I. Product Introduction

NI SCXI-1126 is an 8-channel isolated frequency input module of the SCXI series. Its core is an independent frequency-voltage (F/V) conversion circuit for each channel, suitable for digital/analog periodic signals. It supports high-voltage isolation and programmable triggering, filtering, and is specifically designed for multi-channel frequency, speed, and vibration measurement in industrial environments with strong interference. It is no longer in production (Legacy), but can be repaired or purchased as a second-hand/inventory NI.

II. Model Interpretation

SCXI: Instrument Signal Conditioning Expansion Series

1126: Basic model, 8-channel isolated frequency input module

Part Number: 776572-26

III. Technical Parameters (Official, 25°C)

Channels and Isolation

Channels: 8 independent isolated frequency inputs, isolation between channels and between channels and ground

Isolation Voltage: 250Vrms continuous (between channels / ground), up to 1000VDC with TBX-1316, CAT II, CE certified

Input Overvoltage Protection: withstands 250Vrms during power-on / power-off

Frequency and Conversion

Frequency Range: 15Hz to 128kHz, 10 programmable steps

Trigger Configuration: Programmable threshold (-0.5 to 4.48V), hysteresis (0 to 4.98V), compatible with TTL, 24V, 120/240VAC signals

F/V Conversion Accuracy: ±0.05% FSR (typical), long-term stability guaranteed by low-temperature drift reference source

Output Filtering: 4-level 4-pole low-pass filtering for each channel, cutoff frequencies of 1Hz, 10Hz, 100Hz, 1kHz

Sampling and System

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

Input Signal Types: Digital (TTL/CMOS), Analog (sine / square wave / pulse), High-voltage AC signals

Electrical and Environmental

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

Operating Temperature: 0 to 50°C

Storage Temperature: -40°C to +85°C

Humidity: 5% to 90% without condensation

Size / Weight: 1U SCXI standard (30×173×203mm) / approximately 0.7kg

Calibration: Board-mounted EEPROM stores factory/user calibration constants, supports self-calibration software

IV. Interface and Communication Configuration

Front Panel: 32-pin DIN C connector, equipped with SCXI-1327 (100:1 high-voltage attenuation terminal) or universal terminal, compatible with high-voltage/low-voltage frequency signals

Back Panel: 50-pin ribbon cable connector, connects to the SCXI chassis backplane bus, transmits control signals, timing, and power supply

Communication: No independent communication port, relies on the SCXI bus to communicate with the backend DAQ device (such as PCIe-6251), NI-DAQmx driver configures frequency range, trigger threshold, filtering parameters

Output Mode: Supports multi-channel multiplexing (single channel reads 8 frequency channels) or parallel output (8 independent outputs)

V. Core Functions

8-channel Independent Isolated F/V Conversion: 250Vrms isolation for each channel, blocking ground loop, compatible with high-voltage, floating-ground frequency signals, protecting DAQ and field equipment.

Wide Frequency Range and Programmable Trigger: 15Hz to 128kHz covering industrial common frequencies, threshold / hysteresis programmable, compatible with TTL, 24V, high-voltage AC, etc. types of signals.

Independent Low-pass Filtering for Each Channel: 4-level 4-pole filtering, suppressing high-frequency noise, suitable for different scenarios such as speed (low frequency), vibration (medium frequency), acoustic (high frequency). High-speed scanning and multi-channel multiplexing: 333kS/s sampling rate, 8 channels multiplexed to a single DAQ channel, improving multi-channel acquisition efficiency and reducing system cost.

High accuracy and stability: On-board precise low-drift reference source, F/V conversion accuracy ±0.05% FSR, EEPROM calibration, ensuring long-term measurement stability.

Six. Application scenarios

Industrial speed/frequency measurement: Motor speed, gear pulse, flowmeter, encoder signal acquisition, compatible with 4–20mA frequency transducer.

High-voltage power frequency monitoring: 120/240VAC power frequency, high-voltage equipment vibration frequency measurement, isolation to ensure safety.

Vibration and acoustic testing: Mechanical equipment vibration, bearing fault detection, acoustic sensor frequency signal acquisition, stable measurement in strong interference environment.

Multi-channel periodic signal acquisition: Frequency/pulse signals at multiple stations on the production line, non-destructive testing ultrasonic frequency, environmental monitoring wind speed (pulse) signal.

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: Low-voltage signals directly connect to the 32-pin terminal, high-voltage signals use SCXI-1327 attenuation terminal;严禁 mixing high and low voltage connections， ensure firm and no loose connections.

Configuration： NI-DAQmx sets the frequency range， threshold/lag， filter cut-off frequency for each channel； sampling rate does not exceed 333kS/s (single channel).

System： 68-pin SCSI cable connects the SCXI chassis and DAQ； multi-chassis cascading requires a unique address to avoid conflicts； parallel mode requires a SCXI-1180 interface panel.

Maintenance instructions

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

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

Calibration： Once a year， calibrate F/V conversion accuracy， linearity， isolation performance； precise measurement scenarios calibrate once every six months， update EEPROM calibration constants.

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