In this series of blog posts, we provide a few examples of real-life situations and detail the best way to anticipate problems, save time, money and frustration. In each of our subsequent posts, we will deal with another “best practice”—taken from our field and manufacturing experiences. I invite you to comment or share your thoughts so that we may all learn and prosper from each other. What is that expression, "all ships rise with the tide?" Happy reading, friends, and colleagues.
Integrating a display into a subsystem, whether it is a 24-inch large display for an operator console or a 15-inch rugged panel PC controlling a gun system, may seem like an obvious and straightforward task. Those in the field with real-world integration experiences have a different perspective, however. Multiple factors influence the performance of a video link, regardless of the type of display.
Knowing the video sources
Like most projects, it is critical for a display manufacturer and a customer to align their expectations and performance success metrics upfront—at the beginning of the engagement. Most customers do not initially share a lot of information about the architecture of the system the display will be embedded into. On the surface, a display seems like a pretty simple item to integrate, yet many of the systems we deal with, such as a weapon control station, a multifunction operator console or a large 55" 4K damage control panel, involve many customer-controlled subassemblies that may rely on obsolete legacy video sources.
Assuming that the video feed provided by the customer always meets today’s standards is like shooting in the dark: that may work, but then again, it may not. The issue is the time it takes to diagnose and rectify the situation when the inevitable happens: the final performance of the video link falls short of expectations. A recent representative example worth noting was the request for an HD-SDI port as an alternate video input on a 17” display, without mentioning that the video feed was delivering a 30 Hz signal. The video controller planned for this project was capable of HD-SDI @60Hz and unable to handle a 30Hz signal. This last-minute discovery ended up creating a five-week delay to adjust the ultimate configuration.
Best practice #1: knowing the video sources (whether it is a computer generating a still picture at a given resolution and frequency, a fast-moving video, or a camera feed used as a picture in picture input...) is mandatory to allow the display manufacturer to identify and test each singular component during the design phase and test phases, explicitly with all the video configurations required, prior to shipping.
Understanding the hardware configuration
Avoiding post-delivery issues requires spending the proper amount of time getting grounded in the customer’s system architecture. When you run a rapidly changing high-resolution video on display, it increases the risk of video degradation that can be noticed by the human eye and will flag the need to do a careful evaluation of the complete video link. The typical questions related to the use of KVMs, the length, and nature of the video cables and connectors, the number of cable connections, the type of computer or graphic cards present in the system, the video ports that will be used to feed the display, the nature of the power supply, etc.
Those questions are primary to the usual and mandatory environmental requirement questions. This discovery step should also be conducted by trained engineers. As an example, experience has shown that KVMs are not created equal and that 5 or more DVI segments, each with MIL connectors, are not a rare occurrence in operator consoles. These 2 points alone are sufficient to generate poor video results, especially for high-resolution signals, regardless of the quality of the display itself. The blame is usually rapidly put exclusively on the display because “that’s where the problem became noticeable.”
The experience acquired when dealing with various HMI defense systems allows us to identify these potentially problematic situations quite rapidly and suggest standard design rules to correct or mitigate risks. Among the first ones that come to mind: avoid non-amplified KVMs, verify that EDID files can be read by the computer through the KVM, avoid a high number of cable segments between the computer and the display, carefully specify custom DVI cables by paying attention to twisting and shielding pairs close to the terminations, especially when video signals are expected to be close to the maximum bandwidth of a DVI link.
Another recent example, representative of such a situation was brought to us by a customer complaining about noise coming from the display. The same display was passing all factory tests with no issue, regardless of the video input. We ended up sending one engineer on site to investigate further and finally discovered that the neutral and phase lines were wired incorrectly in the power supply feeding the display. Swapping those two wires addressed the issue, after one month of back and forth.