National Instruments NI 435 Series User Manual

High-precision temperature and voltage meters

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NI 435x User Manual

High-Precision Temperature and Voltage Meters

NI 435x User Manual

September 2003 Edition

Part Number 370841A-01

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Page 1 NI 435x User Manual High-Precision Temperature and Voltage Meters NI 435x User Manual September 2003 Edition Part Number 370841A-01...
Page 2 Thailand 662 992 7519, United Kingdom 44 0 1635 523545 For further support information, refer to the Technical Support and Professional Services appendix. To comment on the documentation, send email to techpubs@ni.com. © 2003 National Instruments Corporation. All rights reserved.
Page 3 The reader should consult National Instruments if errors are suspected. In no event shall National Instruments be liable for any damages arising out of or related to this document or the information contained in it.
Page 4 These classes are known as Class A (for use in industrial-commercial locations only) or Class B (for use in residential or commercial locations). All National Instruments (NI) products are FCC Class A products. Depending on where it is operated, this Class A product could be subject to restrictions in the FCC rules. (In Canada, the Department of Communications (DOC), of Industry Canada, regulates wireless interference in much the same way.) Digital...
Page 5: Table Of Contents
Knowing the Signal Source ...................2-4 Floating Signal Source ...................2-4 Ground-Referenced Signal Source ..............2-4 Using Programmable Ground-Referencing ..............2-4 Using Programmable Open-Thermocouple Detection ..........2-5 Measuring Temperature with Thermocouples ...............2-6 Connecting the Thermocouple ................2-8 Input Ranges....................2-8 © National Instruments Corporation NI 435x User Manual...
Page 6 Contents Optimizing Measurements ................2-8 Auto-Zero ..................2-9 Programmable Ground-Referencing..........2-9 Programmable Open-Thermocouple Detection........ 2-9 AC Noise Effects ................2-10 Thermal EMF ................... 2-10 Measuring DC Voltage....................2-11 Connecting the DC Voltage Signal ..............2-11 Input Ranges ....................2-11 Optimizing Measurements ................2-11 Auto-Zero ..................
Page 7 Contents Appendix B Signal Connections Appendix C Technical Support and Professional Services Glossary Index © National Instruments Corporation NI 435x User Manual...
Page 8: About This Manual
This font is also used for the proper names of disk drives, paths, directories, programs, subprograms, subroutines, device names, functions, operations, variables, filenames and extensions, and code excerpts. © National Instruments Corporation NI 435x User Manual...
Page 9: Related Documentation
Refers to all devices in the National Instruments 4350 and 4351 families. NI 435x for PCI, Refers to the all the devices in the National Instruments 4350 and 4351 PXI and USB families that have the PCI, PXI, and USB buses.
Page 10: Introduction
NI PXI-4351 and NI PCI-4351. In addition, the NI 435x devices have programmable TTL-compatible digital I/O (DIO) for monitoring TTL-level inputs, interfacing with external devices, and generating alarms. © National Instruments Corporation NI 435x User Manual...
Page 11: Using Pxi With Compactpci
Chapter 1 Introduction The NI 435x DAQ devices are Plug and Play compatible and are fully software calibrated. Because the NI 435x devices work with a variety of operating systems, you can develop applications that scale across several platforms. A system based on NI 435x devices offers flexibility, performance, and compact size, making it ideal for service, repair, and manufacturing and for use in industrial and laboratory environments.
Page 12: Ni 435X Software Selection Chart
VirtualBench-Logger. This section explains the software choices available for the NI 435x in more detail. What Is VirtualBench-Logger? VirtualBench-Logger is a high-performance, easy-to-use, virtual instruments application program for use with the NI 435x devices. © National Instruments Corporation NI 435x User Manual...
Page 13: What Is Labview
C—looping and Case structures, configuration management tools, and compiled performance. The LabVIEW Data Acquisition VI Library, a series of VIs for using LabVIEW with National Instruments DAQ hardware, is included with LabVIEW. Use NI-DAQ with LabVIEW to control the NI 435x.
