Re: Multimeter damaged when powered from regulated power suppy.

Thanks to all help with ascii schematic, here are the figures again. In
the DMM, I assume
that HV probe is protected with respect to the Probe GND. But GND
itself is not protected
from the supply gnd. So adding the zener/filter cap must be good enogh
to protect the whole thing. Caution has to be taken to see that the
entire thing is treated as a live circuit.
In that way the battery thing may be more dangerous thing because
changing the battery
means, in case you forget to disconnect the probe you are in danger. (
Just a thought!).


First Picture:

.. DANGER HIGHVOLTAGE
..
.. .---------------. .---------------.
.. L | | 9V | | Probe HV
.. ------------ -------------- ----------
.. | | | |
.. | | | 7107 Mtr |
.. MAINS | 9 V | | |
.. | Supply | | |
.. | | | |
.. | | 0 | |Probe GND
.. ------------| -------------- ----------
.. N ----------------' '---------------'

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Second Picture:

.. DANGER HIGHVOLTAGE
..
.. .---------------. .---------------.
.. L | | 9V | | Probe HV
.. ------------ -------------- ----------
.. | | | |
.. | | | 7107 Mtr |
.. MAINS | 9 V | | |
.. | Supply | | |
.. | | | |
.. | | 0 | |Probe GND
.. ------------| ------|------- ------|---
.. N ----------------' | '---------------' |
.. | |
.. | Elec. Cap |
.. | \] |
.. |--------------|]------------|
.. | /]+ |
.. | |
.. | |
.. --------------->z------------|

Zener


(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Third Picture:

.. Equivalent Circuit.
..
..
.. L
.. ---------------| |
.. | |
.. | Leakage Cap | Leakage Cap
.. --- ---
.. --- ---
.. | |
.. | |
.. | |
.. GND | | GND
.. | |
.. | |
.. |+ |
.. === z Zener
.. /-\ A
.. | |
.. | |
.. | |
.. N | |
.. ------------------ |.

On The assumption that HV Probe is already protected in DMM

Additional protection only for Probe GND
with respect to Supply GND

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

.

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