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National Instruments PCI-6238 User Manual

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Summary of Contents for National Instruments PCI-6238

  • Page 1 PCI-6238...
  • Page 2 DAQ M Series NI 6238/6239 User Manual Isolated Current Input/Current Output Devices NI 6238/6239 User Manual July 2006 371913A-01...
  • Page 3 Thailand 662 278 6777, United Kingdom 44 0 1635 523545 For further support information, refer to the Technical Support and Professional Services appendix. To comment on National Instruments documentation, refer to the National Instruments Web site at and enter ni.com/info the info code feedback ©...
  • Page 4 Instruments Corporation. National Instruments respects the intellectual property of others, and we ask our users to do the same. NI software is protected by copyright and other intellectual property laws. Where NI software may be used to reproduce software or other materials belonging to others, you may use NI software only to reproduce materials that you may reproduce in accordance with the terms of any applicable license or other legal restriction.
  • Page 5 NATIONAL INSTRUMENTS PRODUCTS ARE INCORPORATED IN A SYSTEM OR APPLICATION, INCLUDING, WITHOUT LIMITATION, THE APPROPRIATE DESIGN, PROCESS AND SAFETY LEVEL OF SUCH SYSTEM OR APPLICATION.

  • Page 6: Table Of Contents

    DAQ Hardware ......................2-1 DAQ-STC2......................2-2 Calibration Circuitry..................2-3 Sensors and Transducers....................2-3 Cables and Accessories....................2-4 Custom Cabling ....................2-4 Programming Devices in Software ................2-5 Chapter 3 Connector Information I/O Connector Signal Descriptions ................3-1 RTSI Connector Pinout....................3-3 © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 7 Contents Chapter 4 Analog Input Analog Input Circuitry ....................4-1 Analog Input Range....................... 4-2 Connecting Analog Current Input Signals ..............4-3 Method 1 ......................4-3 Method 2 ......................4-4 Analog Input Ground-Reference Settings ..............4-5 Configuring AI Ground-Reference Settings in Software ....4-7 Multichannel Scanning Considerations.................
  • Page 8 Getting Started with AO Applications in Software ............5-10 Chapter 6 Digital Input and Output I/O Protection.........................6-1 Programmable Power-Up States ..................6-1 Connecting Digital I/O Signals..................6-2 Logic Conventions ......................6-3 Getting Started with DIO Applications in Software ............6-4 © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 9 Contents Chapter 7 Counters Counter Input Applications ................... 7-3 Counting Edges ....................7-3 Single Point (On-Demand) Edge Counting ........7-3 Buffered (Sample Clock) Edge Counting......... 7-4 Non-Cumulative Buffered Edge Counting ........7-5 Controlling the Direction of Counting..........7-5 Pulse-Width Measurement ................7-6 Single Pulse-Width Measurement ............
  • Page 10 Example Application That Prevents Duplicate Count ......7-37 When To Use Duplicate Count Prevention........7-38 Enabling Duplicate Count Prevention in NI-DAQmx ......7-38 Synchronization Modes ...................7-38 80 MHz Source Mode ...............7-39 Other Internal Source Mode..............7-39 External Source Mode...............7-40 © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 11 Contents Chapter 8 Using PFI Terminals as Timing Input Signals .............. 8-2 Exporting Timing Output Signals Using PFI Terminals..........8-3 Using PFI Terminals as Static Digital Inputs and Outputs..........8-3 Connecting PFI Input Signals..................8-3 PFI Filters ........................8-4 I/O Protection ........................ 8-5 Programmable Power-Up States..................
  • Page 12 Appendix B Troubleshooting Analog Input ........................B-1 Analog Output........................B-2 Counters .........................B-3 Appendix C Technical Support and Professional Services Glossary Index Figures Figure A-1. NI 6238 Pinout ..................A-2 Figure A-2. NI 6239 Pinout ..................A-5 © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 13: About This Manual

    The NI 6238/6239 User Manual contains information about using the NI 6238 and NI 6239 M Series data acquisition (DAQ) devices with NI-DAQmx 8.1 and later. National Instruments 6238/6239 devices feature up to eight differential analog input (AI) channels, two analog output (AO) channels, two counters, six lines of digital input (DI), and four lines of digital output (DO).

  • Page 14: Related Documentation

    Programs»National Instruments»NI-DAQ»DAQ Getting Started Guide. The NI-DAQ Readme lists which devices are supported by this version of NI-DAQ. Select Start»All Programs»National Instruments»NI-DAQ» NI-DAQ Readme. The NI-DAQmx Help contains general information about measurement concepts, key NI-DAQmx concepts, and common applications that are applicable to all programming environments.

  • Page 15: Ni-Daqmx Base

    NI-DAQmx Base VI Reference Help. The NI-DAQmx Base C Reference Help contains C reference and general information about measurement concepts. Select Start»All Programs» National Instruments»NI-DAQmx Base»Documentation»C Function Reference Manual. LabVIEW If you are a new user, use the Getting Started with LabVIEW manual to...

  • Page 16: Labwindows™/Cvi

    About This Manual tools. Refer to the following locations on the Contents tab of the LabVIEW Help for information about NI-DAQmx: • Getting Started»Getting Started with DAQ—Includes overview information and a tutorial to learn how to take an NI-DAQmx measurement in LabVIEW using the DAQ Assistant. •...

  • Page 17: Net Languages Without Ni Application Software

    Adobe Acrobat Reader with Search and Accessibility 5.0.5 or later installed to view the PDFs. Refer to the Adobe Systems Incorporated Web site at to download Acrobat Reader. Refer to the www.adobe.com National Instruments Product Manuals Library at ni.com/manuals updated documentation resources. © National Instruments Corporation xvii...

  • Page 18: Getting Started

    The DAQ Getting Started Guide contains non-software-specific information on how to install PCI and PXI devices, as well as accessories and cables. Device Pinouts Refer to Appendix A, Device-Specific Information, for NI 6238/6239 device pinouts. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 19: Device Specifications

    Chapter 1 Getting Started Device Specifications Refer to the NI 6238/6239 Specifications, available on the NI-DAQ Device Document Browser or , for more detailed information ni.com/manuals on NI 6238/6239 devices. Device Accessories and Cables NI offers a variety of accessories and cables to use with your DAQ device. Refer to Appendix A, Device-Specific Information, or...

