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This multimeter is in between a Rpi0 3.3V pin and a BME280 sensor VCC. Most of the time the sensor is sleeping. You can see on the picture, the reading is 620µA, which seems high. Now if I use the range mA the reading is around 0.16mA. From this question (A really basic question about ammeters and their ranges) should I conclude to not use the µA range from this multimeter? Or is there a way to mitigate the shunt knowing both range reading?

multimeter reading

multimeter datasheet

Edit 2 sensor datasheet: sensor datasheet

Edit 3 circuit: Black Crocodile to COM and red crocodile to INPUT of multimeter. The red wire doing an arc above the Raspberry pi 0 was not plugged to the 3.3V pin at the time of the picture. circuit

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    \$\begingroup\$ Can you put a large plastic RF cap across the meter. And repeat measurments? \$\endgroup\$ Jul 15, 2021 at 16:01
  • \$\begingroup\$ I have 0.1µF around, I guess not large enough. I can find bigger. What do you mean by 'across the meter'? \$\endgroup\$
    – user291059
    Jul 15, 2021 at 16:20
  • \$\begingroup\$ Schematic and data sheets required. \$\endgroup\$
    – Andy aka
    Jul 15, 2021 at 17:49
  • \$\begingroup\$ If you're worried about the burden of the ammeter, you might trust the higher scale reading more than the more sensitive scale reading - even though % error is larger. \$\endgroup\$
    – glen_geek
    Jul 15, 2021 at 21:14
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    \$\begingroup\$ 0.1 & 0.01 uF in parallel. \$\endgroup\$
    – Russell McMahon
    Jul 16, 2021 at 0:16

2 Answers 2

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The numbers you are seeing on the meter may be just the result of its inherent inaccuracy. The meter error is specified as \$\pm(1.0\% + 7)\$, where the "7" means a count of 7 in the least-significant digit.

If you are on the \$400\,\mu\text{A}\$ range the meter's accuracy is \$\pm 4.7\mu\text{A}\$. The error increases by a factor of ten as you increase the range by a factor of ten. On the \$40\,\text{mA}\$ range the error is \$\pm 0.47\,\text{mA}\$.

I think your measurements are just noise on the \$\text{mA}\$ range. If you are measuring \$620\mu\text{A}\$ then you must be on the \$4000\,\mu\text{A}\$ range, and the inaccuracy of that value is \$\pm 47\mu\text{A}\$.

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  • \$\begingroup\$ I guess I will have to learn where this multimeter has a reading I can trust and find a good multimeter for mA/v and uA/V. \$\endgroup\$
    – user291059
    Jul 20, 2021 at 2:39
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Check out the resistance that the meter has when used as an ammeter for very low currents. Most multimeters don’t behave like an ideal ammeter ( a short circuit), and so you can get quite a bit of voltage drop across the meter when measuring micro amps. This leads to big errors in low voltage circuits.

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