NI SCXI-1104C
NI SCXI-1104C
NI SCXI-1104C
NI SCXI-1104C
NI SCXI-1104C

NI SCXI-1104C | 32-Channel Medium-Voltage Input Module – Field Service Notes

  • Model: NI SCXI-1104C
  • Alt. P/N: 776572-04C, 183087H-05
  • Product Series: NI SCXI Signal Conditioning
  • Hardware Type: 32-Channel Medium-Voltage Analog Input Module
  • Key Feature: 32 differential inputs with divide-by-10 attenuators and 10 kHz low-pass filters
  • Primary Field Use: Signal conditioning for medium-voltage measurements in industrial environments, multiplexing to DAQ devices for high-channel-count systems.
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Description

Hard-Numbers: Technical Specifications

  • Input Channels: 32 differential
  • Input Voltage Range: ±60 VDC, 30 VACrms, ±42 VACpeak
  • Common-Mode Range: ±60 VDC with respect to CGND
  • Input Impedance: >1 MΩ (powered on), 90 kΩ (powered off), 900 kΩ (overload)
  • Gain Error: 0.02% of reading max (after calibration)
  • Offset Error: 300 μV max (after calibration)
  • Nonlinearity: 0.01% of full-scale range
  • CMRR: 70 dB (50-60 Hz), 70 dB (DC)
  • Output Range: ±10 V
  • Output Impedance: 91 Ω
  • Bandwidth: 10 kHz (-3 dB cutoff), three-pole low-pass filter
  • Step Response: To 0.1% accuracy in 200 μs, to 0.01% accuracy in 1 ms
  • Minimum Sample Interval: 3 μs (0.012% accuracy), 10 μs (0.0061% accuracy)
  • System Noise: 500 μVrms (referenced to input)
  • Digital I/O: Compatible with TTL levels (VIH ≥2 V, VIL ≤0.8 V)
  • Connectors: 50-pin male ribbon cable (rear), 96-pin male DIN C (front)
  • Power Requirements: +5 V at 15 mA max, ±15 V at 150 mA max
  • Operating Temperature: 0°C to 50°C (32°F to 122°F)
  • Storage Temperature: -55°C to 150°C
  • Relative Humidity: 5% to 90% non-condensing
  • Dimensions: 11.5 × 27.3 cm (4.54 × 10.75 in.)
  • Warm-up Time: 20 minutes recommended
  • Calibration Interval: Annually or after operating outside 20-30°C range
    NI SCXI-1104C

    NI SCXI-1104C

The Real-World Problem It Solves

When you need to measure multiple medium-voltage signals (up to ±60 V) and multiplex them into a single DAQ channel, this module provides signal conditioning, filtering, and protection in one package. The divide-by-10 attenuator extends the input range beyond standard ±10 V DAQ inputs while maintaining accuracy.
Where you’ll typically find it:
  • Industrial process monitoring with multiple voltage transducers
  • Power supply testing and validation
  • Battery pack voltage monitoring
  • Motor drive and inverter voltage measurements
  • Automated test equipment for automotive or aerospace components
Bottom line: It converts 32 medium-voltage differential signals into conditioned, filtered outputs that safely interface with standard DAQ devices, reducing the need for external attenuators and protection circuits.

Hardware Architecture & Under-the-Hood Logic

The SCXI-1104C uses a multiplexed architecture where each of the 32 differential inputs passes through an attenuator stage, programmable amplifier, and three-pole low-pass filter before being routed to a single output channel. An analog multiplexer selects which channel appears at the output.
Signal flow and processing logic:
  1. Input Stage: Each differential input has a divide-by-10 attenuator for high-voltage measurements up to ±60 V.
  2. Protection Circuitry: Input protection prevents damage from overvoltage up to ±42 VACpeak or ±60 VDC.
  3. Programmable Amplifier: PGA adjusts gain to match input signal to the ±10 V output range.
  4. Low-Pass Filter: Three-pole filter with 10 kHz cutoff removes high-frequency noise and aliases.
  5. Analog Multiplexer: SCXI bus multiplexer selects one of 32 channels for the output.
  6. Output Stage: Single-ended ±10 V output with 91 Ω impedance drives the DAQ device input.
  7. Digital Control: Digital logic controls multiplexer addressing, gain settings, and calibration constants stored in EEPROM.
  8. Power Distribution: ±15 V and +5 V rails power the analog and digital circuitry respectively.NI SCXI-1104C

Field Service Pitfalls: What Rookies Get Wrong

Exceeding Input Voltage Limits
Techs assume the “medium voltage” label means the module can handle arbitrary high voltages. The maximum working voltage is ±60 VDC or ±42 VACpeak. Exceeding this damages input protection diodes.
  • Field Rule: Always verify sensor output ranges before connecting. Use a multimeter to measure the maximum expected voltage under fault conditions. If you need to measure higher voltages, add external voltage dividers before the SCXI-1104C inputs.
Skipping Warm-up Time
The module requires 20 minutes of warm-up for optimal accuracy. Field technicians often start measurements immediately after power-up, resulting in drift and offset errors that look like sensor faults.
  • Quick Fix: Power up the SCXI chassis at least 20 minutes before critical measurements. Record ambient temperature—if it’s outside the 20-30°C range, you’ll need to recalibrate before the next measurement run.
Calibration Drift After Temperature Excursions
The offset and gain temperature coefficients (50 μV/°C and 20 ppm/°C) apply outside the 15-35°C range. Field deployments in outdoor environments experience accuracy degradation without recalibration.
  • Field Rule: If the module operates outside 15-35°C, recalibrate before critical measurements. Keep a calibration log documenting when temperature limits were exceeded and when recalibration was performed.
Overloading the Output Stage
The analog output is short-circuit protected but not overvoltage-protected. Applying external voltages to the output connector while the module is powered can damage output drivers.
  • Quick Fix: Never connect external voltage sources to the SCXI-1104C output. If you need to monitor the output signal with another instrument, use a high-impedance differential probe—never connect ground-referenced equipment directly.
Incorrect Ground Reference Practices
Floating inputs or improper grounding creates ground loops that introduce noise into measurements. The common-mode range is ±60 VDC relative to CGND.
  • Field Rule: Connect the sensor shield or reference ground to the chassis ground (CGND) terminal at a single point. Avoid creating multiple ground paths between the SCXI-1104C and the device under test. Use twisted-pair shielded cables for differential inputs.
Confusing SCXI-1104 vs. SCXI-1104C Filter Characteristics
The standard SCXI-1104 has a 2 Hz cutoff filter for 60 Hz noise rejection, while the SCXI-1104C has a 10 kHz cutoff for faster response. Using the wrong module for your application compromises either noise rejection or bandwidth.
  • Field Rule: Verify your filter requirements before installation. If you need DC and near-DC measurements with maximum noise rejection, use SCXI-1104 (2 Hz filter). If you need faster dynamic measurements up to 10 kHz, use SCXI-1104C. Never substitute one for the other without confirming the bandwidth requirements.

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