Instrumentation for in-field measurements of energy inputs to tractor-powered agricultural implements

A second generation data acquisition system, integrally mounted on a two-wheel drive 75-PTO kW agricultural tractor, was interfaced to various sensors which measured: (1) time, (2) implement draft, (3) left and right drive axle torque, (4) left and right drive wheel rotation, (5) ground surface displacement, (6) fuel flow, (7) PTO torque, and (8) engine flywheel rotation. This data gathering system was centered around a DEC PDP11/03-LK microcomputer using the RT-11 operating system and having a linkage of MACRO-11 and FORTRAN IV data acquisition routines. Magnetic memory, of the same capacity as two RXOl floppy disks, was subdivided into the system device and the data storage device. Real-time data were displayed in engin-eering units on the operator CRT console. Physical transfer of archived test data for mainframe statistical analysis was accomplished using a TUBS tape drive. Sensors were simultaneously sampled once per second using a crystal controlled hardware interrupt. Before sampling by an A/D board, each analog signal was passed through an active low-pass filter having a one-half Hz cutoff frequency to satisfy the Nyquist Criterion of the Sampling Theorem. Digital signals were counted by an in-house designed counterboard. Digital count values were read and subsequently cleared through software. Digital sensors were (1) two bi-directional optical shaft encoders measuring rear axle speeds, (2) a transducer sensing fuel consumption rates, (3) a single-beam radar unit measuring true ground speeds, and (4) a passive magnetic sensor monitoring engine speeds. Analog sensors included mounted strain gauges detecting drive wheel torques and implement drafts, and a commercial load cell sensing PTO torques. The revised data acquisition system has been field tested for three growing seasons with repeatable results. Specific tests included gathering energy consumption data of tillage operations, and acquiring data showing the energy used throughout the formation of a round bale. In addition, the performance of three ground speed sensors was determined while traversing selected ground surfaces at various operating speeds. Further work is needed on the sensor used for measuring the drafts produced by towed PTO-driven implements. Also, minor adjust-ments to the counterboard are required.