# QA403 input protection

**URL:** <https://forum.quantasylum.com/t/qa403-input-protection/1611>\
**Category:** Uncategorized\
**Created:** [November 2, 2024, 10:14am UTC](https://forum.quantasylum.com/t/qa403-input-protection/1611 "2024-11-02T10:14:19Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![John1](https://avatars.discourse-cdn.com/v4/letter/j/e9bcb4/32.png) [@John1](https://forum.quantasylum.com/u/John1)\
**Post date:** [November 2, 2024, 10:14am UTC](https://forum.quantasylum.com/t/qa403-input-protection/1611/1 "2024-11-02T10:14:19Z")

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Can a 10 Vrms signal that is connected for some seconds in the input to harm it if the QA403 is out of the usb?

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**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\
**Post date:** [November 3, 2024, 5:01pm UTC](https://forum.quantasylum.com/t/qa403-input-protection/1611/2 "2024-11-03T17:01:29Z")

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Hi @John1, no it cannot. When the USB is disconnected, the input attenuator is engaged by default (that is, relay must be energized to turn off attenuator). I would guess even 100Vrms applied to input on unpowered device won’t cause a problem for several seconds.

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**Author:** ![John1](https://avatars.discourse-cdn.com/v4/letter/j/e9bcb4/32.png) [@John1](https://forum.quantasylum.com/u/John1)\
**Post date:** [November 3, 2024, 5:35pm UTC](https://forum.quantasylum.com/t/qa403-input-protection/1611/3 "2024-11-03T17:35:45Z")

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Thank you very much!