NI-9210 Getting Started

NI-9210 Nomenclature

In this article, the NI-9210 with mini-TC and NI-9210 with spring terminal are referred to inclusively as the NI-9210.

NI-9210 Block Diagram


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The channels of the NI-9210 share a common ground isolated from other modules in the system. Each channel passes through a filter, and then a 24-bit analog-to-digital converter (ADC) samples the channel.

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.

Input Impedance

Each channel has a resistor that produces an input impedance 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.

NI-9210 with Mini-TC Pinout


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Table 1. Signal Descriptions
Signal Description
COM Common reference connection to isolated ground
TC Thermocouple connection

NI-9210 with Spring Terminal Pinout


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Table 2. Signal Descriptions
Signal Description
COM Common reference connection to isolated ground
NC No connection
TC Thermocouple connection

Making NI-9210 Thermocouple Connections

Connect the COM terminal to a common-mode voltage reference on the thermocouple.

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A valid common-mode voltage reference is a voltage that is within ±1.5 V of the common-mode voltage of all the connected thermocouples.

Guidelines for Minimizing Thermal Gradients

Changes in the ambient air temperature near the front connector or a thermocouple wire conducting heat directly to terminal junctions can cause thermal gradients. Observe the following guidelines to minimize thermal gradients and improve the system accuracy.

  • Use small-gauge thermocouple wire. Smaller wire transfers less heat to or from the terminal junction.
  • Run thermocouple wiring together near the thermocouple connector to keep the wires at the same temperature.

  • Avoid running thermocouple wires near hot or cold objects.
  • Minimize adjacent heat sources and air flow across the terminals.
  • Keep the ambient temperature as stable as possible.
  • Make sure the NI-9210 terminals are facing forward or upward.
  • Keep the NI-9210 in a stable and consistent orientation.
  • Allow the thermal gradients to settle after a change in system power or in ambient temperature. A change in system power can happen when the system powers on, the system comes out of sleep mode, or you insert/remove modules.
  • If you connect any extension wires to thermocouple wires, use wires made of the same conductive material as the thermocouple wires.

NI-9210 Connection Guidelines

  • Make sure that devices you connect to the NI-9210 are compatible with the module specifications.
  • For the NI-9210 with spring terminal, push the wire into the terminal when using a solid wire or a stranded wire with a ferrule.
  • For the NI-9210 with mini-TC, open the terminal by pressing the push button when using stranded wire without a ferrule.
  • For the NI-9210 with mini-TC, press the push button to remove wires.

NI-9210 with Mini-TC COM Connection Guidelines

Observe the following guidelines when connecting to the COM terminal.

  • You must use 2-wire ferrules to create a secure confecting when connecting more than one wire to a single terminal.
  • Open the terminal by pressing the push button when using stranded wire without a ferrule.
  • Push the wire into the terminal when using a solid wire or a stranded wire with a ferrule.

Thermocouple Measurement Accuracy

Thermocouple measurement errors depend partly on the following factors.

  • Type of thermocouple
  • Accuracy of the thermocouple
  • Temperature that you are measuring
  • Resistance of the thermocouple wires
  • Cold-junction temperature

Cold-Junction Accuracy

Heat dissipated by adjacent C Series modules or nearby heat sources can cause errors in thermocouple measurements by heating the NI-9210 terminals to a different temperature than the cold-junction compensation sensor. Thermal gradient across the terminals can cause the terminals of different NI-9210 channels to be at different temperatures, which creates accuracy errors and affects the relative accuracy between channels.

The temperature measurement accuracy specifications include errors caused by the thermal gradient across the NI-9210 terminals for configurations with the NI-9210 terminals facing forward or upward.

Autozero Channel

The NI-9210 has an internal autozero channel, which can be subtracted from each thermocouple reading to compensate for offset errors. Use the autozero channel if the ambient temperature is less than 15 °C or more than 35 °C. Refer to the documentation for the software that you are using for information about using the NI-9210 autozero channel.