PXI-6255 80-Channel 16-Bit Multifunction PXI DAQ Module
The PXI-6255 is a high-channel-count M Series multifunction data acquisition module designed for laboratory automation, research, design validation and production testing. It combines analog input, analog output, digital I/O, counters, triggering and PXI synchronization in a single 3U module.
The module provides 80 single-ended or 40 differential analog input channels with 16-bit resolution. It supports a maximum single-channel sampling rate of 1.25 MS/s and an aggregate multichannel rate of up to 750 kS/s, making it suitable for scanning a large number of voltage signals with one PXI module.
In addition to analog acquisition, the PXI-6255 includes two 16-bit analog outputs, 24 digital I/O lines and two 32-bit counter/timers. NI-DAQmx software support enables integration with LabVIEW, TestStand and compatible text-based programming environments.
Key Features of the PXI-6255
- 80 single-ended analog input channels
- Up to 40 differential analog input channels
- 16-bit analog input resolution
- 1.25 MS/s maximum single-channel sampling rate
- 750 kS/s maximum aggregate multichannel rate
- Programmable input ranges from ±100 mV to ±10 V
- Two 16-bit analog output channels
- Up to 2.86 MS/s analog output update rate
- 24 TTL/CMOS-compatible digital I/O lines
- Hardware-timed digital waveform support
- Two 32-bit counter/timers
- Analog and digital triggering
- Six DMA channels for high-throughput transfers
- PXI trigger-bus and PXI_STAR synchronization
- Two 68-pin VHDCI front-panel connectors
- SCXI and SCC signal-conditioning compatibility
- NI-DAQmx software support
PXI-6255 Technical Specifications
| Product Model | PXI-6255 |
|---|---|
| Part Number | 779547-01 |
| Product Family | NI M Series multifunction DAQ |
| Product Type | PXI multifunction I/O module |
| Single-Ended Analog Inputs | 80 |
| Differential Analog Inputs | Up to 40 |
| ADC Resolution | 16 bits |
| Maximum Single-Channel Sample Rate | 1.25 MS/s |
| Maximum Multichannel Sample Rate | 750 kS/s aggregate |
| Analog Input Sampling | Multiplexed, nonsimultaneous |
| Input Coupling | DC |
| Analog Input Ranges | ±0.1 V, ±0.2 V, ±0.5 V, ±1 V, ±2 V, ±5 V and ±10 V |
| Maximum Analog Input Level | ±11 V relative to AI GND |
| Analog Outputs | 2 voltage outputs |
| Analog Output Resolution | 16 bits |
| Maximum Analog Output Update Rate | 2.86 MS/s with one channel |
| Analog Output Range | ±10 V |
| Digital I/O | 24 lines |
| Hardware-Timed Digital Port | Port 0, 8 lines |
| Counters/Timers | 2 × 32-bit |
| DMA Channels | 6 |
| Triggering | Analog and digital |
| PXI Synchronization | PXI_TRIG, PXI_STAR and PXI_CLK10 |
| Front-Panel Connectors | 2 × 68-pin VHDCI |
| Dimensions | Standard 3U PXI module |
| Weight | Approximately 236 g |
| Software Driver | NI-DAQmx |
| Recommended Replacement | PXIe-6355 |
| Availability Status | Discontinued by NI |
PXI-6255 Part Number and Accessories
| Item | Part Number | Description |
|---|---|---|
| PXI-6255 | 779547-01 | 80-channel, 16-bit M Series PXI multifunction DAQ module |
| SHC68-68-EPM Cable | Varies by length | Shielded 68-pin VHDCI cable for connecting the module to a terminal block |
| SCB-68A | 782536-01 | Shielded 68-pin screw-terminal block for custom signal wiring |
| CB-68LP | 777145-01 | Low-cost 68-pin connector block with screw terminals |
| BNC-2120 | 779014-01 | Shielded BNC terminal accessory for laboratory signal connections |
| PXIe-6355 | 783632-01 | Recommended X Series PXI Express replacement with 80 analog inputs |
The PXI-6255 has two 68-pin VHDCI connectors. A complete 80-channel installation may require two compatible cables and two terminal accessories, depending on the wiring configuration and signals being used.
Connector 0 carries analog input, analog output, digital I/O, counter and timing signals. Connector 1 provides access to the additional high-density analog input channels. Verify connector assignment and cable quantity before ordering.
80-Channel Analog Input Architecture
The PXI-6255 provides 80 single-ended analog input channels for high-density voltage measurement. This capacity allows a single module to monitor a large number of sensors, test points and control signals while conserving PXI chassis slots.