  • Page 20: Daq System Overview

    DAQ Hardware DAQ hardware digitizes input signals, performs D/A conversions to generate analog output signals, and measures and controls digital I/O signals. Figure 2-2 features the components of the NI 6238/6239 devices. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 21: Daq-Stc2

    Chapter 2 DAQ System Overview Isolation Barrier Analog Input AI GND Analog Output Digital Routing and Clock Interface AO GND Generation Digital Counters Isolators RTSI PFI/Static DI P0.GND PFI/Static DO P1.GND Figure 2-2. General NI 6238/6239 Block Diagram DAQ-STC2 The DAQ-STC2 implements a high-performance digital engine for NI 6238/6239 data acquisition hardware.

  • Page 22: Calibration Circuitry

    Taking Measurements book on the Contents tab. • If you are using other application software, refer to Common Sensors in the NI-DAQmx Help, which can be accessed from Start»All Programs»National Instruments»NI-DAQ»NI-DAQmx Help. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 23: Cables And Accessories

    Chapter 2 DAQ System Overview Cables and Accessories NI offers a variety of products to use with NI 6238/6239 devices, including cables, connector blocks, and other accessories, as follows: • Cables and cable assemblies – Shielded – Unshielded ribbon • Screw terminal connector blocks, shielded and unshielded •...

  • Page 24: Programming Devices In Software

    Chapter 2 DAQ System Overview Programming Devices in Software National Instruments measurement devices are packaged with NI-DAQ driver software, an extensive library of functions and VIs you can call from your application software, such as LabVIEW or LabWindows/CVI, to program all the features of your NI measurement devices. Driver software...

  • Page 25: Connector Information

    AO <0..1> AO GND Output Analog Output Channels 0 to 1—These terminals supply the current output of AO channels 0 to 1. Note: AO <0..1> are isolated from earth ground and chassis ground. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 26 Chapter 3 Connector Information Table 3-1. I/O Connector Signals (Continued) Signal Name Reference Direction Description AO GND — — Analog Output Ground—AO GND is the reference for AO <0..1>. AI GND and AO GND are connected on the device. Note: AI GND and AO GND are isolated from earth ground, chassis ground, P0.GND, and P1.GND.

  • Page 27: Rtsi Connector Pinout

    NI 6238/6239. RTSI Connector Pinout Refer to the RTSI Connector Pinout section of Chapter 10, Digital Routing and Clock Generation, for information on the RTSI connector. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 28: Analog Input

    (MUX) route one AI channel at a time to the ADC through the NI-PGIA. Instrumentation Amplifier (NI-PGIA) The NI programmable gain instrumentation amplifier (PGIA) is a measurement and instrument class amplifier that minimizes settling times © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 29: Analog Input Range

    Chapter 4 Analog Input for all input ranges. The NI-PGIA can amplify or attenuate an AI signal to ensure that you use the maximum resolution of the ADC. M Series devices use the NI-PGIA to deliver high accuracy even when sampling multiple channels with small input ranges at fast rates.

  • Page 30: Connecting Analog Current Input Signals

    AI – side do not exceed the common-mode input range of ±10 V. Common-mode input range is the voltage input range with respect to AI GND (AI + versus AI GND, AI – versus AI GND, or AI + versus AI –). © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 31: Method 2

    Chapter 4 Analog Input Isolation Barrier AI + AI – – – AI GND AI GND Figure 4-2. Analog Current Input Connection Method 1 Method 2 Method 2, shown in Figure 4-3, ties the AI – input to AI GND. When measuring current up to 20 mA, this type of connection ensures that the voltage level on both the positive and negative side are within the common-mode input range for NI 6238/6239 devices.

  • Page 32: Analog Input Ground-Reference Settings

    The NI 6238/6239 device measures the voltage generated across the current input sense resistor during current input measurement. This voltage difference is then routed into the instrumentation amplifier (PGIA) differentially, as shown in Figure 4-5. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 33 Chapter 4 Analog Input Instrumentation Amplifier Current Sense PGIA Resistor Measured in– Voltage AI GND – R × Gain • Figure 4-5. NI 6238/6239 PGIA Analog input ground-reference setting refers to the reference that the PGIA measures against. Differential is the only ground-reference setting for NI 6238/6239 analog input signals, which means that the PGIA always measures the voltages between AI + and AI –...

  • Page 34: Configuring Ai Ground-Reference Settings In Software

    DAQ Assistant Help for more information on the DAQ Assistant. To configure the input mode of your current measurement using the NI-DAQmx C API, set the terminalConfig property. Refer to the NI-DAQmx C Reference Help for more information. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 35: Multichannel Scanning Considerations

    The capacitance of the cable also can increase the settling time. National Instruments recommends using individually shielded, twisted-pair wires that are 2 m or less to connect AI signals to the device.

  • Page 36: Avoid Scanning Faster Than Necessary

    1, and so on. You also could read all 100 points from channel 0 then read 100 points from channel 1. The second method switches between channels much less often and is affected much less by settling time. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 37: Analog Input Data Acquisition Methods

    Chapter 4 Analog Input Analog Input Data Acquisition Methods When performing analog input measurements, you either can perform software-timed or hardware-timed acquisitions. Hardware-timed acquisitions can be buffered or non-buffered. Software-Timed Acquisitions With a software-timed acquisition, software controls the rate of the acquisition.

  • Page 38: Non-Buffered

    Environmental noise can seriously affect the measurement accuracy of the device if you do not take proper care when running signal wires between signal sources and the device. The following recommendations apply © National Instruments Corporation 4-11 NI 6238/6239 User Manual...

  • Page 39: Analog Input Timing Signals

    Chapter 4 Analog Input mainly to AI signal routing to the device, although they also apply to signal routing in general. Minimize noise pickup and maximize measurement accuracy by using individually shielded, twisted-pair wires to connect AI signals to the device.
  • Page 40 Convert Clock would be set to 71428.6 Hz. This rate is determined by taking the fastest channel conversion rate for the device and adding 10 µs, 4 µs (1/250000) + 10 µs, which results in 14 µs or 71428.6 Hz. © National Instruments Corporation 4-13 NI 6238/6239 User Manual...
  • Page 41 Chapter 4 Analog Input When this calculation results in the sampling rate exceeding 35 kHz, there is not enough time between samples to acquire both channels and still add a 10 µs delay per channel, so the Convert Clock rate becomes the sampling rate multiplied by the number of channels being acquired.

  • Page 42: Ai Sample Clock Signal

    Use the AI Sample Clock (ai/SampleClock) signal to initiate a set of measurements. Your M Series device samples the AI signals of every channel in the task once for every ai/SampleClock. A measurement acquisition consists of one or more samples. © National Instruments Corporation 4-15 NI 6238/6239 User Manual...

