Hello all,
In the work life I've been handed an issue with an instrument.
The instrument is powered by a (transformer) isolated DIN rail switch-mode PSU and it's been reported many of them are floating well above ground (sometimes around 80VAC) - my initial instinct is to tie 0V PSU output to mains referenced earth, which has been tried on test equipment and certainly stops the floating issue (and the odd nibble from the damn things), as it is expected to.
However, with isolated PSUs (they're not my area!) is there anything inherently wrong with doing this? They're clearly no longer entirely separated but as the whole installation is well earthed so that isn't an especially great concern to me.
As an aside, and I've spent the morning trying to work though out, these instruments are measuring from sensitive electrodes in to instrument amplifier circuits, the input (and subsequently output) appears much more stable with the PSU 0V to Ground, which is the opposite of what I expected?! Am I going mad or is this plausible?