The inputs can also be configured for differential measurements. Differential wiring provides improved rejection of common-mode noise and is generally preferred for low-level signals, remote signal sources and electrically noisy environments.
The PXI-6255 uses a multiplexed ADC architecture. Input channels are connected sequentially to a shared analog-to-digital converter rather than being sampled simultaneously.
16-Bit Analog Input Resolution
The module digitizes analog input signals with 16-bit resolution. On the ±10 V range, the ADC divides the nominal 20 V span into 65,536 quantization levels.
Actual measurement accuracy also depends on gain error, offset error, noise, source impedance, temperature and calibration. Resolution alone should not be treated as the complete accuracy specification.
1.25 MS/s Maximum Sampling Rate
The PXI-6255 supports a maximum sampling rate of 1.25 MS/s when acquiring one analog input channel. When scanning multiple channels, the maximum aggregate rate is 750 kS/s.
The aggregate rate is shared across all channels in a scan list. For example, when 75 channels are sampled at equal rates, the theoretical maximum average rate is approximately 10 kS/s per channel before accounting for settling requirements and application overhead.
High-impedance signal sources may require a slower channel-conversion rate to allow the input multiplexer and amplifier to settle accurately after switching between channels.
Programmable Analog Input Ranges
The PXI-6255 offers programmable bipolar input ranges of ±100 mV, ±200 mV, ±500 mV, ±1 V, ±2 V, ±5 V and ±10 V. Selecting the smallest suitable range uses more of the ADC span and improves effective voltage resolution.
The selected range must accommodate the complete signal, including offset, noise and expected transient conditions. Inputs should not exceed the module’s maximum working-voltage limits.
Single-Ended and Differential Measurements
Single-ended input configurations provide the maximum channel count and are suitable for short connections to ground-referenced signals with compatible grounding.
Differential mode measures the voltage between two input terminals and provides improved rejection of noise common to both conductors. It is appropriate for floating sources, longer cables and lower-level measurements.
Correct bias-current return paths must be provided for floating signal sources. Without a return path, the input amplifier may drift or saturate and produce unstable readings.
Two 16-Bit Analog Outputs
The PXI-6255 includes two software- or hardware-timed analog voltage outputs. These channels can generate control voltages, test stimuli, setpoints and low-frequency waveforms while the module acquires analog input data.
A single analog output channel supports an update rate up to 2.86 MS/s. When both channels are updated, the available rate is shared according to the hardware timing configuration.
The outputs are intended for voltage generation and limited-current loads. Use an external amplifier or driver when the connected load requires more current or power than the DAQ output can provide.
24 Digital I/O Lines
The module provides 24 TTL/CMOS-compatible digital I/O lines arranged as three 8-bit ports. Each line can be configured as an input or output according to the requirements of the application.
Digital I/O can be used for reading switches, monitoring status signals, controlling relays, selecting fixture states and exchanging logic signals with a device under test.
Port 0 supports hardware-timed correlated digital input and output. The remaining lines are useful for static or software-timed control and monitoring.
Correlated Digital I/O
Correlated digital I/O allows digital waveform operations to share clocks or triggers with analog input, analog output and counter tasks. This enables digital patterns to be generated or acquired in synchronization with analog measurements.
Typical uses include recording device status alongside analog data, applying digital control patterns at defined measurement points and coordinating fixture switching with a test sequence.
Two 32-Bit Counter/Timers
The PXI-6255 includes two general-purpose 32-bit counter/timers. These counters support event counting, edge counting, frequency measurement, period measurement, pulse-width measurement, position measurement and pulse generation.
Counter signals are routed through programmable-function interface terminals. Before wiring a counter application, verify the required source, gate, auxiliary and output terminal assignments.
Analog and Digital Triggering
Analog triggering allows an acquisition to begin, pause or capture a reference position when an analog signal crosses a specified condition. Digital triggering performs similar control using an external logic signal or an internally routed event.
Triggering reduces dependence on software timing and improves repeatability. It is useful for transient capture, automated validation, rotating-machinery measurement and synchronized stimulus-response testing.
PXI Synchronization
The module can use PXI trigger lines, PXI_STAR and the chassis reference clock to coordinate timing with other compatible PXI instruments. This allows multiple DAQ and measurement modules to begin operations from a common trigger.
A phase-locked loop can reference the onboard timebase to PXI_CLK10 or another supported timing source. Shared timing improves long-term alignment between measurements performed by different modules.
