Advanced Technology Video presents…. CCTV from A to Z!. What is CCTV?. A Closed Circuit Television system may consist of a nothing more than a camera and a monitor…. Or it may be a very sophisticated system….
A to Z!
ATV, Inc © 2003
A Closed Circuit Television system may consist of a nothing more than a camera and a monitor…
ATV, Inc © 2003
…with many cameras, monitors, recorders, triggers, alarms, motion detectors, special lighting, wireless transmission, even network access!
Knowing how the equipment works will help you design, build, install and troubleshoot CCTV systems…
And will give you satisfied customers!
Cameras then (around 1975)…
Black and white, 330 lines
Color, 470 lines
Here’s a “portable” camera from 1952…
It weighs in at 60 pounds, including the back pack!
It starts, of course, with a camera…
…which takes pictures at 60 fps (fields per second), which is also 30 frames per second…
Each Frame of video is made of 30 Odd fields, and 30 Even fields.
When you watch TV, your picture is “painted” 60 times each second, first the Even fields, then the Odd.
You’ll need a monitor to watch your video on…
You mean you don’t want to sit in front of the monitor for hours?
Then you have two choices…
Hire someone to do it for you,
Or add a recorder!
So we add a VCR to your system:
…but they only record for a couple of hours,
so you need a time-lapse VCR!
We have a camera, a monitor, a VCR and some cable.
“Now I want more cameras!”
Let’s see what happens when I add just
one more camera to our system…
“How do I plug it into the monitor?!”
With 2 cameras, you could have 2 monitors…
Or we could find a way to show them both on one monitor!
Maybe a Switcher!
Switchers are pretty simple. All they do is simply switch from one camera to the next, and maybe allow you to attach external alarms, such as door contacts.
The problem of course, is that you can only watch, and record, one camera at a time!
And if you have a lot of cameras, there can be quite a gap between images!
“…with the switcher, I can only see one camera at a time!”
Boy, you’re hard to please!
“Can’t you show them both at the same time?”
Sure, but it’ll cost more!
Remember when we mentioned that a camera takes pictures at 60 fps?
That’s 30 Even fields, and 30 Odd fields, each second!
We can use this information to process the video!
If you look at a field on an oscilloscope, it will look something like this:
We can use the sync pulse to figure out where each of the pictures start!
…means that we get 30 Odd, and 30 Even fields from each camera, each second!
If we can measure the start of the sync pulse, and we know if this is an odd or even field, then we can process the video from each camera individually!
How cool is that?!?!?!
Oh, yeah… since we can now process the 2 cameras separately, let’s use a “Splitter” to put them both on a monitor at the same time… like this:
“But now I want 4 cameras!”
You’re becoming annoying…
With this many cameras, we need to replace the Splitter with a “Quad”.
We could even go up to 8 cameras by using a Dual-Page Quad!
“This is getting cool!
a time-lapse VCR, and some cable!
“…when I bring one up to full screen! Then it’s the only one getting recorded!”
That’s what a Quad does!
“But I want to record ALL the cameras, no matter what I’m watching!”
“It’s gonna cost more?”
“How much more?”
Enough to pay for a multiplexer!!
Remember the camera Sync Pulse?
A multiplexer, also known as a “mux”, collects the video signals from all the cameras, uses the sync pulse to stay in time and to know which camera is which.
Then it processes the video signal one way for the monitor, and another way for the recorder. It also places some code on the recording, so it can identify each camera on playback, along with info like labels, alarms, etc.
That way, you can watch whatever you want without messing up the recording !
A Time Lapse VCR and a multiplexer MUST be synchronized so that when you select a particular camera on playback, only the fields from that camera are displayed.
A T/L VCR only records at specific intervals, depending on the recording speed you have selected. In other words, to fit 24 hours (or more) of video on a 2 hour tape, something has to give to make room!
For instance, when recording at 24 hour speed, each camera may get recorded every 2 seconds or so. At 960 hour speed (1 month), the update, or refresh, rate will be around 22 minutes!
To keep the two units in sync, we use something called Camera Switching, or Record Trigger, which is simply two wires connecting the VCR and the mux, so that the mux can set it’s timing according to the VCR’s recording pulse rate.
If you looked at the signal a mux sends to the VCR, you would see all your cameras going by very quickly. That’s “multiplexing”!
