©
National Instruments Corporation
13
NI USB-9213 User Guide and Specifications
The NI USB-9213 multiplexes 16 thermocouple input channels, one
cold-junction compensation (CJC) channel, and one autozero channel to a
single ADC. Each channel has a resistor that produces an input impedance
between the TC+ and COM terminals and between the TC– and COM
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. Refer to the
section for more information
about errors resulting from source impedance.
Figure 10.
Input Circuitry for One Channel of the NI USB-9213
The channels share a common ground, COM, that is isolated from other
modules in the system. The NI USB-9213 common-mode range is the
maximum voltage between any channel and COM. If COM is not
connected, then the common-mode voltage range is the maximum voltage
between any two channels. The NI USB-9213 measures the common-mode
voltage level of each channel and returns a warning in the software if the
signal is outside the common-mode voltage range. Refer to the
section for more information about the common-mode
voltage range.
The NI USB-9213 supports high-resolution and high-speed timing modes.
High-resolution timing mode optimizes accuracy and noise and rejects
power line frequencies. High-speed timing mode optimizes sample rate and
signal bandwidth. Refer to the
section for more information
about the high-speed and high-resolution timing modes. Refer to the
software help for information about setting the timing mode, or conversion
time, in software. Visit
ni.com/info
and enter
cseriesdoc
for
information about C Series documentation.
TC+
TC–
COM
USB-9213
Input
Impedance
Open
Thermocouple
Detection
Current
Filtered
Differential
Amplifier
and
Multiplexer
Isolated
ADC
39 M
Ω
39 M
Ω
