter shows me exactly 3.09V Voltage and 0.19A Current

I have used the 2.5A DC Current Example . I changed the “float Vref = 302.73;” to my initial value and got a 0.0 baseline current ( DC Supply turned off )

As soon I turn on the DC supply I get 190.43mv (or 0.19V ) Voltage and 238.04ma (0.238A) Current as results.

Can anyone point me out, why is that ?

0.238A ( or 238.04ma ) is not even near the exact measured 0.19A?

The voltage output is completely off the charts too ( showing 0.19V instead 3.09V ).

Did I maybe miss something ? Are the values representing not the actually current and voltage ?

The arduino is powered by a USB3 port.

I have the same issue / discrepancy with the 10A sensor as well… Although it uses different sensor type.

Thank you so much for your help

Kindest Regards

…Constantin

Baozhu · April 20, 2020, 12:42am

Note: We use the DC Power Supply in this demo, please set the current to 0A or do not power on it at first

ccorrientes · April 20, 2020, 11:07am

Hello Baozhu, thank you so much for your reply…

Unfortunately the picture was not soo good… I too use a DC Power Supply ( KPS1202D )

I turned it originally off, and then gradually turned it on… It is now on Constant Current 3.1V and 0.20A which matches also my MulitMeter reading…

Yet the DC sensor gives me a 0.18V and 0.23A reading.

Here are some other examples I took :

DC Power Supply = DC Sensor
2.1V / 0.16A = 0.15V / 0.18A ( 151.37mV / 189.21mA )
3.1V / 0.20A = 0.18V / 0.23A ( 185.55mV / 231.94mA )
6.1V / 0.29A = 0.27V / 0.34A ( 273.44mV / 341.80mA )

Kindest Regards

…Constantin

Baozhu · April 21, 2020, 8:55am

I mean you have to calibrate it before you measure it.

ccorrientes · April 21, 2020, 9:42am

Hello Baozhu,

Thank you for replying.

You mean to set the VREF value based on the initialvalue, so it shows 0.0mA on the sensors before turning the DC supply on?

I did this

I start with 0.01ma and have this strange offset in the value anyway ( showing me 238.04mA instead of 200mA / 0.2A )

…Constantin

jiachenglu · April 22, 2020, 4:50am

Dear @ccorrientes
We know your problem.Because there is no DC current sensor module in our office, we have to apply to ship 10A DC current sensor module from the warehouse to the company, and then do a test according to your process, but this process may take 2 days, please wait patiently. Once we have the test results, we will inform you as soon as possible.

Best Regards.
Sincerely

ccorrientes · April 23, 2020, 9:38pm

Hello @jiachenglu you are great. Thank you for this. I can if you like also provide you any kind of access to my demo environment if you like… I am willing to do whatever needs be done, to get the sensor data values precise & accurate. …Constanitn

ccorrientes · April 24, 2020, 11:23am

Dear @jiachenglu, please bear in mind in case you test the system… I don’t have an issue to set the vref value… It is set to the initial value and i get a 0.01 value without any load.

My issue is the accuracy of the sensors. Both sensors ( the 2.5A and 10A ) are showing values with an offset of up to 25% in current and -95% in voltage…

Current
Power Supply Value = DC Sensor Value = Accuracy
0.16A = 0.18A (189.21mA) = 18% off
0.20A = 0.23A (231.94mA) = 15% off
0.29A = 0.34A (341.80mA) = 25% off

Voltage
Power Supply Value = DC Sensor Value = Accuracy
2.1V = 0.15V (151.37mV) = -92% off
3.1V = 0.18V (185.55mV) = -91% off
6.1V = 0.27V (273.44mV) = -95% off

I used the example script for 2.5A and 10A as basis.

github.com

Seeed-Studio/Seeed_ACS70331/blob/master/examples/Seeed_ACS70331_basis_Demo/Seeed_ACS70331_basis_Demo.ino

/*
    Seeed_ACS70331_basis_Demo.ino
    Driver for 2.5A DC Current Sensor (ACS70331)

    Copyright (c) 2018 Seeed Technology Co., Ltd.
    Website    : www.seeed.cc
    Author     : Jenkin
    Create Time: August 2018
    Change Log :

    The MIT License (MIT)

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in

This file has been truncated. show original

@Baozhu mentioned that i might need to calibrate the sensors. If this is the case how can i calibrate them - besides setting the vref value? (I am quite new to this) Are there any how-tos available or should we just kick the project and move to another vendor as those sensors are in reality not as accurate as the datasheet promised ( your honest opinion )?

Thank you so much…

…Constantin

jiachenglu · April 24, 2020, 1:12pm

Dear @ccorrientes
Hello ,We found the root of the problem because our company’s DC current sensor is 0-2.5a, and the error will be larger when measuring small current.You can try to measure some larger current.
The voltage value displayed by our serial monitor refers to the current measured by the sensor is converted into the voltage value, rather than the supply voltage.
The following is the test I made with 10A DC current sensor. I measured the sensor current pictures of 200mA, 500mA, 1a, 2a and 2.5A respectively. In the figure, we use DC power supply, resistor (instead of electric lamp), 10a DC sensor module,Arduino to complete the experiment.