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    Photos of Kearfott Ring Laser Gyro-Based Inertial Reference Units

    [Only about 3 people per decade visit the Laser Equipment Gallery ;-), the existing format was archaic, and I am lazy. So going forward, we will use the Windows App "Web Album Generator" for most of the collections.]

    Note: Most links open in a single new tab or window depending on your browser's settings.

    These are photos of Kearfott navigational Inertial Reference Units (IRUs) or parts of them that use HeNe laser-based Ring Laser Gyroscopes (RLGs). Only two samples of one model at present.

    Note that the terms Inertial Reference Unit (IRU) and Inertial Measurement Unit (IMU) may be used interchangeably. The Kearfott Website uses IMU; the label on the actual device has IRU. Go figure. ;-)

    Kearfott Inertial Reference Unit K600A374-01

    This is a complete system, probably intended for "Sea Navigation" - e.g., in submarines, larger UAVs, and the like. For ships, the Z axis would be largely wasted. ;-) Exactly what the difference is compared to "Land Nav" systems is probably more in the interfaces and other capabilities than the specific functions. The primary physical diffference appears to be of the paint color in the Kearfott brochures: Land Navs are black; Sea Navs are biege. I suppose that black doesn't show dust and dirt like a light color would. ;-)

               

    Kearfott Inertial Reference Unit: Outside (left), Inside Labeled (center), Inertial Sensor Assembly, Platform (ISAP, right)

    For much more information on this IMU, go to Kearfott K600A374-01 IMU with Monolithic Block Triple RLG.

    Kearfott Inertial Reference Unit K600A374-01 #1

    (The photos in the first Web album are courtesy of Ismael Tremblay.)

    See Kearfott Inertial Measurement Unit Assembly K600A374-01 #1 (Web Album, 25 photos).

    The RLUs in this IRU are interesting because all three axes are fabricated in a single block of special low expansion glass or similar material. The accelerometers are totally separate. At present not much else is known other than that the RLGs do power up, at least briefly.

    The last pic shows an ideal application for this IRU. ;-)

    Kearfott Inertial Reference Unit K600A374-01 #2

    This one (#2) is mine and is believed to be identical to #1. In fact, their serial numbers differ by only 5. ;-) However, rather than disassemble the RLG Block of #2, Ismael Tremblay kindly loaned me his RLG Block for the photos. So everything up until the clothes come off the RLG Block are of mine while the naked photos are of his unit. No one shall know. ;-)

    But first, here are some short videos of what happens with the RLG Block when the IRU is powered. Click on the small image to see the corresponding video.

                       

    Overall Setup for Powered ISAP RLG Block Photos (left) and Closeups

    These videos show the naked RLG Block from IRU #1 tethered to the power supply and electronics from IRU #2. Minor rearrangement and camera angle variations similar to the next three are used for all the powered photos in the Web Album, below. The last one has the RLG Block oriented in approximate agreement with the schematic derived from the Kearfott patent. However, even with the thing in-hand and powered, it's virtually impossible to figure out the discharge and beam paths due to the contoured exterior of the block.

    The clicks near the beginning and end of the videos are from the outlet strip power switch - on and off. Around the mid-point of the video, the RLG Block glows brightly three times in succession accompanied by a continuous audible whine (likely from the dither PZT). This behavior is 100 percent repeatable and IRUs #1 and #2 do exactly the same thing, so it's very likely a feature, not a bug. The assumption is that there needs to be some handshaking with whatever the IRU is connected to for it to remain active. The indicator LED does stay lit but that is the only remaining sign of life. So these videos get rather boring after almost no time at all.....

    And now for the good stuff. ;-)

    See Kearfott Inertial Measurement Unit Assembly K600A374-01 #2 (Web Album, ~96 photos so far).

    Description of the Web Album photos for #2:

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    Sam's Laser FAQ, Copyright © 1994-2025, Samuel M. Goldwasser, All Rights Reserved.
    I may be contacted via the
    Sci.Electronics.Repair FAQ Email Links Page.