Figure 8. FD-11613 Block Diagram
TC0+
TC0–
TC7+
TC7–
5.34 M
Ω
Input
Impedance
Open
Thermocouple
Detection
Current
Isolated
ADC
Filter
ISOLATION
Ethernet Ports
Ethernet Switch
Digital Logic
5.34 M
Ω
Input
Impedance
Open
Thermocouple
Detection
Current
Isolated
ADC
Filter
Hardware
Data
The FD-11613 provides channel-to-channel isolation.
•
Input Impedance
—Each channel has a resistor that produces an input impedance
between the TC+ and TC- terminals. The gain and offset errors resulting from the source
impedance of connected thermocouples are negligible for most applications.
Thermocouples with a higher lead resistance can introduce more significant errors.
•
Open Thermocouple Detection
—Each channel has an open thermocouple detection
(OTD) circuit, which consists of a current source between the TC+ and TC- terminals. If
an open thermocouple is connected to the channel, the current source forces a full-scale
voltage across the terminals and the Open Thermocouple LED lights red.
Refer to the
Open Thermocouple Detection (OTD)
topic in the
NI-DAQmx Help
for more
information about how this feature is used in the NI-DAQmx API.
14
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FD-11613 User Guide