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# Flat Film Resistor Slide Rule

IP.com Disclosure Number: IPCOM000090452D
Original Publication Date: 1969-Apr-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 48K

IBM

Chen, CC: AUTHOR

## Abstract

This three-slide slide rule is for use in solving flat-film rectangular resistor design problems. Given the resistor ratings, it is used to compute the length, width, maximum amount of allowable trimming and the power handling capacity of resistors, trimmed or untrimmed. It also selects certain properties of the resistor material such as sheet resistivity or power handling capacity if desired.

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Flat Film Resistor Slide Rule

This three-slide slide rule is for use in solving flat-film rectangular resistor design problems. Given the resistor ratings, it is used to compute the length, width, maximum amount of allowable trimming and the power handling capacity of resistors, trimmed or untrimmed. It also selects certain properties of the resistor material such as sheet resistivity or power handling capacity if desired.

Trimmed and untrimmed flat-film resistors conform to the standard resistor formula R=P(L/A) in which R is resistance, P is resistivity, L length, and A cross- sectional area of the resistor. For flat-film resistors, A is width times thickness, R=ohms, L=in.2, and P=ohm in.

Drawings 1 and 2 show the front and back, respectively of the slide rule. The scales are not drawn with mathematical precision, also only a few divisions are shown. A, B, C, and D are 1-cycle, 10 inch log scales. Scales E and F are 2- cycle, 10 inch log scales. G, H, and I are also 1-cycle, 10 inch log scales and are used to determine trimmed widths. All these scales can be extended to include all values of interest. On scale B UR signifies untrimmed resistor. The power handling capacity arrow is a dummy scale used to manipulate equation 2.

Where thickness is constant, the ratio R/P=L/W (1) is the basis for flat-film resistor design and is represented by scale E/scale F. The power rating of a resistor in terms of its surface area is expressed by the relation PR=LW(PHC)(2), where PR is flat-film resistor...