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Chapter 5

Using the SCXI-1125

©

National Instruments Corporation

5-23

SCXI-1125 User Manual

Perform Offset Null Compensation Using Traditional NI-DAQ (Legacy)
C API

After configuring the system settings and module properties, you
can perform an offset null compensation programmatically using

SCXI_Calibrate

.

SCXI_Calibrate

takes measurements and adjusts the

coarse and fine offset null potentiometers to minimize or eliminate any
electrical offset for a channel. Repeat this process for each channel by
calling the

SCXI_Calibrate

function in a loop. Use the resulting

imbalance in your application as a software correction factor by
determining the residual voltage from the imbalance, and subtracting this
residual offset from each future measurement. For more information
regarding the operation of

SCXI_Calibrate

, refer to the

Traditional

NI-DAQ (Legacy) Function Reference Help

installed by default in

Start»

Programs»National Instruments»NI-DAQ

.

Perform Acquisition Using Traditional NI-DAQ (Legacy) C API

There are several NI-DAQ functions you can use to take measurements.
Usually in SCXI the preference is to take multiple samples from multiple
channels using the

SCAN_Op

function.

SCAN_Op

performs a synchronous,

multiple-channel scanned data acquisition operation.

SCAN_Op

does not

return until Traditional NI-DAQ (Legacy) acquires all the data or an
acquisition error occurs (MIO, AI, and DSA devices only). For this reason,
it is sometimes useful to use

SCAN_Op

in conjunction with the function

Timeout_Config

, which establishes a timeout limit synchronous

functions to ensure that these functions eventually return control to your
application. After acquiring data using

SCAN_Op

, the resultant data is not

organized by channel, so you should demultiplex the data using

SCAN_Demux

.

SCAN_Demux

rearranges, or demultiplexes, data acquired by

a

SCAN_Op

into row-major order, meaning each row of the array holding

Table 5-8.

NI-DAQ Functions Used to Configure SCXI-1125

Channel

Setting

NI-DAQ Function to Use

Significant

Parameters

Possible Parameters

Values

Gain

SCXI_Set_Gain

f64 gain

(gain setting)

1, 2, 5, 10, 20, 50, 100,
200, 250, 500, 1000,
2000

Bandwidth

SCXI_Configure_Filter

f64 freq
(filter cutoff
frequency if
filterMode = 1)

4.0, 10,000.0 Hz

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Содержание 776572-1600

Страница 1: ...SCXI TM SCXI 1125 User Manual SCXI 1125 User Manual October 2009 372425C 01...

Страница 2: ...3400 Lebanon 961 0 1 33 28 28 Malaysia 1800 887710 Mexico 01 800 010 0793 Netherlands 31 0 348 433 466 New Zealand 0800 553 322 Norway 47 0 66 90 76 60 Poland 48 22 328 90 10 Portugal 351 210 311 210...

Страница 3: ...e prior written consent of National 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...

Страница 4: ...symbol is marked on a product it denotes a warning advising you to take precautions to avoid electrical shock When symbol is marked on a product it denotes a component that may be hot Touching this c...

Страница 5: ...xed Scanning 1 5 Connecting the SCXI 1125 to an E M X Series DAQ Device for Parallel Scanning 1 5 Verifying the SCXI 1125 Installation in Software 1 6 Installing SCXI Using NI DAQmx in Software 1 6 Ma...

Страница 6: ...uring Module Property Pages in Traditional NI DAQ Legacy 3 5 Creating a Virtual Channel 3 6 Verifying the Signal 3 6 Verifying the Signal in NI DAQmx Using a Task or Global Channel 3 6 Verifying the S...

Страница 7: ...t Scaling Using Traditional NI DAQ Legacy in LabVIEW 5 20 Analyze and Display Using Traditional NI DAQ Legacy in LabVIEW 5 20 Traditional NI DAQ Legacy in Text Based ADEs 5 21 Configuring System Setti...

