INA219 Voltage Drop when connecting to source

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Divinitous
 
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INA219 Voltage Drop when connecting to source

Post by Divinitous »

I'm an engineer at a company that services a machine that uses fiber optics to detect the meniscus of water inside a glass tube. When the line of sight for the optics is broken the voltage drops from 10.5v to <1v. We have dozens of these systems in the US and the circuit for the fiber optics needs to be tuned to a proper voltage every few months to counteract the degradation of the optics. To do this we need to open the machine and measure the voltages. I am trying to make a small box that would allow us to keep it connected and display the voltage for us.

I have made a few arduino tools to help in the past but I am having trouble with this one. The INA219 seems to not be compatible with the fiber optics circuit. I have the coding and the arduino working perfectly fine. I can measure any voltage inside the acceptable range from an external source. But when I connect it to the optics circuit the voltage that is 10.5v drops down to 8.3v. All voltages are correct in that this is also what I see with my multimeter.

Is there a possible way for me to measure this voltage without adding this interference? When using my multimeter there is no drop.
Why is there when using the INA219? I am using the Bus inputs but have also tried the load input as well. I have no interest in current, only voltage and have the code set to calibrate it to 16v 400mA

Code: Select all

ina219_1.setCalibration_16V_400mA()
.

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adafruit_support_mike
 
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Re: INA219 Voltage Drop when connecting to source

Post by adafruit_support_mike »

Post a photo showing your hardware and connections please.

The only thing that should be in the supply current path should be the 0.1 ohm sense resistor, and that should have no effect on the voltage at Vin.

800x600 images usually work best.

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Divinitous
 
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Re: INA219 Voltage Drop when connecting to source

Post by Divinitous »

adafruit_support_mike wrote:Post a photo showing your hardware and connections please.

The only thing that should be in the supply current path should be the 0.1 ohm sense resistor, and that should have no effect on the voltage at Vin.

800x600 images usually work best.
Mike,
Below is the circuit I need to work with. I cannot make any changes to this. I need to monitor two voltages, A and B. I'm trying to do this by connecting the circuits ground to the arduinos ground and the A to Vin+ on the bus side.
circuit.jpg
circuit.jpg (235.42 KiB) Viewed 289 times

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adafruit_support_mike
 
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Re: INA219 Voltage Drop when connecting to source

Post by adafruit_support_mike »

That shouldn’t cause any problems. What do you have connected to Vin-?

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ImaginaryAxis
 
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Re: INA219 Voltage Drop when connecting to source

Post by ImaginaryAxis »

The INA219 measures a differential voltage centered on some common mode voltage.

From your replies, it sounds like you are connecting V+ or V-; however, they both need to be connected.

Be very mindful of the expected differential voltage and the gain you have the INA219 programmed too as to not rail the output.

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