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

>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
>using ICL7106 and a LCD as a display (in differential mode). Everything
>works but when I close the box and screw it down the ICL readout increases
>by about 20mV. It increases linearily as I tighten the single screw.
>
>The analog voltage is checked and ok with a Fluke DVM. The ICL does this.
>I have never seen such a thing. I have checked that there are no
>components under tension (mechanical). All the modules are hot-glued to
>the front of the box for trials so there is no way some bracket presses
>the wrong way.
>
>The DMM is a module which I have hacked slightly. It is built on 1.8mm FR4
>with through holes, zebra mounted LCD with elastic plastic bracket and the
>ICL is socketed in a solid socket.
>
>The change also occurs if I press on the front of the box (no matter
>where). Nothing touches the parts from the backside (there is a 3/4"
>clearance to the bottom of the box).
>
>Any ideas are very welcome,
>
>thanks,
>
>Peter
>
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Ray Gardiner ray@dsp.com.au
[ 2001 ]

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