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National Instruments SC Express PXIe-4331, Руководство пользователя

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National Instruments SC Express PXIe-4331 Скачать руководство пользователя страница 37

Chapter 2

Using the Module

NI PXIe-4330/4331 User Manual

2-30

ni.com

Digital Triggering

You can configure the NI PXIe-4330/4331 modules to start an acquisition in response to a 
digital trigger signal from one of the PXI Express backplane trigger lines. The trigger circuit 
can respond either to a rising or a falling edge. In addition, the trigger circuit provides a 
programmable filter useful for debouncing noisy trigger signals.

Analog Triggering

Analog triggering allows you to trigger your application based on an input signal and trigger 
level you define. You can configure the analog trigger circuitry to monitor any input channel 
acquiring data. Choosing an input channel as the trigger channel does not influence the input 
channel acquisition capabilities.

The analog trigger signal can be used as a reference trigger only. In a reference-triggered 
acquisition, you configure the module to acquire a certain number of pre-trigger samples and 
a certain number of post-trigger samples. The analog trigger on the NI PXIe-4330/4331 
cannot be used as a start trigger. This restriction is a result of the way the module compensates 
for the filter group delay.

When using an analog reference trigger, the module first waits for the specified number of 
pre-trigger samples to be acquired. Once enough pre-trigger samples are acquired, the 
reference trigger will occur the next time the analog trigger condition is met. You also can 
route the resulting reference trigger event to the NI PXIe trigger bus to synchronize the 
triggering of other modules in the system.

During repetitive triggering on a waveform, you might observe jitter because of the 
uncertainty of where a trigger level falls compared to the actual digitized data. Although this 
trigger jitter is never greater than one sample period, it might be significant when the sample 
rate is only twice the bandwidth of interest. This jitter usually has no effect on data processing, 
and you can decrease this jitter by sampling at a higher rate.

You can use several analog triggering modes with the NI PXIe-4330/4331 modules, for 
instance analog edge, analog edge with hysteresis, and window triggering.

Содержание SC Express PXIe-4331

Страница 1: ...NI SC Express NI PXIe 4330 4331 User Manual NI PXIe 4330 4331 User Manual April 2010 373029A 01...

Страница 2: ...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 Russ...

Страница 3: ...mation retrieval system or translating in whole or in part without the prior written consent of National Instruments Corporation National Instruments respects the intellectual property of others and w...

Страница 4: ...Half Bridge Type I 2 8 Half Bridge Type II 2 10 Full Bridge Type I 2 12 Full Bridge Type II 2 14 Full Bridge Type III 2 16 Force Pressure and Torque Sensor Configurations 2 18 Common Mode Voltage Con...

Страница 5: ...Filters 3 3 Appendix A Offset Nulling Bridge Balancing Appendix B Technical Support and Professional Services Figures Figure 2 1 Basic Wheatstone Bridge Circuit Diagram 2 1 Figure 2 2 Connecting Remo...

Страница 6: ...ridge Type III Circuit Diagram 2 17 Figure 2 17 Force Pressure and Torque Sensor Circuit Diagram 2 18 Figure 2 18 NI PXIe 4330 4331 Signal Conditioning Block Diagram 2 24 Figure 2 19 NI PXIe 4330 4331...

Страница 7: ...rter half and full bridge Setting the DC voltage excitation between 0 625 V and 10 V Selecting 120 350 and 1 k quarter bridge completion resistors Programmable bridge offset null and shunt calibration...

Страница 8: ...r to the NI SC Express 4330 4331 Installation Guide and Terminal Block Specifications for more signal connection information Wheatstone Bridges Many sensors including strain gages load cells pressure...

Страница 9: ...lies it as a reference to its analog to digital converter ADC In this way variations in the excitation voltage are compensated for and the module returns data as a ratio of the bridge output voltage a...

Страница 10: ...across the excitation lead wire resistance Rlead If you do not use remote sensing of the actual bridge voltage the resulting reduction in gain is given by the following equations for half bridge senso...

