Categories: Supporting information

List of symbols

Unit for calculation
Symbol Meaning Metric Imperial
AC Surface area of heating conductor cm2 in2
b Width (ribbon or strip) mm in
Ct Temperature factor (ratio of resistivity at operating temperature to resistivity at room temperature)
d Wire diameter mm in
D Outer coil diameter mm in
I Current A A
L Length of heating conductor m ft
Le Coil length mm in
n Number of turns
p Surface load of heating element W/cm2 W/in2
P Power W W
q Cross-sectional area of heating conductor mm2 in2
r Relative pitch
RT Resistance at working temperature Ω Ω
R20 Resistance at room temperature (20°C, 68°F) Ω Ω
s Pitch mm in
t Thickness (ribbon or strip) mm in
T Temperature K, °C K, °F
U Voltage V V
α Temperature coefficient of resistivity K-1 °F-1
γ Density (old marking) g/cm3 lb/in3
ρ Resistivity Ω mm2/m Ω/smf /cmf*
10 Balancing factor used in the formulas makes possible that the values can be used with units of section 1:
e.g. wire diameter, d, in millimeter (mm) or inch (in) is different from length of heating conductor, l, in meter (m) or foot (ft)

Formulas and definitions (PDF document, 78 kB)

Formulas for values in tables (PDF document, 43 kB)