Connecting Signals
4-11
Figure 4-7. Connecting an Ungrounded Thermocouple
As discussed in “Understanding the DAS-TC/B Inputs” on page 4-8, no
external connection to the B GND terminal is required; the common mode
connection is provided by an internal 10k
Ω
resistor.
Note:
If the junction of a thermocouple is connected in some way to the
output of an isolated power supply, it is sometimes better to connect the
object being monitored to the analog ground (B GND). The capacitance
to ground in even a highly isolated power supply can be hundreds of
picofarads, providing a substantial path for high frequency noise.
Connecting the object being monitored to the analog ground (B GND)
helps this noise to be rejected as a common mode signal, instead of
flowing through the thermocouple and being accepted as part of the
measured signal. Refer also to the next section, “Connecting a Grounded
Thermocouple.” Trial and error is sometimes required to achieve the best
connection for your application.
Thermocouple
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
NC