Page 14 Driver API Library NI-DAQ PXI, PCI (Win2000/XP/Me/9 x ) USB (Win98 or later) NI 435 X Figure 1-2. The Relationship Among the Programming Environment, NI 435x Instrument Drivers, NI-DAQ, and the NI 435x © National Instruments Corporation NI 435x User Manual...
Page 15: What Is The Max Create New Channel Wizard
Chapter 1 Introduction What Is the MAX Create New Channel Wizard? In the past, data acquisition system developers spent a large amount of time defining the signal types, connections, transducer equations, and unit conversions before beginning development of the actual system. For example, if you are using thermocouples, you must perform additional cold-junction compensation (CJC) calculations to convert raw voltage values into actual temperature readings, and then apply scaling factors that...
Page 16 Contact NI. Refer to Appendix C, Technical Support and Professional Services, for contact information. The LED blinks in one-second intervals during each cycle. The LED then waits three seconds before repeating the cycle. © National Instruments Corporation NI 435x User Manual...
Page 17: Optional Equipment
Chapter 1 Introduction Optional Equipment NI offers a variety of products to use with the NI 435x, including cables, connector blocks, terminal blocks, and other accessories, as follows: • Cables and adapters with thermocouple miniconnectors • Connector blocks including isothermal connector blocks •...
Page 18: Safety Information
Safety Information For safety information that is relevant to the NI 435x devices, refer to the Read Me First: Safety and Radio-Frequency Interference document that shipped with your device or to ni.com/manuals © National Instruments Corporation NI 435x User Manual...
Page 19: Operating The Ni 435X Device
VirtualBench-Logger, the NI 435x instrument driver, and the MAX Create New Note Channel Wizard select the measurement mode automatically, depending on the sensor type you specify. © National Instruments Corporation NI 435x User Manual...
Page 20: Choosing A Range
Chapter 2 Operating the NI 435x Device Choosing a Range The volts mode has six bipolar input ranges: ±625 mV, ±1.25 V, ±2.5 V, ±3.75 V, ±7.5 V, and ±15 V. The 4-wire ohms mode has six corresponding input ranges when used with the built-in 25 µΑ...
Page 21 50 and 400 fast * Powerline frequency ** Number of powerline cycles used for filtering *** For resistance ranges of 50 kΩ and higher These rates were obtained without auto-zeroing and cold-junction compensation. Note © National Instruments Corporation NI 435x User Manual...
Page 22: Knowing The Signal Source
Chapter 2 Operating the NI 435x Device Knowing the Signal Source For accurate measurements, you must determine whether the signal source is floating or ground-referenced. Floating Signal Source floating signal source is one that is not connected in any way to the building ground system but has an isolated ground-reference point.
Page 23: Using Programmable Open-Thermocouple Detection
Using Programmable Open-Thermocouple Detection section. You can set open-thermocouple detection on a channel-by-channel basis. Table 2-3 summarizes the settings you should use for open-thermocouple detection. © National Instruments Corporation NI 435x User Manual...
Page 24: Measuring Temperature With Thermocouples
Chapter 2 Operating the NI 435x Device Table 2-3. Using Programmable, Open-Thermocouple Detection Programmable Open-Thermocouple Signal Source Detection Thermocouples On or Off Voltage signal sources other than thermocouples RTDs, thermistors, and resistors connected to the built-in current source Note The default setting for programmable open-thermocouple detection in volts and 4-wire ohms measurement modes is Off.
Page 25 , using the thermistor resistance-temperature cold-junction conversion formula. From this temperature of the cold-junction, T , compute cold-junction the equivalent thermocouple voltage, V , for this junction cold-junction using a standard thermocouple conversion formula. © National Instruments Corporation NI 435x User Manual...
Page 26: Connecting The Thermocouple
Chapter 2 Operating the NI 435x Device Measure the voltage, V , and add the cold-junction voltage, measured , computed in step 2. cold-junction Convert the resulting voltage to temperature using a standard thermocouple conversion formula. Connecting the Thermocouple The NI 435x accessories—the TC-2190, TBX-68T, and CB-68T for the NI 435x for PXI, PCI, and USB—are designed to be used with thermocouples.
