NI-9226 Getting Started

Connector Types

The NI-9226 has more than one connector type: NI-9226 with spring terminal and NI-9226 with DSUB. Unless the connector type is specified, NI-9226 refers to all connector types.

The NI-9226 with spring terminal is available in two types: push-in spring terminal and spring terminal. The push-in type spring terminal connector is black and orange. The spring terminal connector is black. NI-9226 with spring terminal refers to both types unless the two types are specified. Differences between the two types of spring terminal connectors are noted by the connector color.

NI-9226 Block Diagram


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  • RTD channels share a common ground that is isolated from other modules in the system.
  • Each RTD channel is filtered and then sampled by a 24-bit analog-to-digital converter (ADC).

NI-9226 with DSUB Pinout


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Table 1. Signal Descriptions
Signal Description
COM Common reference connection to isolated ground
EX+ Positive sensor excitation connection
NC No connection
RTD+ Positive resistance temperature detector connection
RTD- Negative resistance temperature detector connection

NI-9226 with Spring Terminal Pinout


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Table 2. Signal Descriptions
Signal Description
COM Common reference connection to isolated ground
EX+ Positive sensor excitation connection
NC No connection
RTD+ Positive resistance temperature detector connection
RTD- Negative resistance temperature detector connection

Connecting 3-Wire and 4-Wire RTDs

You can connect any combination of 3-wire or 4-wire RTDs to the NI-9226. Each NI-9226 channel contains circuitry that automatically detects the type of RTD connected to the channel. The NI-9226 scans all eight input channels and automatically configures each channel for the appropriate mode. In 4-wire mode, the EX terminal is a 0.1 mA current source. In 3-wire mode, the RTD+ terminal is a 0.1 mA current source. The NI-9226 compensates for the error that lead resistance causes in 3-wire mode.

If you are using a 4-wire RTD, connect EX to the positive lead of the RTD. If you are using a 3-wire RTD, do not connect the RTD to the EX terminal.

Figure 1. Connecting an RTD to the NI-9226

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For the best measurement results when using the NI-9226 with a 3-wire RTD, use equal-length wires between the RTD+ terminal and the RTD and between the COM terminal and the RTD. Also, keep the lead resistance within 5% of the nominal RTD value. The NI-9226 accuracy specifications account for this lead error.

Note The accessory used with the NI-9226 may introduce additional lead resistance mismatch error in 3-wire mode. Refer to the device specifications for information about errors due to lead resistance mismatch.

NI-9226 Connection Guidelines

Make sure that devices you connect to the NI-9226 are compatible with the module specifications.

Connecting to a Spring-Terminal Connector

What to Use

  • NI-9226 spring-terminal connector
  • 0.8 mm2 to 1.0 mm2 (28 AWG to 18 AWG) copper conductor wire with 7 mm (0.28 in.) of insulation stripped from the end
  • Flathead screwdriver with a 2.3 mm x 1.0 mm (0.09 in. x 0.04 in.) blade, included with the NI-9226

What to Do

Complete the following steps to connect wires to the spring-terminal connector.


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  1. Insert the screwdriver into a spring clamp activation slot to open the corresponding connector terminal.
  2. Press a wire into the open connector terminal.
  3. Remove the screwdriver from the activation slot to clamp the wire into place.

High-Vibration Application Connections

If your application is subject to high vibration, NI recommends that you use the NI-9940 backshell kit to protect connections to the NI-9226 with spring terminal.

Installing the NI-9940

To meet the EMC guidelines in this document and the Electromagnetic Compatibility specifications in the NI-9226 Datasheet, you must use the NI-9940 connector backshell kit.

Figure 2. NI-9940 Connector Backshell Installation

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  1. Install the NI-9940 backshell on the 36-pin spring-terminal connector.
  2. Tighten the NI-9940 backshell screws to 0.45 N · m (4.0 lb · in) torque.

Conformal Coating

The NI-9226 is available with conformal coating for additional protection in corrosive and condensing environments, including environments with molds and dust.

In addition to the environmental specifications listed in the NI-9226 Safety, Environmental, and Regulatory Information, the NI-9226 with conformal coating meets the following specification for the device temperature range. To meet this specification, you must follow the appropriate setup requirements for condensing environments. Refer to Conformal Coating and NI RIO Products for more information about conformal coating and the setup requirements for condensing environments.

Operating humidity (IEC 60068-2-30 Test Db) 80 to 100% RH, condensing