Ray Gardiner wrote:
>
> If I remember the 7106 is a dual slope integrating type, so screwing
> the lid closed is probably just changing the capacitance.
>

Yes, but since it is dual slope, it is relatively insensitive to the
actual capacitor value.

My antenae point toward ground and ground currents.  A return ground
current from some other device may be afecting the DMM, and when you
close the box, which is a fairly lousy path (the actual current divides
between the wire return and the box resistance), then the current which
passes through the ground between the DMM and the central ground point
wavers.  I would measure the voltage between DMM ground and the central
ground.  It is not unusual to see many millivolts.  See if it wavers
when you screw it.  I would make the DMM ground go to the same point of
ground that the voltage source comes from.  Then they go to ground
without carying other return currents.

If that fails, get an antenna and wave it all over the lab until the
management thinks that you are long overdue for a vacation. Mumble
something about EMI invaders.

Chirs


> >Hi,
> >
> >I am completely stumped by this one, so I submit it to an entity with more
> >experience. I have a simple analog measuring circuit that outputs a
> >voltage between 1.5 and 2.5V vs. a reference of 1.5V. This goes to a DMM

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu