NI PXI-6608 | 185745H-02 Counter/Timer Module | High-Performance Timing for Test Systems
NI PXI-6608 | 185745H-02 Counter/Timer Module | High-Performance Timing for Test Systems - Image 2
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NI PXI-6608 | 185745H-02 Counter/Timer Module | High-Performance Timing for Test Systems

  • Model: PXI-6608 (P/N: 185745H-02)
  • Brand: National Instruments (now part of Emerson following 2023 acquisition)
  • Core Function: 8-channel high-speed counter/timer with quadrature encoder support
  • Lifecycle Status: Mature – still available and supported, but superseded by PXIe alternatives
  • Selection Advantages: Proven reliability, deep LabVIEW integration, cost-effective for mid-performance needs
  • Ideal For: Retrofit projects, brownfield expansions, or new systems where PXI (not PXIe) infrastructure exists
Category: SKU: PXI-6608 185745H-02

Description

Technical Specifications

  • Product Model: PXI-6608
  • Manufacturer: National Instruments
  • Platform: 3U PXI (32-bit, 33 MHz PCI interface)
  • Counters: 8 independent 32-bit general-purpose counters
  • Timebase Options: Internal (10 MHz, 100 MHz), external (up to 100 MHz), or PFI lines
  • Input Voltage Range: ±5 V (TTL/CMOS compatible)
  • Max Input Frequency: 100 MHz (with 100 MHz timebase)
  • Features:
    • Quadrature encoder (A/B/Z) support
    • Pulse train generation (up to 20 MHz)
    • Buffered event counting
    • Digital triggering and gating
  • Connector: 68-pin VHDCI (via breakout cable, e.g., CB-68LP)
  • Software Support: NI-DAQmx (fully supported), LabVIEW, MATLAB, Python (nidaqmx)
  • Power Consumption: +3.3 V @ 1.5 A, +5 V @ 1.0 A typical
  • Certifications: CE, FCC, RoHS

Core Performance and Selection Advantages

The PXI-6608 delivers exceptional value in applications requiring deterministic, hardware-timed counting without the overhead of software polling. Its eight dedicated counters operate independently, enabling simultaneous tasks such as:

  • Tracking position from four dual-axis encoders
  • Measuring PWM duty cycle and frequency on multiple motor drives
  • Timestamping fault events across distributed subsystems

Compared to software-based timing or general-purpose digital I/O, the PXI-6608 offers sub-microsecond resolution, immunity to OS jitter, and zero CPU load during operation—critical in real-time test environments.

For system integrators, key advantages include:

  • Seamless integration with existing PXI chassis (e.g., NI PXI-1042, PXI-1045)
  • Extensive driver ecosystem: Fully supported in NI-DAQmx with pre-built examples for encoder, tachometer, and period measurement
  • Cost efficiency: Often available at lower cost than PXIe equivalents when leveraging existing PXI infrastructure
  • Backward compatibility: Works with legacy LabVIEW codebases (LV 7.0+) without major refactoring

System Integration and Scalability

The PXI-6608 integrates natively into NI’s measurement ecosystem:

  • Configured via NI MAX (Measurement & Automation Explorer) for quick validation
  • Programmed using NI-DAQmx API in LabVIEW, C/C++, Python, or .NET
  • Synchronized with other PXI modules via PXI trigger bus and star trigger lines

For multi-chassis systems, it supports RTSI (Real-Time System Integration) bus connectivity for phase-coherent timing across up to 7 chassis—ideal for large-scale structural testing or multi-axis motion control.

While not PXI Express, the PXI-6608 can coexist in hybrid PXI/PXIe chassis (e.g., NI PXIe-1082) using legacy slots, offering a migration bridge for facilities upgrading incrementally.

When to Choose PXI-6608 vs. Newer Alternatives

Scenario Recommendation
Existing PXI system needing encoder inputs ✅ PXI-6608 (lowest TCO)
New design requiring >100 MHz timing or streaming ❌ Use PXIe-6614 or PXIe-6639
Need IEEE 1588 or TSN synchronization ❌ Requires PXIe platform
Budget-constrained retrofit with proven codebase ✅ PXI-6608 is optimal
PXI-6608 185745H-02

PXI-6608 185745H-02

Long-Term Considerations

Although still active, NI advises against using the PXI-6608 in greenfield projects due to:

  • Limited future driver enhancements
  • No path to higher bandwidth or modern protocols
  • Eventual phase-out as PXI inventory depletes

For new designs, PXIe-6614 (8-channel, 100 MHz) or PXIe-6639 (4-channel, 1.25 GS/s timestamping) offer better longevity. However, for maintaining or expanding legacy test stands—especially in aerospace, automotive, or semiconductor equipment—the PXI-6608 remains a reliable, cost-effective, and fully supported solution with predictable availability through 2027–2028 based on current channel stock.

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