Multiplexer Application & Troubleshooting Guide

Multiplexer Application & Troubleshooting Guide

Introduction

Can you get anything out of an applications and troubleshooting guide if you are not the technical type? I hope so. There are many technical explanations in this book which are designed to be understood by anyone who wants to know more about what multiplexers do. Each application reviewed in this text provides information which can help them sell and support the product. If you knew all this information, you would be viewed as a knowledgeable source of product information.
What information is covered in this book?

The Basics: What is a multiplexer?

Multiplexers provide a complete package which allows multiple cameras to display on one monitor and record on one VCR. Multiplexers combine the functionality of several devices in one unit. Multiplexers are an economical alternative to individual components, providing single panel control of a small video security system. We could go on an on. There is no single definition of a multiplexer. They are multi-functional devices which combine the capabilities of several devices in one box. A top line multiplexer does all of the following:
View multi-screen while recording all cameras to tape.
Record on one VCR in the background while reviewing a tape from a second VCR.
View a variety of screen formats, live and playback.
Use alarm inputs to alert the attendant.
Connect with a VCR – switch to a faster speed on alarm.
Video loss alarm.
Camera titling.
Sequential switching.

Multiplexers have all the functionality you would want in most small CCTV applications. They are not designed to do everything. They are building blocks. You will be amazed how much additional functionality can be had by installing a switch.
How do multiplexers display cameras on the monitor? The incoming camera images are digitized and resized to fit into the blocks in the multi-screen display monitor. We will call this the “main monitor.” There is a second monitor output from the multiplexer; called the “call monitor.” This displays full size images which have not been digitized. The camera inputs are just redirected to the call monitor with no digital processing. Want to see the difference between an image which has been digitized and one which has not? Just put the same full size image on the main and call monitor. If you can see the difference, it’s probably because one of the monitors is out of adjustment.

The multiplexer timeshares camera images to the main monitor. If a single full sized image is displayed, it is displayed at a rate of 30 images per second (25, PAL). This is “real time,” just like television. We always send 30 images per second to the monitor. If we display a picture in picture format, we still send 30 images to the monitor. Fifteen are of the main image and fifteen are of the insert picture. Somewhere around 22 images per second, our mind views the image as fluid motion. With a 2×2 screen, the 30 images are divided by four for a total of 7.5 images per second of each image. It is now obvious that the images are not “real time.” The division holds true in the 3×3 and 4×4 screen formats. So the more images you see on the screen, the slower each image updates.

The digitized (sampled) image is processed in a pixel array with 512 pixels horizontally and 464 pixels vertically. In order to make a full size image fit into one of the 2×2 blocks, we need to get rid of some of the information. Every other horizontal pixel and every other vertical line is discarded. Does the resultant picture look as good as the original? Of course it can’t have the same detail, however, the results are surprisingly good. To make the full size image fit in a 4×4 block, we throw out three fourths of the pixels in each direction. No, these small images do not look as good, however they are so small that you hardly notice. How well the image looks with the remaining data depends on how well the program processes the original data. In the 2×2 screen scenario, we discard every other pixel. The program analyzes both the discarded and remaining pixels, then adjusts the remaining pixels accordingly. How elegantly this process is done is more important than the actual number of pixels used.

How do multiplexers record to tape? What goes to tape is unrelated to what is displayed on the monitor. We control the timing of images sent to tape to correspond with what the VCR is expecting. When images are recorded, the VCR is in control. We must accommodate the VCR.

The multiplexer has two issues to be concerned with. In one instance, we can’t switch images as fast as the VCR can record them. In the other instance, we must slow down our switching rate to accommodate the VCR in time-lapse mode. When the VCR is recording at a real time rate (2 hour mode,) it is recording 60 fields per second (same as a home VCR.) Ideally, the multiplexer would switch through cameras at this 60 updates per second rate and we would get really fast updates. The problem is that multiplexers can’t go that fast. There are limitations in the hardware used. We must capture an image, write coded information into the vertical blanking interval and switch to the next camera. Most multiplexers switch at a rate of 20 times per second. Some newer versions (including our new simplex) can switch at 30 times per second. The higher speed is due to upgrades in circuitry. In the “real time” application, we switch as fast as we can and the VCR records it all. Playback speed will be dependent on the record speed.

In time lapse mode, the VCR is capturing fewer images. The VCR has a field delay, which means that it sits idle for some number of fields, then captures a single field. The mechanism typically steps at each capture, rather than stay in continuous motion. There is no standard for field delay on VCRs. Different manufacturers have different field delays at various time lapse settings. The result is a timing problem. There are three possible ways to accommodate this issue.

