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Vibration Isolated Television

Description

The Vibration Isolated Television (VIT) frame is primarily used to provide visual observation of the sea floor during reentry of an existing borehole. Sonar capability, primarily used to locate objects such as reentry cones which are initially out of camera range, is and integral part of the system. The sonar, in conjunction with a compass attached to the VIT frame, provides primary range and bearing from the VIT frame to the reentry cone. An acoustic beacon can be attached to the VIT frame, which allows the ship's dynamic positioning system computers to fix the position of the VIT frame relative to the ship.

The VIT frame is deployed by latching its guide sleeve around the drill string. The drill string is used as a guide as the VIT is lowered to the sea floor by means of an armored coaxial cable attached to a special winch located in the ships moonpool area. Power is transmitted down the coaxial cable to operate the underwater lights, camera and sonar. The TV and sonar signals are then transmitted up the coaxial cable for display and recording on board the ship.

The VIT can also be used to precisely locate spudding sites. Once located, the sites can be marked by dropping an identifying marker from the VIT frame itself, via an acoustic release.

Specifications

• Depth Rating = 22,500 ft (10,000 psi)
  
• Operating Temperatures = -20° to +60°C (-68° to +140°F)
  
• Shock Rating = 100 Gs at 11 milliseconds, 3 axes
  
• Umbilical Cable = double armored coaxial

Design Features

Underwater Lights

• Lamps = 100 and 250 watt quartz halogen, w/reflectors 2000 hours average rated life, 5000 lumens output
  
• Beam pattern = 60-70° field of view in water, 20-40 foot range
  
• Power = 120 volt AC

Remote Video Camera

• Type = Videospection SIT (high sensitivity)
  
• Power = -15 VDC
  
• Video Output = 1VPP negative sync composite video, 75 ohm
  
• Weight = 28 lbs
  
• Light Sensitivity = 0.001 candlepower, low level (star light)

Telemetry System

• Type = TVTM-3015 (CSE) Colmek Systems Engineering
  
• Control = zoom control signals are telemetered to the unit.
  
• Cable Power = (1) Surface: voltage is stepped up to 480VAC, (2) Subsea: voltage is stepped down to 120 V AC
  
• Weight = Multiplexer, 212 lbs
  
• Line voltage = 120 VAC +/- 10%, 60 Hz (at the surface)
  
• Subsea Power = subsea TVTM 8.4 watts, 590 watts available to operate camera and lights.
  
• Video resolution = ~300 TV lines horizontal

Sonar Head

• Type = Simrad Mesotech, model 971
  
• Frequency = 675 kHz
  
• Beam Width = 1.7° horizontal, 60° vertical
  
• Mechanical Resolution = 0.225° (step angle)
  
• Scanning = 360° continuous, or locked
  
• Connector = DG O'Brien 9 pin
  
• Cable = DG O'Brien oil filled assembly
  
• Dimensions = 3.5 in (89 mm) diameter, ~60 in long
  
• Weight = ~75 lbs (in air), ~50 lbs (in water)