  • Page 43: Using An Internal Source

    Chapter 4 Analog Input You can specify an internal or external source for ai/SampleClock. You also can specify whether the measurement sample begins on the rising edge or falling edge of ai/SampleClock. Using an Internal Source One of the following internal signals can drive ai/SampleClock. •...

  • Page 44: Other Timing Requirements

    AI Sample Clock Timebase Signal You can route any of the following signals to be the AI Sample Clock Timebase (ai/SampleClockTimebase) signal: • 20 MHz Timebase • 100 kHz Timebase • PXI_CLK10 © National Instruments Corporation 4-17 NI 6238/6239 User Manual...

  • Page 45: Ai Convert Clock Signal

    Chapter 4 Analog Input • RTSI <0..7> • Input PFI <0..5> • PXI_STAR ai/SampleClockTimebase is not available as an output on the I/O connector. ai/SampleClockTimebase is divided down to provide one of the possible sources for ai/SampleClock. You can configure the polarity selection for ai/SampleClockTimebase as either rising or falling edge.

  • Page 46: Using An External Source

    By default, this delay is three ticks of ai/ConvertClockTimebase. Figure 4-12 shows the relationship of ai/SampleClock to ai/ConvertClock. © National Instruments Corporation 4-19 NI 6238/6239 User Manual...

  • Page 47: Other Timing Requirements

    Chapter 4 Analog Input ai/ConvertClockTimebase ai/SampleClock ai/ConvertClock Delay Convert From Period Sample Clock Figure 4-12. ai/SampleClock and ai/ConvertClock Other Timing Requirements The sample and conversion level timing of M Series devices work such that clock signals are gated off unless the proper timing requirements are met. For example, the device ignores both ai/SampleClock and ai/ConvertClock until it receives a valid ai/StartTrigger signal.

  • Page 48: Ai Convert Clock Timebase Signal

    The polarity of ai/HoldCompleteEvent is software-selectable, but is typically configured so that a low-to-high leading edge can clock external AI multiplexers indicating when the input signal has been sampled and can be removed. © National Instruments Corporation 4-21 NI 6238/6239 User Manual...

  • Page 49: Ai Start Trigger Signal

    Chapter 4 Analog Input AI Start Trigger Signal Use the AI Start Trigger (ai/StartTrigger) signal to begin a measurement acquisition. A measurement acquisition consists of one or more samples. If you do not use triggers, begin a measurement with a software command. After the acquisition begins, configure the acquisition to stop under the following conditions: •...

  • Page 50: Ai Reference Trigger Signal

    Figure 4-14 shows the final buffer. Reference Trigger Pretrigger Samples Posttrigger Samples Complete Buffer Figure 4-14. Reference Trigger Final Buffer © National Instruments Corporation 4-23 NI 6238/6239 User Manual...

  • Page 51: Using A Digital Source

    Chapter 4 Analog Input Using a Digital Source To use ai/ReferenceTrigger with a digital source, specify a source and an edge. The source can be any of the following signals: • Input PFI <0..5> • RTSI <0..7> • PXI_STAR The source also can be one of several internal signals on your DAQ device. Refer to Device Routing in MAX in the NI-DAQmx Help or the LabVIEW 8.x Help for more information.

  • Page 52: Routing Ai Pause Trigger Signal To An Output Terminal

    I/O data transfer mechanisms. Some of the applications also use start, reference, and pause triggers. Note For more information about programming analog input applications and triggers in software, refer to the NI-DAQmx Help or the LabVIEW 8.x Help. © National Instruments Corporation 4-25 NI 6238/6239 User Manual...

  • Page 53: Analog Output

    V-I Converter The V-I converter converts voltage (V) into current (I). AO FIFO The AO FIFO enables analog output waveform generation. It is a first-in-first-out (FIFO) memory buffer between the computer and the © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 54: Analog Output Data Generation Methods

    Chapter 5 Analog Output DACs. It allows you to download the points of a waveform to your M Series device without host computer interaction. AO Sample Clock The AO Sample Clock signal reads a sample from the DAC FIFO and generates the AO voltage.

  • Page 55: Non-Buffered

    With non-regeneration, old data will not be repeated. New data must be continually written to the buffer. If the program does not write new data to © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 56: Analog Output Triggering

    Chapter 5 Analog Output the buffer at a fast enough rate to keep up with the generation, the buffer will underflow and cause an error. Analog Output Triggering Analog output supports two different triggering actions: • Start trigger • Pause trigger A digital trigger can initiate these actions.

  • Page 57: Analog Output Timing Signals

    AO Sample Clock Timebase Signal AO Start Trigger Signal Use the AO Start Trigger (ao/StartTrigger) signal to initiate a waveform generation. If you do not use triggers, you can begin a generation with a software command. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 58: Using A Digital Source

    Chapter 5 Analog Output Using a Digital Source To use ao/StartTrigger, specify a source and an edge. The source can be one of the following signals: • A pulse initiated by host software • Input PFI <0..5> • RTSI <0..7> •...

  • Page 59: Using A Digital Source

    The source also can be one of several other internal signals on your DAQ device. Refer to Device Routing in MAX in the NI-DAQmx Help or the LabVIEW 8.x Help for more information. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 60: Routing Ao Pause Trigger Signal To An Output Terminal

    Chapter 5 Analog Output You also can specify whether the samples are paused when ao/PauseTrigger is at a logic high or low level. Routing AO Pause Trigger Signal to an Output Terminal You can route ao/PauseTrigger out to RTSI <0..7>. AO Sample Clock Signal Use the AO Sample Clock (ao/SampleClock) signal to initiate AO samples.

  • Page 61: Other Timing Requirements

    100 kHz Timebase • PXI_CLK10 • Input PFI <0..5> • RTSI <0..7> • PXI_STAR Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width and the propagation delay of PFI <0..5>. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 62: Getting Started With Ao Applications In Software

    Chapter 5 Analog Output ao/SampleClockTimebase is not available as an output on the I/O connector. You might use ao/SampleClockTimebase if you want to use an external sample clock signal, but need to divide the signal down. If you want to use an external sample clock signal but do not need to divide the signal, then you should use ao/SampleClock rather than ao/SampleClockTimebase.

  • Page 63: Digital Input And Output

    By default, the digital output lines (P1.<0..3>/PFI <6..9>) are set to 0. They can be programmed to power up as 0 or 1. Refer to the NI-DAQmx Help or the LabVIEW 8.x Help for more information about setting power-up states in NI-DAQmx or MAX. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 64: Connecting Digital I/O Signals

    Chapter 6 Digital Input and Output Connecting Digital I/O Signals The DI signals P0.<0..5> are referenced to P0.GND and DO signals P1.<0..3> are referenced to P1.GND. Figures 6-1 and 6-2 show P0.<0..5> and P1.<0..3> on the NI 6238 and the NI 6239 device, respectively.

