Choosing an RTD or Thermistor Measurement System

Publish Date: May 26, 2016 | 146 Ratings | 3.71 out of 5 |  PDF

Overview

This document introduces the available measurement platforms for RTD and Thermistor temperature sensors.

Table of Contents

  1. Platforms for Measuring Temperature 
  2. High-Performance and High-Channel-Count Systems
  3. NI Compatible RTDs
  4. Next Steps

1. Platforms for Measuring Temperature 

Compact measurements

Benchtop or Field Measurements

A CompactDAQ system consists of a chassis, NI C Series I/O modules, and software. Chassis can connect to a host computer over USB, Ethernet, or 802.11 WiFi or operate stand-alone with a built-in controller. With over 50 measurement-specific modules and 1-, 4-, and 8-slot chassis, CompactDAQ provides a flexible, expandable platform to meet the needs of any electrical or sensor measurement system.

  • Multiple timing engines for multiple acquisition rates
  • Advanced counter functionality from NI-STC3 technology

Embedded Data-Logging Measurements

CompactDAQ controllers offer a high-performance platform for embedded measurements and data logging. Controllers feature an integrated computer and nonvolatile storage, so that CompactDAQ can be deployed without an external computer.

  • Includes Intel multicore processing, up to 32 GB nonvolatile storage, and 2 GB RAM
  • Simultaneously stream continuous measurements with sample rates up to 1 MS/s per channel

Extreme Ruggedness and Advanced Control

CompactRIO is a reconfigurable embedded control and acquisition system. The CompactRIO hardware architecture includes a reconfigurable FPGA chassis and an embedded controller. CompactRIO can be used in a variety of embedded control and monitoring applications.

  • A variety of reconfigurable chassis featuring an FPGA for custom timing, analysis, and control
  • Open embedded architecture with small size and extreme ruggedness
What Is CompactDAQ? What Is CompactDAQ?  

 

C Series I/O modules with integrated signal conditioning for temperature with RTDs

NI 9217 Module

The NI 9217 C Series RTD analog input module features four channels and 24 bits of resolution for 100 Ω RTD measurements. You can configure the NI 9217 for two different sampling rate modes. With the high-sampling-rate mode, you can sample at up to 400 S/s (100 S/s per channel). Using the high-resolution mode, you can sample at 5 S/s (1.25 S/s per channel) with built-in 50/60 Hz noise rejection.

The NI 9217, compatible with 3- and 4-wire RTD measurements, automatically detects the type of RTD (3- or 4-wire) connected to the channel and configures each channel for the appropriate mode. The module can provide 1 mA of current excitation per channel and has less than a 1 °C accuracy error over its entire operating temperature range. The NI 9217 contains NIST-traceable calibration and includes a channel-to-earth ground double isolation barrier for safety, noise immunity, and high-common-mode voltage range. 

NI 9219 Measurement System 

The NI 9219 measurement system measures four universal channels at 100 S/s with 24-bit resolution, sending data to a host PC over USB, Ethernet, or 802.11 WiFi.

The NI 9219 is a 4-channel universal C Series module designed for multipurpose testing in any CompactDAQ or CompactRIO chassis. With the NI 9219, you can measure several signals from sensors such as strain gages, RTDs, thermocouples, load cells, and other powered sensors. The channels are individually selectable, so you can perform a different measurement type on each of the four channels. Measurement ranges differ for each type of measurement and include up to ±60 V for voltage and ±25 mA for current. See the manual for detailed specifications and ranges.

 

NI 9216 Module

The NI 9216 RTD analog input C Series module features eight channels and 24 bits of resolution for PT100 RTD measurements. You can configure the NI 9216 for two different sampling rate modes. With the high-sampling-rate mode, you can sample at up to 400 S/s (50 S/s per channel). Using the high-resolution mode, you can sample at 5 S/s (0.625 S/s per channel) with built-in 50/60 Hz noise rejection. The NI 9216, compatible with 3- and 4-wire RTD measurements, automatically detects the type of RTD (3- or 4-wire) connected to the channel and configures each channel for the appropriate mode. The module provides 1 mA of current excitation per channel and has less than a 1.0 °C accuracy error over its entire operating temperature range. The NI 9216 includes a channel-to-earth ground double isolation barrier for safety, noise immunity, and high common-mode voltage range. NI provides calibration services for the NI 9216.

