Ensuring Measurement Accuracy in High-Power CompactRIO Systems (cRIO-9022/4 and/or cRIO-911x)

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This document will help you achieve the highest measurement quality when using high-power CompactRIO systems that contain a cRIO-9022 or cRIO-9024 controller and/or a cRIO-9111, cRIO-9112, cRIO-9113, cRIO-9114, cRIO-9116, or cRIO-9118 reconfigurable embedded chassis (referred to inclusively as the cRIO-911x).

Table of Contents

  1. Module Loading and Installation Requirements
  2. Meeting Maximum Accuracy Specifications
  3. Meeting Typical Accuracy Specifications
  4. Module Exceptions 

For all measurement systems, proper wiring, noise shielding, and grounding practices are essential to achieving high accuracy analog measurements.  Assuring proper connectivity and wiring should be the first step when designing a high accuracy measurement system.  To assist in designing your system we recommend visiting the Measurement Fundamentals Developer Zone article.

CompactRIO systems are designed to provide both high-accuracy measurements and industrial ruggedness.  From the factory, each analog I/O module is calibrated against a NIST-traceable precision source.  Accuracy is guaranteed for at least one year after calibration and each module can be re-calibrated through-out its life.  Because CompactRIO systems are also designed for applications with high shock and vibration, the system avoids the use of failure-prone mechanical cooling components such as rotating fans.  While CompactRIO system components can safely be used together across the rated temperature range, analog module accuracy is sensitive to heat.  The high-performance processors and FPGAs used in the cRIO-9022 or 9024 and cRIO-911x can contribute additional heat to the system.

To help you achieve the specified analog module accuracies for cRIO systems containing a cRIO-9022 or cRIO-9024 and/or cRIO-911x we recommend you adhere to the following guidelines (note exceptions for NI 9211 and NI 9225 in the Module Exceptions section of this document ):

 

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Module Loading and Installation Requirements

You can increase analog module accuracy by loading the modules into your CompactRIO chassis in an arrangement that separates analog modules from high-power-dissipating modules such as digital output, communications, or motion modules and from other thermally significant system components such as external power supplies, relays, -etc.  The maximum power dissipation for each module is specified in the module data sheet.  We recommend loading high-power modules and all digital modules starting with slot 1 on the left side of the chassis, and your analog modules starting on the right side of the chassis.  This will minimize the temperature rise in the analog modules and provide increased accuracy. Additionally, installations must meet the requirements for space and cabling clearance as defined in the CompactRIO Chassis Installation Guide

 

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Meeting Maximum Accuracy Specifications

Maximum specification accuracy assumes a worst case range of component tolerances and a full thermal load on the system (maximum processor and FPGA usage, and a chassis fully loaded with high power modules).  For installations with an ambient temperature at or below 55C the system can be mounted on any material.  For installations with an ambient temperature greater than 55C, the system must be horizontally mounted on a thermally conductive material such as a thick metal panel. 

Mounting configurations to achieve maximum accuracy specifications
Temperature Range Mounting Options
-40C to 55C Any material (metal panel, DIN Rail, Desktop Accessory)
55C to 70C Thermally conductive material (thick metal panel),  horizontal orientation

 

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Meeting Typical Accuracy Specifications

Many analog modules also provide specifications for typical accuracy.  Because most systems are not subjected to such high thermal loads and extreme component tolerance, NI also provides typical accuracies, in addition to maximum accuracies, to help guide you on the accuracy that can be expected from common configurations.  Typical specifications for I/O modules in high-power CompactRIO systems are based on their characteristics when the system is mounted horizontally on a thermally conductive material such as a thick metal panel.  

 Mounting configurations to achieve typical accuracy specifications
Temperature Range Mounting Recommendation
-40C to 70C Thermally conductive material (thick metal panel), horizontal orientation

 

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Module Exceptions 

 

Thermocouple module (NI 9211)

Thermocouple measurements are more sensitive to thermal gradients because in addition to precise voltage measurements they also require accurate junction temperature measurements.  To ensure either maximum or typical accuracy thermocouple measurements using the NI 9211, you must use the NI 9932 connector block kit.  This kit uses a lower-profile connector and a connector shield that provide better isothermal performance.   Additionally, the CompactRIO system must be mounted horizontally on a thermally conductive material such as a thick metal panel. 

Configurations to achieve maximum and typical accuracy specifications for NI 9211 thermocouple module
Accessory Temperature Range Mounting Options
NI 9932 connector block kit -40C to 70C Thermally conductive material (thick metal panel), horizontal orientation

 

Power quality module (NI 9225)

The modules used to measure power quality provide three specifications; a maximum accuracy specification when used over the full temperature range, a maximum accuracy specification when used at 25C, and a typical accuracy specification when used at 25C.  The full temperature range maximum and typical accuracies can be met by following the guidelines in the Meeting Maximum Accuracy Specifications and Meeting Typical Accuracy Specifications sections.  For the maximum accuracy at 25C, the system must be mounted horizontally on a thermally conductive material, such as a thick metal panel, and follow the module loading recommendations in the Module Loading section of this document.

Mounting configurations to achieve maximum accuracy specifications at room temperature for the NI 9225 module
Temperature Range Mounting Recommendation
20C to 30C Thermally conductive material (thick metal panel), horizontal orientation

 

 

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