Oh, The Pressure!

With today’s video technologies continuing to rise in complexity and cost, the pressure of making the right decision… well… The “pressure” here is not the pressure of decision, it is the decision of pressure.

Decision: A pressurized outdoor camera or a sealed outdoor camera (non-pressurized)?

Why have pressurized cameras?

Typically, the location of the camera will be in an area that is known to have some type of air-borne contaminants that could damage the internals of the camera. Contaminants can be anything from oil, water, or any particulate matter from manmade or natural occurrence. The thought here is that if the camera is internally pressurized above ambient pressure, these contaminants will be prevented from entering.

The core purpose of pressurization in an outdoor camera is to “ensure that no water, moisture or dust is able to enter the camera enclosure and cause premature failure of the electrical, mechanical or optical components.”

The above quote was taken from a previous blog entitled “Dry As A Bone” in describing the challenge of building an outdoor camera; to read the entire article click on the link below:

http://gotowti.typepad.com/my_weblog/2009/09/something-sidewinder-related.html.

The manner in which the seals are created for the Sidewinder P/T/Z camera is the same manner in which the seals are created for the all fixed cameras manufactured by WTI. A sealed outdoor camera (from WTI) meets the same core purpose as that of a pressurized camera; contaminants are prevented from entry.

Consider the maintenance cost reduction benefit of a sealed camera: no pressure checks! (Also, no alarm conditions when internal camera pressure drops)

Consider the installation site. Underwater (sea floor monitoring) or extreme altitudes (weather balloon) will indeed require some type of pressurized camera enclosure. Highways, intersections, utility infrastructure sites, building perimeter, etc… Why have pressurized cameras?

~David Scales, C.T.O.

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WTI (Wireless Technology, Inc.)

Video Surveillance Products Dedicated to the Broadcast, Global Security and Transportation Markets!

www.gotowti.com ● www.wirelesstech.com

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Dry as a Bone – How the Sidewinder Camera Gets It’s IP67 Rating

One of the primary challenges of building an outdoor camera is trying to ensure that no water, moisture or dust is able to enter the camera enclosure and cause premature failure of the electrical, mechanical or optical components. Analyzing every nook and cranny that could allow moisture to enter the camera and then engineering an effective solution requires a little creativity and sometimes a little counter-intuitive engineering to achieve the best possible seal performance. Let’s take a look at the various water entry points and the sealing solutions that allow the Sidewinder to be able to be immersed in 1 meter of water for 30 minutes and still remain bone dry inside.

Window Glass – Sealing the viewing window glass presents a bit of a challenge, as two materials with different temperature coefficients of expansion must be joined together. A silicone adhesive with a moderate Shore A hardness of 30 and a -60C to +205C temperature rating was selected. This allows the glass and aluminum components to expand and contract without placing undue stress on the seal interface. Note the shallow groove around the edge of the glass. This groove prevents shear force from delaminating the adhesive from the aluminum surface.

Front and Back Plate to Camera Tube Seal – Sealing the window face plate and the rear plate to the camera housing tube is accomplished using -45C to +120C temperature rated, Shore 65 hardness o-ring seals. The o-rings are greased with a -40C to +95C temperature rated silicone lubricant to provide an air tight and water tight seal. The o-ring seals mate with the precision machined surfaces on the inside front and inside rear of the camera housing tube.

Tilt Shaft to Tilt Seal Housing – The tilt seal housing incorporates five different seals to provide an air and water tight interface between the tilt drive assembly shaft, the main housing plate and the camera housing tube. Wide temperature range seals and wide temperature range silicone lubricants are also used in this assembly to provide the highest possible performance. The tilt drive shaft seal will withstand a 10 PSI pressure differential without leaking over the full -34C to +74C TS-2 temperature range. The four o-ring seals provide an air and water tight interface between the tilt drive seal housing and the main assembly plate of the Sidewinder.

Pan Shaft to Pan Seal Housing – The pan drive seals are arranged and perform in a manner similar to the tilt drive seals.

Cover to Main Plate Assembly – Sealing the Sidewinder cover to the main plate assembly was the most difficult of the design challenges in making the camera capable of achieving an IP67 water immersion rating. Since the length of the edges that need to be sealed is fairly long, a highly reliable method needed to be developed. Also, a method for applying the high joining force was required to be developed. Several gasket designs were tried until the current design shown was found to offer excellent performance. Instead of a wide gasket, which would intuitively seem to offer the best sealing performance, a narrow o-ring style gasket was found to offer much higher sealing pressures along the gasket ridge sealing surface, as the force of the cover screws holding the cover to the plate is concentrated into a much smaller surface area than it would be with a wider gasket. Aluminum reinforcement strips were added behind the flanges of the cover assembly to allow a much higher mounting force to be applied to the cover screws, ensuring a better seal. A special screw sealing compound is also used to prevent water ingress around the screws.

