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SG1

4 Channels, Strain Gauge Measurement

Module SG1 is NAI’s latest generation Strain Gage Measurement Module. This intelligent, four-channel module is used on our Multifunction Embedded I/O Boards and Single Board Computers (SBCs).

While there are several methods of measuring mechanical strain, the most common is with a strain gage. The gage provides electrical resistance that varies in proportion to the amount of strain in the device. The most widely used gage is the bonded metallic strain gage. To measure such small changes in resistance, strain gages are almost always used in a bridge configuration with a voltage excitation source. The general Wheatstone bridge (conventional, 4-arm bridge) consists of four resistive arms with an excitation voltage, Vexc, that is applied across the bridge.

The SG1 module uses four independent, isolated input A/Ds. This module is designed to read output signals from a completed Wheatstone bridge (i.e., it can be used with one or more strain gage elements as a completed 4-arm Wheatstone bridge) and is commonly used in applications requiring pressure, weight, and stress transducers interface/measurement. Each channel incorporates an Σ-Δ modulator, a PGA, and on-chip digital filtering intended for the measurement of wide dynamic range signals. Each channel also contains a fourth order digital filter, with several programmable filter options. When properly applied, the filter has deep notches at either 50 or 60 Hz.

The SG1 module provides a DC excitation, programmable from 2 - 12 VDC for interfacing to most load and accelerometer gages.

The on-board processor/FPGA resources remove the user from the details of managing the A/D interface, register access, and sample timing. The processor firmware provides the user with a simpler user interface with high-level commands and post-calibration data. The module also contains internal factory calibration values stored in Flash. The SG1 automatically recalibrates for changes in reference voltage and die temperature.

Both internal and system calibration are included, providing the user with the option of removing only offset/gain errors internal to the A/Ds or the offset/gain errors of the complete end system.

Specifications
  • Number of Channels: 4 differential input channels for load cell & accelerometer measurement.
  • Input Interface: Conventional 4-arm Wheatstone bridge, 4 or 6-wire interface.
  • A/D Converter: 32-bit Delta-Sigma
  • Output Resolution: 32-bit
  • Accuracy: ± 0.1% Full-Scale (FS) range
  • Digital Output: Percent of Full Scale; Ratio (Vin/Vexc)
  • Gain Settings: 1, 8, 16, 32, 64, and 128 (programmable)
  • Input Impedance: > 10 MΩ
  • Input Coupling: DC
  • Bridge Excitation Voltage (Vexc): Independent Sources, Programmable 2 - 12 VDC
  • Output Current (Maximum): 100 mA / source
  • Remote Voltage Sensing: Yes
  • Output Data Rate: 2.5 to 38,400 Hz (dependent on programmable filter settings) In FIR filter mode, rates are limited to 2.5, 5, 10 & 20 Hz.
  • BIT (Built-in-Test): Continuous background "online" accuracy, open detection capability.
  • ESD Protection: Designed to meet the testing requirements of IEC 801-2 Level 2. (4 kV transient with a peak current of 7.5 A and a time constant of approximately 60 ns)
  • Enhanced Functionality (pending): Each channel provided with: Programmable FFT with selectable sample rate and number of points (up to 64K). User selectable windowing function. Store value of unstrained voltage to include as compensation value
  • Power: 5 VDC @ TB mA typical (est.)
  • Ground: Channels isolated from each other and system ground.
  • Weight: 1.5 oz. (42 g)
Block Diagram

(Click diagram to enlarge)

Documentation
2/2/2021 3:37:11 PM
2/2/2021 3:37:28 PM
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