GENERALIZED SCHEME FOR MEASUREMENT AND CONTROL OF INDUSTRIAL PARAMETERS

Abstract

In the present work, a PC based automatic temperature monitoring and controlling system has been developed. The temperature Is sensed by ERTD, placed In the vicinity of the oven and connected as an arm in the wheat-stone bridge configuration. The output voltage of wheat-stone bridge Is converted to a proportional digital value using an analog-to-digital conversion device .(in the present case a 12-bit AD/DA card is used as analog-to-digital converter) and the same Is fed to the personal computer (PC-AT). The personal computer (PC-AT) controls the heating or cooling in response to the fed digital value. This is set to control a specified range of linear and repetitive processes and thus the need for continuous attention or manual adjustment is eliminated. The heating is controlled by varying the input voltage fed to the heating element with the use of a pulse width modulated (PWM) control circuitry. The width of the pulse is controlled by varying the input signal to the PWM circuit by receiving the calculated controlled voltage (using the software module) through the digital-to-analog converter circuit (in built in the 12-bit AD/DA card). The software module developed in the system for control action and for plotting the behaviour of the process Is simple to use and provides versatility in programming the temperature ranges and timing of processes. Here in the present work, the software module consists of five modes of control. It is also proposed to extend the present scheme for monitoring and controlling the processes like pressure and flow.