Страница 8: ...2 3 Figure 2 3 Connecting a Floating AC Coupled Signal 2 4 Figure 2 4 Connecting a Ground Referenced AC Coupled Signal 2 4 Figure 4 1 SCXI 1125 Block Diagram 4 1 Figure 5 1 Typical Program Flowchart...

Страница 9: ...erties 5 8 Table 5 4 Programming a Task in LabVIEW 5 10 Table 5 5 NI DAQmx Properties 5 15 Table 5 6 Settings for Configuring the SCXI 1125 Through the AI Parameter 5 18 Table 5 7 Configuration Functi...

Страница 10: ...ts that you can use for offset calibration An onboard EEPROM provides nonvolatile storage of software correction constants for both gain and offset The SCXI 1125 provides up to 300 Vrms working isolat...

Страница 11: ...se the SCXI 1125 with an S Series simultaneous sampling DAQ device but only in parallel mode A computer if using an SCXI chassis Cabling cable adapter and sensors as required for your application Soft...

Страница 12: ...connections and module configuration They also explain in greater detail how the module works and contain application hints Accessory installation guides or manuals If you are using accessory products...

Страница 13: ...on software NI DAQ driver software and the DAQ device to which you will connect the SCXI 1125 NI DAQmx 9 0 or later is required to configure and program the SCXI 1125 module If you do not have NI DAQm...

Страница 14: ...e allows Note You can also use the SCXI 1125 with an S Series DAQ device in parallel mode If you have not already installed all the modules refer to the Installing the SCXI 1125 Module into the SCXI C...

Страница 15: ...ecommends auto detecting modules for the first time configuration of the chassis Installing SCXI Using Traditional NI DAQ Legacy in Software Refer to the SCXI Quick Start Guide for information about i...

Страница 16: ...is is powered on Make sure all SCXI modules are properly installed in the chassis Refer to the SCXI Quick Start Guide for proper installation instructions Make sure the cable between the SCXI chassis...

Страница 17: ...the correct slot and select the cabled module A message box appears asking you to confirm the module replacement Click OK Configure the cabled module following the steps listed in the SCXI Quick Star...

Страница 18: ...rt a small signal on a high common mode voltage into a single ended signal with respect to the SCXI 1125 chassis ground With this conversion you can extract the analog input signal from a high common...

Страница 19: ...t give the highest noise immunity Ground Referenced Signal When the negative input signal line is connected either directly or indirectly to earth ground usually at the transducer end connect this lin...

Страница 20: ...he negative input line to chassis ground in the terminal block as shown in Figure 2 2 This eliminates noise that can be on the floating signal If the floating signal is not configured like Figure 2 2...

Страница 21: ...channel to DC reference the input stage of the SCXI 1125 You do not need to use a bias resistor with any high voltage terminal blocks since the terminal blocks already have a resistor between the inp...

Страница 22: ...mage the SCXI 1125 module Pin Assignments The front signal connector is a special 32 pin DIN C male front connector used for connecting analog input signals including the CJC to the analog circuitry o...

Страница 23: ...eans no connection means no pin 32 AI 0 AI 0 31 30 AI 1 AI 1 29 28 NC NC 27 26 AI 2 AI 2 25 24 AI 3 AI 3 23 22 NC NC 21 20 AI 4 AI 4 19 18 AI 5 AI 5 17 16 NC NC 15 14 AI 6 AI 6 13 12 AI 7 AI 7 11 10 N...

Страница 24: ...DAQ device In multiplexed mode the CH 0 signal pair is used for sending all eight channels of the SCXI 1125 and other analog signals from other modules to the connected E M X Series DAQ device If the...

Страница 25: ...3 CH 4 11 12 CH 4 CH 5 13 14 CH 5 CH 6 15 16 CH 6 CH 7 17 18 CH 7 OUT REF 19 20 NC NC 21 22 NC NC 23 24 D GND SER DAT IN 25 26 SER DAT OUT DAQ D A 27 28 NC SLOT 0 SEL 29 30 NC NC 31 32 NC D GND 33 34...

