Manufactured by Friez Instrument Division
Bendix Aviation Corporation
1957 s/n 213
This authentic vintage very low serial number #213 psychrometer was made circa 1957 by Friez Instrument Division of the Bendix Aviation Corporation in Baltimore, Maryland. Manufactured for the Bureau of Naval Weapons, this military model ML-450 A/UM 4.5V DC instrument has seen very heavy usage.
This instrument is authentic, having been discarded but is still intact in original case with original manual. Has not been tested. Selling AS IS for collector's value. Contains 3 original label plates, two large empty distilled water bottles, 1 smaller empty distilled water bottle enclosed within instrument, battery compartment cover, protective air flow cover, shoulder strap, and a very worn but still legible instruction manual dated June 1957. Manual is labeled "NAVAER 50-30FR-530 Instruction 509941" and titled "Instructions for Psychrometer ML-450A/UM and Tables of Dew Point and Relative Humidity".
To repeat, this instrument has not been tested and is offered AS IS for unique authentic collector's value.
Instrument and well worn case are intact (not broken) but the dry bulb thermometer is missing. Wet bulb thermometer is still present. This item is offered as an AS IS Collectible vintage salvaged Naval weapons model ML-450 Bendix Friez battery powered psychrometer with electric fan for air aspiration over dual thermometers. Has not been tested. Selling AS IS for collector's value.
As can be seen in photographs and previously described above, this instrument has seen heavy usage, quite possibly at a Naval Weapons Center or maybe even shipboard while underway at sea. The authentic well worn appearance is perfect for an important addition to any collection of early models of twentieth century military weather instrumentation.
I am in no way qualified as a meteorologist, but here are a few interesting things I've found that describe psychometric in general:
These instruments are used to take in and analyze air samples that are passed over the "dry" and "wet" (covered with a cloth sock soaked in distilled water) bulbs of two matching thermometers in an enclosed small air chamber (white plastic bulb cover).
The precision temperature readings are recorded and then used to determine Humidity, Dew Point, and other additional factors at that time by using various charts contained in the Instruction Manual. (As previously described, this particular instrument is missing the "Dry" thermometer, but the "Wet" thermometer is intact).
This Bendix Psychron Friez Instrument Division military model ML-450A/UM psychrometer uses a battery operated fan to insure adequate existing air is allowed to flow over the bulbs of the two thermometers for a specified time period. When the temperatures of both thermometers have settled, then they are carefully noted and recorded for use as described above.
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