National Instruments NI-9242 C Series Voltage Input Module

The National Instruments NI‑9242 is a 4‑channel, 24‑bit simultaneous analog input module that belongs to the C Series platform for CompactDAQ and CompactRIO systems. It is designed for high‑voltage measurement applications such as phasor measurements, power metering, power quality monitoring, and motor testing. With input voltage ranges of 250 Vrms line‑to‑neutral (L‑N) and 400 Vrms line‑to‑line (L‑L), the NI‑9242 can directly interface with potential transformers or low‑voltage power distribution systems. Each channel features a delta‑sigma ADC with analog prefiltering, providing excellent accuracy and noise rejection.

Technical Specifications

• Model: NI‑9242 (Part number 783107‑01)

• Number of Channels: 4 analog input channels

• ADC Resolution: 24 bits

• ADC Type: Delta‑Sigma with analog prefiltering

• Sampling Mode: Simultaneous

• Maximum Sampling Rate: 50 kS/s per channel (internal master timebase)

• Input Voltage Range:

• L‑N: 250 Vrms (nominal), 500 Vpk max

• L‑L: 400 Vrms (nominal)

• Scaling Coefficient: 59,605 nV/LSB

• Input Impedance: 1 MΩ (AIx‑to‑GND, Neutral‑to‑GND)

• Overvoltage Protection: 500 Vrms continuous, 600 Vrms for 10 s; 8 kV surge withstand

• Accuracy (calibrated, -40°C to 70°C): 0.26% gain error, 0.14% offset error

• Gain Drift: 12.1 ppm/°C

• Offset Drift: 3.4 mV/°C

• Input Noise (at 50 kS/s): 3 mVrms (L‑N, L‑L)

• Operating Temperature: -40°C to +70°C

• Protection Rating: IP40 (when installed in enclosure)

• Connector: 10‑pin spring terminal (0.2–1.5 mm²)

Measurement and Applications

The NI‑9242 is optimized for power‑line frequency measurements (50/60 Hz). It performs single‑ended analog input and can measure up to four voltages simultaneously, making it ideal for 3‑phase voltage monitoring (3 phases plus neutral). The module reports both L‑N and N‑Earth values, enabling detection of ground faults. The wide input range and high isolation allow direct connection to industrial AC supplies without external step‑down transformers, reducing system complexity.

Integration with CompactRIO and CompactDAQ

The NI‑9242 plugs into any C Series backplane of a CompactRIO (cRIO) controller or a CompactDAQ (cDAQ) chassis. It communicates over the High‑Speed Expansion Bus, and data is streamed to the real‑time processor or host PC. The module is supported by LabVIEW and LabVIEW Real‑Time, with example VIs for power monitoring, harmonic analysis, and phasor measurement units (PMUs). The module’s waveform can be triggered and streamed continuously for long‑term logging.

Calibration and Accuracy

The NI‑9242 is factory calibrated. The calibration constants are stored in non‑volatile memory on the module. An external calibration is recommended every 1–2 years to maintain accuracy. The module supports both single‑point and periodic calibration using an external voltage reference. The gain and offset errors are specified over the full temperature range.

Physical and Environmental Data

Dimensions: 89 mm × 76 mm × 35 mm. Weight: 190 g. The module is rated for pollution degree 2 and is UL 61010‑1, CE, and RoHS compliant. It is designed for indoor use at altitudes up to 2,000 m. Vibration: 5g (10–500 Hz); shock: 30g.

Typical Configurations

A typical 3‑phase power monitoring setup uses three NI‑9242 modules (12 channels) for voltage and three NI‑9225 modules for current. Alternatively, a single NI‑9242 can monitor a 3‑phase line (3 voltages) and one additional DC voltage. The module is also used in motor test stands to measure back EMF and phase voltages.

Conclusion

The NI‑9242 offers high‑accuracy, high‑voltage measurement capability in a compact, rugged form factor, making it an excellent choice for power quality analysis and industrial voltage monitoring.