Six DMA Channels
The PXI-6255 provides six DMA channels that can be assigned to analog input, analog output, digital input, digital output and the two counter/timer subsystems.
DMA transfers data directly between the module and host memory with limited processor intervention. This supports higher throughput and allows several hardware-timed measurement tasks to operate concurrently.
SCXI and SCC Signal Conditioning
The PXI-6255 can be combined with compatible SCXI or SCC signal-conditioning hardware to add capabilities such as sensor excitation, filtering, isolation and high-voltage attenuation.
Signal conditioning should be selected according to the sensor type, required bandwidth, accuracy, isolation and environmental conditions. The conditioning output must remain within the PXI-6255 input range.
NI-DAQmx Software Support
The PXI-6255 is controlled through the NI-DAQmx driver. NI-DAQmx provides configuration, timing, triggering, calibration and data-transfer functions for every I/O subsystem on the module.
The driver supports LabVIEW, LabWindows/CVI and compatible C, C++, C# and Python environments. NI Measurement & Automation Explorer can be used to identify the device, configure channels and run basic test panels.
Typical PXI-6255 Applications
- High-channel-count voltage acquisition
- Automated production testing
- Laboratory automation
- Design verification and validation
- Data logging
- Sensor monitoring with external conditioning
- Electronic device functional testing
- Process monitoring and control
- Educational and research systems
- Mixed analog and digital test fixtures
- Frequency and pulse measurements
- SCXI-based measurement systems
High-Channel-Count Data Logging
The 80 analog inputs make the PXI-6255 suitable for monitoring many voltage signals in one system. Applications can include temperature-transmitter outputs, power-supply rails, test-point voltages and conditioned sensor signals.
For long-duration logging, select a sample rate that matches the required signal bandwidth and storage capacity. Unnecessarily high sampling rates increase file size and processing requirements without improving low-frequency measurements.
Production Functional Testing
In a production test system, the PXI-6255 can measure analog voltages, generate stimulus signals, read fixture status lines and control external switching hardware.
Hardware triggering and DMA transfers support repeatable automated sequences. The module can be combined with PXI switches, digital multimeters and programmable power supplies for more complete functional testing.
Research and Laboratory Automation
The combination of analog input, analog output, digital I/O and counters supports experimental systems requiring several types of measurement and control.
Researchers can acquire voltage signals, generate control waveforms and synchronize external instruments from a common PXI platform. Custom LabVIEW applications can provide visualization, logging and automated analysis.
PXI-6255 Troubleshooting
The module is not detected in NI MAX
Confirm that the PXI-6255 is fully installed in a compatible slot. Check chassis power, controller communication and NI-DAQmx installation, then restart NI Measurement & Automation Explorer and rescan the system.
Only some analog input channels are available
Verify that both front-panel connectors and the correct terminal accessories are being used. The additional high-numbered analog input channels are located on the second 68-pin connector.
Measurements are noisy
Use shielded twisted-pair wiring, select differential mode when appropriate and separate low-level signals from power and digital wiring. Check grounding, source impedance and external signal-conditioning requirements.
Readings change when scanning more channels
Reduce the channel-conversion rate and allow more settling time between multiplexed inputs. High source impedance and large voltage differences between adjacent channels increase settling requirements.
The input reads full scale or an unstable value
Confirm that the signal remains within the selected range and maximum working-voltage limit. Floating sources require a bias-current return path to analog ground.
An analog output does not reach the commanded voltage
Check the load impedance and required current. Disconnect the load and measure the output directly to determine whether excessive loading or fixture wiring is causing the voltage drop.
Digital outputs do not switch the connected load
The digital lines provide logic-level signals and are not designed to power high-current loads directly. Use a suitable relay driver, transistor or external digital interface for larger loads.
The acquisition rate is lower than expected
Remember that the 1.25 MS/s rating applies to single-channel acquisition. Multichannel operation has a lower aggregate limit, which is divided across the channels in the scan list.
Counter measurements are incorrect
Verify the PFI terminal assignment, signal voltage levels, grounding and counter configuration. Check whether the task requires edge counting, period, frequency, pulse-width or encoder measurement mode.
