Design And Research Of Control System Of Precision Thermostatic Bath For Temperature And Salinity Verification

Marine equipment is an important tool for people to perceive the physical characteristics of the ocean, which provides a fundamental basis for marine scientific research. The normai use of marine Instrument depends on the measurement and calibration work. Thermostatic bath for temperature and salinity of seawater verification is an important part of the marine instrument temperature calibration device. The main content of this paper is design and research of control system of precision thermostatic bath for temperature and salinity verification, including the works of control system, the design of hardware circuit, the selection of control algorithm, the design and preparation of software and the testing for system performance.In terms of temperature measurements, connecting NTC thermistor resistance and precision resistance with the laboratory precision temperature measurement method(four-wire connection), and combining with high-performance analog-digital conversion and processor computing, the realization of small temperature changes measurement of the amount, which the temperature sensitivity of up to 0.0001 ?, temperature measurement accuracy up to ± 0.01 ?. Control system realizes the function of multi-point timing temperature control, which provides a great convenience for the operators. The temprature control process of thermostatic bath can be divided into fast control and fine tuning in two stages. The latter applys the single-phase thyristor and the semiconductor cooling pieces as the separate heat regulating mechanism, so that the control effect is more quickly and flexibly and accurately. The system utilizes the variable speed integral PID regulation mode as control algorithm, comparing to the normal PID regulator can obtain a better dynamic response. Using the PID parameter self-tuning method based on saturation relay feedback finishes the tuning of PID parameters, improving the accuracy of identification of critical information. Testing the volatility and uniformity of the temperature field of thermostatic bath, according to JJF1030-2010 "The Technical Performance of Thermostatic Bath Test Specification", the results show both of which satisfy the design requirements.Temperature measurement and system control be integrated with the device, and embedded real-time operating system be transpanted on the hardware platform, it makes the system had the function of a certain multi-task management, aslo reserving an additional Ethernet interfaces, these designs conform to the development trend of industrial measurement and control device for integration, intelligent, network. In addition, the system uses the touch screen as the human-computer interface device, which better than LCD liquid crystal screen and its own keys traditionally used, more visualization, standardization and ease of operation.