National Instruments NI PCI-6110, NI PCI-6111 Analog Input and Output

Appendix C Common Questions

© National Instruments Corporation C-3 NI PCI-6110/6111 User Manual

Analog Input and Output

Why is there a minimum sampling rate on the NI PCI-6110/6111?

The NI PCI-6110/6111 makes use of a pipelined ADC in order to achieve

its high sampling rates. Sampling at rates below 20 kS/s can result in

improper digitalization, which would appear as noise in the acquired data.

I connected a DIFF input signal, but the readings are random and drift

rapidly. What’s wrong?

Check the ground reference connections. The signal may be referenced to

a level that is considered floating with reference to the device ground

reference. Even if you are in differential mode, the signal must still be

referenced to the same ground level as the device reference. There are

various methods of achieving this while maintaining a high common-mode

rejection ratio (CMRR). These methods are outlined in Chapter 4,

Connecting Signals.

I’m using the DACs to generate a waveform, but I discovered with a

digital oscilloscope that there are glitches on the output signal. Is this

normal?

When it switches from one voltage to another, any DAC produces glitches

due to released charges. The largest glitches occur when the most

significant bit (MSB) of the D/A code switches. You can build a low-pass

deglitching filter to remove some of these glitches, depending on the

frequency and nature of the output signal.

Can I synchronize a one-channel AI data acquisition with a

one-channel AO waveform generation on the NI PCI-6110/6111?

Yes. One way to accomplish this is to use the waveform generation timing

pulses to control the analog input data acquisition. To do this, follow steps1

through 4 below, in addition to the usual steps for data acquisition and

waveform generation configuration.

1. Enable the PFI5 line for output, as follows:

• If you are using NI-DAQ, call

Select_Signal(deviceNumber, ND_PFI_5,

ND_OUT_UPDATE, ND_HIGH_TO_LOW).

• If you are using LabVIEW, invoke Route Signal.vi with signal

name set to PFI5 and signal source set to AO Update.

Contents

Main Page Important Information Warranty Copyright Trademarks Patents Compliance FCC/Canada Radio Frequency Interference Compliance Determining FCC Class FCC/DOC Warnings Class A Contents Chapter 4 Connecting Signals Page About This Manual Conventions National Instruments Documentation Related Documentation Introduction About the NI PCI-6110/6111 What You Need to Get Started Software Programming Choices NI-DAQ National Instruments ADE Software Optional Equipment Custom Cabling Unpacking Safety Information Page Page Installing and Configuring the NI PCI-6110/6111 Installing the Software Installing the Hardware Configuring the Device National Instruments Corporation 3-1 NI PCI-6110/6111 User Manual Hardware Overview DAQ - STC RTSI Bus Figure 3-1. NI PCI-6110 Block Diagram I/O Connector Analog Input Input Mode Note The inputs are differential only in the sense that the ground loops are broken. The I/O Connector RTSI Bus Input Polarity and Input Range Considerations for Selecting Input Ranges Input Coupling Analog Output Analog Trigger Figure 3-3. Analog Trigger Block Diagram for the NI PCI-6110 Figure 3-4. Analog Trigger Block Diagram for the NI PCI-6111 Page Page Digital I/O Timing Signal Routing Page Programmable Function Inputs Device and RTSI Clocks RTSI Triggers Connecting Signals I/O Connector Figure 4-1. 68-Pin I/O Connector Pin Assignment for the NI PCI-6110/6111 Figure 4-2. 50-Pin Connector Pin Assignments for the NI PCI-61 10/6111 I/O Connector Signal Descriptions Table 4-2. Signal Descriptions for I/O Connector Pins Page Page Table 4-3. I/O Signal Summary for the NI PCI-6110/6111 Table 4-3. I/O Signal Summary for the NI PCI-6110/6111 (Continued) Connecting Analog Input Signals Types of Signal Sources Floating Signal Sources Ground-Referenced Signal Sources Differential Measurements Differential Connection Considerations Differential Connections for Ground-Referenced Signal Sources Figure 4-4. Differential Input Connections for G round-Referenced Signals Differential Connections for Nonreferenced or Floating Signal Sources Common-Mode Signal Rejection Considerations Working Voltage Range Analog Output Signal Connections Digital I/O Signal Connections Power Connections Timing Connections Programmable Function Input Connections DAQ Timing Connections TRIG1 Signal TRIG2 Signal Page STARTSCAN Signal Page CONVERT* Signal AIGATE Signal SISOURCE Signal SCANCLK Signal EXTSTROBE* Signal Waveform Generation Timing Connections WFTRIG Signal UPDATE* Signal UISOURCE Signal General-Purpose Timing Signal Connections GPCTR0_SOURCE Signal GPCTR0_GATE Signal GPCTR0_OUT Signal GPCTR0_UP_DOWN Signal GPCTR1_SOURCE Signal GPCTR1_GATE Signal GPCTR1_OUT Signal GPCTR1_UP_DOWN Signal Page FREQ_OUT Signal Field Wiring Considerations Page Calibration Loading Calibration Constants Self-Calibration External Calibration A Specifications Analog Input Input Characteristics Accuracy Information Transfer Characteristics Amplifier Characteristics Dynamic Characteristics Stability Analog Output Output Characteristics Transfer Characteristics Voltage Output Dynamic Characteristics Stability Digital I/O Timing I/O General-Purpose Up/Down Counter/Timers Frequency Scaler Triggers Analog Trigger Digital Trigger External Input for Digital or Analog Trigger (PFI0/TRIG1) Page Environmental Safety Electromagnetic Compatibility CE Compliance Page Figure B-1. 68-Pin Connector Pin Assignment for the NI PCI-611 0/6111 Figure B-2. 50-Pin Connector Pin Assignment for the NI PCI-611 0/6111 C Common Questions General Information Installing and Configuring Analog Input and Output Timing and Digital I/O Page Page D Technical Support and Professional Services Page Glossary Numbers/Symbols A B C D E F G H I K L M N O P Page R S T U V W Index Symbols Numerics A B C D E F G H I K L M N O Q R S T U V W