Страница 11: ...strain by changing the resistance of an arm in the bridge by some known amount This is accomplished by shunting or connecting a large resistor of known value across one arm of the bridge creating a k...

Страница 12: ...ion resistor located inside the NI PXIe 4330 4331 R3 must be equal to the nominal resistance of the active gage R4 RS Shunt calibration resistor located inside the NI PXIe 4330 4331 R4 Active element...

Страница 13: ...nding configurations Figure 2 6 shows the quarter bridge type II circuit wiring diagram Figure 2 5 Quarter Bridge Type II Measuring Axial and Bending Strain A quarter bridge type II has the following...

Страница 14: ...stor located inside the NI PXIe 4330 4331 R4 Active element measuring tensile strain RL Lead resistance GF Gage Factor specified by the gage manufacturer VCH Measured voltage of the bridge VEX Excitat...

Страница 15: ...ns Figure 2 8 shows the half bridge type I circuit wiring diagram Figure 2 7 Half Bridge Type I Measuring Axial and Bending Strain A half bridge type I has the following characteristics Two active str...

Страница 16: ...ring tensile strain RL Lead resistance GF Gage Factor specified by the gage manufacturer Poisson s ratio defined as the negative ratio of transverse strain to axial strain longitudinal strain Poisson...

Страница 17: ...figuration Figure 2 10 shows the half bridge type II circuit wiring diagram Figure 2 9 Half Bridge Type II Rejecting Axial and Measuring Bending Strain A half bridge type II configuration has the foll...

Страница 18: ...331 R4 Active element measuring tensile strain RL Lead resistance GF Gage Factor specified by the gage manufacturer VCH Measured voltage of the bridge VEX Excitation voltage provided by the NI PXIe 43...

Страница 19: ...s the full bridge type I circuit wiring diagram Figure 2 11 Full Bridge Type I Rejecting Axial and Measuring Bending Strain A full bridge type I configuration has the following characteristics Four ac...

Страница 20: ...libration resistor located inside the NI PXIe 4330 4331 RL Lead resistance GF Gage Factor specified by the gage manufacturer VCH Measured voltage of the bridge VEX Excitation voltage provided by the N...

Страница 21: ...e 2 13 Full Bridge Type II Rejecting Axial and Measuring Bending Strain A full bridge type II configuration has the following characteristics Four active strain gage elements Two are mounted in the di...

Страница 22: ...ed inside the NI PXIe 4330 4331 RL Lead resistance GF Gage Factor specified by the gage manufacturer Poisson s ratio defined as the negative ratio of transverse strain to axial strain longitudinal str...

Страница 23: ...idge type III circuit wiring diagram Figure 2 15 Full Bridge Type III Measuring Axial and Rejecting Bending Strain A full bridge type III configuration has the following characteristics Four active st...

Страница 24: ...r specified by the gage manufacturer Poisson s ratio defined as the negative ratio of transverse strain to axial strain longitudinal strain Poisson s ratio is a material property of the specimen you a...

Страница 25: ...ensors typically use a full bridge configuration with a 350 nominal bridge resistance but other configurations and nominal bridge resistances can be used Figure 2 17 shows the force pressure torque se...

Страница 26: ...are specified as pairs of corresponding physical and electrical values electrical1 physical1 and electrical2 physical2 These should be based on the calibration certificate of the sensor if one is avai...

Страница 27: ...Considerations The NI PXIe 4330 4331 supports common mode voltages between 2 V The majority of full bridge sensors are balanced between the upper and lower arms of the bridge resulting in a common mo...

Страница 28: ...reduce the excitation voltage to a level that results in a common mode voltage that is within range To find the maximum excitation voltage that meets this criterion solve the following equation setti...

