Connecting Signals
4-13
The upper two circuits of the diagram require the addition of resistors to
provide a bias-current return. You can determine the value of the bias
return resistors (R
b
) from the value of the source resistance (R
s
), using the
following relationships:
●
When R
s
is greater than 100
Ω
, use the connections in the upper
circuit. The resistance of each of the two bias return resistors must
equal 2000 R
s
.
●
When R
s
is less than 100
Ω
, use the connections in the middle circuit.
The resistance of the bias return resistor must be greater than 1000 R
s
.
In the lower circuit, bias current return is inherently provided by the
source. The circuit requires no bias resistors.
Figure 4-11. Three Types of Connections for Wiring a Signal Source to a DAS-1800HC
Series Board Configured for Differential Inputs
Channel
n High
Signal
Source
+
-
AGND
DAS-1800HC Series Board
R
b
R
b
R
s
Channel
n Low
Where R
s
> 100
Ω
R
b
= 2000 R
s
Channel
n High
Signal
Source
+
-
AGND
DAS-1800HC Series Board
R
b
R
s
Channel
n Low
Where R
s
< 100
Ω
R
b
= 1000 R
s
Channel
n
High
DC
Supply
+
-
DAS-1800HC Series Board
Channel
n Low
AGND
Bridge
R
s
R
v
Where R
v
is a
variable resistor for
balancing the
bridge
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