1. Work with every imaginable VCR manufacturer and VCR to acquire the field delay information, then write a routine in the multiplexer firmware to evoke this information on demand. This can be a long, hard, difficult task. New models are coming out every day. (Most multiplexer manufacturers do it this way.)

2. Write the multiplexer program to be flexible enough to work with any VCR, regardless of the VCR field delay. This is the method we use. Just set the VCR speed and the multiplexer speed to the same number. This works because it takes a worst case position, ensuring that all cameras will update. The down side is that we could update faster (and do) if we know the VCR field delay and set our time to a more appropriate setting. The up side is that you don’t have to think about it. It just works

3. Wire the VCR timing output directly to the multiplexer. This is the ideal situation and future multiplexers will be timed in this manner. In effect, the VCR tells the multiplexer when it switches to another camera and the multiplexer switches with it. Most VCRs now have the switched output available. Some do not, so, the other methods will have to be maintained for these VCRs.

How do multiplexers display cameras on a monitor?
How do multiplexers record to tape?
What’s the difference between simplex and duplex?
What’s the difference between activity detection and motion detection?

The Nuts and Bolts

This section contains an in-depth view of the multiplexer rear panel. It will explain the purpose, functions and what to expect from each connector. The signals at each BNC connector are composite video. Each BNC connector is intended for a particular purpose, however, since a standard video signal is involved, it can be used for any purpose.
Camera inputs: There are 16 camera input BNC connectors. These inputs are expecting to see a 1 volt peak to peak composite video signal. This signal typically comes from a camera, however, it can come from any video source (VCR, monitor loop out, etc.)

Camera outputs: There are 16 loop out BNC connectors. These connectors are a convenience for sending camera inputs to additional devices.

Main monitor out: This BNC connector provides multi-screen video for display on a monitor. Depending on the buttons selected on the multiplexer front panel, it will display full screen images, sequenced images, picture in picture, 2×2, 3×3 and 4×4 displays.

Call monitor out: This BNC provides full screen images. The camera displayed is selected from the multiplexer front panel (or, remote panel,) or, selected as a result of an alarm input.

VCR Out: This signal is intended for connection to a VCR input for the purpose of recording multiplexed images. It outputs alternately switched cameras at a speed based on the VCR record setting selected in the menu. Time, date and camera information is encoded in the vertical blanking interval.

VCR Input: This input is intended to receive the playback output of a VCR. The multiplexer decodes this input and displays as selected by the operator.

* The VCR in and out can be used to connect multiplexers “back to back.” See the applications section for details.

S-VHS Out: This connector provides S-VHS output for recording on an S-VHS recorder.
S-VHS In: This connector receives the playback output of an S-VHS VCR.

* When the VCR BNC outputs are used, the S-VHS connectors are disabled, and vice versa.

Power Connector: This input power connector is expecting 12 volts DC from a wall mount power supply. All multiplexers use l2VDC at 1.5 amps. This is the minimum requirement.

Remote connector: The 25 pin connector allows remote control of the multiplexer, either from a remote panel (up to 1000 feet distance,) or, from a remote source of ASCII commands (typically a PC.)

Alarm Connector: This connector allows one alarm input per camera. Alarm inputs will work as contact closures, or, UL (0 – 5 volts.) There is a contact closure alarm output intended for use with a VCR.

A discussion of what the multiplexer is expecting to see at its inputs and outputs.

Lookout!

This section alerts you to things that go bump in the night. When your equipment interfaces with a variety of equipment supplied by a variety of manufacturers, you can bet there will be situations where each will exhibit a mind of its own.
Lookout! Do you have a device triggering your VCR into the record mode, like an alarm input through a multiplexer, quad, or, another device? There are situations where you could lose valuable data recorded on a tape.

Most time lapse VCRs, while recording, will accept an alarm input which will trigger the VCR into “real time” speed for some period of time. Most VCRs disable this feature while the tape is being played back. After all, you are probably playing back the tape in the same VCR you recorded on, install in the same system. An incoming alarm which triggers the recorder to record, could write over potentially valuable images already recorded on the tape.

The danger arises while the tape is stopped. Some VCRs will still accept that alarm input and start the VCR recording, with potentially negative results. Make sure you protect your recorded data by disabling the alarm input to the VCR while reviewing a tape. Using two VCRs, one for record and another for playback is the safest way (the playback VCR will not have an alarm input wired to it.) A switch wired into the alarm lead is very effective for single VCR applications. Breaking the write protect tab on the valuable tape is a good safety precaution.

