I. Product Introduction

NI SCXI-1125 is an 8-channel independent isolation programmable gain analog input module of the SCXI series. Each channel has an independent instrumentation amplifier and low-pass filter, specially designed for high-precision, high-speed multi-channel signal conditioning in industrial strong interference environments. It is suitable for millivolt-level weak signals to high-voltage signals, and supports thermocouples, strain bridges, 4-20mA sensors, etc. It is discontinued (Legacy), but can be repaired or purchased as a second-hand / inventory item.

II. Model Interpretation

SCXI: Instrument Signal Conditioning Expansion Series

1125: Basic model, 8-channel independent isolation programmable gain input module

Part Number: 776872-25

III. Technical Parameters (Official, 25℃)

Channels and Isolation

Channels: 8 differential isolated inputs, each channel isolated independently

Working Isolation Voltage: 300Vrms continuous (channel to channel / ground), CE certified double insulation, CAT II

Input Impedance: Differential > 1GΩ, Common Mode > 10GΩ

Common Mode Suppression Ratio CMRR: ≥100dB (DC～60Hz)

Input Range and Gain

Basic Input Range: ±2.5mV～±5V (software programmable gain 1/10/100/1000)

Extended Range: With SCXI-1313 high-voltage attenuation terminal, it can reach ±300V; with TBX-1316, it can reach ±1000VDC (680Vrms)

Resolution: 16 bits

Non-linearity: ≤±0.01% FSR

Gain Error (Calibrated): ≤0.05% reading

Temperature Drift: ≤10ppm/℃

Filtering and Sampling

Low-pass Filter: Each channel can be software-selected as 4Hz (anti-power frequency) or 10kHz (high-speed)

Maximum Sampling Rate: 333kS/s (single channel), multi-channel random scanning

Scanning Mode: Supports random scanning of any channel order without polling all channels

Electrical and Environmental

Power Supply: 5V ≤ 30mA; ±15V ≤ 200mA (backplane of the chassis)

Operating Temperature: 0～50℃

Storage Temperature: -40℃～+85℃

Humidity: 5%～90% without condensation

Size / Weight: 1U SCXI standard (30×173×203mm) / approximately 0.64kg

Calibration: Built-in EEPROM stores factory/user calibration constants, supports self-calibration software

IV. Interface and Communication Configuration

Front Panel: 96-pin DIN C connector, equipped with SCXI-1313 (high-voltage attenuation), SCXI-1322 (thermocouple / isolation), or universal terminal

Back Panel: 50-pin ribbon cable connector, connected to the SCXI chassis backplane bus, for data, timing, and power transmission

Communication: No independent communication port, relies on the SCXI bus to communicate with the backend DAQ device (such as PCIe-6251), NI-DAQmx driver configuration parameters, and data reading

Cabling: Supports floating ground / grounded signals, compatible with thermocouples, RTD, strain gauges, 4-20mA transmitters, high-voltage DC

V. Core Functions

8-channel independent isolation and amplification: Each channel 300Vrms isolation + independent programmable gain, no interference between channels, suitable for micro signals from various types of sensors.

Ultra-wide range coverage: Basic ±2.5mV～±5V, extended up to ±1000VDC, covering both weak signals and industrial high voltages, no additional conditioning module required.

Independent Filtering per Channel: 4Hz/10kHz software selectable, static measurement anti-power frequency interference, dynamic measurement retains high-frequency signals, suitable for different scenarios. High-speed random scanning: 333kS/s sampling rate, supports arbitrary channel sequence scanning, enhancing multi-channel acquisition efficiency.

High precision and stability: 16-bit resolution, low drift, onboard calibration, ensuring long-term measurement accuracy, suitable for precise testing scenarios.

Six. Application scenarios

Multi-channel precise testing: strain testing, pressure/weight measurement, vibration monitoring, compatible with strain bridges, LVDTs, piezoelectric sensors.

Industrial high-voltage / floating ground signal acquisition: high-voltage equipment monitoring, signal acquisition from different ground potential systems, isolation to ensure safety and accuracy.

High-speed temperature / process monitoring: 8 channels of thermocouples (with external CJC), RTD, 4-20mA transmitters signals, balancing rate and anti-interference.

Data acquisition in strong interference environments: factory workshops, power equipment, rail transit, etc., with strong electromagnetic interference.

Seven. Usage and Maintenance Instructions

Usage instructions

Installation: Power off and insert the SCXI chassis, tighten the fixing screws; supports hot swapping, modules can be replaced during operation.

Connection: Firmly connect the isolation terminals, high-voltage signals use SCXI-1313, thermocouples require external CJC;严禁 mixing high and low voltage.

Configuration： NI-DAQmx sets the gain， filter bandwidth， input range for each channel； sampling rate should not exceed 333kS/s (single channel).

System： 68-pin SCSI cable connects the SCXI chassis and DAQ； multi-chassis cascading sets a unique address to avoid conflicts.

Maintenance instructions

Environment： Keep dry and ventilated， prevent condensation； away from strong electromagnetic sources， vibration sources， avoid high-temperature exposure.

Regular inspection： Check terminals， connectors， cables every quarter for looseness， oxidation， damage； clean surface dust to maintain good heat dissipation.

Calibration： Once a year， calibrate gain， linearity， isolation performance； in precise measurement scenarios， calibrate once every half year， update EEPROM calibration constants.

Fault handling： Data drift → perform self-calibration； signal jump → check grounding， shielding， terminal tightening； isolation failure → stop and test isolation circuit and terminal insulation.