Truly Synchronized Data

Even today, too many engineers are faced with using four different acquisition systems to record the analog, CAN (digital), GPS, and video data sources. This presents a terrible challenge when it comes time to make sense of it all. If the data are not synchronized to begin with (which is the norm, since the systems have no common time source), making a cohesive analysis of the data from all these sources is difficult at best, and impossible at worst. If you add in other important sensors and technologies, such as infrared cameras for measuring temperature on surfaces that you can’t easily make contact with (like a disk brake in a moving car, for example), or even high-speed video cameras running at hundreds or even thousands of pictures per second, the challenge is exacerbated exponentially.

But so, too, is the opportunity for greatness. Imagine if you could do all of that in a single, integrated platform, and that all the inputs were recorded in a synchronous way. This would clearly result in more meaningful recordings, and more importantly, a richer understanding of test results. Figure 1 shows the integrated display of analog sensor outputs, CAN bus data, synchronous video, and 200-Hz speed and distance outputs from GPS.

Tests like this formerly required multiple instruments for the acquisition, and an incredible amount of post-processing time due to the nearly impossible task of trying to synchronize the recordings from these disparate devices after the fact. But with today’s convergence of video, GPS, and analog data, all of these inputs are recorded and displayed in a truly synchronized way.

Figure 2. Aerospace acquisition from PCM data streams, analog, video, and IRIG sources.

For this application, a special interface called a bit and frame synchronizer, along with a decommutator, are used to receive and reconstruct the transmitted data. Normally, the digital data stream coming from the aircraft or spacecraft has hundreds of channels of information, at all different rates and bit depths. In this sense, PCM data is similar to the CAN bus data found in most cars. It is normally much faster and contains more parameters.