Being aware of the potential danger is crucial. Know what your VCR is going to do when an alarm is encountered. The VCR and multiplexer must work together. Only the VCR knows for sure whether it is recording, playing back, or, sitting idle.

Things to look out for – Cameras: We accept most cameras used in the industry. We are looking for a one volt peak to peak composite video signal with no DC offset. Most modern cameras follow this convention, however, you can run into lots of strange situations with existing installations.

We are looking for a signal with a very low voltage level. The standard video signal is a composite signal which contains video, horizontal sync pulses and vertical sync pulses. This is also called base band video, which is the NTSC standard with out the carrier frequencies and lots of other things used in broadcast video. These signals are combined so they can be sent through a single coax cable. The device at the other end separates the signals and uses them accordingly.

The horizontal sync pulse is a negative going pulse, centered around a zero volt reference. If the reference raises very far above the zero volt level, the sync pulse is no longer negative (below 0 volts.) If it is too high a reference it may damage the input of the multiplexer. High, but less than danger level high, will result in loss of sync and a continually rolling picture. There is a fringe area where the picture will roll occasionally, or, continually jump up and down. Try to use cameras you are familiar with. When installing the multiplexer in a system with existing cameras, be careful. Why would a camera have a DC offset? There are a few cameras which provide power through the same coax as the composite video signal. Whatever you do, don’t use these cameras with the multiplexer. Improper grounding could provide any number of problems.

Things to look out for – Monitors: Generally, monitors are more forgiving than most devices. Monitor manufacturers know that they are going to see a wide variety of input levels from old, new and soon to be developed cameras. A camera with a DC offset, which will not work through a multiplexer, will probably work fine when connected directly to a monitor. Is it a monitor, or, a television? Televisions are showing up more and more often in CCTV systems. There are several things to consider. Price is certainly is one consideration. You can probably buy a nice 31″ TV for the same price as a dinky little monitor. So, size and price are certainly on the side of the TV. Before you run out to the local home appliance store, consider this:

A TV will probably have RCA connectors for video. This requires an adapter to BNC and they can fall out.
You will have to set the TV to a “line,” or, “direct” mode to accept composite video. Otherwise, you will have to install a modulator on the video input.
TVs over scan (the edges of the picture run off the viewable area.) This may cause the time/date to run off the top of the screen and/or the camera titling to run off the edge of the screen. Typically, there are no screen size adjustments on televisions.
TV resolution is generally lower than a monitor.
The larger the monitor, the poorer the picture (you are displaying the same number of scan lines on a larger surface.)
Multiplexers sample each scan line and convert the results into a pixel matrix which is processed, then converted back to standard video for display. The resultant video will have a black line around the edge of the viewable picture. Such a black line on your home TV would certainly be considered a problem. This is done intentionally with the multiplexer. This allows full viewing of each camera in multi-screen modes. If we over scanned the image, we would lose a large portion of the images around the perimeter of a 4×4 screen.
Things to look out for – VCR: The VCR is often the most complicated device in a CCTV system. Did you ever try to set the time on your home VCR? Just think how difficult things can get with time-lapse VCRs. There are many manufacturers and types of VCRs. We run into almost all of them in a variety of applications. Let’s start with some basic definitions of VCRs. What is the accepted terminology for the different types of VCRs? Like most devices in CCTV, there seems to be several terms used for description of each device. What is the meaning of standard, industrial, commercial, home style, time-lapse and 24 hour real-time VCR?

Standard: This is anybody’s guess. Standard means different things to different people. We need to be more descriptive. We don’t know if the speaker is referring to a standard home VCR a standard time-lapse VCR, or, some other interpretation of standard.

Industrial: This too is anybody’s guess. Industrial usually refers to something rugged, typically used in industry.

A discussion of what to expect from devices connected to a multiplexer.

How’s That Again?

This section contains explanations of phenomenons associated with multiplexer technology. There are tradeoffs which must be made in order to record multiple cameras on a single VCR tape.

Are we recording frames, or, fields?
A frame contains twice as much information as a field. A frame is a consecutive odd and even field of the same camera. In multiplexing and in time-lapse recording, where individual fields of alternating cameras are recorded, there is no opportunity to reassemble consecutive fields of the same video source. Therefore, virtually all multiplexed and time-lapsed applications utilize fields, not frames. In order to fill the screen, the information from the missing field is still needed. This is typically accomplished by duplicating the content of each scan line of the existing field on the following line. This process is called line doubling.