Page 27: Auto-Zero
Programmable Open-Thermocouple Detection To detect open or broken thermocouples, switch on open-thermocouple detection on that channel. Then, if the thermocouple breaks, the voltage on © National Instruments Corporation NI 435x User Manual...
Page 28: Ac Noise Effects
Chapter 2 Operating the NI 435x Device that channel rises rapidly above 100 mV, at which point you can conclude that the thermocouple is open. Notice that when open-thermocouple detection is on and the floating thermocouple is not broken, a very small amount of current is injected into the thermocouple.
Page 29: Measuring Dc Voltage
To make accurate voltage measurements, program the onboard ground-referencing and open-thermocouple detection appropriately. Also consider problems associated with AC noise effects, thermal EMFs, and other errors as discussed in the following sections. © National Instruments Corporation 2-11 NI 435x User Manual...
Page 30: Auto-Zero
Chapter 2 Operating the NI 435x Device Auto-Zero Auto-zero is a method that instruments use to remove offset errors in the measurement. Analog channel 1 (CH1) on the CB-27T, TBX-68T, and CB-68T is dedicated for auto-zero. CH1+ is connected to CH1– on these accessories.
Page 31: Ac Noise Effects
Resistance, RTD, or Thermistor. When using the NI 435x instrument driver, set the measurement mode to Resistance. These modes return the measurements in units of resistance (ohms) by dividing the measured © National Instruments Corporation 2-13 NI 435x User Manual...
Page 32: Introduction To Rtds
Chapter 2 Operating the NI 435x Device voltage with the calibrated value of the precision current source stored onboard. Introduction to RTDs An RTD is a temperature-sensing device whose resistance increases with temperature. An RTD consists of a wire coil or deposited film of pure metal.
Page 33 (α = 0.003911), or the International Temperature Scale (ITS-90), which is used with wire-wound RTDs (α = 0.003925). Table 2-4 lists the Callendar-Van Dusen coefficients for each of these three platinum RTD curves. © National Instruments Corporation 2-15 NI 435x User Manual...
Page 34: Connecting The Rtd
Chapter 2 Operating the NI 435x Device Table 2-4. Callendar-Van Dusen Coefficients Corresponding to Common RTDs Temperature Coefficient α Standard 3.9083 × 10 –5.775 × 10 –4.183 × 10 –3 –7 –1 IEC751 0.00385055 3.9080 × 10 –5.8019 × 10 –4.2735 ×...
Page 35 Another variation of the 3-wire RTD configuration is shown in Figure 2-7. In this configuration, the effects of the lead wire resistance cancel out as long as all three wires have the same lead resistance. © National Instruments Corporation 2-17 NI 435x User Manual...
Page 36: Introduction To Thermistors
Chapter 2 Operating the NI 435x Device , or I EX0+ EX1+ CH n + CH n – n +1 n +1 , or I EX– EX0– EX1– – R if R CH n CH (n +1 ) Figure 2-7. 3-Wire RTD Measurement and Lead Wire Resistance Compensation Refer to Figure 2-10 for an example of how you can use different transducers connected to analog channels in the same measurement setup.
Page 37 The thermistor has been used primarily for high-resolution measurements over limited temperature ranges. Continuous improvements in thermistor stability, accuracy, and availability of interchangeable thermistors have prompted increased usage of thermistors in all types of industries. © National Instruments Corporation 2-19 NI 435x User Manual...
Page 38: Resistance-Temperature Characteristic Of Thermistors
Chapter 2 Operating the NI 435x Device Resistance-Temperature Characteristic of Thermistors The resistance-temperature behavior of thermistors is highly dependent upon the manufacturing process. Therefore, thermistor manufacturers have not standardized thermistor curves to the extent that thermocouple or RTD curves are standardized. Typically, thermistor manufacturers supply the resistance-versus- temperature curves or tables for their particular devices.
Page 39: Connecting The Resistor
Consult the accessory installation guide for instructions on how to connect the resistors. Figures 2-10 and 2-11 show examples of how to use different transducers connected to analog channels in the same measurement setup. © National Instruments Corporation 2-21 NI 435x User Manual...
