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High_resolution_continuous_output_sampled_bridge

2016-05-14 20:58  
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High_resolution_continuous_output_sampled_bridge
High_resolution_continuous_output_sampled_bridge
Figure 4-18 shows a sampled bridge with continuous output and high resolution.Figure 4-19 shows the waveforms. Traces A, B, C, and D show the A1A output, Q3 emitter, complementary output to A2 loop, and the 74C221 delayed pulse to Q5.The circuit applies 100 V across a 10-V, 350-0 strain-gauge bridge for short periods of time. The high pulsed-voltage drive increases bridge output proportionally, without forcing excessive dissipation. The average bridge power is far below the normal 29 mA obtained with the usual 10-Vdc excitation. Combining the 10× higher bridge gain (300 mV full-scale versus the normal 30 mV) with a chopper-stabilized amplifier in the sample-hold output stage is the key to the high resolution. To calibrate, simply adjust the 50-kΩ zero control for zero output with the bridge at mechanical zero. Although the output is continuous, information is collected at a 1-Hz rate, and the Nyquist limit applies when interpreting results. LINEAR TECHNOLOGY, APPLICATION NOTE 43, P. 23.