Value of an sensitive Analogsensor changes heavy with other power sup. than USB

Hi,

now I measured the voltage with my multimeter at the Arduino pins and the result was good.

When I connect the multimeter to the pins the value on my LCD directly sinks from approx. 60 to 34 with no load and the Multimeter shows 0.00 VOLT. (Knows everyone why the Value on the LCD directly sinks??)

When I add a weight of approx 600 g. to the sensor my value on the LCD raises to approx 924 and the multimeter shows 4,5 Volt.

Looks like everything is fine ?

The only small problem I have now is that the value raises logarithmic (as described in the datasheet) and I would like to have it more linear fo accuracy.

Is it a possibilty to use an "amplifier" as an MCP6001 or something else?

The conversion from Voltage to Newton is of course no problem either way.

Thanks for your help

Ralf