Страница 26: ...and how to verify the signal using both NI DAQmx and Traditional NI DAQ Legacy Common Software Configurable Settings This section describes the most frequently used software configurable settings for...

Страница 27: ...configure the SCXI 1125 module s Configurable Settings in MAX Note If you are not using an NI ADE using an NI ADE prior to version 7 0 or are using an unlicensed copy of an NI ADE additional dialog bo...

Страница 28: ...u set the minimum and maximum range of NI DAQmx Task or NI DAQmx Global Channel the driver selects the best gain for the measurement You also can set it through your application Modes of operation con...

Страница 29: ...er 3 Configuring and Testing for more information 10 Click the Device tab and select the autozero mode and lowpass filter cutoff frequency 11 If you are creating a task and want to set timing or trigg...

Страница 30: ...ed to an E Series DAQ device select that device by using Connected to If you want this E Series DAQ device to control the chassis confirm there is a check in the This device will control the chassis c...

Страница 31: ...following information a What DAQ hardware will be used from the drop down list b What channel on your DAQ hardware from the drop down list c Which analog input mode will be used from the drop down li...

Страница 32: ...Signal in Traditional NI DAQ Legacy This section discusses how to verify the signal in Traditional NI DAQ Legacy using channel strings and virtual channels Verifying the Signal Using Channel Strings T...

Страница 33: ...k Test Panels 5 Enter the channel string 6 Enter the input limits 7 Select the Data Mode 8 Select the Y Scale Mode Refer to the LabVIEW Help for more information and for proper formatting of channel s...

Страница 34: ...different gain settings from 1 to 2000 enabling signal ranges 5 V to 2 5 mV When the SCXI 1125 is used with a terminal block that provides attenuation the input range expands up to 1000 V Refer to Ap...

Страница 35: ...f LabVIEW LabWindows CVI or Measurement Studio By combining hardware anti aliasing with digital filtering you can choose any cutoff frequency The Advanced Analysis functions are only available in LabV...

Страница 36: ...channels to a single channel on the E M X Series DAQ device Note The SCXI 1125 parallel outputs continuously drive the rear signal connector output pins even when you configure the module in multiplex...

Страница 37: ...ode Theory of Parallel Hardware Operation In parallel mode the CH 0 signal on the rear signal connector is configured as the output of the SCXI 1125 analog input channel 0 The rear signal connector ca...

Страница 38: ...ing This design reduces the CJC errors which might reduce the accuracy of your temperature measurement Most SCXI terminal blocks available for the SCXI 1125 contain a cold junction temperature sensor...

Страница 39: ...mperature reading from the thermocouple junction National Instruments software ADEs have useful conversion functions for CJC In LabVIEW virtual channels with the CJC channel invoked or the Convert The...

Страница 40: ...about 3 times this or 300 nVpk because of the 4 Hz filter In this example you might or might not be able to average out the noise The total error is 1 73 V at the full scale temperature range which gi...

Страница 41: ...nclude a cold junction sensor so you can combine thermocouple measurements with high voltage measurements When making signal connections or when working with high voltage signals refer to the terminal...

Страница 42: ...l channel in unlicensed mode These dialog boxes continue to appear until you install version 7 0 or later of an NI ADE This section describes how to configure and use NI DAQmx to control the SCXI 1125...

Страница 43: ...ask Programmatically Create Task in DAQ Assistant or MAX No Hardware Timing Triggering Create Task Using DAQ Assistant No Yes No Yes Configure Channels Further Configure Channels Start Measurement Rea...

Страница 44: ...ing or when many properties differ between channels in the same task If you are using an ADE other than an NI ADE or if you want to explicitly create and configure a task for a certain type of acquisi...

