W A T L O W

Table of Contents

Introduction

Electric Heaters
This Application Guide is to assist youin understanding the principles of electric thermal systems and compo-nents as they apply to various heating tasks. Its purpose is to give you theory, general calculations and engineering data along with examplesfor solving heating problems. ThisApplication Guide is not a how-tomanual or a substitute for specific information related to complex and/or critical applications. Watlowengineers are available to provide you detailed information on engineeringapproaches not included in this guide.When designing any thermal system,caution must always be exercised to comply with safety requirements, localand/or national electrical codes,agency standards, considerations for useintoxic or explosive environmentsand sound engineering practices.Integrity and suitability of any thermal system design/specification is ultimately the responsibility of those selecting and approving system components.This Application Guide is organizedinto sections dealing with the basicfacets of an electric thermal system: the electric heaters, temperaturesensors andtemperature and powercontrollers. Information about wiringpractices along with reference dataand examples are also provided.As always, Watlow Electric Manufac-turing Company stands ready to provide you advice or engineeringexpertise to design and producecomponents to meet your electric heating requirements. Temperature controllers Temperature sensors
Product Overview. . . . . . . . . . . . . . . . 74Thermal Control Principles. . . . . . . . 81Control Output Types. . . . . . . . . . . . . 88Control Output Comparison. . . . . 90Limit Control Protection forTemperature Process. . . . . . . . . . . . . 93Agency Recognition for Controllers. . . . . . . . . . . . . . . . . . . 94Control System Tuning. . . . . . . . . . . . 94Typical Thermal control System Chart Recordings. . . . . . . . . . . . . . . . 97Controller Overview. . . . . . . . . . . . . . 99Data Communications. . . . . . . . . . . . 100 Customer Assistance
Manufacturing Facilities. . . . . . . . . . . . 3 Sales Offices. . . . . . . . . . . . . . . . . . . . .4Product Overview. . . . . . . . . . . . . . . . 34Contact Temperature Sensors Types and Comparisons. . . . . . . . . . . 36Thermocouples. . . . . . . . . . . . . . . . . . 37 Product Overview. . . . . . . . . . . . . . . ..7Power Calculations. . . . . . . . . . . . . . . 15Power Evaluation. . . . . . . . . . . . . . . . . 19Review of Heater Application Factors. . . . . . . . . . . . . . . 20Select Heater. . . . . . . . . . . . . . . . . . . . 22Reference Data. . . . . . . . . . . . . . . . . . 24Heat Loss Factors and Graphs. . 26Quick Estimates of Wattage Requirements. . . . . . . . . 30 Resistance Temperature detectors(RTDs). . . . . . . . . . . . . . . . . . . . . . . . . . 49Thermistors. . . . . . . . . . . . . . . . . . . . . 52Non-Contact Temperature Sensor Basics. . . . . . . . . . . . . . . . . . . 54Defining an Application andDetermining a Solution. . . . . . . . . . . . 60Reference Data. . . . . . . . . . . . . . . . . . 61Thermocouple and Resistance Wire INDUSTRIAL RTD Initial Calibration Tolerances. . . . . . . . . . . . . . . . . . . 61RTD Resistance vs. TemperatureTables (Standard Thermistors). . 63RTD Resistance vs. TemperatureTables (DIN Platinum RTDs). . . . . 70 1