Page 40 Chapter 2 Operating the NI 435x Device or I Voltage here is EX0+ {–2.5V + [(20 kΩ + R cjthermistor ) × 25 µA]} CH5+ Ground-Referencing: Off thermistor Open-Thermocouple Thermistor Detection: Off CH5– CH4+ Ground-Referencing: Off Open-Thermocouple Ground-Referenced Thermocouple Detection: On Voltage here is CH4–...
Page 41: Input Ranges
These ranges correspond to the six input ranges available for measuring DC voltages developed across resistors. These ranges are ±625 mV, ±1.25 V, ±2.5 V, ±3.75 V, ±7.5 V, and ±15 V. The NI 4351 for © National Instruments Corporation 2-23 NI 435x User Manual...
Page 42: Optimizing Measurements
Chapter 2 Operating the NI 435x Device PXI and PCI has six additional ranges of 625 Ω, 1.25 kΩ, 2.5 kΩ, 3.75 kΩ, 7.5 kΩ, and 15 kΩ with the 1 mA current source. To determine the most suitable input range for the application, estimate the voltage developed across the resistor by following the procedure outlined in Figures 2-10 and 2-11.
Page 43: Programmable Ground-Referencing
Table 2-5. Guidelines for Resistance Measurement Resistance Being Measured (Ω) Measurement Technique R ≤ 1 kΩ 4-wire 1 kΩ < R ≤ 10 kΩ 4-wire or 3-wire R > 10 kΩ 4-wire, 3-wire, or 2-wire © National Instruments Corporation 2-25 NI 435x User Manual...
Page 44: Self-Heating
Chapter 2 Operating the NI 435x Device Self-Heating The current source on the NI 435x is designed so that any error resulting from self-heating is negligible in most cases. When current is passed through an RTD or a thermistor (both are resistive devices), the power dissipated is equal to I R, which heats the resistive devices.
Page 45: Thermal Emf
You can use the DIO lines as an interface to control processes; control events such as turning on and off heaters, relays, motors, or lights; generate patterns for testing; and communicate with peripheral equipment. If the © National Instruments Corporation 2-27 NI 435x User Manual...
Page 46: Connecting The Digital Input And Output
Chapter 2 Operating the NI 435x Device current and voltage specifications of the DIO lines are not appropriate for the requirements, you can use external signal conditioning such as electromechanical relay, solid-state relay, opto-coupler, and so on. You can use the digital input lines to trigger analog acquisitions. To trigger analog acquisitions with the LabVIEW or NI 435x instrument driver, set up the analog acquisition configuration, then poll the digital input line for the trigger condition and, upon getting the trigger, start the analog acquisition.
Page 47 Then you can determine the logic level based on the thresholds of the logic family of the digital signal you are monitoring. Table 2-6 shows the thresholds of CMOS and TTL logic families using analog inputs as digital inputs. © National Instruments Corporation 2-29 NI 435x User Manual...
Page 48 Chapter 2 Operating the NI 435x Device Table 2-6. Logic Family Thresholds Logic Family High CMOS <0.8 V >2.0 V <0.8 V >2.0 V Note: Check the logic family data sheets for any variations. NI 435x User Manual 2-30 ni.com...
Page 49 Specifications improve with ground-referencing enabled and open-thermocouple detection disabled for a floating thermocouple. The specifications also assume that the cold-junction sensor is between 15 °C and 35 °C. © National Instruments Corporation NI 435x User Manual...
Page 50 Appendix A Specifications Error (°C) 0 °C–15 °C, 15 °C–35 °C, 1 Year 35 °C–55 °C Filter Setting Temperature Accessory Thermocouple Coefficient Error Type °C 10 Hz 50 Hz 60 Hz (°C/°C (°C –100 0.68 0.84 1.08 0.03 0.26 0.54 0.67 0.86 0.42...
Page 51 RTD specifications assume that the 625 Ω range (1 mA current source) is used and worst case common-mode voltage for this range is present. Specifications improve if actual common-mode voltage is less than worst case. © National Instruments Corporation NI 435x User Manual...