  • Page 65: Logic Conventions

    NI is not liable for any damage resulting from such signal connections. Logic Conventions With NI 6238/6239 devices, logic “0” means that the Darlington output switch is open, while logic “1” means closed. Table 6-1 summarizes the expected behavior. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 66: Getting Started With Dio Applications In Software

    Chapter 6 Digital Input and Output Table 6-1. NI 6238/6239 Logic Conventions Logic Device NI 6238 (Source) P1.GND P1.VCC NI 6239 (Sink) P1.VCC P1.GND Getting Started with DIO Applications in Software You can use NI 6238/6239 devices in the following digital I/O applications: •...
  • Page 67 Caution When making measurements, take into account the minimum pulse width and time delay of the digital input and output lines. Refer to the NI 6238/6239 Specifications for more information. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 68 Chapter 7 Counters Input Selection Muxes Counter 0 Counter 0 Source (Counter 0 Timebase) Counter 0 Gate Counter 0 Internal Output Counter 0 Aux Counter 0 HW Arm Counter 0 A Counter 0 TC Counter 0 B (Counter 0 Up_Down) Counter 0 Z Input Selection Muxes Counter 1...

  • Page 69: Counters

    You can route the pause trigger to the Gate input of the counter. You can configure the counter to pause counting when the pause trigger is high or when it is low. Figure 7-3 shows an example of on-demand edge counting with a pause trigger. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 70: Buffered (Sample Clock) Edge Counting

    Chapter 7 Counters Counter Armed Pause Trigger (Pause When Low) SOURCE Counter Value Figure 7-3. Single Point (On-Demand) Edge Counting with Pause Trigger Buffered (Sample Clock) Edge Counting With buffered edge counting (edge counting using a sample clock), the counter counts the number of edges on the Source input after the counter is armed.

  • Page 71: Non-Cumulative Buffered Edge Counting

    Always count down • Count up when the Counter n B input is high; count down when it is For information on connecting counter signals, refer to the Default Counter Terminals section. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 72: Pulse-Width Measurement

    Chapter 7 Counters Pulse-Width Measurement In pulse-width measurements, the counter measures the width of a pulse on its Gate input signal. You can configure the counter to measure the width of high pulses or low pulses on the Gate signal. You can route an internal or external periodic clock signal (with a known period) to the Source input of the counter.

  • Page 73: Period Measurement

    Gate signal. You can calculate the period of the Gate input by multiplying the period of the Source signal by the number of edges returned by the counter. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 74: Single Period Measurement

    Chapter 7 Counters Single Period Measurement With single period measurement, the counter counts the number of rising (or falling) edges on the Source input occurring between two active edges of the Gate input. On the second active edge of the Gate input, the counter stores the count in a hardware save register and ignores other edges on the Gate and Source inputs.

  • Page 75: Semi-Period Measurement

    You can calculate the semi-period of the Gate input by multiplying the period of the Source signal by the number of edges returned by the counter. Single Semi-Period Measurement Single semi-period measurement is equivalent to single pulse-width measurement. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 76: Buffered Semi-Period Measurement

    Chapter 7 Counters Buffered Semi-Period Measurement In buffered semi-period measurement, on each edge of the Gate signal, the counter stores the count in a hardware save register. A DMA controller transfers the stored values to host memory. The counter begins counting when it is armed. The arm usually occurs between edges on the Gate input.

  • Page 77: Method 1B-Measure Low Frequency With One Counter (Averaged)

    Average the remaining K period measurements to determine the average period of F1. The frequency of F1 is the inverse of the average period. Figure 7-12 illustrates this method. © National Instruments Corporation 7-11 NI 6238/6239 User Manual...

  • Page 78: Method 2-Measure High Frequency With Two Counters

    Chapter 7 Counters Intervals Measured … Gate 1 2 ... N 1..N … 1..N Source Buffered Period Measurement + … N × Average Period of F1 = K × Ft Frequency of F1 = + … N Figure 7-12.

  • Page 79: Method 3-Measure Large Range Of Frequencies Using Two Counters

    Figure 7-14. Assume this signal to measure has frequency F1. Configure Counter 0 to generate a single pulse that is the width of N periods of the source input signal. © National Instruments Corporation 7-13 NI 6238/6239 User Manual...

  • Page 80: Choosing A Method For Measuring Frequency

    Chapter 7 Counters Signal to SOURCE Measure (F1) COUNTER 0 Signal of Known SOURCE Frequency (F2) COUNTER 1 GATE 3 … N CTR_0_SOURCE (Signal to Measure) CTR_0_OUT Interval (CTR_1_GATE) to Measure CTR_1_SOURCE Figure 7-14. Method 3 Then route the Counter 0 Internal Output signal to the Gate input of Counter 1.
  • Page 81 • Method 3 measures high and low frequency signals accurately. However, it requires two counters. Table 7-2 summarizes some of the differences in methods of measuring frequency. © National Instruments Corporation 7-15 NI 6238/6239 User Manual...

  • Page 82: Position Measurement

    Chapter 7 Counters Table 7-2. Frequency Measurement Method Comparison Measures High Measures Low Number of Frequency Frequency Number of Measurements Signals Signals Method Counters Used Returned Accurately Accurately Poor Good Many Fair Good 1 or 2 Good Poor Good Good For information on connecting counter signals, refer to the Default Counter Terminals...
  • Page 83 You can program this reload to occur in any one of the four phases in a quadrature cycle. © National Instruments Corporation 7-17 NI 6238/6239 User Manual...

  • Page 84: Measurements Using Two Pulse Encoders

    Chapter 7 Counters Channel Z behavior—when it goes high and how long it stays high—differs with quadrature encoder designs. You must refer to the documentation for your quadrature encoder to obtain timing of channel Z with respect to channels A and B. You must then ensure that channel Z is high during at least a portion of the phase you specify for reload.

  • Page 85: Two-Signal Edge-Separation Measurement

    The counter then stores the count in a hardware save register and ignores other edges on its inputs. Software then can read the stored count. Figure 7-20 shows an example of a single two-signal edge-separation measurement. © National Instruments Corporation 7-19 NI 6238/6239 User Manual...

  • Page 86: Buffered Two-Signal Edge-Separation Measurement

    Chapter 7 Counters Counter Armed Measured Interval GATE SOURCE Counter Value HW Save Register Figure 7-20. Single Two-Signal Edge-Separation Measurement Buffered Two-Signal Edge-Separation Measurement Buffered and single two-signal edge-separation measurements are similar, but buffered measurement measures multiple intervals. The counter counts the number of rising (or falling) edges on the Source input occurring between an active edge of the Gate signal and an active edge of the Aux signal.

