The Challenge:

Developing a PC-Based real time control and monitoring system for temperature of a oven.

The solution:

Using Field Point Network Module, Field Point Thermocouple Input Module, Field Point Analog (0-20mA) Output Module, Field point Digital output modules, personal Computer, Serial Link between PC and Field Point Network module, LabView and PID toolkit for LabView.

Introduction

The PC Based oven controller consists of National Instruments’ Field Point based Hardware to connect the Thermocouple, status inputs & 0-20mA, Relay outputs for control. The Field Thermocouple modules provides the PC with the temperature input. The 0-20mA output provides PID control to the Thyristor fired heating circuit and Relay contacts are used to turn on the heater circuit Field point relay modules are used turn on and off the damper and blower.

The software for controlling the temperature is developed using National Instrument’s graphical programming language LabVIEW. The control is achieved using National Instrument’s PID control toolkit which ensures optimum power delivery to the heating element. The software has got the facility to run the furnace with any number of and any combination of Ramp and Soak cycle. The operator can observe the temperature trending as well as the setpoint on a graph. Software averaging of the thermocouple being selected and read is done to provide the process variable input to the software PID controller. Damper and blower are used to control the cooling of the system.

System Requirements

To control and monitor temperature of a oven which can be taken to a temperature of 250 șC through a user defined rate of heating. It maintains the temperature at soak temperature for user define soak temperature and interval. Provision for selecting the thermocouples for averaging and reject thermocouple dynamically if during the process any of the thermocouple gets open. Provision for storing cycle information as well logging of the data being acquired for each thermocouple and selected thermocouple average.

Hardware design

The PC Based furnace controller consists of the following hardware:

Software Architecture

This PC-Based Control and Monitoring System for Oven is based four panels. The first panel is for navigation. The second panel allows the user to delete and select or enter new temperature cycle with facility for entering various cycle identifying parameters. The cycle consists of ramps and soaks. User can choose any combination of thermocouples out of eight thermocouples for averaging. The software rejects a thermocouple from average if it gets opened during the on going process. In the third panel the user can observe average temperature trend as well as other status of the on going process such as reading of all the thermocouples, open thermocouple indication, cycle status.In the fourth panel the user can select the logged data see the logged data in spreadsheet as well as graphical format in to separate panels.

Controlling of the temperature is achieved using National Instruments PID toolkit. Ramp and soak cycles are generated by the software .The temperature is read using a J-type thermocouples average of the selected thermocouple is which is fed to the PID vi and whose output is scaled to 0-

20mA to fire the thyristor which in turn controls the power delivered to the heater. Cooling is achieved by turning the damper and blower using Field point digital output module.

Separate panel are provided for viewing and taking printouts of the logged data of each thermocouple and the average separately in graph as well spreadsheet format.

System Capabilities

The system is capable of maintain of maintaining temperature to a high degree of accuracy. It is capable of dynamic averaging of thermocouple so that the user can concentrate on a particular portion of the oven. In is capable of running any combination and number of ramp and soak cycles. It provides facility to log and view the real time data being acquired.

Results

The system gives a real time monitoring and control of temperature with enough flexibility to the user to choose required process cycle and conditions.