Страница 45: ...se Table 5 3 to determine what kind of properties you need to set to configure the module for your application For a complete list of NI DAQmx properties refer to your ADE help file Note You cannot ad...

Страница 46: ...ide controls and gauge indicators NI ADEs have tools that allow you to easily save the data to files such as spread sheets for easy viewing ASCII files for universality or binary files for smaller fil...

Страница 47: ...in the DAQ Assistant They are only available for the present session of the task in LabVIEW Adjust Timing Settings optional DAQmx Timing vi Sample Clock by default This VI is optional if you created...

Страница 48: ...ive Channels the properties are set on all of the channels in the task 6 Right click ActiveChans and select Add Element Left click the new ActiveChans box Navigate through the menus and select the pro...

Страница 49: ...w property left click it and select the property you wish to define Note Refer to the LabVIEW Help for information about property nodes and specific NI DAQmx properties Specifying Channel Strings in N...

Страница 50: ...ith different properties separate the lists of properties with another ActiveChans box and assign the appropriate channel to each list of properties 6 Right click ActiveChan and select Add Element Lef...

Страница 51: ...arameters you define in MAX and the device defaults To change a property of the channel programmatically use the DAQmxSetChanAttribute function Note Refer to the LabWindows CVI Help for more informati...

Страница 52: ...ion 7 0 or later of an NI ADE This section describes how to configure and use Traditional NI DAQ Legacy to control the SCXI 1125 in LabVIEW LabWindows CVI Measurement Studio and other text based ADEs...

Страница 53: ...ds using the virtual channel for ease of use Refer to Appendix B Using SCXI Channel Strings with Traditional NI DAQ Legacy 7 0 or Later for more information about how to create a virtual channel The S...

Страница 54: ...design your application using a typical program flow such as the one shown in Figure 5 3 Figure 5 3 Typical SCXI 1125 Program Flow with Traditional NI DAQ Legacy Virtual Channel Create Virtual Channel...

Страница 55: ...is called The AI parameter VI merely changes the configuration in the driver memory When called the AI Start VI reads the configuration settings in the driver memory and then sends the actual control...

Страница 56: ...tion you can use the intermediate analog input functions AI Config VI AI Start VI AI Read VI and AI Clear VI to create your data acquisition application You can find the intermediate data acquisition...

Страница 57: ...IEW User Manual You also can use the LabVIEW Help for more detailed information about how to use these nodes to perform mathematical calculations such as scaling conversions Analyze and Display Using...

Страница 58: ...the Traditional NI DAQ Legacy C API Refer to the ADE user documentation for more information about how to use the high level data acquisition tools that are provided in your NI ADE For more advanced...

Страница 59: ...le to its default state You also can use SCXI_Reset to reset the SCXI chassis Slot 0 scanning circuitry or reset the entire chassis The SCXI 1125 default conditions are Gain set at 1000 0 4 Hz lowpass...

Страница 60: ...several NI DAQ functions you can use to take measurements Usually in SCXI the preference is to take multiple samples from multiple channels using the SCAN_Op function SCAN_Op performs a synchronous m...

Страница 61: ...tion regarding SCXI_Scale refer to the Traditional NI DAQ Legacy Function Reference Help installed by default in Start All Programs National Instruments NI DAQ After you have adjusted the measurement...

Страница 62: ...scan list When the application program runs the channel string is used for programming the channel information into the SCXI system The format of the channel string is as follows obx scy mdz channels...

Страница 63: ...emperature drifts in the analog circuitry You can subtract these offsets from subsequent input readings to correct for temperature drift Refer to Appendix A Specifications for determining how temperat...

Страница 64: ...CJC automatically Note Virtual analog input channels can be randomly scanned therefore virtual channels can be entered in any order or repeated in the channel string Performing a Multiplexed Scan To...

Страница 65: ...r must match the total number of channels programmed in step 2 You are now ready to acquire the channel data with the E Series DAQ device If you are using a multifunction E Series DAQ device you can u...

