# Signal DC offset only in MIM

**URL:** <https://forum.liquidinstruments.com/t/signal-dc-offset-only-in-mim/1098>\
**Category:** Moku:Pro\
**Created:** [January 14, 2025, 9:49pm UTC](https://forum.liquidinstruments.com/t/signal-dc-offset-only-in-mim/1098 "2025-01-14T21:49:04Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![sgmt](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@sgmt](https://forum.liquidinstruments.com/u/sgmt)\
**Post date:** [January 14, 2025, 9:49pm UTC](https://forum.liquidinstruments.com/t/signal-dc-offset-only-in-mim/1098/1 "2025-01-14T21:49:04Z")

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Hi all,

I’m measuring a signal from a photodiode. If I use the oscilloscope or lock-in as a single instrument it shows up normally, positive signal with a zero DC offset, and it disappears when I block the detector. However, if I set up an oscilloscope or lock-in in multi-instrument mode (even if it’s the only instrument), there is an offset of ~30mV. If I block the signal or even disconnect the photodiode, the offset remains. I’m using 0 db attenuation and 50 ohm impedance for both configurations. I’m using DC coupling but even if I change it to AC coupling the offset still remains.

Is there any reason why an offset could appear only in multi-instrument mode? Any suggestions for troubleshooting this and acquiring more reliable data in MIM?

Thank you

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**Author:** ![indira](https://yyz1.discourse-cdn.com/flex035/user_avatar/forum.liquidinstruments.com/indira/32/317_2.png) [@indira](https://forum.liquidinstruments.com/u/indira)\
**Post date:** [January 21, 2025, 9:31pm UTC](https://forum.liquidinstruments.com/t/signal-dc-offset-only-in-mim/1098/2 "2025-01-21T21:31:45Z")

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Hi @sgmt,

Unfortunately I’m not able to reproduce what you’re describing, are you able to share with my what firmware version you are using? I have just been made aware that there was a bug in a previous firmware where there is this offset in Multi-Instrument Mode but not Single instruments, as you are describing. If this applies to you, I suggest upgrading to the latest firmware via the App or API, which you can find [here](https://liquidinstruments.com/resources/software/).

Let me know if an update helps.

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**Author:** ![sgmt](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@sgmt](https://forum.liquidinstruments.com/u/sgmt)\
**Post date:** [January 22, 2025, 9:21am UTC](https://forum.liquidinstruments.com/t/signal-dc-offset-only-in-mim/1098/3 "2025-01-22T09:21:01Z")

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Hi @indira thank you for the response!  
Indeed, I must have missed an update. After updating the firmware the problem seems to be solved!