Operational Amplifier: A Useful Tool for Forestry Research

An operational amplifier costing approximately $200 was developed by the North Central Forest Experiment Station in an investigation of the force and energy requirements for crosscut shearing and chipping. In the first study strain gages were used to measure the cutting force and, in the second, to measure the torque exerted by the chipper shaft. The electrical responses of the strain gages were applied to an operational amplifier where they were integrated with respect to time. The integrated results were plotted along with the load vs. time curves. The maximum value of the integral was proportional to the energy consumed and the average load could be obtained by dividing the maximum value by the total time during which the load was applied and multiplying by a calibration constant. The data were analyzed by the operational amplifier in approximately 10 percent of the time that would have been required using the planimeter method. The approximate cost of the operational amplifier for these applications was $200.

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