## Current VS time graph about ADC-16

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skyNAH

### Current VS time graph about ADC-16

Hi,
I'm encounting a problem that if my input voltage more than 2v so that i need to use the voltage devider circuit provided by the terminal board of ADC-16. By using this voltage divider circuitry, i'm able to get the Voltage VS time graph. Now If I WANT TO GET THE CURRETN VS TIME, WHAT SHOULD I DO????(ASSUME I ALREADY USING THE VOLTAGE DIVEDER CIRCUITRY and If i'm not using the voltage divider circuitry, then i know i can get the current VS time by just set some parameter when i set up the channel. )
Thanks very much!!!!!!!!

skyNAH
why no body help??

Sarah
Hi

Thank you for your post.

If you want to measure current then I would suggest you nee to use a shunt resistor circuit rather than a voltage divider. If you are using a voltage divider then you are measuring voltage from the start.

You could use calculated parameters to scale any reading you are getting.

Hope this helps

Best Regards

skyNAH
Ok,for the shunt resistor circuitry,i have 2 questions to ask:
1st: If input voltage is more than 2.5V, how can we biuld up the circuitry?
2nd: For input smaeer than 2.5v, one terminal of Rb should connect to
ground, and how about another one? connect to postiove voltage or what??

Thanks a lot. PLS reply ASAP...

Sarah
Hi

Thank you for your post.

I am rather confused as to what you are trying to measure. If as you say your voltage is bigger than 2.5V then you need to use a potential divider. I was under the impression that you required to measure a current (ie A or mA) not a voltage.

The shunt resistor needs to be used for a current input in order to turn it into a voltage. In which case you use Ohms law to figure out what size of resistor you will need.

I'm afraid I do not know what you mean by "input smaeer".

Hope this helps

Best Regards

skyNAH
ok,I tell you my case.
I wanna measure current of a MP3 player. The MP3 using a li-on battery(3.5v to 4.2v). So how i can measure it?
Thanks for your help

Sarah
Hi

Thank you for your post.

You are going to need a very small resistor. Something like 50mOhms, however you will need investigate the size of this yourself.

This resistor needs to be connected in serial so you can measure the voltage across it.

The problem you could see is that the current in these applications is very small, thus you need a very small resistor and it could prove difficult to measure.

Hope this helps

Best Regards

skyNAH
Hi, according to the user guide of ADC-16 terminal board, it said to measure a current, i need to connect a shunt resistor, the value of the resistor is R=2.5v/Imax. In my case,if my mp3 player maximum current is around 700mA, so should i use the R=2.5v/0.7A=3.5ohms?

Further more, they said this method can't apply for measureing main current? So can you tell me what does that mean??

Sarah
Hi

Thank you for your post.

The equation you have stated sounds correct.

With regards the comment on mains current, this means you should not try to use this method for measuring the current of mains electricity - ie a plug socket.

Hope this helps

Best Regards

Guest
what is a voltage divider?

Sarah
Hi

Thank you for your post.

A voltage divider is something which attenuates a voltage - ie, makes it smaller. See this website for more details:

http://www.electronics2000.co.uk/data/i ... potdiv.htm

Hope this helps

Best Regards