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  • PIC18F2550 based Resistance Temperature Detector

  • Created: Jun 08, 2016

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The circuits that require high current application and which functionality can be directly affected by thermal temperature need to be monitored for proper functioning. The reference design is a PIC18F2550 based resistance temperature detector that measures the temperature through the changes in resistance of the resistance thermometers (resistance temperature detector “RTD”). The design features the PIC18F2550 an 8BIT 32KB flash MCU that offers the advantages of all PIC18 microcontrollers with high computational performance, enhanced flash program, and more suitable for power sensitive application. The reference design uses the platinum RTD chip temperature sensor from ENERCORP Instruments Ltd. The MCP9804T is a digital temperature sensor that converts temperatures between -40°C and +125°C to a digital word with ±0.25°C/±1°C (typical/maximum) accuracy.

The functionality of the reference design starts when RTD changes its resistance. The MCP3551 reads the changes in resistance from the RTD and compare it to the output of MCP1701AT, which is the reference voltage of MCP3551. The MCP9804 then converts the data coming from MCP9804 and the PIC18F2550 processes the data. The MCP9804 can send warning through the ALERT pin when the temperature is beyond the specified limits. The user has the option of setting the ALERT output signal polarity as an active-low or active high comparator output for thermostat operation, or as a temperature ALERT interrupt output for microprocessor-based systems. It can also be set as a warning for critical temperature output. The data coming from PIC18F2550 is displayed on computer using thermal management software in strip chart format.

The reference design RTD resistance can vary from its typical value ranging from 100Ω-5kΩ. The approach of the reference design is a simple solution for plug-and-play application with minimal adjustments. However, system accuracy is dependent on several factors such as biasing circuit tolerance and stability, error due to power dissipation or self-heat, and RTD nonlinear characteristics.



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