  • Page 87: Counter Output Applications

    After the Start Trigger signal pulses once, the counter ignores the Gate input. Figure 7-23 shows a generation of a pulse with a pulse delay of four and a pulse width of three (using the rising edge of Source). © National Instruments Corporation 7-21 NI 6238/6239 User Manual...

  • Page 88: Retriggerable Single Pulse Generation

    Chapter 7 Counters GATE (Start Trigger) SOURCE Figure 7-23. Single Pulse Generation with Start Trigger Retriggerable Single Pulse Generation The counter can output a single pulse in response to each pulse on a hardware Start Trigger signal. The pulses appear on the Counter n Internal Output signal of the counter.

  • Page 89: Pulse Train Generation

    Counter n Internal Output signal is equal to the frequency of the Source input divided by M + N. For information on connecting counter signals, refer to the Default Counter Terminals section. © National Instruments Corporation 7-23 NI 6238/6239 User Manual...

  • Page 90: Frequency Generation

    Chapter 7 Counters Frequency Generation You can generate a frequency by using a counter in pulse train generation mode or by using the frequency generator circuit. Using the Frequency Generator The frequency generator can output a square wave at many different frequencies.

  • Page 91: Frequency Division

    The waveform thus produced at the counter’s output can be used to provide timing for undersampling applications where a digitizing system can sample repetitive waveforms that are higher in frequency than the Nyquist © National Instruments Corporation 7-25 NI 6238/6239 User Manual...

  • Page 92: Counter Timing Signals

    Chapter 7 Counters frequency of the system. Figure 7-28 shows an example of pulse generation for ETS; the delay from the trigger to the pulse increases after each subsequent Gate active edge. GATE D2 = D1 + ∆D D3 = D1 + 2∆D Figure 7-28.

  • Page 93: Routing A Signal To Counter N Source

    Routing Counter n Source to an Output Terminal You can route Counter n Source out to any output PFI <6..9> or RTSI <0..7> terminal. All PFIs are set to high-impedance at startup. © National Instruments Corporation 7-27 NI 6238/6239 User Manual...

  • Page 94: Counter N Gate Signal

    Chapter 7 Counters Counter n Gate Signal The Counter n Gate signal can perform many different operations depending on the application including starting and stopping the counter, and saving the counter contents. Routing a Signal to Counter n Gate Each counter has independent input selectors for the Counter n Gate signal. Any of the following signals can be routed to the Counter n Gate input.

  • Page 95: Counter N A, Counter N B, And Counter N Z Signals

    To begin any counter input or output function, you must first enable, or arm, the counter. In some applications, such as buffered semi-period measurement, the counter begins counting when it is armed. In other applications, such as single pulse-width measurement, the counter begins © National Instruments Corporation 7-29 NI 6238/6239 User Manual...

  • Page 96: Routing Signals To Counter N Hw Arm Input

    Chapter 7 Counters waiting for the Gate signal when it is armed. Counter output operations can use the arm signal in addition to a start trigger. Software can arm a counter or configure counters to be armed on a hardware signal. Software calls this hardware signal the Arm Start Trigger. Internally, software routes the Arm Start Trigger to the Counter n HW Arm input of the counter.

  • Page 97: Routing Frequency Output To A Terminal

    M Series default PFI lines for counter functions are listed in Physical Channels in the NI-DAQmx Help or the LabVIEW 8.x Help. © National Instruments Corporation 7-31 NI 6238/6239 User Manual...

  • Page 98: Counter Triggering

    Chapter 7 Counters Counter Triggering Counters support three different triggering actions—arm start, start, and pause. Arm Start Trigger To begin any counter input or output function, you must first enable, or arm, the counter. Software can arm a counter or configure counters to be armed on a hardware signal.

  • Page 99: Other Counter Features

    Pass Signal) Pass Filter Not Pass Filter 125 ns 125 ns 100 ns 6.425 µs 6.425 µs 6.400 µs 2.55 ms ~101,800 2.55 ms 2.54 ms Disabled — — — © National Instruments Corporation 7-33 NI 6238/6239 User Manual...

  • Page 100: Prescaling

    Chapter 7 Counters The filter setting for each input can be configured independently. On power up, the filters are disabled. Figure 7-29 shows an example of a low-to-high transition on an input that has its filter set to 125 ns (N = 5). RTSI, PFI, or Filtered input goes high PXI_STAR Terminal...

  • Page 101: Duplicate Count Prevention

    Source pulses between rising edges on the Gate signal. Example Application That Works Correctly (No Duplicate Counting) Figure 7-31 shows an external buffered signal as the period measurement Source. © National Instruments Corporation 7-35 NI 6238/6239 User Manual...

  • Page 102: Example Application That Works Incorrectly (Duplicate Counting)

    Chapter 7 Counters Rising Edge of Gate Counter detects rising edge of Gate on the next rising edge of Source. Gate Source Counter Value Buffer Figure 7-31. Duplicate Count Prevention Example On the first rising edge of the Gate, the current count of 7 is stored. On the next rising edge of the Gate, the counter stores a 2 since two Source pulses occurred after the previous rising edge of Gate.

  • Page 103: Example Application That Prevents Duplicate Count

    Even if the Source pulses are long, the counter increments only once for each Source pulse. Normally, the counter value and Counter n Internal Output signals change synchronously to the Source signal. With duplicate count prevention, the © National Instruments Corporation 7-37 NI 6238/6239 User Manual...

  • Page 104: When To Use Duplicate Count Prevention

    Chapter 7 Counters counter value and Counter n Internal Output signals change synchronously to the 80 MHz Timebase. Note that duplicate count prevention should only be used if the frequency of the Source signal is 20 MHz or less. When To Use Duplicate Count Prevention You should use duplicate count prevention if the following conditions are true.

  • Page 105: 80 Mhz Source Mode

    In other internal source mode, the device synchronizes signals on the falling edge of the source, and counts on the following rising edge of the source, as shown in Figure 7-35. © National Instruments Corporation 7-39 NI 6238/6239 User Manual...

  • Page 106: External Source Mode

    Chapter 7 Counters Source Synchronize Count Figure 7-35. Other Internal Source Mode External Source Mode In external source mode, the device generates a delayed Source signal by delaying the Source signal by several nanoseconds. The device synchronizes signals on the rising edge of the delayed Source signal, and counts on the following rising edge of the source, as shown in Figure 7-36.

