Load/Strain (Module G5)68C3 Operations Manual North Atlantic Industries, Inc. 12/19/2014Rev: 2014-12-19-0947 www.naii.com Page 160 of 330LOAD/STRAIN (MODULE G5)Principles of OperationThe G5 module is an intelligent four-channel module utilizing four A/Ds and the motherboard resourcesprocessor/FPGA. The G5 module is designed to read output signals, and supply excitation voltages that arecommonly used in applications with pressure transducers, weigh scales, and strain gages. Each channelincorporates an Σ-Δ modulator, a PGA, and on-chip digital filtering intended for the measurement of wide dynamicrange signals. Each channel contains a fourth order digital filter, with several programmable filter options. Whenproperly applied the filter has deep notches at either 50 or 60 Hz.The G5 may be utilized with AC or DC excited load cells. When using AC excitation, the G5 module switches thepolarity of the excitation voltage from cycle to cycle. When utilizing AC excitation, consecutive A/D samples areaveraged using different reference voltage polarity removing any system wide dc offsets.The ‘on-board’ processor removes the user from the details of managing the A/D communication, register accessand sample timing. The processor firmware provides the user with a simpler user interface with high-levelcommands and post calibration data. The module also contains internal factory calibration values, stored in Flash.The G5 automatically recalibrates for changes in reference voltage and die temperature.Both internal and system calibration are included on chip; thus, the user has the option of removing offset/gainerrors internal to the A/Ds only, or removing the offset/gain errors of the complete end system.A /DToMotherboardResoucresD/AIN-HIIN-LOEXC-LOEXC-HIEXC-SNS-HIEXC-SNS-LO A /DData/ControlAGalvanic IsolationCPLDMODCTRLAChannelIsolated Power SupplyIsolated Circuit VCCG5 Strain Gage (4 CH isolated)Single Channel Example Block4-Arm Strain Gage/Bridge(External – item to be measured)Front and/or Rear I/O+5V systemA 6-wire load cell with SENSE_HI and SENSE_LO, with connections as shown allows the G5 to compensate forDC drops in wires connecting the Gauge to the module. The type of connection is typically referred to as a Kelvinconnection. Some load cells may also have additional internal resistors, for temperature compensation purposes.Built-In Test (BIT) / Diagnostic CapabilityAutomatic background BIT Built in Test functionally checks for correct A/D operation using on board dedicatedtest voltage divider resistor network.BIT also monitors for any open leads. Any failure triggers an interrupt (ifenabled) with the results available in status registers. The testing is transparent to the user, requires no externalprogramming and has no effect on the operation of this card. It can be enabled or disabled.