PXI-6255 Comparison with Similar DAQ Modules
| Model | Primary Configuration | Best Suited For |
|---|---|---|
| PXI-6251 | 16 AI, 2 AO, 24 DIO, 16-bit | General multifunction DAQ with lower channel count |
| PXI-6254 | 32 AI, 48 DIO, 16-bit | Additional digital I/O without analog outputs |
| PXI-6255 | 80 AI, 2 AO, 24 DIO, 16-bit | High-channel-count multifunction acquisition |
| PXI-6259 | 32 AI, 4 AO, 48 DIO, 16-bit | More analog outputs and digital I/O |
| PXIe-6355 | 80 AI, 2 AO, 24 DIO, 16-bit X Series | Modern PXI Express replacement |
PXI-6255 vs PXI-6251
The PXI-6255 provides 80 single-ended analog inputs, while the PXI-6251 provides 16. Both offer multifunction analog and digital I/O, but the PXI-6255 is better suited to systems requiring substantially greater input density.
Select the PXI-6251 for smaller systems with fewer measurement points. Choose the PXI-6255 when conserving chassis slots is important and many analog channels must be scanned.
PXI-6255 vs PXI-6259
The PXI-6255 emphasizes analog input density with 80 input channels. The PXI-6259 provides fewer analog inputs but offers four analog outputs and 48 digital I/O lines.
Select the PXI-6255 for high-channel-count voltage acquisition. Choose the PXI-6259 when the application requires additional waveform outputs or more digital control lines.
PXI-6255 vs PXIe-6355
The PXIe-6355 is NI’s recommended replacement for the discontinued PXI-6255. Both provide 80 analog inputs, 16-bit resolution, two analog outputs and 24 digital I/O lines.
The PXIe-6355 uses the newer X Series architecture and PXI Express interface. The PXI-6255 remains useful for maintaining existing M Series systems, software configurations and test fixtures.
Recommended Related Products
- PXI-6251 Multifunction DAQ Module
- PXI-6254 32-Channel Multifunction DAQ Module
- PXI-6259 Multifunction DAQ Module
- PXIe-6355 80-Channel X Series DAQ Module
- USB-6255 Multifunction I/O Device
- View More NI PXI and PXI Express Modules
Selecting the Right Multifunction DAQ Module
Choose the PXI-6255 when the application requires as many as 80 analog inputs together with analog output, digital I/O and counter/timer functions in a single PXI slot.
Select a lower-channel-count M Series module when fewer inputs are needed. Choose the PXI-6259 when additional analog outputs and digital lines are more important, or the PXIe-6355 for a newer PXI Express system.
Why Choose the PXI-6255?
- Provides 80 analog inputs in one PXI module
- Offers 16-bit voltage measurement resolution
- Supports single-channel rates up to 1.25 MS/s
- Includes two hardware-timed analog outputs
- Provides 24 digital I/O lines
- Includes two versatile 32-bit counter/timers
- Supports analog, digital and PXI triggering
- Uses DMA for efficient multistream data transfers
- Integrates with NI-DAQmx and LabVIEW
- Supports existing M Series and SCXI test systems
Frequently Asked Questions
What is the PXI-6255?
The PXI-6255 is a high-channel-count M Series PXI multifunction DAQ module with analog input, analog output, digital I/O and counter/timer functions.
How many analog inputs does it provide?
The module provides 80 single-ended analog input channels or up to 40 differential channels, depending on the wiring configuration.
What is the maximum sampling rate?
The maximum single-channel rate is 1.25 MS/s. The maximum aggregate rate when scanning multiple analog input channels is 750 kS/s.
Does the PXI-6255 sample every channel simultaneously?
No. It uses a multiplexed ADC, so channels in the scan list are converted sequentially rather than simultaneously.
How many analog outputs are included?
The PXI-6255 provides two 16-bit analog voltage outputs with a maximum single-channel update rate of 2.86 MS/s.
How many digital I/O lines are available?
The module provides 24 digital I/O lines. Port 0 supports correlated hardware-timed digital waveform operations.
Does it include counters?
Yes. The PXI-6255 has two 32-bit general-purpose counter/timers for frequency, period, pulse, event and position measurements.
Which connectors does the module use?
It uses two 68-pin VHDCI connectors. Two compatible cables and terminal accessories may be required to access the complete signal set.
Which software controls the PXI-6255?
The module is controlled with NI-DAQmx and can be programmed using LabVIEW, LabWindows/CVI and compatible text-based environments.
What is the PXI-6255 part number?
The standard NI part number for the PXI-6255 is 779547-01.
What is the recommended replacement?
NI recommends the PXIe-6355 as the replacement for new PXI Express systems requiring a similar 80-channel multifunction I/O configuration.
Request a Quote for the PXI-6255
Contact us for current availability, condition, lead time and project pricing for the PXI-6255 80-Channel 16-Bit Multifunction PXI DAQ Module. We can also help identify compatible VHDCI cables, terminal blocks, PXI chassis and replacement DAQ modules.
