Module SG1 is NAI’s latest generation Strain Gage Measurement Module. This intelligent, four-channel module is used on our multi-function embedded boards and 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 can be used with either AC or DC excited load cells. With AC excitation, this module switches the polarity of the excitation voltage from cycle to cycle and consecutive A/D samples are averaged using dissimilar reference voltage polarity, which minimizes system-wide DC offsets.
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.