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---------------- Begin Forwarded Message ---------------- Date: 9/22/99 3:05 PM Received: 9/22/99 9:03 PM From: John Walker, techdive@ea*.ne* To: Jim Cobb, cobber@ci*.co* A bit of history. Lesson #1. Part II will be the bend-omatic An anologe decompression computer built by Foxboro Company in Foxburo, Massachusetts, was submitted to NEDU in Oct 1955. Its two compartment pnueumatic design was based on the Grove and Munk report. The two compartments tyo be simulated had halftimes of 40 and 75 minutes and surface ratios (compartment nitrogen pressure to ambient pressure) of 1.75:1 for both compartments. The computer used five bellows to determine decompression status. Nitrogen absorption and elimination from the compartments was simulated by the flow of gas through porus resistors between bellows, which were exposed to the ambient pressure, and bellows sealed in a vacum, kept under a constant pressure by a spring. This device was the result of communication between two brothers, Dr. Hugh Bradner (member of the Committee of Undersea Warfare) and Mead Bradner ( head or research and development at Foxboro). The operation of the unit involved balancing the color on a disk viewed through a window on the right side of the device. The disk was divided into three sections. One-half was white, one quarter was red, and one quarter was green. If the dial showed any green through the half-disk window, the diver was safe. If any red was showing, the diver had exceeded the safe ascent depth and would have to descend. Optimal decompression was achieved by keeping just the white half of the disk visible through the window. Results of the evaluation by the NEDU stated that the device gave readings within the U.S. Navy Table decompression range for some dives and outside the range for others. The major reason for this was that compartment half-time values were mistaken for the time constants of the bellow. The actual compartment half times simulated by the device were 27.7 and 52 minutes, causing deviation from tables. The device was returned to Foxboro for re-evaluation and modification but was never resubmitted to the Navy. In 1957 the Navy published new air no-decompression/decompression tables, and repeditive dive tables. The Navy apparently rejected the idea of a decmpression computer and accepted option "a" of the Grove and Monk report (i.e., depth guage and watch, tables, and wits). ----------------- End Forwarded Message ----------------- ------------------------------------------------------------------- Learn About Trimix at http://www.cisatlantic.com/trimix/trimix.html -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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