Why can’t I “fast search” a tape recorded with a multiplexer?
First, what’s the difference between fast forward and fast search? Fast forward is like rewinding a tape, only in the opposite direction. The heads are moved away from the tape and the tape is wound quickly. You can not see images while the tape is in fast forward. Fast search is when the tape is moved past the playback head at four, or, five times the normal playback speed. In this mode, the images appear to be moving very quickly with four, or five lines running through the picture horizontally. Most people erroneously say fast forward when they are talking about fast search.

So why are the lines on the screen in fast search? With a typical home style VCR, you are usually viewing a movie which is a single video source with what appears to be continuous motion. Video is actually a series of still images displayed closely together in time to give the impression of fluid motion. The individual “fields” of video are recorded on the VCR tape in a long diagonal strip. The VCR usually plays back the individual fields in order, and you see the resultant moving picture. When the tape is moved past the read head very rapidly, the head scans across portions of several of these strips of video at the same time. The lines shown on the screen are the dead areas between the fields of video. The fields are separated in time by 1/60th. of a second (NTSC, 1/50th. PAL) so the result is what appears to be a fast moving picture with lines running through it. A time lapse VCR in “real time” two hour mode acts identically to the home VCR.

What’s different about a multiplexed tape? Multiplexers record several cameras on one VCR by time-sharing images to tape. With four cameras, you are recording one camera at a time while cycling through all the available cameras (1,2,3,4, 1,2,3,4, etc.) The advantage is that some images of all cameras are recorded on a single tape. The disadvantage is that the recording of each camera is not continuous. When the tape is played back, the system decodes whatever is on the tape. You can view a single camera, or, several cameras in multi-screen format. When you fast search the tape, you still get the horizontal lines which separate the portions of each consecutive field. This time, however, the field portions are from different cameras. You see fast motion, horizontal lines and strips of different camera views. How do you fix this? You can’t. It isn’t broken. It is a limit of the technology. This is one of the trade offs necessary to allow multi-camera recording on a single VCR.

Why do I need a multiplexer to play back a tape recorded through a multiplexer?
Using the information we learned in the previous section, we know that the multiplexer causes the recorder to record fields of alternating cameras. The multiplexer encodes the time date and camera number in the vertical blanking interval following each field. When played back, the multiplexer decodes this information and displays the camera views which you select with the multiplexer front panel. If you play back the tape without the multiplexer, no decoding takes place and you see exactly what is recorded on the tape, changing images of several cameras. The speed at which the images change depends on the record speed used when the tape was made. A “two hour” tape will be unintelligible, with rapidly changing images (20, or, 30 per second) depending on the multiplexer used to make the recording.

In an “emergency,” with no multiplexer available, you can see still images if the playback VCR has a pause/still function. Press the pause/still button to stop the tape. You can then single step to your heart’s content. You will quickly agree that using a multiplexer is a more attractive alternative. When the tape is played back through a multiplexer, the individual camera images are decoded and displayed as selected from the front panel. You can view individual cameras, PIP, 2×2, 3×3, or, 4×4. In fact, any screen format you can select in live mode may be selected in tape playback, as well. The update speed is limited by the speed at which they were recorded and the selected playback speed.

A discussion of some phenomenon’s associated with multiplexer technology.

Troubleshooting

This section contains information on isolating problems. This is divided into two parts. The first part addresses isolating problems in a system which contains a multiplexer. The second section provides information for bench testing a multiplexer.
Troubleshooting on Site

Troubleshooting a system containing a multiplexer isn’t much different than any other type of problem isolation. You need to know a few things which are specific to our multiplexers, however, most of the process is common sense. Video system problems are relatively convenient to isolate because you don’t need test equipment for most problems. You can isolate using the cameras and monitors available on site. Typically, one end of all the cameras will conveniently terminate at the multiplexer, or, in the same room as the multiplexer.
If a problem is reported, there is indeed a problem. Test the system to see if you can make it fail, rather then to see if you can make it work. If it does not fail, you need to have the person experiencing the problem work through the system operation with you. Identify where they were encountering the problem. If the error does not surface at that time, work with the operator to determine what other factors come into play which could be causing an intermittent problem. Is the complete system powered from the same source? Could components be powered off from other locations? Is operation carried out correctly by all operators? Etc., etc., etc.

