Photos of Kearfott Ring Laser Gyro-Based Inertial Reference Units

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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.

Kearfott Inertial Reference Unit K600A374-01

This is a complete Kearfott Inertial Measurement Unit (IMU), 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 IMU functions specifically. 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.

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

Kearfott Inertial Reference Unit K600A374-01 #2

See Kearfott Inertial Measurement Unit Assembly K600A374-01 #2 (Web Album, 35+ photos).

Description of the LEG photos for #2:

• Overall views (Front, Right, Front_Right, Right, Back_Right, Back, Back_Left, Left, Front_Left): These are virtually identical in appaerance to the sample on the Kearfott Website under "Sea Nav IMUs".

• Closeups of the five military-style circular connectors:
  • J1 (66 pins): Control / Signal / Information.
  • J2 (15 pins): Power input. 28 VDC nominal, 30 W max. 24 VDC OK. +Vin: Pins A,B; -Vin: Pins M,N. Case GND: Pin P. No other pins used.
  • J3 (13 pins): ????
  • J4 (22 pins): ????
  • J5 (13 pins): ????

  (J3 and J5 have the same pin configuration but are keyed differently.)

• Label: This has both the numbers as described above.

• Optical Sensor: This is also visible in the lower right corner of the Label photo. It is some sort of device in a TO18 package with a clear cover. I am calling it an optical sensor but it does NOT look like a photodiode or an LED and is thus a mystery. Something similar is present in all the Kearfott photos as well.

• Caution Label: Like we didn't know. ;-)

• Inside Top: This is what greets you after removing the cover. It's a very clean layout with only 3 or 4 major subassemblies (depending on how they are counted): Main PCB Assembly (top of photo, mostly hidden), "Inertial Sensor Assembly, Platform" (ISAP, the round can on elastomer mounts, lower left) - the heart with the ring laser gyro block and accelerometers; and the power input, conditioning, and interface modules (lower right).

• Main PCB in Situ: What's visible is the top PCB; a similar size board is mounted on the other side of the aluminum frame.

• Connector PCB in Situ: At least for some of the connectors.

• Top Main PCB: Some LSI parts but mostly smaller ICs. The black polka-dot rectangular affair at the right is the high voltage power supply for the RLG.

• Bottom Main PCB: More chips including a Texas Instruments TMS320 DSP. I would guess that the black painted-over 32 pin packages contain the firmware. ;-)

• Power Connector Module Inside: This is what is behind J2. It shows the very simple but almost impossible to follow wiring due to the use of all white insulation. ;-)

• Power Filters: These appear to be RFI-type filters for the input power. (Look up their Martek part numbers!) Also visible is the Power Connector Module.

• DC Power Converter: This is another readily identifiable Martek module. It is a DC-DC converter that takes 28 VDC (nominal) and provides +5 VDC and ±15 VDC for all the electronics. The spec is actually 14 to 40 V in, so fortunately it will run happily off 24 VDC, which is a lot more common for powering on the bench with a fixed supply. ;-)

• Interface PCB: Function of this PCB is unknown but it has a bunch of opto-isolators on it so it must have something to do with interacing in a nasty electrical environment.

• RLG HV Connector: This is really just a white wire with high voltage insulation and a female contact secured with a black plastic cap for the positive (anode) to the HeNe lasers inside the RLG block.

• ISAP in Situ: Another view.

• ISAP with Mounts: Front, Right Side, Back, Left Side, Top, Bottom. The upper cable is for the RLG, the lower cable is for the accelerometers. The +HV socket for the RLG is also visible.

• ISAP Label: And S/N 670. ;-)

• Inertial Measurement Unit Labeled: And an interior view with major assemblies annotated. ;-)

• ISAP Housing Mounts Shroud: Exposing the cylinder with the RLG block and accelerometers

  The purpose of the Shroud is not entirely obvious as it is not structural. But it is made of a thin soft ferrous material which is perhaps Mu-metal, and thus may be a serving as a magnetic shield. It is conceivable that even weak magnetic fields could affect the behavior of the lasers in the RLG at the margins of precision. If that isn't its function, it must be to make disassembly more annoying. ;( ;-)

• ISAP Shroud Label: The wording of the label on the shroud is strange (and probably unrelated to the shroud itself): "KEARFOTT CORPORATION IS THE INITIAL TRANSFERER OF THIS PRODUCT, WHICH CONTAINS THORIUM LICENSED UNDER 10 CFR 40.13(c)(i)(ii)". It's even stranger looking up the definition of 10 CFR 40.13. ;-) 10 CFR 40 is part of the "Code of Federal Regulations" dealing with nuclear energy. ;-) Part 13 states that the company is exempt from regulations because there is very little of the stuff present. Thorium is a weak Alpha emitter so a trace amount may have been placed inside the RLG block to assist starting of the HeNe lasers. Any Alpha particles would be totally blocked by the block (no pun intended intentionally) so forget your Gieger counter. ;-)

• ISAP RLG PCB Top: The RLG monolithic block is below this PCB. The wires in the 3 ribbon cables (5, 6, 7 wires each) and 3 sets of individual orange, yellow, and green wires need to be carefully unsoldered to remove the PCB. That's a total of 27 wires and they are a lot thinner and closer together than they appear in the photos. In fact everything in the "can" is actually smaller than it appears in the photos. ;( ;-) Detaching (and re-attaching) the wires requires a steady hand, super fine tip soldering iron, and Mark II upgraded eyeballs (or a good magnifier or microscope).

• ISAP Accelerometers with PCB: The three accelerometer units are attached to a metal frame and wired to their PCB.

• ISAP Accelerometer Interface ICs: A fancy part for each one. ;-)

• ISAP RLG Block in Situ: The visible portion of the RLG block exposed when the accelerometer assembly is removed. The purpose of the foam is not known as it's not likely to provide much damping or thermal isolation. Three of the six mirrors are visible with their PZTs for cavity length control.

Stay tuned, more to come. ;-)