Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 21, 2000
Publication Date: N/A
Interpretive Summary: Automatic measurement of soil water content and salinity is important in many fields of engineering, agriculture (particularly irrigation control), resource management, and environmental monitoring. Time domain reflectometry (TDR) is increasingly used for these measurements, but programs for automatic control of TDR systems are few and lack useful capabilities. This paper describes a computer program, TACQ, suitable for low-power, unattended field systems, as well as laboratory systems. The program controls systems of up to 256 probes. It works with and controls TDR equipment from three manufacturers. It allows user control of the number and type of probes read, their distance from the TDR instrument, and the type of data acquired. The program has been used in an automatic irrigation system, in a remote, solar-powered crop water use measurement system, and in agriculture, resource management, and environmental monitoring work by researchers and engineers in the U.S. and several countries. The program was commercialized through a Cooperative Research and Development Agreement with Dynamax, Inc. of Houston, Texas, and is available for free download on the Internet.
Technical Abstract: Despite the increased use of time domain reflectometry (TDR) for measurement of soil water content and bulk electrical conductivity (BEC), there are few releases of software for TDR system control. The TACQ program, under development since the early 1990s, allows control of multiplexed systems supporting up to 256 TDR probes. The program is DOS-based in order to ease creation of low-power, embedded computer systems; and, to eliminate resource conflicts and timing difficulties inherent to multi-tasking operating systems. It runs on IBM PC/XT or AT compatible computers with 640 kbytes of RAM and 1 Mbyte of expanded memory, and with Hercules, ATT, EGA, or VGA graphics. Embedded computer systems based on the PC-104 specification have been implemented using TACQ. Using a parallel port, the program controls multiplexers from both Campbell Scientific, Inc. and Dynamax, Inc.; and it allows reading of probes in any user-defined order if using the latter. The user has complete control ove multiplexer address assignments, interconnection of multiplexers, and probe locations on each multiplexer; including individual settings for probe length, window width, averaging, distance to each probe, gain, and kind of data acquired (wave form, travel time, apparent permittivity, water content, BEC, or a combination of these). Interfaces to TDR instruments including all Tektronix 1502 series cable testers are implemented through an RS-232 port. System power control is implemented through the computer's own power management capabilities, and through direct control of power to the TDR instrument and video subsystem where applicable, thus allowing creation of very low-power systems.