General Questions: Establish whether this is a new problem, or, one that always existed.

Did the system ever work? Is this a new problem, or, was it always this way?
Have you ever tried to use this function before?
If this was a recent failure, what happened around the time of the failure?
Has anyone been working on the system, or, installed any new equipment?
The operator is the best person to ask. Ask what problem they have encountered. Listen to the answers, but, don’t rely on the information. Operators report symptoms. The actual problem may lie in an area other than reported by the operator. Symptom recognition: Take a quick overall look at the system. See if the reported problem is evident during your initial test. Symptom elaboration: Perform all functions of the system. Look for any additional symptoms and problems. You may uncover additional symptoms which were not reported by the operator. Often the reported problem is easier to solve when additional symptoms are revealed.
Isolating the faulty system component: No video when pressing camera button number three on a multiplexer may look like a defective multiplexer, however, it could be a bad camera, lens, cable, or, any number of other things in the system. Your troubleshooting abilities are limited by the test equipment at hand. Having a known good test monitor, camera, VCR and test cables make the job much easier. Testing on the bench in your repair shop allows easy access to all components in the system. The troubleshooting methods change from shop to field. We will discuss both scenarios. Field problem isolation: Obvious problems are just that. Obvious. No power to a monitor can be determined easily (no power light, no power cable, etc.) We will concentrate on a total test of a system once the obvious has been eliminated. Even with no test equipment available, some part of the system must be working. You can use the working parts to isolate the problem. Start by assembling a basic video system, (camera, cable and monitor.) Connect a camera directly to a monitor. Do you have a picture? This part must work before going on to anything else. If you don’t have a picture, is the monitor plugged in and powered on? Is the power light lit? Are the monitor switches and knobs adjusted properly? (Intensity turned up, A/B switch in the right position, etc.) Is the coax cable connected to the right input connector? Is there video coming out of the cable? Does video still come out if you wiggle the connector? This is where the test monitor comes in handy. If you don’t have video, any of the components in this small system can be bad (monitor, cable, camera.) Try a different monitor. Wiggle the coax cable to see if the video appears. (Remember that the most common problems are defective coax cables.) Try another camera input. If you are fortunate enough to be able to see the camera, does it have power? Is the lens adjusted properly? Once you have convinced yourself that you have these three basic components working properly, you are ready to investigate the rest of the system. Tee connectors, and/or, barrel connectors are good to have. Connect one of the connectors to the incoming video cable, then test a few other cables by connecting them from the input video cable to the monitor. Wiggle them at each connector end to ensure that they are really good cables. Reconnect the incoming video cable to the multiplexer camera input. Press the live button on the multiplexer, then press the largest multi-screen display button (2×2, 3×3, 4×4.) Do all the attached cameras display? If one, or, more inputs are missing, connect the known good camera into the missing camera input. Does it display properly? If so, you need to investigate the defective camera and cable input (the camera is often out of sight, far away, perhaps on a roof top somewhere – good luck.) Don’t overlook the obvious. Make sure that all the cameras are selected. Press the select key, then all the cameras in order to fill the multi-screen display.

Once all the live multiplexer functions are known to be good, we need to test the tape playback capability. With duplex multiplexers, there is a test mode which will allow you to let the multiplexer directly decode its own coded VCR output. Disconnect the two video output cables which connect the multiplexer “VCR in and VCR out” to the VCR. Connect a short coax cable from the multiplexer VCR output connector to the multiplexer VCR input connector (they are right next to each other.) Press and hold the “Function” button, while pressing the “tape” button. Hold both buttons for a few seconds. The multiplexer will switch to the playback mode and display images at the rate it normally sends updates to the VCR based on the menu setting, (VCR record hrs.) With this menu setting to 2 hours, the images will update at a rate of 20 per second, (30 on some newer models) divided by the number of cameras attached. Check out all the “live” functions. You are actually testing the live and playback functions. If everything works up to this point, the multiplexer is working correctly. Press the live button to exit this test.

Before removing the multiplexer from the site, do a factory reset. Strange things which may have scrambled the multiplexers memory may be overcome by a simple reset to a known condition. See the “Undocumented Multiplexer Functions” section for information on resetting various multiplexers.

VCR Problems: Check the “Lookout” section for a quick review of different types of VCRs if you are not already familiar with this topic.

Isolating problems in a system.
Isolating multiplexer problems on the workbench.

Undocumented Multiplexer Functions

MV9Oe series (includes MV94e, MV99e, MV96e, MV16i.)

