Microprocessor-Based Data Acquisition and Control Software for Plant Growth Chambers (Spar System)

Abstract

ABSTRACT COMPUTER software has been developed for a microprocessor-based data acquisition and control system to measure 64 transducers and to maintain closed loop environmental control for three sunlit Soil-Plant-Atmosphere Research (SPAR) units at Florence, SC. An assembly language program and a BASIC program were written to run concurrently by using a real-time inter-rupt. The assembly language program performs the data acquisition, real-time control, and time keeping. The BASIC program performs the dynamic signal condition-ing, the computation of control parameters, and the con-version and output of the acquired data in engineering units. Environmental control algorithms were im-plemented in software to control temperature, C02 con-centration, and relative humidity. The BASIC program utilizes the history of the absolute deviation from the control levels to compute the control parameters for the assembly language program to implement. The temperature control algorithm enabled control within 0.5 C for control temperatures ranging from 15 C to 35 C with ambient temperatures ranging from 4 C to 32 C. A proportional control algorithm written in BASIC enabled C02 control for three SPAR units within 10 mg/L under changing radiation load with full canopy closure using one infrared gas analyzer. A C02 control algorithm using light response curves is derived to pro-ject C02 uptake and absolute deviations from the control level to correct the coefficients of light response curves. Dynamic environmental control of the SPAR units, which involves process feedback influenced by random climatic variations, can be obtained using an inexpensive microprocessor-based system. This enables researchers to conduct precise experiments involving climatic variables to provide the necessary inputs for crop simula-tion modeling.