A very important thing to consider when using a mux is that the video you see on playback will not be “real-time”. It will be time lapsed, meaning that there will be gaps in the movement on screen.
“What does that look like?”
It will look a little like an old movie, sort of like a Charlie Chaplin flick. Depending on the recording rate, you might see a person enter a room, then the next image shows them 5 feet further, or more.
If you need real-time video, with no information loss, like a lot of casinos demand, then you need each camera going directly to it’s own recorder. And that can get very expensive!
Well, yes, but there are a number of issues, both legal and technical.
“I want to record audio… can I do that?”
Legally, in the United States, it is OK to record video without peoples knowledge, but not audio. You have to post signs stating where you are recording audio.
…and there are technical issues too. For one, you can’t time-lapse record audio like you can for video. Generally, audio has to be recorded at at least 20 fps. And, on DVR’s audio can take up a LOT of hard drive space that could have been used for video.
“Wow, there’s more to it than I thought!!!”
What a surprise…
Of course you do…
“I’m tired of changing tapes!”
“And they wear out too soon!”
Guess what again?
Yep… now you need to replace the VCR with a DVR; a Digital Video Recorder!
“Will I be happy then?”
I doubt it…
Just kidding! You’ll love it!
There are a couple of ways we can do this. We can keep your existing multiplexer, and add a single channel DVR. That works with your mux exactly the same way a VCR does, and is less expensive than a full DVR.
Or you can replace both with a Multi-channel DVR, such as ATV’s “Falcon”. This replaces both the recorder and the mux, doing the job of both. It may also give you other options, such as remote access.
DVR’s give us some new options. Because of the limits of space on a hard drive, we still do time lapse recording but we can also decide to lower the image quality of each sampled image to make smaller file sizes… then maybe record at a faster rate and higher quality when there’s motion or an alarm is triggered!
We can do the things we did with VCR’s, but have even more options, and they’re usually easier to do!
Well, let’s take a look…
“I want to add some cameras…but there’s a problem…”
I’d be shocked if there wasn’t…
“A couple of the cameras I want to add are a pretty good distance from the mux…”
Let’s get “Twisted.”
“I don’t like anything kinky…”
I mean the camera cable!
We’ve run a lot of cable so far. All the camera cable has been “coaxial”, or coax, usually a type called RG-59. Here’s some useful info:
Cable type Distance
RG-59 coax 750 ft.
RG-6 coax 3000 ft.
Twisted pair 10,000 ft. or more
This assumes good quality, 95% braid cable, with only a connector at each end. Each additional splice costs you about 10% signal loss.
As you can see, unshielded twisted pair wire is handy for covering long distances, but remember: it requires a transmitter at the camera, and a receiver at the multiplexer, for each camera.
“You didn’t let me finish! I can’t read the license plates of the cars in front of my office… they’re too small!”
Leave school too soon?
We could install a PTZ camera…
“Are you making fun of my reading again?”
It stands for Pan / Tilt / Zoom! They are cameras like ATV’s OmniView camera, that can turn 360 degrees and zoom in, making that license plate appear up to 25 times larger. They can even be set up to trigger on motion!
With the PTZ, you’ll need a controller. It lets you program the special functions, like tours, presets and macros.
“What’s that little screen on the keyboard?”
ATV’s controller has an color LCD screen built in. And since you can also control the PTZ camera from the Falcon DVR, you can have the keyboard in a separate room. It’s almost like a free second monitor!
“Did you say Free?”
Just a figure of speech, don’t get excited!
That’s another option, like radio, or microwave,… You’ll need a transmitter and receiver for each camera, and one more thing to consider…
Some of these methods are line-of-sight only, meaning that the two locations, the camera and the mux or DVR, have to be able to see each other. There can’t be any obstructions in the way…
A number of ways; over phone lines, over the internet, LAN, satellite… it depends on how far you are from the site, what options are available to you at both ends… and what you’re willing to pay!
CCTV is a series of compromises. We want to see multiple cameras on a single screen, record them all, and do it at a reasonable cost. That’s why we use muxes, VCR’s, tapes, and now DVR’s.
To do this, we are willing to accept some things like time-lapse recording, and various levels of image quality.
I appreciate your business, I really do, but can you do me a favor?
We’ve got all your equipment installed, working great, and programmed just the way you want it…
Now promise me you won’t touch it!
“Oh… OK… I guess.”
Advanced Technology Video, Inc.www.atvideo.com