Цифровые мультиметры PXI

NI PXI Digital Multimeters

What Is a PXI Digital Multimeter?

A PXI Digital Multimeter, or PXI DMM, is a modular instrument installed in a compatible PXI or PXIe chassis. It is controlled by an embedded PXI controller or an external computer connected through a supported remote-control interface.

Unlike a handheld or standalone bench multimeter, a PXI DMM is optimized for programmable test sequences. It can coordinate measurements with switches, programmable power supplies, source measure units, signal generators and other PXI instruments without requiring an operator to reconnect the DUT manually.

A typical automated sequence may power the DUT, route a test point through a switch matrix, select the appropriate DMM range, wait for settling, perform the measurement and compare the result against a pass/fail limit. The sequence can then advance automatically through hundreds of test points or multiple DUTs.

PXI DMM Measurement Functions

Current NI PXI Digital Multimeter Models

Both modules occupy one PXIe peripheral slot and support precision scalar measurements together with isolated waveform digitization. The PXIe-4080 is a strong general-purpose choice for automated electrical test, while the PXIe-4081 adds higher resolution, wider voltage and current capability and improved performance for demanding precision measurements.

PXIe-4080 vs PXIe-4081

The PXIe-4081 should not be selected solely because it has more digits. If the PXIe-4080 already meets the required uncertainty, range and throughput, it may be the more appropriate system choice. Select the PXIe-4081 when the additional resolution or extended ranges materially improve the measurement.

How to Select a PXI Digital Multimeter

1. Define Every Required Measurement

Begin with a complete list of DUT parameters: DC voltage, AC voltage, current, resistance, frequency, diode, temperature or transient waveform acquisition. Record the minimum and maximum expected values and the uncertainty required at each test point.

If the application also requires controlled voltage or current sourcing, compliance limits or I-V sweeps, add a PXI programmable power supply or SMU. A DMM measures electrical quantities but is not a complete substitute for a source measure unit.

2. Separate Resolution From Accuracy

Resolution describes the smallest change the DMM can represent. Accuracy describes how closely the result is expected to agree with the true value under defined conditions. A higher digit count can reveal smaller changes, but it does not independently define measurement uncertainty.

The usable result is affected by the selected range, gain and offset errors, temperature, aperture, noise, calibration age, cabling and switching path. Compare accuracy specifications at the actual signal level instead of comparing digit count alone.

3. Select the Correct Voltage and Current Ranges

The selected range must accommodate the maximum normal signal and any expected transient or fault condition. Using the smallest suitable range normally improves effective resolution, while choosing a range that is too small causes an overrange condition.

For current measurements, also evaluate burden voltage. The DMM introduces a voltage drop while measuring current, and that drop can change the DUT operating point in low-voltage or low-power circuits. Very small leakage-current measurements may require an SMU or electrometer-style instrument.

4. Calculate the Required Measurement Uncertainty

A practical uncertainty budget can include DMM accuracy, range contribution, temperature coefficient, measurement noise, calibration interval, test leads, relay contacts, fixture resistance, thermal EMF and DUT settling. The combined uncertainty should be sufficiently smaller than the permitted DUT tolerance.

Production test limits may require guard bands so that measurement uncertainty does not create unacceptable false passes or false failures. Define these requirements before choosing between a general-purpose and higher-accuracy DMM.

5. Balance Aperture Time, NPLC and Throughput

A longer measurement aperture generally reduces noise and improves rejection of power-line interference. DMM integration time is often expressed in number of power-line cycles, or NPLC. Integration matched to the local 50 Hz or 60 Hz supply can improve line-noise rejection.

Shorter apertures increase reading speed but may increase noise and reduce effective resolution. The maximum published reading rate normally assumes fast settings such as disabled auto-zero, minimum aperture and no added settling time. Benchmark the intended configuration rather than treating the maximum rate as the guaranteed application throughput.

6. Choose 2-Wire or 4-Wire Resistance

A 2-wire measurement includes resistance from the test leads, connectors, switch contacts and fixture. It is generally suitable when these contributions are insignificant compared with the DUT resistance.

A 4-wire Kelvin measurement uses separate force and sense connections so voltage drop in the force leads has much less influence on the result. It is recommended for low-value resistors, shunts, relays, connectors, cables and PCB conductors.

If switching is used, the complete path must support four-wire routing. Installing a four-wire-capable DMM does not create a Kelvin measurement when the switch or fixture only routes two conductors.

7. Determine Whether Digitizer Mode Is Required

The PXIe-4080 and PXIe-4081 can acquire isolated voltage or current sample records at up to 1.8 MS/s. This is useful when a scalar reading does not show enough information about how the signal changes over time.

Digitizer mode can be used to analyze power-up behavior, inrush current, relay switching, voltage sag, overshoot and other moderate-bandwidth events. Review both sample rate and analog bandwidth, because a high sampling rate does not guarantee that all high-frequency signal content will pass through the input circuitry.

For fast edges, high-frequency signals or advanced waveform triggering, select a dedicated PXI oscilloscope or digitizer.

8. Check Electrical Safety and Common-Mode Limits

Maximum input voltage is not the only safety specification. Confirm the measurement category, terminal-to-ground voltage, common-mode voltage, input protection, fuse rating and permitted environmental conditions.

PXIe-4080 and PXIe-4081 must not be used for Measurement Category III or IV circuits. High-energy distribution systems, mains installations and field wiring may require instruments with a different safety architecture. Always follow the product documentation and applicable laboratory safety procedures.

9. Plan Switching and Channel Expansion

One DMM can measure many DUT channels when combined with a suitable PXI switch. The switch routes each test point to the DMM sequentially, reducing instrument count in high-channel-count systems.

