Omega Engineering OMB-DBK-34A, User Manual

Page: 208 / 250

Card Configuration
Factory Defaults
•
100K bias resistors – Enabled
•
Low-Pass Filter – Bypassed (Disabled)
•
Gain – x1
Input Termination
DBK18 provides two 100 K
Ω
bias resistors for
each analog input. For balanced 200 K
Ω
input
impedance, both resistors should be switched in.
An 8-position DIP switch (SW5) can selectively
engage the bias resistors. The input circuit and
switch positions are shown in the figure. The
switches must be in the closed position to engage
the termination resistors. For unbalanced high
input, only the (-) resistor should be used. If
neither resistor is used, some external bias current
path is required.
4-
4+
3-
3+
2-
2+
1-
1+
6
7
8
5
2
3
O
PEN
14
+
-
A A
N
100 k
Ω
S
W
5
Terminal
Block
+ _
Input Impedance/Termination
Examples of Bias Resistor Selection Options
Gain Settings
On the card, each channel has a gain-set switch labeled GAIN 1 (SW1) to GAIN
4 (SW4) and holes for gain resistors labeled RG1 to RG4. The table in the figure
shows gain values for switch settings 0 to 4. If a custom gain is desired, the
switch is set to position 0; and a gain resistor must be mounted and soldered onto
the card. The value of the gain resistor is determined by the formula:
R
GAIN
= [40,000 / (Gain -1)] - 50
Ω
Address Configuration
Up to 4 DBK18s can be connected to each analog channel. Since this is a
daisy-chain interface, each card must have a unique address (channel number
and card number). Note that the default setting of SW6 is Card 1.
To configure the card, locate the 16 × 2-pin header labeled JP1 near the front of
the board. The 16 jumper locations on this header are labeled CH0 through
CH15. Place the jumper on the channel you wish to use. Only one jumper is
used on a single card. Four cards in the daisy-chain can have the same channel
number as long as each card number is unique.
Set switch SW6 for each of the 4 DBK18s on a single channel. Verify that only
one card in a system is set to a particular channel and card number.
DBK18, pg. 2
918894
DBK Option Cards and Modules