NI CompactDAQ Controller Mounting and the Impact on Measurement Accuracy

NI cDAQ-9138/9 controllers are designed to provide both high-accuracy measurements and industrial ruggedness. From the factory, each analog I/O module is calibrated against an NIST-traceable precision source. Accuracy is guaranteed for at least one year after calibration and each module can be re-calibrated throughout its life. Because the NI cDAQ-9138/9 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 CompactDAQ system components can safely be used together across the rated temperature range, analog module accuracy is sensitive to heat. The high-performance processors and components used in the NI cDAQ-9138/9 can contribute additional heat to the system.

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 NI recommends visiting the Measurement Fundamentals article.

To help you achieve the specified analog modules accuracy for CompactDAQ systems containing an NI cDAQ-9138/9 NI recommends you adhere to the following guidelines:

You can increase analog module accuracy by loading the modules into your NI CompactDAQ controller 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. Additionally, installations must meet the requirements for space and cabling clearance as defined in the NI cDAQ-913x User Manual.

Maximum accuracy specifications assume a worst case range of component tolerances and a full thermal load on the system (maximum processor usage, and a controller fully loaded with high power modules).

The following table provides mounting configurations where the module maximum accuracy specifications may be achieved for both the NI cDAQ-9138/9.

For reference, the following figure shows an NI cDAQ-9138/9 controller mounted horizontally with an NI Desktop Kit.

The NI cDAQ-9138/9 systems are intended for applications where measurement accuracy is critical.  Many analog modules provide specifications for typical accuracy.  Because the NI cDAQ-9138/9 controller is a high-power/high-performance system, module typical accuracies cannot be achieved for every specific mounting condition.  The following table provides mounting configurations where the module typical accuracy specifications can be achieved.

Thermocouple modules

Thermocouple measurements are more sensitive to thermal gradients because in addition to precise voltage measurements they also require accurate junction temperature measurements. The following table shows the C Series modules that can be used to make thermocouple measurements.

NI 9211

Because the NI cDAQ-9138/9 controller is a high-power/high-performance system, the maximum accuracy and typical accuracy specification for thermocouple measurements using the NI 9211 cannot be achieved with any mounting conditions.

NI 9213 / NI 9214 / NI 9219

NI recommends using the NI 9213 or NI 9214 for thermocouple measurements in the NI cDAQ-9138/9 controller. If channel-to-channel isolation is required, the NI 9219 is recommended. 

Typical accuracy for these modules can be met by following the mounting guidelines listed in the Meeting Typical Accuracy Specifications section. 

The following table provides mounting configurations where the module maximum accuracy specifications can be achieved for the NI 9213, NI 9214 and NI 9219.

cDAQ-9138/9 Isothermal Module Maximum Accuracy for NI 9213 / NI 9214 / NI 9219

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 accuracy can be met by following the guidelines in the Meeting Maximum Accuracy Specifications section.  The typical accuracy specification can be met by following the guidelines listed in the Meeting Typical Accuracy Specification section. 

Maximum accuracy specifications at 25C cannot be achieved when used in the NI cDAQ-9138/9 controller for any mounting conditions.

DC servo drive module (NI 9505)

The NI 9505 is a high power full h-bridge brushed DC servo drive module.  Because the NI cDAQ-9138/9 controller is a high-power/high-performance system, the published ambient temperature versus current capability for the NI 9505 is not valid.  Please contact NI for ambient temperature versus current capability for the NI 9505 for use in the NI cDAQ-9138/9 controller.