NI 9226 Module

The NI 9226 RTD analog input C Series module features eight channels and 24 bits of resolution for PT1000 RTD measurements. You can configure the NI 9226 for two different sampling rate modes. With the high-sampling-rate mode, you can sample at up to 400 S/s (50 S/s per channel). Using the high-resolution mode, you can sample at 5 S/s (0.625 S/s per channel) with built-in 50/60 Hz noise rejection. The NI 9226, compatible with 3- and 4-wire RTD measurements, automatically detects the type of RTD (3- or 4-wire) connected to the channel and configures each channel for the appropriate mode. The module provides 0.1 mA of current excitation per channel and has less than a 1.1 °C accuracy error over its entire operating temperature range. The NI 9226 includes a channel-to-earth ground double isolation barrier for safety, noise immunity, and high common-mode voltage range. NI provides calibration services for the NI 9226.

C Series I/O modules with integrated signal conditioning for temperature with thermistors

NI 9219 Measurement System 

The NI 9219 can theoretically be used for thermistor measurements though it was not specifically designed for them. The KnowledgeBase article Thermistor Measurements Using the NI 9219 covers the details and limitations of using the NI 9219 with thermistors.

 

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2. High-Performance and High-Channel-Count Systems

 

The PXI platform offers a variety of chassis, controller, and module options so you can create a measurement system to meet your specific application needs. The SC Express strain modules can provide up to 0.02 percent accuracy at up to 102.4 kS/s. PXI scales to thousands of strain and bridge-based measurement channels for large applications and provides both wired and wireless synchronization options.

  • Configurable desktop, rack-mount, and distributed multichassis systems
  • Compatibility with a wide range of sensors and transducers
  • More than 1,500 PXI modules available, including CAN, vision, motion, and GPS

PXI I/O modules with integrated signal conditioning for measuring RTDs

PXIe-4357 RTD Module

The NI PXIe-4357 input module provides integrated data acquisition and signal conditioning for resistance temperature detector (RTD) measurements. This 20-channel module features five 24-bit delta-sigma analog-to-digital converters with antialiasing and lowpass filters for superior accuracy. The NI PXIe-4357 offers sampling rates up to 100 S/s per channel in high-speed mode or 1 S/s with typical measurement accuracies of 0.09 °C in high-resolution mode.

A front-mount terminal block provides screw terminal connectivity for 2-, 3-, or 4-wire RTDs. The NI-DAQmx device driver software included with the module gives you the flexibility of per channel software-programmable configurations and automatically scales measured data into engineering units. The signal conditioning circuitry on the NI PXIe-4357 is optimized for PT100 RTDs but can also measure resistors between 0 Ω and 400 Ω.

 

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3. NI Compatible RTDs

 

Ready-made RTDs offer solutions for cost-sensitive temperature measurement applications. Each RTD element is sealed in an Alumina tube with three Teflon-coated leads, and can measure up to 400 °F (204 °C). Teflon offers good resistance to abrasion and moisture. Each RTD is sold individually and is available in lead lengths of 1 m (39.4 in.) and 2 m (78.7 in.).

Features

  • 3-wire leads
  • 1 m and 2 m lengths
  • Ideal for starter and educational applications
  • Measure up to 400 °F (204 °C)
  • Platinum 100 Ω at 0 °C (alpha=0.00385)
 

NI field-cuttable RTDs are ideal for a wide variety of temperature applications. With field-cuttable RTDs, you can cut the probe to your desired length, from 3.5 in. to 24 in. (8.9 cm to 61 cm). Therefore, you can use one stock of RTDs for all of your temperature measurements to reduce inventory cost and production downtime. These RTD probes can measure up to 900 °F (482 °C). For applications using thermal wells, the optional spring-loaded fitting reduces installation time while ensuring contact with the thermal well. Each probe has glass braid insulated leads and is sold individually.

Features

  • Reduces inventory cost and downtime
  • 3-wire
  • Measures up to 900 °F (482 °C)
  • Platinum 100 Ω at 0 °C (alpha=0.00385)
  • Probes can be field cut to within 3.5 in. of tip (maximum length 24 in.)
  • Lead length is 6 in.

 

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