TYPES OF MOUNTING AND PHYSICAL SIZES
Resistors are available in almost any size ranging from 0.065 inches diameter by.125 inches long to 12 inches in Diameter to several feet high (for very high voltage resistors). The most common form is cylindrical with leads coming out either end. You are able to find other resistor sizes at http://www.riedon.com. Riedon is a manufacturer of resistors.
TYPE OF MOUNTING.
The term “Leads” is used in the general sense as a means of connecting the resistor. They may be lugs, wire leads, pins, or any means of connecting the resistor to the circuit.
Resistors are available in a surface mounting configuration. This is generally associated with chip resistors that are mounted by solder reflow techniques.
Fuse Clip Mounting.
The fuse clip type is made such that it will mount directly into a fuse clip. Fuse resistors are sometimes made like this.
The Single Inline Package is normally associated with resistor networks consisting of several resistors in the same package. It is a rectangular flat shaped package with the several leads coming out one surface generally the narrow, long surface.
Dual Inline Package (DIP).
The Dual Inline Package is again normally associated with resistor networks. The main difference is that leads extend out both narrow, long surfaces and are formed to either flush mount on a PC Board or thru hole mount on a PC board.
The Flat Pack are roughly the same as Dual Inline Packaging except the leads come straight out and are not formed for surface mounting or thru hole mounting. This is just a variation of DIP mounting.
Axial Leads – Axial Lead mounting is what most of us are familiar with using. It consists of a cylindrical (or rectangular or any shape body) with the leads extending out either end parallel to the resistor’s major axis.
Radial Lead mounting is similar to Axial Lead mounting except the lead come out of the body perpendicular to its major axis.
PC mounting consists of both leads of the resistor coming out the same surface so that it is easier to mount a resistor (or any other device) vertically. The resistor may be cylindrical or rectangular. Another great resource is the resistor WIKI
4 Terminal Mounting.
Most styles will offer a 4 terminal means of mounting for low values. This is important when the leads become a significant part of the value. This establishes the point on the leads where the value in within the desired tolerance. It is fixed and prevents changes in the value due to mounting variations.
The Precision Wirewound is a highly accurate resistor with a very low TCR and can be accurate within.005 %. The frequency response of this type is not good. These are generally used in highly accurate DC measuring equipment, and reference resistors for voltage regulators and decoding networks.
The accuracy is maintained at 25oC(degrees Celsius) and will change with temperature. The maximum value available is dependent upon physical size and is much lower than most other types of resistor. Their power rating is approximately 1/10 of a similar physical size in a carbon composition. They are rated for operation at +85 oC or +125 oC with maximum operating temperature not to exceed +145 oC. This means that full rated power can be applied at +85 (125) oC with no degradation in performance. It may be operated above +125 (85) oC if the load is reduced. The derating is linear, rated load at +125(85) oC and no load at +145 oC. Life is generally rated for 10,000 hours at rated temperature and rated load. The allowable change in resistance under these conditions is 0.10 %. If operated at lower temperatures and reduced power levels, extended life can be achieved. End of life requirements are generally defined by the manufacturer or in some case by user specification. Some degradation in performance can be expected. In some cases, particularly if the tolerance is very low and the TC is low, the rated power is reduced to improve resistor stability through life. Precision Resistors regardless of type, are designed for maximum accuracy and not to carry power. The materials used in these resistors are highly stable heat treated materials that do change under extended heat and mechanical stress. The manufacturing processes are designed to remove any stresses induced during manufacture.
There is little detectable noise in this type of resistor. The stability and reliability of these resistors is very good and their accuracy can be enhanced by matching the absolute value and the temperature coefficient over their operating range to achieve very accurate voltage division.
Resistors are available in almost any size ranging from 0.065 inches diameter by.125 inches long to 12 inches in Diameter to several feet high (for very high voltage resistors). The term “Leads” is used in the general sense as a means of connecting the resistor. They may be lugs, wire leads, pins, or any means of connecting the resistor to the circuit.
The maximum value available is dependent upon physical size and is much lower than most other types of resistor. In some cases, particularly if the tolerance is very low and the TC is low, the rated power is reduced to improve resistor stability through life.