Definition of terms

Definition of terms
Nominal Resistor Value (RN):
Nominal (printed) resistor value, i.e. 22R (value of the order).
Absolute Resistor Value:
Real resistor value of the resistor, i.e. 22R0253.
Max. allowed deviation of the absolute resistor value from the nominal
resistor value in percent from the nominal resistor value.
(delivery tolerance), i.e. 22R ±1%
Resolution / number of digits from the mantissa of the nominal resistor
value, i.e. 5K045 (4 digits accuracy). The accuracy is not the tolerance
even if there is a cohesion.
Max. allowed change of the absolute resistor value depending from time
and stress. Normally it is mentioned in percent from the absolute resistor
value at t = 0 (reference value).
Temperature Change:
Change of the absolute resistor value dependency of the temperature at
the resistance element. It is normally mentioned in ppm (parts per
million) of the absolute resistor value at the reference temperature T0
(relative change of temperature dR/R).
Temperature Coefficient (TC):
Relative change of temperature of the absolute resistor value at
temperature T relative to the change of temperature (T - T0).
For Ultra-precision resistors the reference temperature T0 is 25°C.
It is stated in ppm/K.
TCR-Alignment (Tracking):
Max. allowed TC difference of different resistors. (i.e. double-resistors,
pair resistors or networks)
Power Dissipation:
When applying an electric voltage in a resistor, the energy is converted
into heat. The result of the energy per unit time is the power dissipation.
(P = W / t, P = U * I, P = R * I2, P = U2 / R).
Depending on the heat removal, there is a temperature rise of the
resistance element.
Inherent Temperature:
Real temperature of the resistance element.
The inherent temperature is the sum of the ambient temperature and the
additional temperature of the power dissipation. (excess temperature dTR).
Limiting Temperature:
Max. allowed inherent temperature in exceeding the limiting temperature
it is possible to have non-reversible alteration of the resistance, a change
in it properties or its demolition.
Nominal Power Dissipation:
Max. permanent allowed power dissipation without exceeding the
limiting temperature of the resistance. The nominal power dissipation
mentioned in the specifications belongs to these conditions:
- Free-standing assembly.
- Ambient temperature of 70°C without additional cooling or,
- Assembled on a heatsink with optimal fixed mounting (pressurized and
use of a heat conduction paste).
Riedon Inc.
300 Cypress Avenue
Alhambra CA 91801
(626) 284-9901
(626) 284-1704
Page rev. 03/2006A
Thermal Resistance (Rth):
Factor of proportionality between power dissipation and over-temperature
Rth = dT / P. The specifications mentioned in the data sheet for heatsink
mounted resistors (Rthj-c) are defined as thermal resistance between the
resistance element and case bottom plate.
Impulse Strength:
Max. allowed short-duration (impulse) electric energy, without exceeding
the limiting temperature.
Limiting Voltage:
Also referred to dielectric strength; max. allowed voltage applied to the
Limiting Current:
Max. allowed current through the resistor.
Insulation Strength:
Also referred to breakdown rating; max. allowed voltage between the
resistance element and the environment (i.e. chassis or heatsink).
Standard Conditions:
Measurement conditions for defining the absolute resistor value, tolerance
and stability of the resistor. In the laboratory and production process the
reference temperature is 25°C ± 2°C.
Riedon Inc.
300 Cypress Avenue
Alhambra CA 91801
(626) 284-9901
(626) 284-1704
Page rev. 03/2006A