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### Topic: Multimeter current reading range? (Read 191 times)previous topic - next topic

##### Sep 21, 2019, 06:10 pm
Hello,

I am trying to lower the energy consumption of my projects for long term baterry usage. It is the first time I really try to measure current with my cheap multimeter.

When the MMeter is on the 200μA range and it shows 00.2 doesn't this mean 0.2μA? Surely this is not possible, it is too low. Is my range wrong? I am confused.

#### wvmarle

#1
##### Sep 21, 2019, 06:21 pm
Why would that be too low?

And: what does the manual of your multimeter have to say about it?
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

#2
##### Sep 21, 2019, 07:05 pm
Firstly, thanks for your reply. The manual was my first thought. I think it aggrees with me that 00.2 is 0.2μA (see attached).

Project layout starts from a 9V battery connected to a step down buck converter to get 5V for the arduino and a PIR sensor (HC-SR501).

My sketch should do 2 things (Nano powered from the 5V pin/  power on led was removed for saving energy):
State 1. Be in power down mode.
State 2. When the PIR senses movement it wakes the arduino which lights its onboard led and triggers a piezo 'alarm'.

The PIR is consuming energy all the time (quiescent current as per datasheet is 50μA.

So what I get is:
State 1. Range: 200μA Measurement: 00.2
State 2. Range: 200μA Measurement: 00.5

The difference between states is very small I think.

#### jremington

#3
##### Sep 21, 2019, 09:28 pmLast Edit: Sep 21, 2019, 09:29 pm by jremington
I agree that the reading seems too low. Measure just the PIR sensor current to see what the meter reads.

You should also check the meter with a large resistor, for example 1 Megohm, in series with the 9V battery. The current should then be about 9 uA.

If "power down" is correctly implemented and you have no other current drains, then the ATmega328 processor should consume less than 200 nanoAmperes. See this excellent tutorial.

#### srnet

#4
##### Sep 21, 2019, 09:38 pmLast Edit: Sep 21, 2019, 09:38 pm by srnet
Is my range wrong?
You have the multimeter plugged into the socket for the 10A range.
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#5
##### Sep 22, 2019, 12:24 am
You have the multimeter plugged into the socket for the 10A range.
Correct, I did that since the mA range did not give me a reading at all. Finally, I determined that the fuse of the mA range is toast... I'll get a new one on Monday and post results.

Thanx everybody!!!

#### srnet

#6
##### Sep 22, 2019, 08:05 am
Correct, I did that since the mA range did not give me a reading at all. Finally, I determined that the fuse of the mA range is toast... I'll get a new one on Monday and post results.
Think how much time would have been saved if in your first post you had told us the full story !
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#### MarkT

#7
##### Sep 22, 2019, 09:30 pm
The most common reason the fuse blows is leaving the multimeter probe plugged into the current
input - so always leave it plugged into the voltage input after taking a current reading - its so easy to
stick the probes across a voltage supply without thinking.
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