Optimizing Test Time Part 4, The Nerves

This is the final part of our four-part Optimizing Test Time series, in which we look at the ‘anatomy’ of an automated test system and how the various parts can be made to perform faster. The four key areas for test time optimization are:

We’ve reviewed test software (a smart “brain”) to mastermind the test operation and data collection, test instruments (strong “muscles”) performing the test execution, and synchronization (the “heart”) to coordinate the test operations. The last piece of the puzzle is the connectivity bus, or the “nerves” of the automated test system.

Connectivity bus refers to the communication link between different instruments and the test system controller. For standalone instruments, this would be the likes of GPIB, RS-232, LXI, and USB. For modular instruments, it is typically VXI, PCI, or PXI. (See our previous post comparing the different connectivity technologies of standalone instruments.)

These nerves connect all the parts together and are vital for ensuring that the messages that transact between the brain, heart and muscles are delivered as quickly and as accurately as possible. Below, we look at the aspect of throughput, or the rate of successful message delivery, in analyzing connectivity.

Bandwidth and Latency

Bandwidth is the most common factor that is considered when looking at connectivity bus performance. Bandwidth tells us the data rate, or speed of data transfer between two or more points, typically measuring the download or upload of data in a certain period of time. If test equipment is not properly optimized, bandwidth delays can skew the test results.

The other parameter to consider in throughput is latency. This is a measure of time - how long it takes for the data to be transferred from source to destination. For measurements of single or few data points, which means the size of the data block is small, latency should be given higher consideration, as bandwidth may not have much impact. A typical example of such measurements would be a few cycles of “open channel - make single point measurement - close channel” sequence. Some busses have higher overheads in the packets, which increases the latency.

When the chunk of the data that needs to be transferred becomes sufficiently large, bandwidth of a bus usually dominates the throughput performance. Typically, measurements that involve multiple data points (e.g. waveforms) or burst readings fall into this category. Ultimately, it boils down to how many bytes of data are being transferred and how many of them are large data blocks when determining which parameter – bandwidth or latency - will have the biggest impact on overall test time optimization.

In conclusion, careful consideration of the four key areas we have covered in this series - test software, test instruments, synchronization and connectivity bus - is required to help you fine tune and improve your test times and throughput. Do you have questions about optimizing your equipment? Contact MATsolutions, and we’ll be happy to work with you.