  • Page 107: Pfi

    Each PFI <6..9>/P1.<0..3> can be configured as a timing output signal from AI, AO, or counter/timer functions or a static digital output. Figure 8-2 shows the circuitry of one PFI output line. Each PFI line is similar. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 108: Using Pfi Terminals As Timing Input Signals

    Chapter 8 Isolation Barrier Timing Signals Digital PFI <6..9>/P1.<0..3> Isolators Static DO Buffer Figure 8-2. NI 6238/6239 PFI Output Circuitry When a terminal is used as a timing input or output signal, it is called PFI x (where x is an integer from 0 to 9). When a terminal is used as a static digital input or output, it is called P0.x or P1.x.

  • Page 109: Exporting Timing Output Signals Using Pfi Terminals

    All PFI input connections are referenced to P0.GND. Figure 8-3 shows this reference, and how to connect an external PFI 0 source and an external PFI 2 source to two PFI terminals. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 110: Pfi Filters

    Chapter 8 I/O Connector PFI 0 PFI 2 PFI 0 PFI 2 Source Source P0.GND M Series Device Figure 8-3. PFI Input Signals Connections PFI Filters You can enable a programmable debouncing filter on each PFI, RTSI, or PXI_STAR signal. When the filters are enabled, your device samples the input on each rising edge of a filter clock.

  • Page 111: I/O Protection

    To access this KnowledgeBase, go to and enter the info ni.com/info code rddfms I/O Protection Each DI, DO, and PFI signal is protected against overvoltage and undervoltage conditions as well as ESD events on NI 6238/6239 devices. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 112: Programmable Power-Up States

    Chapter 8 Consult the device specifications for details. However, you should avoid these fault conditions by following these guidelines. • Do not connect any digital output line to any external signal source, ground signal, or power supply. • Understand the current requirements of the load connected to the digital output lines.
  • Page 113 Chapter 8 P1.VCC P1.0 P1.<0..3> Digital Isolators P1.1 P1.GND P1.GND P0.0 P0.GND P0.GND Figure 8-5. NI 6238 Digital I/O Connections (DO Source) © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 114 Chapter 8 P1.VCC Buffer P1.0 P1.GND P1.<0..3> Digital Isolators P1.1 P1.GND P1.GND P0.0 P0.GND P0.GND Figure 8-6. NI 6239 Digital I/O Connections (DO Sink) Caution Exceeding the maximum input voltage or maximum working voltage ratings, which are listed in the NI 6238/6239 Specifications, can damage the DAQ device and the computer.

  • Page 115: Isolation And Digital Isolators

    Barrier Analog Input AI GND Analog Output Digital Routing and Clock Interface AO GND Generation Digital Counters Isolators RTSI PFI/Static DI P0.GND PFI/Static DO P1.GND Figure 9-1. General NI 6238/6239 Block Diagram © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 116: Digital Isolation

    Chapter 9 Isolation and Digital Isolators The non-isolated ground is connected to the chassis ground of the PC or chassis where the device is installed. Each isolated ground is not connected to the chassis ground of the PC or chassis. The isolated ground can be at a higher or lower voltage relative to the non-isolated ground.

  • Page 117: Reducing Common-Mode Noise

    If the device’s isolated ground is being connected back to earth ground, verify that this is done in the most direct way possible. • Reduce source impedances if possible. The parasitic currents react with these impedances. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 118: Digital Routing And Clock Generation

    ÷ 8 80 MHz Output Selectors) Oscillator External 80 MHz Timebase Reference RTSI <0..7> Clock PXI_CLK10 ÷ 20 MHz Timebase PXI_STAR ÷ 100 kHz Timebase Figure 10-1. M Series Clock Routing Circuitry © National Instruments Corporation 10-1 NI 6238/6239 User Manual...

  • Page 119: 80 Mhz Timebase

    Chapter 10 Digital Routing and Clock Generation Caution RTSI signals are not isolated from the chassis. 80 MHz Timebase The 80 MHz Timebase can be used as the Source input to the 32-bit general-purpose counter/timers. The 80 MHz Timebase can be generated from either of the following. •...

  • Page 120: 10 Mhz Reference Clock

    Real-Time System Integration (RTSI) is set of bused signals among devices that allow you to do the following. • Use a common clock (or timebase) to drive the timing engine on multiple devices © National Instruments Corporation 10-3 NI 6238/6239 User Manual...

  • Page 121: Rtsi Connector Pinout

    Digital Routing and Clock Generation • Share trigger signals between devices Many National Instruments DAQ, motion, vision, and CAN devices support RTSI. In a PCI system, the RTSI bus consists of the RTSI bus interface and a ribbon cable. The bus can route timing and trigger signals between several functions on as many as five DAQ, vision, motion, or CAN devices in the computer.

  • Page 122: Using Rtsi As Outputs

    10 MHz Reference Clock • Counter n Source, Gate, Z, Internal Output • FREQ OUT • Input PFI <0..5> Note Signals with a * are inverted before being driven on the RTSI terminals. © National Instruments Corporation 10-5 NI 6238/6239 User Manual...

  • Page 123: Using Rtsi Terminals As Timing Input Signals

    Chapter 10 Digital Routing and Clock Generation Using RTSI Terminals as Timing Input Signals You can use RTSI terminals to route external timing signals to many different M Series functions. Each RTSI terminal can be routed to any of the following signals. •...

  • Page 124: Pxi Clock And Trigger Signals

    To access this KnowledgeBase, go to and enter the info ni.com/info code rddfms PXI Clock and Trigger Signals Note PXI clock and trigger signals are only available on PXI devices. Other devices use RTSI. © National Instruments Corporation 10-7 NI 6238/6239 User Manual...

  • Page 125: Pxi_Clk10

    Chapter 10 Digital Routing and Clock Generation PXI_CLK10 PXI_CLK10 is a common low-skew 10 MHz clock reference clock for synchronization of multiple modules in a PXI measurement or control system. The PXI backplane is responsible for generating PXI_CLK10 independently to each peripheral slot in a PXI chassis. PXI Triggers A PXI chassis provides eight bused trigger lines to each module in a system.
  • Page 126 Enabling filters introduces jitter on the input signal. For the 125 ns and 6.425 µs filter settings, the jitter is up to 25 ns. On the 2.55 ms setting, the jitter is up to 10.025 µs. © National Instruments Corporation 10-9 NI 6238/6239 User Manual...
  • Page 127 Chapter 10 Digital Routing and Clock Generation When a PFI input is routed directly to RTSI, or a RTSI input is routed directly to PFI, the M Series device does not use the filtered version of the input signal. Refer to the KnowledgeBase document, Digital Filtering with M Series and CompactDAQ, for more information about digital filters and counters.

