SCXI-1120: Product OverviewThe National Instruments SCXI-1120 is an 8-channel isolated analog input module designed for the SCXI platform, serving as a signal conditioning front-end for data acquisition systems. This module functions as an interface between field sensors and measurement instruments, providing electrical isolation and signal conditioning for accurate analog measurements in industrial environments. Its role is to protect sensitive measurement equipment from ground loops, voltage transients, and common-mode voltages that are prevalent in industrial settings.Installed in an SCXI chassis, the module accepts analog signals from various sensors and transducers, conditioning them for digitization by a downstream data acquisition device. Each of the eight channels provides independent differential inputs with high common-mode voltage rejection, allowing accurate measurement of small sensor signals in the presence of electrical noise. The module supports multiple input types including voltage signals and resistance temperature detectors (RTDs), with software-selectable input ranges to optimize measurement resolution for different signal levels.
NI SCXI-1120
SCXI-1120: Technical Specifications
• Model Number: SCXI-1120
• Manufacturer: National Instruments
• Product Type: Isolated Analog Input Module
• Number of Channels: 8 differential channels
• Isolation Voltage: 300 Vrms channel-to-bus
• Input Types: Voltage, 4-wire RTD
• Voltage Ranges: Software-selectable: ±100 mV, ±500 mV, ±1 V, ±5 V, ±10 V
• Maximum Voltage: ±10 V continuous
• Input Impedance: >10 GΩ (differential)
• CMRR: >100 dB at 60 Hz
• Accuracy: ±0.02% of reading (typical at 25°C)
• Excitation Current: 1 mA (for 4-wire RTD measurements)
• Connector: 96-pin D-Sub
• Operating Temperature: 0°C to 50°C
• Power Consumption: 3.5 W typical
NI SCXI-1120
Core Features & Customer ValueIsolation and Signal Integrity: The 300 Vrms channel-to-bus isolation provides critical protection for measurement systems in industrial environments where ground potential differences and electrical noise can compromise signal accuracy. This isolation prevents ground loops that cause measurement errors and protects expensive measurement equipment from voltage transients. For engineers designing systems for factory floors or electrical substations, this feature ensures reliable operation and reduces equipment damage risks.Flexible Input Configuration: The software-selectable input ranges allow the same module to handle both low-level signals (±100 mV) and higher-level signals (±10 V) without hardware modifications. This flexibility simplifies system design and reduces inventory requirements, as a single module type can serve multiple measurement purposes. The high input impedance (>10 GΩ) minimizes loading errors when measuring signals from high-impedance sources.4-Wire RTD Capability: The integrated current excitation (1 mA) and dedicated sense lines support true 4-wire RTD measurements, eliminating lead resistance errors that affect temperature measurement accuracy. This is particularly valuable for precision temperature monitoring in process control applications where ±0.1°C accuracy requirements are common. The 4-wire configuration provides laboratory-grade temperature measurements in industrial environments.Typical ApplicationsIn process industry applications, the module conditions signals from RTD temperature sensors in heat exchangers and reactors, providing accurate temperature monitoring for control and safety systems. The isolation ensures reliable operation despite electrical noise from motor drives and power equipment.For power generation monitoring, the input channels measure voltage signals from transducers monitoring generator outputs and bus voltages. The high common-mode rejection ratio (CMRR) maintains measurement accuracy in the presence of electrical noise common in switchgear and control rooms.In structural testing, the differential inputs accurately measure strain gauge outputs while rejecting noise induced in long cable runs between test specimens and data acquisition systems. The isolation protects the measurement system from potential differences between test structure grounds and instrument grounds.
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