C Series High-Speed Digitizer Module

NI C Series High-Speed Digitizer Modules

High-Speed Digitizer Measurement Functions

Key High-Speed Digitizer Considerations

Sample Rate and Usable Bandwidth

Sample rate determines how often the module converts the input signal, while usable bandwidth describes the frequency content that can be measured accurately. Start with the highest frequency of interest, then select a module and sample rate that provide suitable oversampling and anti-alias protection.

A module’s maximum sample rate should not be treated as its guaranteed measurement bandwidth. Input filtering, analog front-end performance, signal source characteristics and analysis requirements all affect the practical result.

Simultaneous Sampling

Simultaneous sampling is important when the timing or phase relationship between channels must be preserved. Examples include three-phase power analysis, vibration measurements, modal testing, motor analysis and correlation between force, pressure and acceleration signals.

Multiplexed analog-input architectures can be suitable for slower signals, but channels are measured at slightly different times. Confirm the acquisition architecture when phase accuracy is part of the test requirement.

Input Range and Signal Integrity

Select the smallest supported input range that accommodates the maximum expected signal, including sensor offset, startup transients and fault conditions. A smaller suitable range generally improves the effective use of the digitizer’s available resolution.

Also review source impedance, common-mode conditions, grounding, cable shielding and expected electrical noise. High-speed acquisition can reveal interference that is not visible in slower measurement systems.

Resolution, Noise and Dynamic Range

ADC resolution indicates the number of digital code levels available, but it does not alone define measurement quality. Input noise, gain error, offset, linearity, filtering and environmental interference affect the usable dynamic range and effective resolution.

For low-level dynamic signals, evaluate sensor sensitivity, cable length, grounding and required input range together. An unsuitable front end can limit performance even when the converter resolution appears high.

Triggering and Record Length

Triggered acquisition is useful when the event of interest occurs at a known condition, such as a switching transition, impact, command signal or fault threshold. Confirm required trigger source, trigger level, edge direction, pretrigger history and post-trigger duration.

Record length determines how much waveform data is retained for each event. Long captures with many active channels can create substantial memory and storage requirements.

How to Select a C Series High-Speed Digitizer Module

1. Define the Signal and Maximum Frequency

Identify the source type and expected signal range. Determine the highest frequency or fastest transient that must be captured, rather than selecting hardware from the nominal physical measurement alone.

A vibration sensor, motor current probe, voltage transducer and strain-gauge conditioner can all produce voltage outputs, but their bandwidth, source impedance, noise level and grounding requirements may be very different.

2. Calculate the Required Sample Rate

Select the sample rate from the required measurement bandwidth, desired waveform detail and analysis method. Provide margin for anti-alias filtering, transient visibility and any post-processing requirements.

For a multichannel system, confirm whether the published rate applies per channel, across all enabled channels or under a specific acquisition configuration.

3. Confirm Channel Count and Sampling Architecture

Count all waveform channels that must be acquired during the same test. Determine whether the application requires simultaneous sampling, synchronized sampling across modules or only independent time-based logging.

Include reference signals, tachometer inputs, trigger channels and auxiliary measurements in the channel plan. These signals are often needed later for correlation and troubleshooting.

4. Match the Input Interface

Verify voltage range, connector type, input coupling, terminal arrangement and supported input topology. Confirm whether the connected sensor requires external excitation, an IEPE supply, a charge amplifier, a bridge conditioner or another dedicated signal-conditioning stage.

Do not connect a sensor directly to a high-speed voltage digitizer unless its electrical output and required conditioning are known to be compatible.

5. Plan Continuous Data Streaming

Long-duration high-speed acquisition requires sufficient system bandwidth and storage performance. Estimate the payload rate using the active channels, sample rate and stored bytes per sample:

Data rate = active channels × sample rate × stored bytes per sample.

Allow additional margin for driver activity, software processing, file format overhead, display updates and other system traffic. Validate the final configuration using the intended record duration and channel configuration.

6. Review Isolation and Grounding

Isolation can help manage ground-potential differences and common-mode conditions, especially in industrial and power-test environments. The required isolation topology depends on the installed equipment, sensor grounding, cable routing and voltage exposure.

Proper shielding and grounding remain important even with isolated hardware. Avoid routing low-level measurement cables beside switching power wiring, motor leads or relay-control cables where practical.

CompactDAQ and CompactRIO Platform Use

CompactDAQ systems are suitable for PC-based waveform logging, portable test and dynamic measurement applications. They can combine high-speed digitizer inputs with digital, temperature, communication and other C Series I/O in one modular system.

CompactRIO systems support embedded applications that may require real-time monitoring, deterministic control or FPGA-based preprocessing. FPGA processing can reduce transferred data, apply custom trigger logic or make time-critical decisions before data reaches the controller.

Verify the exact digitizer module’s compatibility with the selected chassis, controller, operating system, driver version and intended programming environment before ordering.

Software, Synchronization and Data Management

Supported C Series high-speed digitizer modules are commonly configured with NI-DAQmx or the applicable CompactRIO software environment. The software architecture should separate time-critical acquisition from file writing, visualization, analysis and network communication.

Use appropriate clocking and trigger methods when correlating data from multiple modules. For applications requiring phase accuracy, verify the complete synchronization design rather than assuming that all modules in the same chassis share an identical timing relationship.

For high-rate recordings, use buffered acquisition and sequential block writes. Avoid performing frequent small file writes or intensive graphical processing inside the acquisition loop, as these can contribute to buffer overflow or lost data.

Typical Applications

• Transient voltage and current capture
• Motor, inverter and power-electronics testing
• Vibration, shock and structural-response measurement
• Automotive and aerospace component validation
• Machine condition monitoring and rotating-equipment analysis
• Actuator, valve and electromechanical response testing
• High-speed sensor waveform recording
• Switching-event and fault analysis
• Laboratory waveform acquisition and FFT analysis
• Embedded real-time monitoring with CompactRIO

C Series High-Speed Digitizer Module Procurement Guide

FAQ

What is the difference between a high-speed digitizer and a standard analog input module?

A high-speed digitizer is selected for faster waveform capture, transient visibility and dynamic-signal analysis. Standard analog input modules are often better suited to slower process, temperature or general monitoring measurements.

Is the highest sample rate the same as usable bandwidth?

No. Sample rate defines how frequently data is converted, while usable bandwidth depends on the analog front end, filtering, signal quality and required measurement accuracy.

Do I need simultaneous sampling?

Simultaneous sampling is recommended when phase or timing relationships between channels matter, such as in power, vibration, force, pressure or structural testing.

Can a high-speed voltage input connect directly to every sensor?

No. Some sensors require excitation, bridge completion, IEPE power, charge conversion or another conditioning stage. Confirm the sensor’s electrical output before connection.

Why can a continuous acquisition stop even when the module sample rate is supported?

Continuous streaming also depends on chassis bandwidth, controller performance, memory buffers, storage throughput, software design and file-writing behavior. The full data path must be validated for the required test duration.

Related NI Modular I/O Solutions

NI C Series High-Speed Digitizer Modules from PXISOURCE

PXISOURCE helps engineers and procurement teams select compatible NI high-speed digitizer modules, review CompactDAQ and CompactRIO system requirements, match signal-conditioning accessories and source modules for new test systems, spares and legacy replacements.