Video Multi-Meters Find Niche In CCTV Market
Video Multi-Meters Find Niche In CCTV Market CCTV technicians can use upgraded technology to improve skill level, which can’t be measured in price
By Charlie Pierce
For more than 15 years, I have been a discernible oscilloscope technician. I have held on, with the last fibers of my being, to the belief that the only way to properly adjust a video camera and/or system was with an oscilloscope. I have watched as various hand-held video meters have appeared on the scene and I have waited. I have waited until I was convinced that we truly had meters that could be portable, save money and, most importantly, do an accurate job. Well, the time is here. Video multi-meters finally have their niche in the market and are reaching for their potential.
Video multi-meters are somewhat limited in their individual capabilities compared to the oscilloscope. Thus, you will need at least two meters to do the job of one oscilloscope. Unlike the oscilloscope, however, these meters require little or no training, can be used straight out of the box, are significantly less intimidating and cost substantially less. The two most common meters on the market today are the video meter and the synchronizing meter. As with all solid state tools, there are several things that you should review prior to purchasing one of these meters.
There are four important criteria when choosing which video meter to invest in: readout, flexibility, accuracy and durability. I purposely omit size and cost. The size varies only slightly; they range form fitting into the palm of your hand to being held comfortably with one hand. Cost, in my opinion, is never a factor with any quality tool. First, you usually get what you pay for; second, a good tool that is properly used will pay for itself in a short time.
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A video signal is made
up of three important parts:
video, pedestal or black level, and
synchronization pulses
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I understand that your company doesn’t pay for your tools and you have house payments to make. I also understand that you want to be a professional, make more money and be considered irreplaceable. This means investing in yourself and reaching out to become the best that you can. Cost is not a factor.
Currently, there are several different types of video multi-meters on the market. Some units are climbing LED scales to give their measurements; other use digital displays. LED scales tend to hold cost down, but digital displays lend to the accuracy of the results. Some meters measure the video signal in voltage (peak to peak) while others measure the video signal in IRE units.
IRE units were established as the true measurement medium for video in the late forties. It wasn’t until the sixties and the increased availability of the oscilloscope that we started relating the video signal in peak-to-peak voltage measurements. A video signal is made up of three important parts: video, pedestal, or black level, and synchronization pulses. Color signals have the above as well as a color burst. Composite video is the combination of all three pieces measured together. Each portion of the video signal has its own separate level. Video should measure at 100 IRE (0.7143 volts peak to peak). Sync should measure 40 IRE (0.2857 volts peak to peak). In color cameras, the color burst will measure 40 IRE, and the composite video signal on all cameras should equal 140 IRE (1.000 volts peak to peak). A good hand-held video meter will give you the ability to measure sync, luminance (video white level), composite video and color bursts individually. In addition, you should be able to set the focus and/or back-focus of the camera, based on the video signal. The better the meter, the more variety or options for measurements you will have.
One key portion of the video signal that we used to balance the iris of the lens to the camera is the luminance, which is the white level of the video. Too much luminance will result in a bright, washed out picture. Too little will give you a flat, low contrasting, blah picture. Wide-bank oscilloscopes, unless equipped with an IRE luminance filter, combine the luminance with the chrominance of the video signal. To the inexperienced technician, this combination of signals can result in false readings on the oscilloscope that can be 10% to 20% higher than the true luminance. Quality, hand-held video meters will have an IRE luminance filter built in. This ultimately makes the hand-held meter a more accurate tool for adjusting manual and auto irises than the oscilloscope.
One problem that has developed with the introduction of electronic shuttering in cameras is low video signals. This is primarily due to the fact that activation of the electronic shuttering cuts back on video level out-puts of the camera. If the iris is not properly compensated after initiation of the electronic shutter, video levels will remain low and pictures will be poor. Again the oscilloscope was the best tool for the field technician. However, this notion has been challenged and beaten by the hand-held digital video meters.
Another feature that a quality digital video meter offers is focus, which is accomplished through the high-frequency levels of the video signal. It is not always feasible to have a monitor in the field. In addition, monitor screens can favy in focus accuracy. A well-trained, experienced technician can use an oscilloscope to set the focus on a camera without a monitor. A novice, with a quality hand-held digital video meter can set the focus of a camera without a monitor and be as, or more, accurate than if they had used a monitor. (Where were these meters when I was in the field 15 years ago?)
