Issues with 1608G SE voltage capture

[Dan Schultz]

Hello,

We just purchased a 1608G for simple 0-5V SE capture monitoring a PLL.  We had been using a pair of Minilab 1008's for years (we need 16 channels) but wanted to both simplify and something with better resolution.  What I am finding is with a sample rate at anything over 20S/sec, all channels will "follow" each other.  If any channel goes high, they all do.  If I drop the sample rate to under 5S/sec, it improves, but there is still interference on surrounding channels (ie if channel 3 goes high, channels 4 and 5 will also).  Any help would be appreciated.

Thanks

[DAQman]

Left unconnected, the inputs will charge to stray voltages. This phenomenon is partly due to the chips used to switch the channels to the A/D converter. On some devices, the designers add 5M or 10M ohm resistors connected to the ground, which tend to pull the input back closer to zero when left unconnected. Long story short, connect the channels that are not in use to the ground or disable them in software.