Hold in the “function” button while pressing:
Menu = Enter the menu.
Up Arrow = “Soft reset” to factory menu settings.
Down Arrow = Color bars (no function in these models.)
Left Arrow = Alarm count screen (on later models only.)
Right Arrow = Toggle time/date on/off.
Tape = Diagnostic mode (decodes its own output when a cable is connected from VCR out to VCR in.)
Holding in the highest number camera button while applying power provides a hardware reset which configures the unit properly for Robot brand.
Hold camera 4 button and apply power = MV94e.
Hold camera 9 button and apply power = MV99e.
Hold camera 16 button and apply power = MV96e & MVl6i.
* This will happen regardless of the number of camera inputs. (Ex. If you hold in camera button 4 on an MV96e, it thinks it is an MV94e.
Holding in the “next to highest” camera button while applying power provides a hardware reset which configures the unit for American Dynamics brand. There will be some minor differences in the menu. The time/date screen will say “Chromaplex.” There will be no color bars on the menu screens.

MV209 and MV216 additional items:

“Function,” “Down Arrow” = Motion set-up summary screen.
“Function,” “Left Arrow” = Alarm summary screen.

Older multiplexer versions (MVI6E, Mv94, Mv99, MV96.)

On the oldest units, the “Function” button is labeled “CTRL” for control.

“Function,” (or, CTRL) “Up Arrow” does a soft reset to factory menu settings. There is no warning screen. This can be done accidentally.

“Function,” “Down Arrow” and “Function,” “Left Arrow” have no effect.

“Function,” “Right Arrow” toggles the time/date only on software version 1.3 and 1.4. The date can not be removed on earlier versions.

To perform a hardware reset, hold in the #3 camera button while applying power.

Older Simplex Versions (SMV99, SMV96, SMV16.)

Limited functionality.
“Function,” “Seq.” = enter menu. No others active.
“Function.” Up Arrow” = reset to factory menu defaults.
New Simplex (SMV9O4, SMV99, SMV916, SMV1O4, SMV116.)Hardware reset is accomplished by holding in the highest camera button while applying power.
“Function,” “menu” = enter menu.
“Function,” “Up Arrow” = reset to factory menu defaults.
“Function,”” Down Arrow” no function.
“Function,” “Left Arrow” Alarm count screen.
“Function,” “Right Arrow” = Toggle time/date.
Functionality Test – Duplex: The overall functionality of a duplex multiplexer can be verified by performing a “loop back” test. Install a cable from the VCR in to the VCR out connectors on the multiplexer. Hold in the “function” button while pressing the “tape” button. This puts the multiplexer in a mode where it will decode its own output. The decoded video will display on the screen. The update speed will be dependent on the record speed set in the menu. Set the unit to the fastest speed for best results. The loop back function (cable from VCR out to VCR in and pressing Function/Tape) will not work on simplex units. It does not have the circuitry to do both encoding and decoding at the same time.
To reset AD multiplexer versions, hold in the next to the highest camera button while applying power.

A list of multiplexer resets.
A list of functions

Typical Multiplexer Applications

Multiplexers are one of the building blocks used in designing a CCTV system. The type and number of multiplexers will vary with the application. The questions to ask yourself are:
What are you trying to accomplish? Define success so that you will recognize it when you see it.
What is the primary objective? What really needs to be accomplished?
What additional functionality would be nice to have, if the price was right?
What additional functionality is likely to be needed in the future?
Once this is established…
What components do we need to assemble to provide an acceptable solution for the application?
Sometimes it is relatively easy to add additional hardware later to enhance system capabilities. Sometimes it is not. You need to consider this in designing the system. If you have an existing simplex multiplexer and now need duplex features, you must make an expensive change. Working closely with the customer during the initial system design will help avoid an unexpected surprise in the future. A duplex multiplexer might be the right initial choice even though all the features are not needed immediately.
Remember that multiplexers are one of the building blocks in a system. Sometimes more than one multiplexer is appropriate. VPD multiplexers come in 4, 9 and 16 input versions. Why not 32? The law of diminishing returns comes into play at some point. We are time sharing (multiplexing) camera images to tape. These are played back with a time delay between updates of each image, based on the number of cameras in the cycle. At some point, that time delay makes the whole idea of recording all the cameras on one VCR seem less attractive. It just takes too long to see anything happen. It is more practical to use a second multiplexer and VCR.