Page 52 Appendix A Specifications Thermistor Accuracy (with I or I Accuracy (°C) Temperature 15 °C–35 °C, 1 Year, Coefficient Filter Setting: 10 Hz, 0 °C–15 °C, 50 Hz, 60 Hz 35 °C–55 °C Thermistor °C °C °C/°C 5,000 Ω 0–50 0.03 0.001 DC Voltage Accuracy Add µV...
Page 53 1 s setting time. Resistance specifications assume worst case common-mode voltage for the given range. Specifications improve if actual common-mode voltage is less than worst case. Measurement accuracy is affected by source impedance. © National Instruments Corporation NI 435x User Manual...
Page 54 Appendix A Specifications Accuracy Calculation Examples The following are accuracy calculation examples: • Measurement of 760 °C using J-type thermocouple at 28 °C ambient temperature; filter setting of 10 Hz: accuracy is 0.42 °C • Measurement of 760 °C using J-type thermocouple with NI 4350 at 38 °C and accessory (cold-junction sensor) at 23 °C;...
Page 55 Range ≥2.5 V ........80 dB Range <2.5 V ........100 dB NMR (50 Hz, 60 Hz, 400 Hz) ....>100 dB Dynamic Characteristics Bandwidth ..........20 Hz Step response (full-scale step) Accuracy Time(s) ±0.1% ±0.01% ±0.0015% © National Instruments Corporation NI 435x User Manual...
Page 56 Appendix A Specifications Accuracy Time(s) ±0.001% ±0.0004% Excitation Note The exact value of the excitation current is stored on the hardware. NI-DAQ uses this value when taking resistance measurements. Number of channels........2 Parameter or I 25 µA Level 1 mA Maximum Load 600 kΩ...
Page 57 Maximum working voltage refers to the signal voltage plus the common- mode voltage. Range >2.5 V ......... Each input should remain within ±15 V of ground Range ≤2.5 V ......... Each input should remain within ±2.5 V of ground © National Instruments Corporation NI 435x User Manual...
Page 58 Appendix A Specifications Environmental Operating temperature ......0 to 55 °C Storage temperature ........–20 to 70 °C Humidity ..........Up to 80% RH, noncondensing Maximum altitude........2,000 m Installation Category.......I Pollution Degree (indoor use only) ..2 Safety ♦ PCI/PXI Only The NI PCI/PXI-4051 meets the requirements of the following standards for safety and electrical equipment for measurement, control, and laboratory use: •...
Page 59 Refer to the Declaration of Conformity (DoC) for this product for any additional regulatory compliance information. To obtain the DoC for this product, visit , search by model number or product line, and click the ni.com/hardref.nsf appropriate link in the Certification column. © National Instruments Corporation A-11 NI 435x User Manual...
Page 60 Table B-1. Using the NI 435x (USB, PXI, PCI) with the TBX-68 NI 435x (USB, PXI, PCI) TBX-68 Signal Name Screw Terminal CH0+ CH0– CH1+ CH1– CH2+ CH2– CH3+ CH3– CH4+ CH4– CH5+ CH5– CH6+ © National Instruments Corporation NI 435x User Manual...
Page 61 Appendix B Signal Connections Table B-1. Using the NI 435x (USB, PXI, PCI) with the TBX-68 (Continued) NI 435x (USB, PXI, PCI) TBX-68 Signal Name Screw Terminal CH6– CH7+ CH7– CH8+ CH8– CH9+ CH9– CH10+ CH10– CH11+ CH11– CH12+ CH12– CH13+ CH13–...
Page 62 Screw terminals 10 and 44 are AGND on the NI 4350 only and are not labeled AGND on revision C or later of the TBX-68T. The current available may be limited to less than 50 mA (typical) when using the NI 4350 (USB). © National Instruments Corporation NI 435x User Manual...
Page 63 Technical Support and Professional Services Visit the following sections of the National Instruments Web site at for technical support and professional services: ni.com • Support—Online technical support resources include the following: – Self-Help Resources—For immediate answers and solutions, visit our extensive library of technical support resources available in English, Japanese, and Spanish at .