  • Page 128: Bus Interface

    FIFO. Each DMA controller acts as a PCI Master device. The DMA controllers support scatter-gather operations to and from host memory. Memory buffers may be used in linear or circular fashion. © National Instruments Corporation 11-1 NI 6238/6239 User Manual...

  • Page 129: Pxi Considerations

    Chapter 11 Bus Interface Each DMA controller supports packing and unpacking of data through the FIFOs to connect different size devices and optimize PCI bus utilization and automatically handles unaligned memory buffers. PXI Considerations Note PXI clock and trigger signals are only available on PXI devices. Other devices use RTSI.

  • Page 130: Using Pxi With Compactpci

    DMA is a method to transfer data between the device and computer memory without the involvement of the CPU. This method makes DMA the fastest available data transfer method. National Instruments uses DMA hardware and software technology to achieve high throughput rates and to increase system utilization.

  • Page 131: Interrupt Request (Irq)

    Chapter 11 Bus Interface Interrupt Request (IRQ) IRQ transfers rely on the CPU to service data transfer requests. The device notifies the CPU when it is ready to transfer data. The data transfer speed is tightly coupled to the rate at which the CPU can service the interrupt requests.

  • Page 132: Triggering

    A rising edge is a transition from a low logic level to a high logic level. A falling edge is a high to low transition. Figure 12-1 shows a falling-edge trigger. High Digital Trigger Falling Edge Initiates Acquisition Figure 12-1. Falling-Edge Trigger © National Instruments Corporation 12-1 NI 6238/6239 User Manual...
  • Page 133 Chapter 12 Triggering You also can program your DAQ device to perform an action in response to a trigger from a digital source. The action can affect the following. • Analog input acquisition • Analog output generation • Counter behavior NI 6238/6239 User Manual 12-2 ni.com...

  • Page 134: Device-Specific Information

    NI 6238 Pinout Figure A-1 shows the pinout of the NI 6238. For a detailed description of each signal, refer to the I/O Connector Signal Descriptions section of Chapter 3, Connector Information. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 135: Figure A-1. Ni 6238 Pinout

    Appendix A Device-Specific Information AI 0+/CAL+ AI 0– AI 1– AI 1+ AI GND AI 2+ AI 2– AI 3– AI 3+ AI GND AI 4+ AI 4– AI 5– AI 5+ CAL– AI 6+ AI 6– AI 7+ AI 7– AO POWER SUPPLY AO 0 AO 1...
  • Page 136 Refer to for other accessory options including new devices. ni.com Screw Terminal National Instruments offers several styles of screw terminal connector blocks. Use an SH37F-37M cable to connect an NI 6238 device to a connector block, such as the following: •...
  • Page 137 Appendix A Device-Specific Information vision, and motion devices. Since PXI devices use PXI backplane signals for timing and synchronization, no cables are required. Cables In most applications, you can use the following cables: • SH37F-37M-x—37-pin female-to-male shielded I/O cable, UL Listed derated to 30 Vrms, 42.4 V , or 60 VDC •...

  • Page 138: Figure A-2. Ni 6239 Pinout

    32 (PFI 1) P0.1 CTR 0 B 33 (PFI 2) P0.2 CTR 1 SRC 15 (PFI 3) P0.3 CTR 1 GATE 34 (PFI 4) P0.4 CTR 1 AUX 16 (PFI 5) P0.5 © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 139 Refer to for other accessory options including new devices. ni.com Screw Terminal National Instruments offers several styles of screw terminal connector blocks. Use an SH37F-37M cable to connect an NI 6239 device to a connector block, such as the following: •...
  • Page 140 R37F-37M-1—37-pin female-to-male ribbon I/O cable SH37F-P-4—37-pin female-to-pigtails shielded I/O cable • Custom Cabling and Connectivity Refer to the Custom Cabling section of Chapter 2, DAQ System Overview, for more information about custom cabling solutions. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 141 Troubleshooting This section contains some common questions about M Series devices. If your questions are not answered here, refer to the National Instruments KnowledgeBase at . It contains thousands of documents that ni.com/kb answer frequently asked questions about NI products.

  • Page 142: Analog Output

    Appendix B Troubleshooting In an isolated device, leaving the AI GND terminal unconnected will cause the signal to drift and eventually rail. How can I use the AI Sample Clock and AI Convert Clock signals on an M Series device to sample the AI channel(s)? M Series devices use ai/SampleClock and ai/ConvertClock to perform interval sampling.
  • Page 143 Chapter 7, Counters, for more information. How do I connect counter signals to my M Series device? Default Counter Terminals section of Chapter 7, Counters, has information on counter signal connections. © National Instruments Corporation NI 6238/6239 User Manual...

  • Page 144: Technical Support And Professional Services

    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 at ni.com/support include the following: – Self-Help Resources—For answers and solutions, visit the...
  • Page 145 Appendix C Technical Support and Professional Services Calibration Certificate—If your product supports calibration, • you can obtain the calibration certificate for your product 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 146: Glossary

