Analog Discovery 3 loud clicking noise when changing gain range

[Walid]

Hi,

I just started working with the Analog Discovery 3 and noticed when changing gain ranges from 500mV/div to 1V/div (going from 5Vpk-pk to 50Vpk-pk) there is a rather loud "click" from what sounds like a mechanical switch (perhaps a reed relay?). I'm just wondering if this is normal behavior as it is silent when gain range changing on the AD2, and also if there is any lifetime issues with such a loud mechanical switch?

Thanks,

Walid 

Edited June 19, 2023 by Walid
Forgot to mention "Analog Discovery 3"

[attila]

Hi @Walid

Yes, this is normal. In Analog Discovery 3, the oscilloscope input ranges are switched by relays.
The electrical endurance is rated at 10^5, but since it is used to switch very low current and capacitance, we can take the mechanical durability of 10^8 (100M) as a guide.

[Walid]

Thank you Attila, that is good to know this sound is normal and the device has very long lifetime. Was there a performance reason why mechanical relays were used instead of an electrical FET switch?

Thanks,

Walid

[attila]

Probably to reduce the internal and input capacitance.