# Measuring external subsystem with shunt

**URL:** <https://forum.qoitech.com/t/measuring-external-subsystem-with-shunt/295>\
**Category:** Support\
**Created:** [May 29, 2019, 7:48pm UTC](https://forum.qoitech.com/t/measuring-external-subsystem-with-shunt/295 "2019-05-29T19:48:36Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![moirelabs](https://avatars.discourse-cdn.com/v4/letter/m/49beb7/32.png) [@moirelabs](https://forum.qoitech.com/u/moirelabs)\
**Post date:** [May 29, 2019, 7:48pm UTC](https://forum.qoitech.com/t/measuring-external-subsystem-with-shunt/295/1 "2019-05-29T19:48:36Z")

</div>

Hello,  
Otii is great help for us in the office. I have recently tried to sense how much current is sourced though the battery so I have connected a 0R1 in series to to the battery positive lead and connected to DUT. Accorsingly connected ADC+ before and ADC- after the shunt. I have also connected the AGND to the negative battery lead.

What im getting seems like a correct graph, but incorrect scale and im getting both positive and negative values for current which seems strange. Voltage seems allright.

[![](https://europe1.discourse-cdn.com/flex017/uploads/qoitech/original/1X/fc58ecf2f9ed0d8f79bf311a0a03d31507d945c4.png) ](https://dl.dropboxusercontent.com/s/uaohby68dspqzsu/Screenshot%202019-05-29%2021.50.34.png?dl=0)

Any ideas?

Marcel

---

<div class="post-metadata">

**Author:** ![bjorn.rosqvist](https://dub1.discourse-cdn.com/flex017/user_avatar/forum.qoitech.com/bjorn.rosqvist/32/238_2.png) [@bjorn.rosqvist](https://forum.qoitech.com/u/bjorn.rosqvist)\
**Post date:** [June 3, 2019, 9:42am UTC](https://forum.qoitech.com/t/measuring-external-subsystem-with-shunt/295/2 "2019-06-03T09:42:00Z")

</div>

Hi Marcel,

This looks strange.  
If you only open the ADC current channel and measure current, without anything connected, do you get a large offset?

Best regards,  
Björn

---

<div class="post-metadata">

**Author:** ![moirelabs](https://avatars.discourse-cdn.com/v4/letter/m/49beb7/32.png) [@moirelabs](https://forum.qoitech.com/u/moirelabs)\
**Post date:** [June 4, 2019, 11:41am UTC](https://forum.qoitech.com/t/measuring-external-subsystem-with-shunt/295/3 "2019-06-04T11:41:04Z")

</div>

Without anything connected the current offset is in average -0.5uA and V offsetmaxes at 6mV.

---

<div class="post-metadata">

**Author:** ![bjorn.rosqvist](https://dub1.discourse-cdn.com/flex017/user_avatar/forum.qoitech.com/bjorn.rosqvist/32/238_2.png) [@bjorn.rosqvist](https://forum.qoitech.com/u/bjorn.rosqvist)\
**Post date:** [June 5, 2019, 6:38am UTC](https://forum.qoitech.com/t/measuring-external-subsystem-with-shunt/295/4 "2019-06-05T06:38:34Z")

</div>

Hi,

Could you share a picture, or block diagram, of your complete setup?  
If you do not want to share it here, then create a case in our case system.

Best regards,  
Björn