Страница 66: ...ltage data by using SCXI_Scale Refer to the Traditional NI DAQ User Manual for additional information about parallel scanning of SCXI modules Other Application Documentation and Material Refer to the...

Страница 67: ...tails about the analog stability of your SCXI 1125 module Calibration Procedures You can calibrate the offset on the SCXI 1125 using National Instruments software When calibrating the offset on the SC...

Страница 68: ...channel at a time b Select internal calibration as the calibration operation you are going to perform c Select the Default EEPROM load area as the area you want to update d The offset varies with the...

Страница 69: ...e d Since offset varies with gain enter the gain setting for which you are calibrating offset e Enter 1 for the terminal block gain since it is not used f Enter 0 0 as the input reference voltage 3 Re...

Страница 70: ...1 and 5 2 for extended range using the SCXI 1313A SCXI 1327 and TBX 1316 Table A 1 Input Signal Range Versus Gain Overall Gain Overall Voltage Range SCXI 1125 Gain 1 5 Vpeak or VDC 1 2 2 5 Vpeak or V...

Страница 71: ...x A Specifications SCXI 1125 User Manual A 2 ni com Overvoltage protection Isolated connector pins Powered on and off 300 V Inputs protected CH0 CH7 Non isolated connector pins Powered on and off 5 5V...

Страница 72: ...00 7 0 05 5500 30 200 3100 58 12 183 1013 8 50 7 0 1 5500 30 200 3100 58 6 111 511 8 25 7 0 2 5500 32 200 3100 63 3 48 255 8 10 7 0 5 5500 35 200 3100 77 1 19 1 104 0 5 1 5000 10 200 3100 54 0 53 8 6...

Страница 73: ...y at full scale is determined using the following assumptions Temperature Range 15 C to 35 C NumberOfAverages 16 TimeAfterSelfCalibration 1 month For example on the 5 V range the absolute accuracy at...

Страница 74: ...oad 4 5 M With SCXI 1327 1 M With TBX 1316 40 M Input bias current 100 pA typical 1 nA max Filter type 3 pole Butterworth filter response Bandwidth Filter options 4 Hz and 10 kHz 10 kHz filter Full po...

Страница 75: ...75 dB All other channels 90 dB Input coupling Default DC Using SCXI 1305 or TBX 1329 AC or DC Power Consumption 18 5 V 140 mA max 18 5 V 140 mA max 5 V 10 mA max Output Characteristics Output range 5...

Страница 76: ...tions National Instruments Corporation A 7 SCXI 1125 User Manual Calibration External calibration interval 1 year Physical Figure A 1 SCXI 1125 Dimensions Weight 641 g 22 6 oz 3 0 cm 1 2 in 17 2 cm 6...

Страница 77: ...us voltages 42 4 Vpk 60 VDC are present on any channel all channels are considered hazardous Ensure that external wiring or any circuits connected to the device are properly insulated from human conta...

Страница 78: ...Group 1 Class A emissions AS NZS CISPR 11 Group 1 Class A emissions FCC 47 CFR Part 15B Class A emissions ICES 001 Class A emissions Note For the standards applied to assess the EMC of this product re...

Страница 79: ...ntal regulations and directives with which NI complies as well as other environmental information not included in this document Waste Electrical and Electronic Equipment WEEE EU Customers At the end o...

Страница 80: ...tries configures multiple modules for scanning When the application program runs the channel string is used for programming the channel information into the SCXI system The format of the channel strin...

Страница 81: ...repeated in the channel list Notes Using parenthesis surrounding multiple channels in a channel string is important for correct scanning operation of the SCXI channels In a single chassis system the...

Страница 82: ...y the installed modules 4 Right click the module or chassis you want to delete and click Delete 5 You are presented with a confirmation window Click Yes to continue deleting the module or chassis or N...

