Review of the Adafruit Panel Current Meter

[modeller]

I got a little off topic with this in another thread so I thought it better to start anew.

Let's take a look at the specs of the panel current meter -

Power specifications:

4.5V to 30V DC power
0-9.99 Amp DC current sensing
14cm long wires, 26 AWG for power wires, 20 AWG for current wires
0.01 ohm shunt
3-4mA draw
Red LED display
Reverse polarity protected

First test - current draw of the meter itself (the current sensing wires are not used in this test). The meter circuitry uses 24 mA with 10 V supplied. The specs say it uses "3 - 4 mA". That's not correct. And yes, that lab power supply is correct, I checked it against that Tek DMM you see in the pic. Heck, a single LED can use from 10 - 20 mA not to mention the other components on the board so I don't know where that spec came from. Even supplying the lowest voltage to it (4.5V) it uses 20 mA.

Note: the breadboard you see is inactive - it's just a paperweight at the moment.

Moving on - We have a halogen lamp load, the panel current meter is low side sensing - a very simple circuit.

First example:

Lab PS reads 1.748 A
Panel current meter reads 1.71 A

Since the lab PS is also providing the 24 mA to the panel current meter, we have to subtract that from the lab PS current reading to obtain the current for the load only.

1.748 - 0.024 = 1.724 A load current
The panel current meter is therefore off by 1.724 - 1.71 = 0.014 A

Now for a little higher current:

Lab PS reads 2.00 A
Panel current meter reads 1.92 A

2.00 - 0.024 = 1.976 A load current
The panel current meter is therefore off by 1.976 - 1.92 = 0.056 A

The above load current measurements were verified with the Tek DMM.

I see three issues:

The panel current meter really can only indicate from 0.01 - 9.99 A, not 0 - 9.99 A.
The meter draws 20 - 24 mA - not "3 - 4 mA"
The meter is not very accurate at low currents but gets better as the current gets higher, but still isn't as good as comparable technology in the class, such as the DMM. I can do more tests if you want.

[adafruit_support_bill]

Thanks for the detailed analysis. Not sure that I would consider a $10 panel meter to be in a class comparable to a Tek DMM though.

I'll check one out on the bench and see if it performs similarly.

[modeller]

Thanks for the detailed analysis.

No problem. I probably wouldn't have dome it at all if it would have just read out 20 mA from my LED test.

I'll check one out on the bench and see if it performs similarly.

I'd be interested also.

Not sure that I would consider a $10 panel meter to be in a class comparable to a Tek DMM though.

Well, that DMM is probably about 15 - 20 years old, and I figure the technology has improved enough by now to match it with inexpensive technology. Case in point: see the attached pic? That meter on the right is a $2.99 Chinese El-Cheapo DMM I got at Harbor Freight Tools. I throw one in my car and keep another one in the garage. They are so cheap you can by 2 or 3 and toss them here and there. See that LED circuit? It's pulling 20 mA, and that El Cheapo meter can measure it quite nicely. It's $7 cheaper than the Panel Current Meter. As I said, the little meter won't even begin to register a current until it gets to 100 mA.

I Googled for that little meter trying to find out who really makes it. I do see you used boilerplate description for it which is the same as many other vendors are using so I understand how the specs could fly under the radar. I never was able to find the original manufacturer to see their original specs. I do believe something got lost in the translation.

I'm pretty happy with the panel voltmeter, but I doubt I'll use the panel current meter now. It's not like I'm trying to make sure a pacemaker is working correctly with it, but since I'm anal retentive I want to see accurate readings. You know how it is I'm sure.

[modeller]

I'll check one out on the bench and see if it performs similarly.

Any results yet? I have another idea but I don't want to try it until I hear what your results were.

[adafruit_support_bill]

It's in the queue. Possibly this afternoon. I want to test it with a a dual supply also to see if it makes a difference.

[adafruit_support_bill]

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.

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%.

All-in-all, not bad for a $10 meter.

[modeller]

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) -

Power specifications:

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 ...

[adafruit_support_bill]

You have some valid points and we will review the product descriptions. If you are not satisfied with the meter we can offer you a refund. Just contact support@adafruit.com with a link to this thread.

[adafruit]

Hi there, the 3-4mA measurement was a mixup copy&paste from the mini panel meter (those are much simpler/tinier and use less current) - thanks for alerting us to the typo description text has been updated!

[modeller]

I'm so confused ... I think we're talking in circles or something.

What's a "mini panel meter"?

You said -

Hi there, the 3-4mA measurement was a mixup copy&paste from the mini panel meter (those are much simpler/tinier and use less current) ...

What I got was the panel current meter -

https://www.adafruit.com/products/574

If that's not a mini panel meter, what is?

If you go to one of the distributors you list like this one -

http://shop.eeinabox.com/Panel-Current- ... egoryId=-1

You can see the specs are the same as what you had (I do see you changed them now)

eeinabox.com lists this -

Power specifications:

4.5V to 30V DC power
0-9.99 Amp DC current sensing
14cm long wires, 26 AWG for power wires, 20 AWG for current wires
0.01 ohm shunt
3-4mA draw
Red LED display
Reverse polarity protected

You can see if you Google it that all the distributors that sell this got the same boilerplate specs as you had from some source.

So I'm curious what the "mini panel meter" is that you are now referring to - the one you copy/pasted the 3-4 mA spec from? Maybe I'll buy one ...

Look the good news is that I got the Arduino kit and it's running fine so we're beginning to go on a positive slope ...

[adafruit]

this is a mini panel meter, as you can see its much smaller
http://adafruit.com/products/460
the copy we write for all our products is original, so if you see anyone else using suspiciously-similar text (and including our typos) then you can be pretty sure all these other shops just copy & pasted our text without reading or even checking its the same product

[modeller]

this is a mini panel meter, as you can see its much smaller
http://adafruit.com/products/460

OK thanks, I searched for it yesterday but didn't type in the proper terms.

the copy we write for all our products is original, so if you see anyone else using suspiciously-similar text (and including our typos) then you can be pretty sure all these other shops just copy & pasted our text without reading or even checking its the same product

FYI - you're being plagiarized by a fair amount of other sellers of this. They must like your writing.

For example, these sellers have the same exact writeup but I don't see they gave you credit for it if it's your words -

http://nicegear.co.nz/electronics-gear/ ... ent-meter/

http://www.emmeshop.it/product.php?id_product=557

Anyway, I think we're done. I do commend you for sticking with it and I admire your company for even attempting to provide support for a lot of products that are going to be used by learners and tinkerers who may not know what they are doing and even zap products that they'll want to return. That's a huge commitment so my hat's off to you.

OK back to the Arduino on my bench. What was I going to do? I think send random PWM values to some LEDS and observe the show for a while. I do have an idea coming forming involving the Arduino, the wave shield, and model railroads but we'll see.

By the way, do you want a review of the Adafruit Arduino kit? LOL - just kidding.

Thanks.

[adafruit]

A few of those might be our distributors - http://adafruit.com/products/574#distributors