Are you limited by the functionality of the multiplexer, or, are you limited by the budget of the customer? Don’t limit your thinking to what a multiplexer can do. Design a solution to the problem first. You can compromise on price versus functionality later. It could take a second multiplexer to do all the things that the customer wants to do at one time. However, all the items might be performed one at a time by a single multiplexer. An example:

We are often asked why you can’t view all cameras live on one monitor while reviewing a tape of all the cameras on the second monitor. If you paid attention to the simplex/duplex descriptions in this manual, you already know the answer, there just isn’t enough hardware for one multiplexer to do this. Could we redesign a multiplexer to make it view multi-screen live while playing back multi-screen? Perhaps. However, we wouldn’t have enough hardware left to do the recording. This would not be a practical device as all customers would have to pay for this additional functionality when only a few would use it. Could you assemble such a solution now? Sure you could.

You can view 16 cameras live, record the same 16 cameras and review a tape of the 16 cameras, all at the same time. This requires two monitors, two VCRs and two multiplexers. Use a duplex multiplexer to view live and record. Use the second VCR to playback to the simplex. You have two monitors side by side, both multi-screen, one live, one playback. Want to see two different views of the live cameras? Loop the cameras from the duplex to the simplex. You have two independent live displays when you are not using the simplex for tape review. You can use two additional monitors as call monitors. Want a tape with only alarm images recorded? Use a third VCR on the loop out of the duplex call monitor. Leave the VCR in idle and have the multiplexer trigger it to record on alarm.

Don’t limit your thinking. Your design ability and the customer budget are the real limits. Most multiplexers are installed into applications with 16, or, fewer cameras. Few are as elaborate as the situation described in the previous paragraph. Although almost any combination of devices is appropriate in installations with a large number of cameras and particular customer needs, most small systems using multiplexers fall into the following categories:

View Only.
Record Only
Review only.
View and Record.
View and Record and Review.
View Only:(Config #1). The objective with this configuration is to allow the operator to manage the cameras available in the system. Minimum requirements to accomplish this objective are; cameras, a simplex multiplexer and a monitor. As long as there is no need to record the cameras, this system is complete. You can enhance attendant capabilities by adding a Call Monitor and installing alarm inputs to alert the operator to important events.
Record Only:(Config. #2). The objective with this configuration is to record images for later review. Minimum requirements to accomplish this objective are; cameras, a simplex multiplexer and a VCR. A monitor is not necessary, however, it is a good idea to have some viewing capability to ensure yourself that the system is actually working. Many record only Systems are locked in closets and available to authorized personnel only. Often the tapes are routinely picked up and taken to another location for storage and review.

Review Only:(Con fig. #3). The objective with this configuration is to review tapes which were recorded at other locations. Minimum requirements to accomplish this objective are; a simplex multiplexer, a VCR and a monitor. The type of VCR used must be compatible with the VCRS used at the record locations.

View and Record:(Config. #4). The objective with this configuration is to allow an operator full control of live viewing of cameras while all cameras are recorded to tape. Minimum requirements to accomplish this objective are; cameras, a duplex multiplexer, a monitor and a VCR. Attendant capabilities may be enhanced by adding a Call Monitor and alarm inputs to alert the operator to important events. This configuration is typically used to review tapes, as well, using the same VCR. Of course, while tapes are reviewed, the VCR is not available for recording. Care must be taken to disable the VCR alarm input to prevent accidental recording while a tape is reviewed. It is better to use two VCRs, one to record, a second for playback.

View and Record and Review:(Config. #5). The objective with this configuration is to allow an operator full control of live cameras, record all cameras to tape and to review previously recorded tapes, all at the same time. Minimum requirements to accomplish this task are, cameras, two monitors, two VCRs, and two multiplexers (a simplex and a duplex). Often people ask for this functionality, then settle for the View and Record configuration. It depends on how serious the application is for reviewing tapes. If the previous days tape must be reviewed while the current information is being viewed and recorded, you really need two systems (View and Record, and, Review Only). Using both configurations in the same application allows you to observe two different multi-screen displays of live video when the playback system is not used to review a tape. For instance, you can watch a 4×4 display on one monitor and a 2×2 on another, or, two 2×2 screens with the lower quadrant(s) sequencing. Alarms will show on the call monitor.

A listing of the most common multiplexer applications

Additional Multiplexer Applications

Multiplexers are building blocks. They can be used along with other devices to solve almost any application challenge. The following capabilities are worth consideration:
Remote Control.
Multiplexers “back to back.”
Multiplexers combined with camera control.
Multiplexers controlled with HyperScan.
Multiplexer compatibility with other devices.

