Browse Prior Art Database

Closed Loop Control of Granular Chrome Evaporation

IP.com Disclosure Number: IPCOM000076804D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 30K

Publishing Venue

IBM

Related People

Hanlon, JS: AUTHOR [+3]

Abstract

Because source chrome used in vapor deposition of granular type chrome reaches vapor phase by sublimation, it is generally considered difficult to achieve precise control over rate of deposit accumulation. Fine control of deposit rate would be useful to hold product uniformity and tolerances and to avoid material stress.

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Closed Loop Control of Granular Chrome Evaporation

Because source chrome used in vapor deposition of granular type chrome reaches vapor phase by sublimation, it is generally considered difficult to achieve precise control over rate of deposit accumulation. Fine control of deposit rate would be useful to hold product uniformity and tolerances and to avoid material stress.

The illustrated closed-loop system provides such fine control of deposit rate. Deposition monitor 1, a crystal oscillator, changes frequency as chrome is evaporated upon it. TEMESCAL unit 2 provides a buffered frequency output related to deposit thickness. Frequency monotor 3, a modified ELDORADO Type 1607 Frequency Meter, converts the output of unit 2 to a digital representation; conveniently in binary-coded decimal (BCD) notation form. Digital Process Controller 4, typically an IBM 1800 Process Control System, samples outputs of monitor 3 and produces power adjustment control outputs at critically timed, discrete adjustment intervals of not less than 6 and not more than 12 seconds. The power control output is converted to analog form in the power subsystem 5 and controls the supply of evaporation inducing energy to source chrome 6.

The controller 4 interacts with its stored program 7 to calculate the power adjustment factor for each adjustment interval by:
1) sampling deposit thickness data represented by outputs

of meter 3, at discrete subintervals of each power

adjustment interval (one sample per second is suitable).
2) calculating deviation of samples from mean calculated

for selected samples of previous adjustment factor

computing interval.
3) selecting and stor...