Appendix C-Insulated Boxes for Protecting Video Cameras
Four camera systems were designed and built to provide video documentation of tests in which instrumented fire shelters and vehicles were burned over by simulated wildfires. A wildfire is able to reach temperatures of 1093 °C for short periods and 815 °C for longer times. Each system uses a video camera (no recorder) in an insulated box with a video tape recorder and battery in another box buried underground.
The camera is a Sony SSC-DC30 with a threaded "C" mount that accepts various lenses. Lenses from 3.5 to 50 mm are available. This camera requires a 12- to 18-volt, 4.5-amp current and outputs a standard NTSC video signal.
The recorder is a Sony Hi8 camcorder (CCD-TR700). The camera portion of this unit is not used. The video signal from the SSC-DC30 camera is fed directly into the video tape recorder. The camcorder requires a 6.5-volt, 2-amp current.
One battery powers both units. The battery is a 14-volt, 5-amp-hour Gates Cell that is fused. The camera is powered directly from the battery; the camcorder uses an adapter to reduce the voltage.
The insulated box, made of 16-gauge stainless steel (Type 306), has tripod mounts welded on the bottom. The insulation inside the box is 1-inch thick ceramic board. This ceramic has a continuous- use temperature of 1260 °C. Its thermal conductivity at 815 °C is 0.95 BTU inches Hr °F Ft2.
The window for the camera is a thermopane design using Corning Vycor glass on the outside and a hot mirror on the inside. The Vycor glass is 96% silica and 4% boric oxide. It can be used continuously at 898 °C and intermittently to 1298 °C. This glass has a high resistance to heat shock. It can be heated to 900 °C and plunged into ice water without breaking. The inner glass is a dichroic mirror that transmits 90% of visible light (400 to 700 nm) and reflects 98% of the infrared light (wavelengths greater than 700 nm). The metal coating on the glass faces the outside of the box. This prevents radiant energy from heating the camera.
The Sony SSC-DC30 camera uses 4.5 watts of power. This will generate heat that raises the temperature inside the insulated box 0.0033 °C per second or 24 °C in 2 hours. The resulting temperature would be higher than the maximum recommended temperature of 52 °C. To keep the camera cool, 16 ounces of blue ice is frozen and placed under the camera mount. The power and video cables connecting the camera to the battery and recorder are routed through woven ceramic sleeving that is routed through steel conduit. The conduit is then wrapped with ceramic blanket (rated for continuous use at 1300 °C) and the assembly is wrapped with aluminized fire shelter material.
The camera must be within 5 to 10 feet of the subject. If the camera is farther away, smoke is likely to obscure the subject. The camera is mounted on the aluminum base plate, placed in the insulated box, and connected with a coax cable to the Tektronics waveform/video monitor. The Tektronics monitor becomes the viewfinder. The waveform is used to adjust the camera exposure. After the exposure has been adjusted, the monitor is disconnected and the camera is connected to the video camcorder/video tape recorder (VTR). The recorder can record for 2 hours.
Instructions for the Video Camera Systems
1-Freeze the blue ice 2 days before use (some freezers will not freeze the ice overnight).
2-Bolt the tripod legs to the box with 14-inch bolts. Insert the power cable and the coax cable into the box one at a time. Connect the insulated conduit to the bottom of the box.
3-Choose the camera location and set up the boxes. The wide-angle camera lenses allow the camera boxes to be within 5 to 10 feet of the subject. This is important because smoke can obscure the subject. Cameras inside vehicles must use the 3.6 mm Computar lens.
4-Mount the camera on the aluminum channel with a 14-inch flathead bolt. Connect the power cable. Connect the coax cable to "video out" using a rightangle BNC adapter.
5-The switches on the back of the camera are:
6-The switches on the side of the camera are:
When using the Computar lens (black), plug the lens cable into the lens terminal.
When using the Angenieux Lens (silver):
7-The battery box is placed in the ground (not too deep at first, because dirt tends to fall inside the box before it is sealed). The power cable, the coax cable, and the remote control cable are fed through the hole in the lid. The hole is taped to prevent dirt from entering.
8-Connect the power cable to the battery. Connect the camcorder power cable to the battery and to the camcorder.
9-Connect the coax cable from the Tektronics monitor to the coax cable from the camera using a female-female phono adapter.
10-Turn on the camera and the Tektronics monitor. The PIX button shows the picture from the camera. The WFM button shows the waveform (exposure).
11-Focus the lens on infinity (the wideangle lenses do not focus). The lens mount must be adjusted by loosening the Phillips screw (LOCK) on the side of the camera and turning the lens thumbscrew on top of the camera. Use the Tektronics monitor (PIX) to view the picture.
12-The Computar lenses have two adjustments:
To adjust the exposure, put the Tektronics monitor on WFM. The scale on the waveform is from 0 to 100%. It is okay to have some spikes above 100%, but if there is a solid line above 100%, the video is overexposed. When setting up the camera inside a vehicle, the windows will be overexposed. After fire and smoke surround the vehicle, the exposure will be fine. Start with the ALC in the middle and adjust the LEVEL. Inside the vehicle it is better to set the ALC toward A (average).
13-Disconnect the camera coax cable from the Tektronics monitor and plug it into the video jack (yellow) on the camcorder. Use a right-angle phono plug adapter. The CCD-TR101 has a switch that must be set to input.
14-Plug the remote control into the REMOTE jack. Then turn the camcorder power switch to VTR. The power switch on the remote can turn the power on or off only if the power switch on the camera is set to VTR. Insert a 120-minute tape. Look into the viewfinder to confirm that the video signal is coming from the camera. If it is not, check all power and cable connections.
15-Record some video by pressing the two REC buttons on the remote control. Rewind and play the tape. The remote control will show the counter running and a round dot will display, confirming that the camcorder is recording. The playback can be viewed in the viewfinder or by connecting the Tektronics monitor to the camcorder video jack.
16-Close the boxes and start recording just before the fire. Seal the camcorder box and the remote control in a plastic bag and bury them. Be careful not to depress any buttons when burying the remote control.
|©2005 Colorado Firecamp, Inc.||home schedule blog ENGB facility about us FAQ's|