    A measure of the capability of an instrument or sensor to faithfully indicate the value of the measured signal. This term is not related to resolution; however, the accuracy level can never be better than the resolution of the instrument. Application development environment. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 147 Glossary 1. Analog input. 2. Analog input channel signal. AI GND Analog input ground signal. AI SENSE Analog input sense signal. analog A signal whose amplitude can have a continuous range of values. analog input signal An input signal that varies smoothly over a continuous range of values, rather than in discrete steps.
  • Page 148 When that relationship is known, the instrument may then be adjusted (calibrated) for best accuracy. calibrator A precise, traceable signal source used to calibrate instruments. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 149 Glossary cascading Process of extending the counting range of a counter chip by connecting to the next higher counter. European emissions control standard. channel Pin or wire lead to which you apply or from which you read the analog or digital signal.
  • Page 150 ) port. SCXI modules are considered DAQ devices. DAQ-STC2 Data acquisition system timing controller chip. data acquisition The general concept of acquiring data, as in begin data acquisition or data acquisition and control. See also DAQ. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 151 Glossary data transfer A technique for moving digital data from one system to another. Options for data transfer are DMA, interrupt, and programmed I/O. For programmed I/O transfers, the CPU in the PC reads data from the DAQ device whenever the CPU receives a software signal to acquire a single data point.
  • Page 152 A voltage pulse from an external source that causes a DAQ operation to begin. EXTREF External reference signal. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 153 Glossary FIFO First-In-First-Out memory buffer—A data buffering technique that functions like a shift register where the oldest values (first in) come out first. Many DAQ products and instruments use FIFOs to buffer digital data from an A/D converter, or to buffer the data before or after bus transmission.
  • Page 154 2. The number of scans read or updates written per second. Input/Output—The transfer of data to/from a computer system involving communications channels, operator interface devices, and/or data acquisition and control interfaces. © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 155 Glossary impedance 1. The electrical characteristic of a circuit expressed in ohms and/or capacitance/inductance. 2. Resistance. Inch or inches. instrument driver A set of high-level software functions that controls a specific GPIB, VXI, or RS232 programmable instrument or a specific plug-in DAQ device. Instrument drivers are available in several forms, ranging from a function callable language to a virtual instrument (VI) in LabVIEW.
  • Page 156 An MIO product can be considered a miniature mixed signal tester, due to its broad range of signal types and flexibility. Also known as multifunction DAQ. © National Instruments Corporation G-11 NI 6238/6239 User Manual...
  • Page 157 National Instruments. NI-DAQ The driver software needed to use National Instruments DAQ devices and SCXI components. Some devices use Traditional NI-DAQ (Legacy); others use NI-DAQmx. NI-DAQmx The latest NI-DAQ driver with new VIs, functions, and development tools for controlling measurement devices.
  • Page 158 2. A digital port, consisting of four or eight lines of digital input and/or output. posttriggering The technique used on a DAQ device to acquire a programmed number of samples after trigger conditions are met. © National Instruments Corporation G-13 NI 6238/6239 User Manual...
  • Page 159 The time from the rising to the falling slope of a pulse (at 50% amplitude). A rugged, open system for modular instrumentation based on CompactPCI, with special mechanical, electrical, and software features. The PXIbus standard was originally developed by National Instruments in 1997, and is now managed by the PXIbus Systems Alliance. PXI Express PCI Express eXtensions for Instrumentation—The PXI implementation of...
  • Page 160 RTSI Real-Time System Integration. RTSI bus Real-Time System Integration bus—The National Instruments timing bus that connects DAQ devices directly, by means of connectors on top of the devices, for precise synchronization of functions. Seconds. Samples.
  • Page 161 Glossary SCXI Signal Conditioning eXtensions for Instrumentation—The National Instruments product line for conditioning low-level signals within an external chassis near sensors so that only high-level signals are sent to DAQ devices in the noisy PC environment. sensor A device that responds to a physical stimulus (heat, light, sound, pressure, motion, flow, and so on), and produces a corresponding electrical signal.
  • Page 162 Output delay time. transducer A device that responds to a physical stimulus (heat, light, sound, pressure, motion, flow, and so on), and produces a corresponding electrical signal. See also sensor. © National Instruments Corporation G-17 NI 6238/6239 User Manual...
  • Page 163 Glossary trigger 1. Any event that causes or starts some form of data capture. 2. An external stimulus that initiates one or more instrument functions. Trigger stimuli include a front panel button, an external input voltage pulse, or a bus trigger command. The trigger may also be derived from attributes of the actual signal to be acquired, such as the level and slope of the signal.
  • Page 164 Signal source voltage. virtual channel See channel. waveform 1. The plot of the instantaneous amplitude of a signal as a function of time. 2. Multiple voltage readings taken at a specific sampling rate. © National Instruments Corporation G-19 NI 6238/6239 User Manual...
  • Page 165 AI Sample Clock Timebase signal, 4-17 getting started with applications in AI Start Trigger signal, 4-21 software, 5-10 AI timing signals, 4-12 signals, 5-5 ai/ConvertClock, 4-18 timing signals, 5-5 ai/ConvertClockTimebase, 4-21 trigger signals, 5-4 ai/HoldCompleteEvent, 4-21 © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 166 Index triggering, 5-4 troubleshooting, B-2 cables, 2-4, A-3, A-6 ANSI C documentation, xvii choosing for your device, 1-2 AO FIFO, 5-1 custom, 2-4 AO Pause Trigger signal, 5-6 calibration certificate (NI resources), C-2 AO Sample Clock signal, 5-8 calibration circuitry, 2-3 AO Sample Clock Timebase signal, 5-9 cascading counters, 7-33 AO Start Trigger signal, 5-5...
  • Page 167 10-3 prescaling, 7-34 specifications, 1-2 pulse train generation, 7-23 diagnostic tools (NI resources), C-1 retriggerable single pulse differential, analog input generation, 7-22 (troubleshooting), B-1 simple pulse generation, 7-21 single pulse generation, 7-21 © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 168 Index enabling duplicate count prevention in digital NI-DAQmx, 7-38 input and output, 6-1 encoders, quadrature, 7-16 isolation, 9-3 encoding isolators, 9-1 X1, 7-16 routing, 10-1 X2, 7-17 signals, connecting, 6-2, 8-6 X4, 7-17 source, triggering, 12-1 equivalent time sampling, 7-25 digital I/O examples (NI resources), C-1 circuitry, 6-1...
  • Page 169 7-8 installation single pulse-width, 7-6 hardware, 1-1 single semi-period, 7-9 NI-DAQ, 1-1 single two-signal edge-separation, 7-19 other software, 1-1 two-signal edge-separation, 7-19 instrument drivers (NI resources), C-1 interface, bus, 11-1 © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 170 7-8 multiple device synchronization, 10-3 single, 7-8 PFI, 8-1 connecting input signals, 8-3 exporting timing output signals using PFI National Instruments support and terminals, 8-3 services, C-1 filters, 8-4 NI 6238 using terminals as static digital I/Os, 8-3 accessory options, A-3...
  • Page 171 Counter n HW Arm, 7-29 filters, 10-6 Counter n Internal Output, 7-30 using as outputs, 10-5 Counter n Source, 7-26 using terminals as timing input Counter n TC, 7-30 signals, 10-6 Counter n Up_Down, 7-29 © National Instruments Corporation NI 6238/6239 User Manual...
  • Page 172 Index synchronizing multiple devices, 10-3 Counter n Z, 7-29 counter timing, 7-26 synchronous counting mode, 7-35 counters, 7-26 exporting timing output using PFI terminals, 8-3 technical support, xviii, C-1 FREQ OUT, 7-30 terminals, default counter, 7-31 Frequency Output, 7-30 Timebase minimizing output glitches, B-2 100 kHz, 10-2 simple pulse generation, 7-21...
  • Page 173 8-3 using RTSI as outputs, 10-5 X1 encoding, 7-16 terminals as timing input signals, 10-6 X2 encoding, 7-17 using short high-quality cabling, 4-8 X4 encoding, 7-17 V-I Converter, 5-1 © National Instruments Corporation NI 6238/6239 User Manual...

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