In multiple camera systems, it is always important to ensure that the composite video levels of all cameras are balanced to each other. Nothing is more aggravating than watching a series of cameras switching where one picture is bright, one flat, one dark and another altogether different than the other three. In addition to the aggravation of viewing an out-of-balance system are the technical problems, including picture rolling, horizontal tearing, jumpy playback and poor resolution. Signal losses (assuming the use of appropriate copper coaxial cables) are quite often attributed to partial or complete short circuits between center conductors and shields, double terminations of the video cables, lock of termination of the video cable or improper impedance connectors. Regardless of the cause, the problems must be identified and corrected. In the past, the oscilloscope was the only tool that gave the well-trained field technician the ability to identify signal losses. Today, with the use of high-quality, digital video meters, a field technician can quickly and easily narrow in on a whole barrage of signal symptoms.
Digital video multi-meters can be used to measure luminance-to-chrominance level inequalities. This is the slope loss of the video signal in the high-frequency range, cause by long cable runs. In simpler terms, this information will help the field technician determine whether to install a simple video amplifier or a more complex line equalization unit. The major problem in making these types of readings with the hand-held units is that a color camera must be installed, temporarily, in place of the black and white camera at the end of the line, because the hand-held units use the color burst to do comparisons. If you used an oscilloscope to do the same “slope loss” checks, you wouldn’t need to switch to a color camera. This is one advantage that the oscilloscope still holds over the hand-held meters. The end result in installing a proper amplifier and balancing it to the cable accurately will be improved picture detail and resolution.
The one point where I am still a strong supporter of the filed oscilloscope is in the location and identification of noise in the video signal. Hand-held meters can save you time and money in making a large variety of accurate video level adjustments. They cannot, however, show you the type of RF or electromagnetic noise that is infecting your video signal. Likewise, these meters cannot show you if the noise is traveling on the video or sync; the oscilloscope is still the only tool that does this well and can be used a s a major troubleshooter. If I had to advise today as to which is the better investment, I would sway the serious field technician toward a high-quality, hand-held, digital video meter. I would save recommendation on the field oscilloscope for the companies that were installing 100 cameras or more per year. Even then, the oscilloscope would be a consideration after the video multi-meter.
One feature that I look for in all field tools that work on batteries is “timed shut-down.” This means, simply, that a unit will shut itself off after a predetermined amount of time. I for one am constantly forgetting to shut my field meters off, which results in arriving at a job site and not being able to use the meter because of dead batteries. Some video multi-meters have auto-shutoff circuits and some don’t. If you never forget to turn off the power to your equipment, don’t worry about it. If you are like me, you will look for this feature and engulf it.
When comparing the durability of the video multi-meter to that of the field oscilloscope, there is no contest. Oscilloscopes have a CRT that is easily knocked out of center if the unit id dropped or bumped. Hand-held meters are 100% solid state. This gives them the advantage of going to the field as a partner of the technician. It doesn’t mean the technician can drop the units from 20 feet. And expect them to stay in one piece. It does mean that if an oscilloscope and a video multi-meter were both knocked about and dropped equally, the multi-meter would stand a better chance of surviving.
As far as cost of the various hand-held video multi-meters compared to oscilloscopes, there is a large gap. Low end video multi-meters start in the $100 range, while your higher-quality, digital units will be closer to $500. Oscilloscopes start on the low end at $600 or $700 and go as high as your imagination.
I am sold on the ability of the hand-held, digital, video multi-meters. I finally have been impressed and look forward to carrying my units into the field versus lugging my oscilloscope with me everywhere. There are still times where I will not be able to work without an oscilloscope, due primarily to the advanced nature of my position in troubleshooting video signals. I can honestly say, however, that for the first time in 15 years my portable oscilloscope, a long and trusted friend, is starting to gather dust as I refer to it less and less. My new-found, hand-held, digital friends, on the other hand, are starting to show the battle scars of field work as the nicks, bumps and knocks earn them a position in my respect of accuracy, ease of operation and easy portability.
