adafruit_support wrote:I tested with power from the circuit as well as with separate power for the meter supply. The results were similar. Meter power draw ranged from about 11-24 mA depending on voltage and how many segments were lit. The variability due to display means that the 24mA constant in your error calculations is not quite valid and the actual discrepancy is likely smaller. I found it to be generally within about 3% of my supply.
#1. It's valid for the meter I got ... The lowest current draw at a supply voltage of 4.5V was 20 mA, your meter acts different than mine. Nevertheless, the stated spec of a "3 - 4 mA draw" is incorrect on the product specification page. We agree on that.
#2. You didn't mention the other fact that the meter doesn't read from "0.00 - 9.99 A" - that's impossible since the meter can only start giving a reading at 0.01 mA. It simply doesn't have the physical digits to give a reading lower than .01 mA. You need to change that spec since, if a customer wanted one to read from 1 mA to .01 mA, they are going to be disappointed by the stated specs of 0.00 - 9.99 A.
#3. I also just now noticed this - the power rating on the side on the unit I have says input must be between 4.5 and 28 V. Your spec says 4.5 - 30V! That's wrong too.
Even using your calculated calculated error
At 1.71A (indicated) was less than 1% (0.014)
And at 1.92A (indicated) it was just over 3%.
But of course we are now talking about an accuracy spec that isn't even stated. You can't say if it's acting correct or not without referencing the accuracy you measured against what it is claimed to have by the manufacturer - and the spec is missing that number. But I can judge it against a very cheap meter ($2.99) that beats it easily. Since you seem to use the "It ain't bad for a $10 meter" benchmark I can use that same logic and trump you because my meter is $7 less than yours and is better.
All-in-all, not bad for a $10 meter.
I don't agree at all. It's not good for a $10 meter that is only dedicated to measuring current. That's all it has to do. The $2.99 Chinese El cheapo meter is less money and more accurate and does a lot more, so I can't agree with this statement. It gets' beat hands-down by a less expensive/more capable unit.
The whole problem with this thing is one of expectations vs. realities. If the spec said this (modified specs) -
4.5V to 28V DC power <-- this is now correct
0.01 -9.99 Amp DC current sensing <-- this is now correct
14cm long wires, 26 AWG for power wires, 20 AWG for current wires
0.01 ohm shunt
12 - 25 mA draw <-- this is now correct
3 - 4% accuracy <-- this is now correct
Red LED display
Reverse polarity protected
I would have nothing to complain about. Do you understand?
I just got my Adafruit Arduino kit today so I'm off to see about that ...