Remote Control:(Config. #6). Most VPD multiplexers can be controlled remotely by a remote panel which has the same appearance as the multiplexer control panel. Control signals are sent through telephone type wire with RJ11 connectors at each end. The maximum recommended wire length is 1000 feet. New versions of the remote panel are addressable and will operate up to 16 individual multiplexers. Older versions were designed for single multiplexer control. Both styles will allow you to loop to additional control panels (five total).
Any device capable of providing ASCII commands can control multiplexers remotely. ASCII commands emulate all front panel functionality of the multiplexer.

Multiplexers “back to back.”(Config. #7). The encoded output from the multiplexer VCR out connector is intended to be recorded by a VCR. The tape of encoded information is later decoded when sent to the multiplexer’s VCR input connector. You can eliminate the middle man (the VCR) with a duplex multiplexer by looping back the output to the input. The “loop back” test (hold in Function, while pressing the Tape button,) will allow the duplex multiplexer to decode its own output. This is a great test. It is not available on simplex multiplexers because there is no hardware to “loop back” to.

You can connect the VCR out of one multiplexer to the VCR in of another. This allows you to send up to 16 encoded cameras on a single coax cable. With a duplex multiplexer, you can do it in both directions. Imagine that you have two buildings with 16 cameras each. Connecting the encoded video between the multiplexers allows you to see the “local” cameras in “live mode,” and the remote cameras while in “tape mode.” The update speed is limited by the VCR record speeds set in the menus of the multiplexers. The “back to back” solution has been used in a variety of applications. Do not overlook the standard remote panel as it allows direct control of the “remote” multiplexer.

Multiplexers combined with camera control:(Config. #8). A Touchtracker Dome control device may be used in conjunction with a multiplexer. The Touchtracker (VM16, or, ADTT16,) controls the domes and the multiplexer view from the convenient hand control.

Multiplexers controlled with HyperScan:(Config, #9). HyperScan receiver software version 2.2 provides remote control of the multiplexer display through phone lines. This allows a single HyperScan transmitter to view 16 cameras through a single camera input. The update speed for all 16 cameras in 4×4 mode is the same as a single camera update.

Multiplexer compatibility with other devices: All input and output video from multiplexers is standard composite video. This will allow devices which convert from NTSC and PAL to another form, then back again, to work in conjunction with multiplexers. The multiplexer has nothing to do with transfer of information. The degree of success achieved is dependent on the capabilities of the transfer devices used.

Other devices can control the multiplexer’s functions by sending ASCII data to the appropriate pin on the remote connector. “Compatibility” is limited to the ability to duplicate the same functionality available at the multiplexer front panel. The external device will not add additional functionality to the multiplexer. It will add additional functionality to the overall system by allowing control from somewhere other than the multiplexer front panel.

A listing of additional multiplexer capabilities worth consideration

Application Diagrams

Drawings showing typical multiplexer applications.


This manual provides general information about system components which are used in conjunction with multiplexers. It is intended as general background information which can be used by salespeople as general product knowledge, by technical support people to explain operation and applications, and by technical people to isolate and solve problems associated with multiplexers.

Design Philosophy

KISS: Keep it simple stupid. Don’t make me think about it. Just make it work.
Easy to use.
Easy to install.
Extremely reliable.

We make multiplexer products which are reliable, easy to install and ready to use. The feature set is designed for a mass market. Almost everyone will use the multiplexer as it is defaulted at the factory. Most installers change only the time and date and set the record speeds.
There are many things to consider when installing a multiplexer. There are features which may be turned on, or, off to accommodate a particular application. If you do not know about a feature, or, don’t know how to use it, we don’t punish you by making you figure it out before you can use the multiplexer. The most common mode of operation is set as a default from the factory.

We provide an elegant product which is the best combination of feature set and ease of use. Some of the newer entries in the multiplexer market allow you (and in some cases, force you) to go through a check list of activities to customize the unit to the installation site. They too make a trade off between functionality and ease of installation and use (lost of function – at a price.) Is it worth a few hours of set-up time to customize the feature set for a particular operator (often aggravating other operators,) or, would you rather be done in fifteen minutes? The argument can be made that you only do the set-up once, so, the extra effort is warranted. I would counter that the set-up is only done once because it is so difficult to do that no one wants to go through the process again. Our on screen menus make it easy to change settings. Operators often change settings when they start a shift.

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