Page 64 Appendix C Technical Support and Professional Services • Calibration Certificate—You can obtain the calibration certificate for NI 435x products at ni.com/calibration If you searched and could not find the answers you need, contact ni.com your local office or NI corporate headquarters. Phone numbers for our worldwide offices are listed at the front of this manual.
Page 65 – 6 –3 milli kilo mega giga tera Numbers/Symbols ° degree – negative of, or minus Ω percent ± plus or minus positive of, or plus +5 V output signal amperes alternating current © National Instruments Corporation NI 435x User Manual...
Page 66 Glossary AC coupled allowing the transmission of AC signals while blocking DC signals analog-to-digital converter—an electronic device that converts an analog voltage to a digital number AGND analog ground signal ANSI American National Standards Institute AT bus See bus. attenuation decreasing the amplitude of a signal auto-zeroing the process of removing an offset error from a measurement...
Page 67 DAQPad-1200, which connects to your computer parallel port, are all examples of DAQ devices. SCXI modules are distinct from devices, with the exception of the SCXI-1200, which is a hybrid. DGND digital ground signal digital input and output © National Instruments Corporation NI 435x User Manual...
Page 68 Glossary drivers software that controls a specific hardware device such as a DAQ device or a GPIB interface dynamic range the ratio of the largest signal level a circuit can handle to the smallest signal level it can handle (usually taken to be the noise level), normally expressed in decibels EEPROM electrically erasable programmable read-only memory—ROM that can be...
Page 69 (1) Mega, the standard metric prefix for 1 million or 10 , when used with units of measure such as volts and hertz; (2) mega, the prefix for 1,048,576, or 2 , when used with B to quantify data or computer memory © National Instruments Corporation NI 435x User Manual...
Page 70 1,048,576 bytes/s Measurement & a controlled centralized configuration environment that allows you to Automation Explorer configure all of your National Instruments DAQ, GPIB, IMAQ, IVI, (MAX) Motion, VISA, and VXI devices NI-DAQ National Instruments driver software for DAQ hardware...
Page 71 NI 435x samples an analog signal sigma-delta technology used for analog to digital conversion sinter to cause to become a coherent mass by heating without melting © National Instruments Corporation NI 435x User Manual...
Page 72 Glossary system noise a measure of the amount of noise seen by an analog circuit or an ADC when the analog inputs are grounded thermistor a semiconductor sensor that produces a repeatable change in electrical resistance as a function of temperature. Most thermistors have a negative temperature coefficient (NTC).
Page 73 (note), 2-29 bus interface specifications, A-9 logic family thresholds (table), 2-30 preventing safety hazards (caution), 2-29 documentation, NI resources, C-1 drivers (NI resources), C-1 dynamic characteristics, A-7 © National Instruments Corporation NI 435x User Manual...
Page 74 (NI resources), C-1 patterns (table), 1-7 excitation specifications, A-8 external circuits, connecting to, 2-25 measurement mode, choosing, 2-1 floating signal source, 2-4 National Instruments support and services, C-1 NI 4350 (USB) ground-referenced signal source, 2-4 LEDs ground-referencing, programmable patterns (table), 1-7...
Page 75 (table), 2-3 AC noise effects, 2-26 reference junction, 2-6 auto-zero method, 2-24 resistance accuracy specifications (table), A-5 connecting to external circuits, 2-25 resistance measurement guidelines for resistance connecting resistors measurement (table), 2-25 © National Instruments Corporation NI 435x User Manual...
Page 76 Index multiple transducer connections to definition, 2-14 analog channels (figures), 2-22 measuring temperature, 2-14 preventing safety hazards optimizing measurements, 2-24 (caution), 2-23 relationship of resistance and input ranges, 2-23 temperature, 2-14 optimizing resistance-temperature curve AC noise effects, 2-26 (figure), 2-15 auto-zero method, 2-24 connecting to external circuits, 2-25 guidelines for resistance...
Page 77 2-10 purpose and use, 2-1 thermistors range selection, 2-2 accuracy specifications (table), A-4 advantages and disadvantages, 2-18 connecting, 2-20 optimizing measurements, 2-24 Web resources, C-1 resistance-temperature characteristics, 2-20 © National Instruments Corporation NI 435x User Manual...

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