A laser-based triggering system for remote actuation of tractor-mounted instrumentation

Instrumented tractors equipped with data acquisition systems developed in the last 10 years allow measurement of many vehicle and implement operational parameters. However, some systems lack the capability to initiate and terminate data acquisition precisely at predetermined points as the tractor is operated through the field. Results of previous experiments have indicated that measurement errors associated with manually actuating the data acquisition instrumentation can be considerable. Thus, a laser-based triggering device was developed to allow automatic remote actuation, both initiation and termination of data acquisition, of a tractor-mounted instrumentation system as a test vehicle was operated back and forth over a field plot, typically 60 m in length. The triggering device consists of three subsystems: a laser emitting unit, a laser receiving unit, and an interfacing unit. Two 5-mW helium-neon lasers are used to provide precise reference lines for the system. A photodiode in the laser receiver is used as the sensing element. An optical filter included in the receiver package eliminates much of the influence of sunlight. Two alternative triggering prototypes were designed. In the final system, laser light is continuously detected at the laser receiving unit. When the moving vehicle interrupts the laser beam, a radio transmitter in the laser receiving unit is actuated. Signals generated by the transmitter are used to excite a radio receiver designed to be mounted on the instrumented vehicle. The radio receiver then initiates or terminates, as appropriate, the data acquisition process. Laboratory tests indicate that the triggering system was able to repeatedly time events with a precision of 0.01 second.