NI 9213E Operating Instructions and Specifications
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NI 9213E Circuitry
Each channel of the NI 9213E passes through a differential filter
and then is multiplexed and sampled by a 24-bit analog-to-digital
converter (ADC). Each channel also 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. Refer to Figure 5 for an illustration of
the input circuitry for one channel of the NI 9213E.
The NI 9213E multiplexes 16 thermocouple input channels,
1 cold-junction compensation (CJC) channel, and 1 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.
