NI PXI-6238 Multifunction I/O Module Overview
The NI PXI-6238 (Part Number: 779624-01) is a 16-bit, 250 kS/s (kiloSamples per second) multifunction I/O module from National Instruments' M Series. It's designed to provide a mix of analog input (AI), analog output (AO), digital input (DI), digital output (DO), counter/timer, and triggering functionalities within a single PXI module. A key feature of the PXI-6238 is its bank isolation, making it ideal for applications with high voltages or electrical noise where isolation between banks of channels is crucial for safety and signal integrity.
Product Detailed Description
Multifunctionality: The PXI-6238 combines several I/O types into one module, making it a versatile tool for various data acquisition and control tasks. This reduces the need for multiple specialized modules in a PXI chassis.
Current Input (AI): It is primarily designed for current measurements, featuring 8 differential current input channels with a range of ±20 mA. This is crucial for interfacing with industrial sensors and transducers that output current signals (e.g., 4-20 mA).
Analog Output (AO): It provides 2 analog output channels with 16-bit resolution, capable of sourcing 0-20 mA. These outputs can be used to control industrial actuators, valves, or other devices that accept current signals.
Digital I/O (DI/DO): The module includes 6 lines of digital input and 4 lines of digital output. These digital I/O lines are compatible with 24V signals, making them suitable for direct connection to industrial control systems (PLCs, relays, etc.). The digital outputs are sourcing.
Counters/Timers: Two 32-bit counter/timers are integrated, enabling precise timing, pulse generation, event counting, and frequency measurement.
Bank Isolation: A significant feature is its bank isolation, which provides electrical separation between different groups of channels. This protects the module and connected equipment from ground loops and transient voltages, crucial in noisy industrial environments.
High Resolution and Speed: With 16-bit resolution for both analog inputs and outputs, it offers high precision. The 250 kS/s sample rate for analog inputs and 500 kS/s update rate for analog outputs (single channel) allow for capturing and generating fast signals.
PXI Platform Integration: As a PXI module, it benefits from the PXI platform's integrated timing and synchronization capabilities, high-performance backplane, and modularity. This allows for building flexible, scalable, and high-performance test systems.
Software Defined: It leverages NI's software-defined approach, primarily through NI-DAQmx drivers and development environments like LabVIEW, enabling users to program and configure the module for specific application needs.
Auto-Calibration: Supports auto-calibration to correct for time and temperature drift, ensuring accuracy over time.
Product Parameters
Analog Input (AI):
Channels: 8 differential current inputs
Resolution: 16 bits
Sample Rate: 250 kS/s (maximum)
Input Range: ±20 mA
Input Impedance: 92 Ω ±10% in parallel with 100 pF (AI+ to AI-)
Timing Accuracy: 50 ppm of sample rate
Input FIFO Size: 4,095 samples
Analog Output (AO):
Channels: 2
Resolution: 16 bits
Update Rate: 500 kS/s (1 channel), 450 kS/s (2 channels per channel)
Output Range: 0 mA to 20 mA
Output Coupling: DC
Power-on State: 0 mA
Output FIFO Size: 8,191 samples (shared among channels)
Digital Input (DI):
Channels: 6 (PFI<0..5>/P0.<0..5>)
Input Voltage Range: 0 V to 30 V
Logic "0" Level: 0 V to 4 V
Logic "1" Level: 10 V to 30 V
Minimum Input Impedance: 3.3 kΩ
Debounce Filter: Selectable settings (125 ns, 6.425 µs, 2.56 ms, disable)
Digital Output (DO):
Channels: 4 (Port 1)
Output Type: Sourcing
Max External Supply Voltage (P1.VCC): 30 V
Max Current: 100 mA per line (simultaneous), 350 mA (single line)
Counters/Timers:
Bus Interface: PXI Hybrid Slot compatible (can be used in both PXI Express hybrid slots and standard PXI slots)
Power Consumption: (Refer to specific datasheet for exact values, typically low power for PXI modules)
Operating Temperature: 0 °C to 50 °C
Storage Temperature: -20 °C to 70 °C
Dimensions: Standard 3U PXI module
Part Number: 779624-01
Product Advantages
High-Voltage and Noise Immunity: Bank isolation provides excellent protection against common-mode noise and ground loops, making it suitable for industrial applications with high voltages or noisy electrical environments.
Versatile I/O: Combines current AI, current AO, digital I/O, and counter/timer functions in one module, reducing system complexity and cost.
High Accuracy and Resolution: 16-bit resolution ensures precise measurements and control for demanding applications.
PXI Platform Benefits: Integrates seamlessly into the PXI ecosystem, offering benefits like synchronized measurements across multiple modules, high data throughput, and a rugged, modular form factor.
Compatibility with Industrial Signals: Directly accepts ±20 mA current inputs and provides 0-20 mA current outputs, ideal for connecting to standard industrial sensors and actuators.
24V Digital Compatibility: Digital I/O is compatible with 24V industrial signals, simplifying integration with PLCs and other control components.
Software Support: Backed by NI's comprehensive NI-DAQmx driver software and programming environments like LabVIEW, enabling rapid development and deployment of test and control applications.
Precautions
PXI Chassis Requirement: The PXI-6238 requires a compatible PXI chassis (standard PXI or PXI Express hybrid slot) with sufficient power and cooling.
Proper Wiring: Adhere strictly to the wiring diagrams in the NI PXI-6238 user manual. Incorrect wiring, especially for current inputs/outputs and power supply, can damage the module or connected equipment.
Grounding: Ensure proper grounding practices are followed to maximize the benefits of isolation and minimize noise.
Environmental Conditions: Operate the module within its specified temperature and humidity ranges. While robust, extreme conditions can affect performance and longevity.
Self-Calibration and External Calibration: To maintain specified accuracy, perform self-calibration (software-based) after a warm-up period (at least 15 minutes) and before measurement sessions. External calibration (by an accredited lab) is recommended at least once per year.
Current Loop Considerations: When connecting current inputs, ensure the current loop is properly terminated and powered. For current outputs, ensure the load impedance is within the module's specifications.
ESD Precautions: Always handle the module with electrostatic discharge (ESD) precautions to prevent damage.
Software Drivers: Ensure the correct version of NI-DAQmx drivers is installed and compatible with your operating system and development environment.
Product Applications
The NI PXI-6238 is well-suited for a variety of demanding test, measurement, and control applications, particularly those involving current signals and requiring isolation.
Industrial Process Control:
Reading 4-20 mA signals from process sensors (pressure, flow, temperature, level).
Controlling valves, pumps, and actuators using 0-20 mA current outputs.
Monitoring and controlling industrial machinery in noisy environments.
Automated Test Equipment (ATE):
Testing and validating industrial control systems.
Simulating sensor inputs and actuator outputs for hardware-in-the-loop (HIL) simulations.
Automating production line testing of devices that use current-based signals.
Machine Monitoring and Control:
Energy Management Systems:
Laboratory and Research:
Remote Monitoring:
