1. INTRODUCTION

There has always been some confusion and misunderstanding regarding the calculations of watt densities for mica band and strip heaters. The procedures outlined in the sales bulletins are based on standard post terminal constructions and are intended to give the reader a quick method for estimating watt density, however problems arise for flexible lead and non-standard constructions. The purpose of this technical memo is to outline an exact method for calculating watt density based on the typical no heat area for each type of heater construction.. The watt density procedures outlined in the sales literature can still be used for quick estimates, but when an exact watt density calculation is required or when the heater is not a standard post terminal construction, this memo should be referred to.

2. DEFINITION OF HEATED AREA

The heated area of band or strip heater is defined as the wind length times the overall width of the heater. This represents the heated surface area in contact with the heated part.

The heated area is calculated by determining the total heater surface area in contact with the part and then deducting all the no heat areas in the heater.

HEATED AREA = (SURFACE AREA) - (NO HEAT AREA)