Analog input voltage changes when connected to USB 6008 DAQ,

[jarhead]

Hi, I'm using an USB6008 daq measuring a simple voltage drop across a temperature diode. My range is set for +,- 5V and using Diff input. Using a DMM, I measure .576Vdc when I connect the leads to the Daq it drops to 0.570Vdc. A second channel is measuring pressure with a PCB ICP transducer and signal conditioner. Open circuit I measure 1.223Vdc, when I connect the leads to the Daq it jumps up to 1.341Vdc. Not sure what is going on! 

[SnowMule]

Use a voltage follower buffer between the sensor and DAQ.

Meter's impedance is >1megΩ.  600x is about 140kΩ. 

[jarhead]

Thanks, makes sense. Most Daqs are High Impedance, why design it with 144K input?

[SnowMule]

600x is low-cost, not high-performance.  You get what you pay for.  (Bang-for-buck though, they're a damn good deal IMO.)

621x's are a lot better all around, and they're about 6x the price.