Measurement Computing DBK Part 2 - Manual (Page 148)

Source impedance below 1000 ohms will create negligible error. Above 1000 ohms, the effects are
increasingly noticeable. An accurate source in series with a variable resistance will readily demonstrate
this. Although the effect is exponential, an easy reference point to remember is that 25K of source
impedance will result in approximately a 10% error.
Reading Error vs. Source Resistance
Analog Ground
J7 and J8 provide access to analog ground. The most common use for them is to provide a ground
reference point for differential measurements. This is discussed in the Signal Management section of
Chapter 1.
Although J7 and J8 are electrically equivalent to the "L" signal of the excitation source,
they should never be used as the return point for the excitation source.
Card Configuration
Configuration of the DBK80 involves setting the channel address and selecting the
excitation output voltage.
Up to sixteen DBK80 cards can be attached to a single LogBook or Daq device, providing
up to 256 differential input channels.
Since multiple cards are connected via a parallel interface, each card must have a unique
channel address. To assign a channel number to the card, locate the 16×2-pin header
(labeled JP1). JP1’s jumper locations are labeled CH0 through CH15. Place the jumper
on the two pins that correspond with the intended channel.
Only one channel configuration jumper is to be used per card.
Each card in the system must have a unique jumper setting.
DBK80 pg. 4 989494 DBK Option Cards and Modules