Microprocessor-based, tractor-mounted soil cone penetrometer

A microprocessor-based, tractor-mounted soil cone penetrometer was developed for automating soil strength measurements. This unit was designed to operate over a 4-row (3-m) width and to a maximum penetrating depth of 61 cm. The penetrating force was applied to the penetrometer shaft via a hydraulic cylinder. The hydraulic cylinder and associated depth and force measuring sensors were mounted on a carriage assembly which traveled along a 4-m track. The carriage was moved laterally along the track by a cable assembly driven by a DC winch. The penetrometer frame and track were attached to a 4-row toolbar which had a category II, 3-point hitch.

Optical position encoders were used to measure depth of penetration and carriage position along the track. Force of penetration was calculated by measuring hydraulic pressure acting on the hydraulic cylinder.

A microprocessor-based control unit activated all moving mechanisms and automatically recorded data on magnetic tape for computing depth versus force of penetration profiles. Liquid crystal displays provided visual output of these measurements. The control unit was field programmable for operating in various modes. Seven parameters which affected operation of the penetrometer could be changed depending upon the application of the test.

The control unit consisted of two modules: (1) the MRU module which included a 8-bit Microprocessor Unit (MC6802), 4K RAM, 4K EPROM, two peripheral interface adapters, an asynchronous interface adapter, 12-bit analog-to-digital converter, three 8-bit data latches, and a BAUD rate generator; (2) the input/output module included two liquid crystal displays, key pad, and light emitting diodes.