EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: masoudium on February 15, 2016, 07:56:42 am
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Hi,
I'm trying to measure the current change of a 24V DC powered device in the range of some mili-amps, and send the measured value to a PC.
I have designed a board with an Atmega8 and a 2 Ohm shunt resistor placed in series configuration in the power line of the device. I used a differential amplifier circuit to amplify the voltage across the shunt resistor to measure this voltage with uC ADC.( The schematics is attached)
It seems that this Idea is not working, as it reads a constant value across the shunt resistor even when there is no current passing through it!
What am I doing wrong? :-//
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1. Is the load isolated or share common ground?
2. Maybe the Op amp need negative supply?
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The problem is the positive common mode voltage:
The LM324 has a supply voltage of +5V but the shunt is connected to +24V. That does not work.
Better use an IC spefically designed for highside current sensing.
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1. Is the load isolated or share common ground?
2. Maybe the Op amp need negative supply?
Hi,
thanks
1.No it is not isolated. :(
2. LM324 is a single supply op-amp.
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The problem is the positive common mode voltage:
The LM324 has a supply voltage of +5V but the shunt is connected to +24V. That does not work.
Better use an IC spefically designed for highside current sensing.
Hi Bktemp
Thanks, Can you please refer me to a good IC for this application. I need to measure the current in milli-amps resolution. The current won't go higher than 1 Amp.
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Its not so precision, but maybe can be used
http://www.aliexpress.com/item/1-Pcs-New-5A-ACS712-Range-Current-Sensor-Module-Electronic-Parts-Hall-Effect-Detector/32387779613.html?spm=2114.10010108.100010.8.lBYGxH (http://www.aliexpress.com/item/1-Pcs-New-5A-ACS712-Range-Current-Sensor-Module-Electronic-Parts-Hall-Effect-Detector/32387779613.html?spm=2114.10010108.100010.8.lBYGxH)
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Its not so precision, but maybe can be used
http://www.aliexpress.com/item/1-Pcs-New-5A-ACS712-Range-Current-Sensor-Module-Electronic-Parts-Hall-Effect-Detector/32387779613.html?spm=2114.10010108.100010.8.lBYGxH (http://www.aliexpress.com/item/1-Pcs-New-5A-ACS712-Range-Current-Sensor-Module-Electronic-Parts-Hall-Effect-Detector/32387779613.html?spm=2114.10010108.100010.8.lBYGxH)
Thanks han,
It is not appropriate for what I'm trying to do, But I think I can use this chip on other projects.
Thanks
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Your description lacks details... For example could you move sensing to the low side? That would help.
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Your description lacks details... For example could you move sensing to the low side? That would help.
Hi Kilrah
Sorry what do you mean by "moving sensing to the low side"?
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http://electronicdesign.com/power/what-s-difference-between-high-side-and-low-side-current-sensing (http://electronicdesign.com/power/what-s-difference-between-high-side-and-low-side-current-sensing)
This from the article is the issue you are running into.
A few special considerations must be taken into account when using high-side current measurement. For one, the precision amplifier across the sense resistors must be able to deal with the supply voltage as a common-mode voltage.
Also you say the Hall effect current sensor is not appropriate but you don't say why. Hard to advise you that way.
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http://electronicdesign.com/power/what-s-difference-between-high-side-and-low-side-current-sensing (http://electronicdesign.com/power/what-s-difference-between-high-side-and-low-side-current-sensing)
This from the article is the issue you are running into.
A few special considerations must be taken into account when using high-side current measurement. For one, the precision amplifier across the sense resistors must be able to deal with the supply voltage as a common-mode voltage.
Also you say the Hall effect current sensor is not appropriate but you don't say why. Hard to advise you that way.
Oh thanks that really helped.I need to test this method.
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Also you say the Hall effect current sensor is not appropriate but you don't say why. Hard to advise you that way.
I didn't say that Hall effect current sensor is not appropriate for my job! I just checked that sensor manual and the precision was not what I needed in my project.I need to measure current change in milli-amps precision if you know any hall-effect sensor that has this precision I would thank you if you let me know about it.
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The Adafruit INA219 is a quick and painless solution. It is also a 12bit ADC giving 4x the accuracy of the 10 bit ADC.
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The Adafruit INA219 is a quick and painless solution. It is also a 12bit ADC giving 4x the accuracy of the 10 bit ADC.
Wow. Thanks so much. This is exactly what i was looking for! :-+ :-+ :-+