Connecting Signals
4-15
Figure 4-11. Connecting a Grounded Signal Source
A common mode connection should be made directly between the ground
of the signal source and the analog ground (B GND). This low-resistance
external connection essentially overrides the internal 10k
Ω
resistor of the
DAS-TC/B.
Note:
Connect the analog ground (B GND) to the ground of the
grounded object. Do not connect the analog ground (B GND) to the Low
input connection at the board. Connecting the analog ground (B GND) to
the Low input at the board—or allowing the internal 10k
Ω
resistor to
make such a connection by default—causes any noise current between the
grounded object and the analog ground to flow across the Low signal
lead, resulting in a noise voltage across the lead. The input amplifier then
accepts this noise voltage as part of the Low input signal, instead of
rejecting the noise voltage as a common-mode signal.
Refer also to the note in “Connecting a Grounded Thermocouple” on page
4-12.
Channel n High
Channel n Low
Optional Shield
Es
STA-TC/B
or
STP-TC/B
Chassis
GND
Input
Amplifier
(To chassis via S-1800
cable for STA-TC/B)
B GND
R
WIRE
Do not join Low
to GND at the
board
Es
Signal
Source
+
-
Signal Source
Ground V
g1
V
g2
- V
g2
V
g1
V =
cm
V
cm
