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Case Studies

Study 1 - Transmission Unit Output Loads

Background:
mk37 gyrocompassThe Gyro Systems Company was tasked by its customer Military Sealift Command (MSC) to perform an evaluation and groom of a MK 37 gyrocompass system onboard one of its' vessels.

The MK 37 system consisted of:

  • 2 MK 37 master units
  • 2 MK 37 control units
  • 2 MK 37 transmission units
  • 1 MK 37 transfer panel
  • Various analog and digital ship's course indicators
  • Heading step by step input to various ship's equipments

Upon light off and initial evaluational of the system, all heading step by step inputs from the transmission units to the ship's course indicators were functioning properly. Inputs to the ship's equipment from the transmission units were not turned on upon turn on of the inputs to the ship's equipments. Alarms at the transfer panel were noted. Troubleshooting of the step by step output of the transmission units revealed that the steps were degraded. At this point each output of the transmission units was turned off individually. Upon turning off the output of the transmission units "INMARSAT" the alarms at the transfer panel cleared and testing of the transmission unit step by step output revealed that the steps were restored.

Resolution:
Further analysis of the output of the transmission unit marked "INMARSAT" revealed that it did not feed the INMARSAT equipment and was, in fact, an old unused feed. Gyrosystems was instructed by MSC to remove the INMARSAT label from the transmission unit output switch and to mark it as not to be turned on.

Conclusions:
Degrading of the step by step heading output of the Mk 37 gyrocompass transmission units can be caused by external output load problems. The problem load can be determined quickly by individually turning each one off until step output is restored. Proper labeling of transmission loads and removal of loads that are no longer used is essential for proper system operation.


Study 2 - Simulation and Test Modes

Background:
sperry mk27 gyrocompassGyro Systems Company was tasked to install a MK 27F Gyro Attitude and Heading Reference System )AHRS) on board the HSV-2 Swift to prove ship’s roll and pitch data primarily to SGSI as well as other ship’s systems requiring this data. After the installation and during testing of the MK27F roll and pitch data transmission to the SGSI system it was noted that the MK27F allows for two distinctly different selectable roll and pitch formats:

  • US NAVY: Positive Pitch is bow down, Positive roll is starboard up
  • STANAG 4222: Positive pitch is bow up, Positive roll is port up

These outputs are selectable “only” during normal operation mode and are directly related to the type of sentence used to output roll and pitch data. NAVAIR requires the SGSI system receive the US NAVY format in both the normal operation mode and in the simulation mode. The simulation mode outputs roll and pitch data only in the STANAG 4222 format.

Resolution:
The Original Equipment Manufacturer (OEM), Sperry Marine Systems was made aware of this issue and indicated they would make software changes to correct the problem.

Conclusions:
Installation and test personnel should take note of the format of equipment output data in simulation or test modes to insure it is the proper format for user equipment under test.


Study 3 - MK 227 Gyrocompass Torquer Spring Assembly Failure

Background:
sperry mk27 gyrocompassGyro Systems Company was tasked by MSC to evaluate a problem with a MK 227 gyrocompass system on one of it's vessels. The vessel was reporting that gyro #2 level meter M1 indication was not changing when tilt azimuth switch S4 was operated in the manual level circuit mode. During this evaluation it was found that if tilt azimuth switch S4 was operated for 30 to 45 seconds the tilt meter would finally start to indicate the gyro tilt but in an erratic manner. Once the meter indicated that the gyro was level it was placed in the run mode. The gyrocompass then settled and functioned properly.

Resolution:
Slow and erratic operation of the tilt azimuth switch in the manual level circuit mode is symptomatic of a loose, misadjusted or failed torquer spring assembly within the gyrocompass binnacle. Adjustment or replacement of the torquer spring assembly requires a gyrocompass overhaul and repair facilitiy and should not be attempted by ship's personnel.

Conclusions:
Ship's personnel were informed of the nature of the manual leveling problem and it was recommended that the torquer spring assembly be adjusted or replaced as required at the ship's soonest availability.