Power Supply Base Seal – The power supply base seal was actually pretty straight forward to implement. Since the main camera base structure is very heavy duty, large bolts could be used to apply the force necessary to get a highly reliable seal. A special laser cut gasket is used to seal both the mounting rim and the mounting bolts.

Bottom Egress Cable Seal – A water tight integrated cable seal and strain relief was used to seal the cable exit point on the bottom of the camera. A silicone sealant is used to seal the strain relief to metal housing joint. The strain relief provides a water tight seal around the cable itself.

Flying Cable Seal – The connector end of the flying umbilical cable must also be sealed, to prevent water from entering either the camera or the attached umbilical cable hanging down from it. The inside of the connector assembly is potted with an electrically compatible silicone sealing compound to prevent any water from entering the cabling system.

Sealing all of the various potential water entry points in a camera with moving parts is a much more challenging enterprise than it is for a fixed camera. It was necessary to develop several different approaches to solve all of the unique material interfaces that resulted from the operational requirements of the various components. In the end, though, it is very satisfying to be able to immerse the camera entirely under 3 feet of water and know that it is completely protected from any potential water damage.

~Dale Roche, Director of Engineering

WTI (Wireless Technology, Inc.)

www.gotowti.com or www.wirelesstech.com

Wireless System Installation Tips

When selecting a location for your WTI wireless video systems, there are a few important things you need to take into consideration.


1.) Line-of-Sight (LoS)

To achieve optimal performance, from any high frequency wireless device, a clear line-of-sight is necessary. Line-of-sight refers to a clear, unobstructed path between the transmitter and receiver antennas. The antennas produce an invisible beam that can be compromised by building obstructions, ground and/or water reflection. Well designed RF products can withstand a 20% loss of this invisible beam before performance reduction is detectable.

To get the best possible signal with your WTI wireless system, you need to have LoS or transmit through the least amount of materials on the peripheral of the LoS. Problems will occur when you try to transmit through any type of metal or steel-reinforced concrete. If there is a significant amount of metal too close to the transmitter antenna, reflected RF may cancel some of the transmitted signal and reduce the range and the quality of the signal. For maximum radio frequency (RF) propagation, a clear LoS is best.


2.) Antenna Height

Antenna height and line-of-sight usually go hand in hand, though not always. Many times LoS is achieved but the consideration that traffic may pass through the RF path is not always thought through. This scenario occurs often at truck depots, airports and shipyard installations. Mounting the antennas above traffic not only eliminates intermittent signal loss it also helps a link achieve optimal performance. By mounting the antennas as high as possible it will allow the link to operate in air space that is less crowded with other RF noise. Mounting the antennas above other RF noise gives the receiver less to contend with by allowing it to hear the information it has transmitted more clearly, therefore processing that information more efficiently and accurately. The bottom line: make sure that your wireless system will be mounted high enough to prevent traffic from passing between the transmitter and receiver. If the system is placed too low, the quality of the signal will be reduced every time a large object passes between the two antennas.



3.) Antenna Mounting

Make sure that each system antenna is mounted to a solid structure that does not allow for antenna movement during strong winds. Although WTI’s antenna design allows for small movements this tolerance lessens the further the RF signal must be propagated. A 30° movement on our 2 mile links with our patented phase array antenna would not affect the signal very much but the same movement on a 50 mile link could miss its target by miles. That being said: please keep in mind that our product mounting requirements dwarf when compared to the monstrous and rigorous concrete and steel mounting required for super higher frequency microwave, a simple solid pole will do.


4.) Testing

It is good practice to bench test your WTI system before installation. Even though WTI is an ISO 9001:2000 certified company with a strict quality control processes, equipment can be damaged during shipping or a miscommunication to what was ordered could take place. This is why the equipment should be tested at the shop. Bench testing allows for confirmation that the correct equipment was shipped, that it works properly, and it builds confidence in the overall system operation before the permanent installation.

We’re not done yet! Before permanently mounting the system, we also recommend testing the system at the site where it will be permanently mounted. This will ensure that the system is working properly at that site and not affect by other RF that may be in the area.



These are just a few basic things that can be done to ensure a working installation. By following these tips we hope to reduce and/or eliminate the risk of your installation exceeding its estimated time and cost. WTI’s products are designed for easy installation and we understand the temptation to just put it up and let it ROCK but its always good practice to test before hand. In the long run this will save you money!



Here are two forms to help you plan your next WTI (Wireless Technology, Inc.) wireless system installation.

Wireless Application:
http://www.gotowti.com/Info/WTI_WirelessSiteSurveyForm.pdf

Ethernet/IP Application:
http://www.gotowti.com/Info/WTI_EthernetSiteSurvey.pdf



~Eric Myers, Director of Wireless Products