Страница 29: ...EX AI 2 25 QTR SC EX AI 24 QTR SC RS RS 23 AIGND EX AI 3 22 QTR SC EX AI 21 QTR SC RS RS 20 DGND T0 T1 No Channel 19 T3 T0 T1 18 T3 T2 T2 17 DGND T4 T5 16 T7 T4 T5 15 T7 T6 T6 14 AIGND EX AI 4 13 QTR...

Страница 30: ...ected based on the selected excitation voltage level Table 2 2 I O Connector Signal Descriptions Signal Names Direction Description AIGND Analog Input Ground AI 0 7 AI 0 7 Input Analog Input Channels...

Страница 31: ...an configure the NI PXIe 4330 4331 to select between internal 120 350 and 1 k quarter bridge completion resistors In addition you can enable programmable shunt calibration resistors individually or in...

Страница 32: ...order to acquire data at the specified rate The DDS clock can be generated either using an onboard oscillator or using the 100 MHz backplane clock provided by PXI Express Running the DDS clock from t...

Страница 33: ...nals with frequencies lower than fs 2 This maximum frequency is known as the Nyquist frequency The bandwidth from 0 Hz to the Nyquist frequency is the Nyquist bandwidth ADC The NI PXIe 4330 4331 ADCs...

Страница 34: ...esented correctly while others contain aliased artifacts Lowpass filtering to eliminate components above the Nyquist frequency either before or during the digitization process can guarantee that the d...

Страница 35: ...al filtering performed by the NI PXIe 4330 4331 produces a delay of many samples worth of time between when an event occurs on the input signal going into the NI PXIe 4330 4331 and when the data assoc...

Страница 36: ...e maximum rate for the module Timing and Triggering This section contains information about timing and triggering theory of operation Sample Clock Timebase The ADCs require an oversample clock to driv...

Страница 37: ...rigger samples The analog trigger on the NI PXIe 4330 4331 cannot be used as a start trigger This restriction is a result of the way the module compensates for the filter group delay When using an ana...

Страница 38: ...ge triggering you add a window above or below the trigger level This triggering mode often is used to reduce false triggering due to noise or jitter in the signal For example if you add a hysteresis o...

Страница 39: ...ses above 4 2 mV V as shown in Figure 2 22 Figure 2 22 Analog Edge Triggering with Hysteresis on Falling Slope Window Triggering A window trigger occurs when an analog signal either passes into enters...

Страница 40: ...inate clock drift between modules in long duration operations You can synchronize the analog input operations on two or more NI PXIe 4330 4331 modules to extend the channel count for your measurements...

Страница 41: ...slaves at DAQmx Trigger Advanced Synchronization Synchronization Type to Slave and that of the Master to Master Also query DAQmx Timing More Synchronization Pulse Synchronization Time on all modules...

Страница 42: ...pop up menu To programmatically configure TEDS call the DAQmx Configure TEDS VI Accessory Auto Detection NI SC Express modules automatically detect compatible accessories or terminal blocks The RSVD p...

Страница 43: ...ules in a PXI Express measurement or control system The PXI Express backplane is responsible for generating PXIe_SYNC100 independently to each peripheral slot in a PXI Express chassis For more informa...

Страница 44: ...as a trigger signal for input operations An SC Express module is not a System timing controller An SC Express module can be used in the system timing slot of a PXI system but the system will not be a...

Страница 45: ...s When the filter clock has sampled the signal high on N consecutive edges the low to high transition is propagated to the rest of the circuit The value of N depends on the filter setting Refer to Tab...

Страница 46: ...e bridge while not under load and then use this measurement as the initial bridge voltage when scaling readings from the bridge This method is simple fast and requires no manual adjustments The disadv...

Страница 47: ...you may renew to continue your benefits For information about other technical support options in your area visit ni com services or contact your local office at ni com contact Training and Certificati...

Страница 48: ...PXIe 4330 4331 User Manual B 2 ni com this manual You also can visit the Worldwide Offices section of ni com niglobal to access the branch office Web sites which provide up to date contact information...

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