Total scan time depends on more than DMM reading rate. Include relay operation, contact bounce, signal settling, autoranging, aperture time, auto-zero, trigger latency and software overhead. High-impedance signals may require significantly more settling time after switching.

10. Verify Chassis, Software and Calibration

The PXIe-4080 and PXIe-4081 require PXI Express-compatible peripheral slots. A classic PXI-only slot cannot accept a PXIe module. Check the chassis slot map, controller, operating system and supported driver versions before ordering.

NI-DMM provides programmatic configuration and acquisition functions. InstrumentStudio supports interactive setup and measurement, while LabVIEW and TestStand can be used to create automated validation and production-test applications.

Both measurement performance and traceability depend on calibration conditions. Confirm the required calibration interval, documentation, traceability, warm-up period and whether system-level verification is needed after the module is installed with its cables, switches and fixture.

PXI DMM, DAQ, Digitizer or SMU?

DMM and Switch System Design

Combining a DMM with a multiplexer or matrix switch is one of the most common PXI automated-test architectures. It allows one precision measurement engine to serve tens or hundreds of channels.

When designing the signal path, confirm:

• Maximum switched voltage and current
• 2-wire or 4-wire routing requirements
• Relay contact resistance and thermal EMF
• Signal settling after each switching operation
• Isolation and common-mode limits
• Switch bandwidth and leakage
• Connector and cable pinout
• Hardware trigger and handshaking support

The DMM, switch, cabling and fixture should be treated as one measurement system. A high-accuracy DMM cannot remove errors introduced by unsuitable relays, unstable contacts or incorrectly routed Kelvin connections.

Typical PXI Digital Multimeter Applications

• Automated PCB and electronic assembly functional test
• Semiconductor and component characterization
• Power-supply rail and reference-voltage verification
• Battery, converter and power-electronics validation
• Cable, harness and connector continuity testing
• Relay and contact-resistance measurement
• Automotive and aerospace electronic-system test
• Precision resistance and temperature measurement
• Laboratory automation and calibration-oriented systems
• High-channel-count switch-scanning applications

Legacy PXI DMM Replacement

Older systems may use classic PXI models such as PXI-4065, PXI-4070, PXI-4071 or PXI-4072. Replacing one with a current PXIe module is not necessarily a direct substitution, even when the new instrument provides better headline specifications.

Compare the following before approving a replacement:

• Classic PXI or PXI Express slot compatibility
• Voltage, current and resistance ranges
• Resolution and accuracy at the actual signal level
• Reading rate and aperture configuration
• Digitizer and L/C measurement requirements
• Front-panel connections and cable assemblies
• Trigger routing and switch handshaking
• NI-DMM driver and operating-system support
• Calibration procedure and measurement correlation
• Required test-station requalification

For a validated production system, sourcing the original model may reduce software, fixture and requalification work. For a new platform, migration to PXIe can provide a better foundation for current chassis, controllers and software.

PXI Digital Multimeter Procurement and RFQ Guide

When comparing quotations, confirm the exact model, product condition, included accessories and calibration documentation. For pre-owned instruments, request device-recognition results, functional measurement testing and inspection of the front-panel and backplane connectors.

Часто задаваемые вопросы

What is the difference between PXIe-4080 and PXIe-4081?

The PXIe-4080 is a 6½-digit DMM with voltage ranges up to ±300 V and current ranges up to 1 A. The PXIe-4081 provides 7½-digit resolution, voltage ranges up to ±1,000 V and current ranges up to 3 A. Both include an isolated 1.8 MS/s voltage and current digitizer.

Does a 7½-digit DMM always provide a better measurement?

No. Additional resolution is useful only when the complete accuracy, noise, range, calibration and test setup support it. A 6½-digit DMM may already exceed the requirements of a general automated functional test.

Can a PXI DMM capture waveforms?

Selected NI FlexDMM models, including PXIe-4080 and PXIe-4081, provide isolated digitizer modes for voltage and current waveform acquisition. Review analog bandwidth as well as sample rate. A dedicated oscilloscope remains preferable for high-speed transient analysis.

When should four-wire resistance be used?

Use four-wire Kelvin measurement when lead, connector, relay or fixture resistance is significant relative to the DUT. Typical examples include shunts, contacts, cables, PCB traces and low-value resistors.

Can one PXI DMM measure hundreds of channels?

Yes. An appropriate multiplexer or matrix switch can route many DUT points sequentially to one DMM. Channel count and throughput depend on the switch topology, settling time, relay speed, measurement aperture and wiring configuration.

Should I use a DMM or SMU for semiconductor testing?

Use a DMM for precision passive measurements of voltage, current and resistance. Use an SMU when the test also requires controlled sourcing, compliance protection, I-V sweeps or very low leakage-current measurement.

Can PXIe-4080 or PXIe-4081 be installed in a classic PXI slot?

No. These are PXI Express modules and require compatible PXIe peripheral or hybrid slots. Confirm the exact chassis slot map before ordering.

Do PXIe-4080 and PXIe-4081 measure capacitance or inductance?

These functions should not be assumed for either model. If L/C measurement is required, select a DMM platform that explicitly supports those functions or use a dedicated LCR meter.

Recommended NI PXI Digital Multimeters

Related NI PXI Test Solutions

Build a complete automated test system with compatible PXI switches, PXI programmable power supplies and SMUs, PXI oscilloscopes and digitizers, or browse the complete NI PXI Modules category.

NI PXI Digital Multimeters from PXISOURCE

PXISOURCE supports engineers, system integrators, production-test teams and procurement departments with PXI DMM model selection, chassis compatibility review, switch integration, legacy replacement and sourcing for new systems, expansion projects and spare inventory.

Send the required measurement functions, signal ranges, uncertainty, channel count, throughput, chassis model and calibration requirements for a technically matched quotation.