Страница 83: ...ws that secure the SCXI 1125 to the chassis counterclockwise until they are loose but do not completely remove the thumbscrews 5 Remove the SCXI 1125 by pulling steadily on both thumbscrews until the...

Страница 84: ...th TBX 1316 Isolation 250 Vrms 300 Vrms Gains 1 2 5 10 20 50 100 200 250 500 1000 and 2000 jumper selectable 1 2 5 10 20 50 100 200 250 500 1000 and 2000 software selectable Filters 4 Hz or 10 kHz jum...

Страница 85: ...isolate the problem If requesting technical support by phone have your system near at hand so that you can try these measures immediately Can I use the unused analog input channels of the E M X Serie...

Страница 86: ...channels work with parallel mode operation on the SCXI 1125 The E M X Series DAQ device must be directly connected to the module in parallel mode operation Also virtual channels that use built in CJC...

Страница 87: ...NI DAQ Legacy there is no VI available to do this You must use the configuration utility in MAX to configure the filter setting of each channel In C can I randomly scan the SCXI 1125 using low level T...

Страница 88: ...l Glossary Symbol Prefix Value p pico 10 12 n nano 10 9 micro 10 6 m milli 10 3 k kilo 103 M mega 106 G giga 109 T tera 1012 Numbers Symbols Degrees Greater than or equal to Less than or equal to Ohms...

Страница 89: ...opment AI GND analog input ground AI HOLD COMP AI HOLD clock that triggers scanning amplification A type of signal conditioning that improves accuracy in the resulting digitized signal by increasing s...

Страница 90: ...channels chassis The enclosure that houses powers and controls SCXI modules CJ TEMP cold junction temperature sensor signal CJC cold junction compensation CLK clock input signal CMRR common mode reje...

Страница 91: ...thmic measure of the ratio of two signal levels dB 20 log10 V1 V2 for signals in volts DC direct current device A plug in data acquisition board module card or pad that can contain multiple channels a...

Страница 92: ...n decibels gain accuracy A measure of deviation of the gain of an amplifier from the ideal gain gain error See gain accuracy GND ground H Hz hertz I I O input output The transfer of data to from a com...

Страница 93: ...of terminal blocks increases thermocouple measurement accuracy K K kelvin L linearization A type of signal conditioning in which software linearizes the voltage levels from transducers so the voltages...

Страница 94: ...motors generators transformers fluorescent lights soldering irons CRT displays computers electrical storms welders and radio transmitters and internal sources such as digital clocks microprocessors a...

Страница 95: ...erial authorization rms root mean square RSVD reserved bit signal RTI referred to input Calculates a specification relative to the input range S s seconds sample An instantaneous measurement of a sign...

Страница 96: ...ght sound pressure motion flow and so on and produces a corresponding electrical signal Primary characteristics of sensors are sensitivity frequency range and linearity settling time The time required...

Страница 97: ...VIEW software module VI which consists of a front panel user interface and a block diagram program virtual channels Channel names that can be defined outside of the application and used without having...

Страница 98: ...overview 5 30 two point gain and offset calibration 5 32 channel string calgnd channel string D 3 SCXI 5 25 virtual 5 26 channels C language scanning D 4 questions about D 3 unused analog input channe...

Страница 99: ...ts 5 4 I input characteristics A 1 installation connecting SCXI 1125 to DAQ device for parallel scanning 1 5 connecting to DAQ device for multiplexed scanning in PXI combination chassis 1 5 3 2 in SCX...

Страница 100: ...figure 2 8 table 2 8 removing SCXI 1125 from Measurement Automation Explorer C 1 from SCXI chassis C 1 S SCXI channel string 5 25 SCXI chassis connecting SCXI 1125 to DAQ device 1 4 3 2 SCXI 1125 cali...

Страница 101: ...7 stability A 6 transfer characteristics A 6 stability specifications A 6 T temperature measurements using thermocouples 5 1 accurate method for temperature determination 5 2 guide for calculating ove...

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