3. PACEMAKER LEAD ANNEALING/VACUUM OVEN (PURGED)

A. Problem/Issue

A Major Pacemaker Company wanted an annealing oven for the lead insulation that connects the pacemaker electronics case with the heart. They wanted to have the oven bring the leads quickly up to a predetermined high temperature (without exceeding a set limit) and then dropping back down. This had to accomplished in a nitrogen atmosphere to avoid oxidation or contamination of the extruded polyurethane material. Another requirement was that the total interior of the chamber must be profiled to avoid any hotspots or coldspots. The company had three of it's own engineers assigned to the project over an eighteen month time span without success.

B. Analysis

An analysis of the temperature profile proved that the temperature span was too great and needed to be reduced. Over the next two months, a series of tests showed that the variation was being caused by the two independent heating sources. One was the coils inside the vacuum chamber and the other was the in-line blower. Both of these sources was connected to independent controllers. Randomizing the power to these sources resulted in unpredictable behavior and using only one source proved too slow. There needed to be one controller that operated both heat sources with a carefully programmed program.

C. Solution/Results

We installed a microprocessor-timer combination that could be precisely programmed using ladder logic. A series of testing proved that the temperature could be achieved, but the profile was still too erratic. A new way of delivering the heat and shielding the components was prototyped and installed. A shroud was used to shield the leads from the coils inside the chamber and an EDM-cut SS tube was used to blow the in-line circulated nitrogen directly on the leads. The slots were cut in a "Bernoulli-calculated" manner to ensure that an adequate nitrogen supply was delivered exactly where it was needed. After a few more weeks of testing, the system was ready to be validated. A validation was done along with a troubleshooting/maintenance guide. The ovens are now standard equipment in facilities all over the world. The equipment has never been questioned by any FDA audits to date.