Model 10A74-4C Four Channel DC Strain Gage Conditioner
Intended primarily for stress analysis applications, the Model 10A74-4C receives and conditions up to four independent inputs from one-arm (1/4-bridge), two-arm (1/2- bridge), and four-arm (full-bridge) strain gage configurations attached directly to the stressed material. To minimize “time-skew” effects, each 10A74-4C input has a separate TRACK/HOLD circuit. Upon application of a “HOLD” command, the channel will instantly freeze its present value in analog memory until application of a “TRACK” command, whereupon normal tracking of the input signal is resumed. By applying a “HOLD” command simultaneously to all four channels, the user can be assured of a set of readings coherent to within a few microseconds.
The TRACK/HOLD function is normally controlled through an external logic signal to the 10A74-4C’s rear I/O connector, when a System 10 Bridge Completion Connector or the optional Model 10VAC is not being used. Unless all four inputs originate from full-bridge transducers, the 10A74-4C requires external completion of each strain gage input to full bridge, by means of one of the following:
a System 10 Bridge Completion Connector—one of the following models:
- 10QBC-4-120 for 2- or 3-wire 120-Ω quarter-bridge connections
- 10QBC-4-350 for 2- or 3-wire 350-Ω quarter-bridge connections
- 10QBC-4-1K for 2- or 3-wire 1000-Ω quarter-bridge connections
- 10HBC-4 for 4- or 6-wire half-bridge connections
- 10FBC-4 for 5-wire full-bridge connections
- a Daytronic Model 10CJB-4 Quad Bridge Completion Card or an equivalent circuitry supplied by the user
The 10A74-4C provides selectable low-level excitation (1, 2, 5, or 10 V-DC). Using low excitation helps reduce gage heating effects in stress analysis of materials with low thermal conductivity. Note, however, that with the 10A74-4C, the selection of excitation level is not “per channel”; the same level applies simultaneously to all four 10A74-4C channels.