National Instruments NI-9242 C Series High-Voltage Analog Input Module

The National Instruments NI-9242 (Part Number 783107-01) is a 3‑channel, 24‑bit C Series analog input module for CompactRIO and CompactDAQ systems. Specifically designed for high-voltage measurements, the NI-9242 is ideal for power quality monitoring, phasor measurement, 3‑phase power metering, motor testing, and voltage monitoring from potential transformers. The module's wide input range (250 Vrms line‑to‑neutral, 400 Vrms line‑to‑line) allows direct connection to industrial AC supplies without external voltage dividers, simplifying system design.

Technical Specifications

Functional Description

The NI-9242 performs single-ended analog input on three independent channels, simultaneously sampling at up to 50 kS/s per channel. The wide measurement range makes it ideal for high-voltage applications such as phasor measurement, power metering, power quality monitoring, and motor testing. The module's 24‑bit delta‑sigma ADC provides high dynamic range and noise rejection, enabling accurate measurements even in the presence of harmonic distortion. Each channel includes an anti-aliasing filter (AAF) and is equipped with overvoltage protection up to 500 Vrms continuous.

Power Quality and 3‑Phase Measurement

The NI-9242 is optimized for power‑line frequency measurements (50/60 Hz). It can be used in 3‑phase, 4‑wire wye systems (3 voltages + neutral) or 3‑phase, 3‑wire delta systems. The module reports both line‑to‑neutral and line‑to‑line voltage values, and through the host software, can calculate real power, reactive power, apparent power, power factor, and harmonics up to the 50th order. The simultaneous sampling feature ensures that phase angles between channels are measured accurately, essential for power calculations.

Integration with CompactRIO and CompactDAQ

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

Calibration and Accuracy

The NI-9242 is factory calibrated, with calibration constants stored in non‑volatile memory on the module. An external calibration is recommended every 1–2 years to maintain specified 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 of -40°C to +70°C.

Physical and Environmental Data

The module is rated for pollution degree 2 and is UL 61010‑1, CE, and RoHS compliant. Vibration resistance: 5g (10–500 Hz); shock resistance: 30g. The IP40 rating (when installed in a chassis) provides protection against dust. The operating temperature range of -40°C to +70°C makes the NI-9242 suitable for outdoor installations and unheated control rooms.

Typical Configurations

A typical 3‑phase power monitoring setup uses three NI-9242 modules (9 channels) for voltage measurements, paired with three NI-9225 modules for current measurements. Alternatively, a single NI-9242 can monitor a 3‑phase line (3 voltages) plus one additional DC voltage. The module is also used in motor test stands to measure back EMF and phase voltages, and in substation automation for voltage sag/swell monitoring.

Programming and Data Access

Using LabVIEW, the user can read raw voltage data from each channel in engineering units (Volts). The NI-9242 returns data as 24‑bit signed integers, which are scaled using the module's factory‑calibrated coefficients. The built‑in functions (NI-DAQmx driver) handle scaling automatically. The module also supports Finite and Continuous acquisition modes, with software‑configurable sample rates.

Safety and Compliance

The NI-9242 is certified for use in measurement categories CAT II (250 Vrms) and CAT I (400 Vrms). It is designed to meet IEC 61010‑1 safety standards and has a reinforced insulation rating of 250 Vrms (channel‑to‑earth). The module is suitable for use in hazardous environments when installed in an appropriately rated chassis.

Conclusion

The National Instruments NI-9242 offers high‑accuracy, high‑voltage measurement capability in a rugged, compact C Series form factor, ideal for power quality analysis, motor testing, and 3‑phase power monitoring in industrial environments.