Application rules: How to choose a system to match your needs

Sep 1, 2000 12:00 PM, CHARLIE R. PIERCE

As I travel around the world talking about the use and application of CCTV systems, I hear a recurring theme: "How do I know what equipment to use?" ... "Who has the best this or that?" ... "Should I use this camera or that one?" There is generally too much worry about which piece of equipment to use and not enough thought given to where the equipment will be used and under what circumstances. Unfortunately, the misdirected emphasis reflects how little planning goes into the design of the CCTV system being equipped. Don't get me wrong, there will always be times when two or more pieces of equipment will meet the needs of an application. However, if done properly, the application will drive you to the equipment that you need, not the other way around.

A technique I have used for years is to develop shopping lists. Think about it. Have you ever walked into a grocery store with money in your pocket, hunger in your belly, and no list? I remember my wife sending me out, several years ago, for a single gallon of milk. I came home with three bags of junk. It looked good when I bought it all, but in the end, it was three bags of junk and I forgot the milk. The same applies to purchasing CCTV equipment. If you have money in your pocket, a general need, but no list, you will end up with a couple of bags of junk and you'll forget the milk. Especially if you are into gadgets, under pressure to produce, or hungry.

So where do we start? Logically, I should work in a straight line from the camera to the controlling system, one piece of equipment at a time. Over the past 50 years, little has changed in the typical CCTV application. It's just that now you have more options and tools available to achieve our visual goals. Golden rule number one: A CCTV system is a camera, transmission method and monitor. Nothing more. Starting with an example, Camera Number 1, let's list our needs and specifications. Once this task is accomplished, choosing equipment is a matter of comparing specification sheets to find the piece(s) of the puzzle that fit best.

Camera 1 will be installed on a 30-foot pole in the west parking lot, which is 250 feet long and 150 feet wide (see illustration at right). The tower will be mounted 50 feet from the south side of the parking lot, centered. We will need it to provide general surveillance of the overall lot and be able to identify individual(s) walking across the far side (about 300 feet away), at night, dressed in black. The camera will have a general area swing of 180 degrees panning from the east to the west across the north side of the parking lot. Camera 1 will be used for general observation from 8 a.m. to 6 p.m. seven days a week and for specific identification of individuals and activities at other times. Obstacles to view include several small trees (average of 15 feet tall) and lamps, at 50-foot intervals between parking rows and running perpendicular to the straight-out view. The camera will be installed in an open area exposed to four seasons and to full elements of weather.

Based on this description, we have already begun our equipment specification list. We now know that we need a camera of specific sensitivity and resolution, a zoom lens, and a pan/tilt. We know that the camera will be facing the sun from time to time and that we will have some obvious blind spots.

Step one: We determine the sensitivity requirements of the camera. This specification is determined by the minimum amount of reflected light from the parking lot (at night) minus the amount of lens light loss in full telephoto. The formula would look like this:

ambient light times reflective base - lens light loss factor in full zoom position

We have an average of 0.09 fc (foot candles) of ambient light at the farthest point of observation. A black asphalt base has a 5 percent reflection. So, 0.09 times 0.05 equals 0.0045 fc available light.

The lens of preference (8 X 80mm zoom) has a f-stop of 2.8 at full telephoto, two f-stop difference from the camera's testing lens of f-1.4. Each f-stop equals an individual 50 percent decrease in light passage. So, we divide 0.0045 fc (reflective light) by two, two times (equivalent of subtracting 50% twice).

0.0045/2 = 0.00225/2 = 0.001125.

Rounding up to three or four points, the net result is a sensitivity need of 0.0011 fc of light using an 80mm zoom lens at night.

Step two: We determine that the average person, at 300 feet, using a zoom lens with a telephoto range of 8mm to 80mm, on a 1/3-in. formatted camera, will be within a 16-foot-wide area at the point of recognition. I choose a 1/3-in. camera during my lens calculation.

It could have been a 1/4-in., or 1/2-inch or whatever. However, to determine the size of the overall scene or what lenses we might have available, we must know the camera format size. So, using a 1/3-in. formatted camera with an 80mm zoom lens, and trying to identify a two-foot wide person (overall U.S. average), our object of identification will take up a little more than a third of the overall horizontal scene.

Step three: As a consequence of the above, and for the purpose of identification, we will most probably require a higher resolution camera. Somewhere between 400 (minimum) and 520 horizontal lines should do the trick. (We can verify the choice with a live demonstration prior to commitment, however. It's not a high-resolution camera, but it's not the bottom of the line either.

Our shopping list is growing. Camera Number 1 will now be a 1/3-in. format with a 0.001 fc or lower sensitivity, 400 (minimum) to 500 horizontal line resolution, using a 8mm to 80mm zoom lens, on a pan/tilt. Additionally, since we have determined the minimum resolution necessary to produce a good, identifiable image, we can add 400 HL, or higher, resolution to our recorder and transmission method lists. The resolution of the system will depend on its weakest link.

The next step is to add to our list(s) any features or automation we may need at our camera location. In this case, after careful consideration, several items come to mind:

First: Noting weather considerations we realize that our housing will need a heater/fan assembly.

Second: To enhance our system, I would also like to have a digital zoom capability built into the camera or controller. The physical zoom of the lens will ensure clarity; however, I may want to get a closer look. A digital zoom enlarges the camera's image beyond what the lens can provide. (Note that digital zooms are limited by the resolution or quality of image they start with.)

Third: Considering the overhead parking lamps and to avoid problems of iris shut-down (caused by direct view of the lamps), we will want to either reverse the bright lamps or ignore them completely. So we add the requirement to our undefined capability list. Remember, it's a list of capabilities we want, although we aren't sure if they exist or if they're affordable. It is easier to investigate a list of "undefined" features all at once, versus doing each one individually as we go.

Fourth: Because we will be looking into the sun from time to time, we might want to consider backlighting compensation.

Fifth: There are several homes neighboring our parking lot. To avoid any incidents of our guards looking into windows, either by accident or with purpose, we should add image blocking technology to our system. It goes on a list and will, in this case, need to be a separate "black box" technology, since our application will call for specific digital blocking capabilities (windows) versus blocking entire quadrants as some controllers do.

Now ask yourself a question: Is the application leading us to some very specific decisions about what equipment we should use or purchase? Answer ... Yes! Let's go back to what we know about Camera Number 1. We have plenty of information to direct our choice of a specific piece of equipment.

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© 2008 Penton Media Inc.

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