M228 1MSPS Aperture A/D (Part 1)

We are excited about our newest M-Module, the M228 1MSPS Aperture A/D. In fact, we are so excited that I'm planning not just one, but a series of articles about this module, this being part 1. This module has some unique features that position it well in the data acquisition market.

First the basics: The M228 is a 1 Mega-sample per Second (MSPS) 14-bit A/D Converter capable of sampling and storing differential analog signals (up to +/-60V) at a rate up to 1MSPS. All samples can be stored at the specified sample rate or an aperture feature allows real-time selective storage of samples based on software configuration. A 32-bit timestamp is stored along with the data to allow correlation of stored data with real time. The data and the timestamp are together referred to as a time-value pair. The M228 is capable of storing up to 32M time-value pairs in onboard RAM.

The aperture feature will be discussed in detail in part 2 of this series but it merits a brief description here. The basic behavior of the aperture feature is that an aperture window will be configured using aperture high and aperture low settings. When an A/D sample is within this window, the data is discarded. When an A/D sample exceeds this window the sampled data is stored along with its 32-bit timestamp. The aperture windows (there are actually 2 aperture windows) can be configured in many different ways providing a lot of flexibility in how the user configures the M228 to selectively store samples. For example, the aperture window can be fixed to absolute values or can be relative to the last stored value in which case the window will move along with the analog signal whenever it exceeds the current aperture window. Again, the details of the aperture feature will be discussed in part 2.

On a side note, the notion of selectively storing data is a concept that we term data extraction. At a higher level, we classify it as transient data acquisition. In data extraction, the hardware is configured to extract only the data that is of interest to the user thus reducing the amount of data that needs to be stored and reducing the amount of software and processing power needed to analyze the data. In addition, since the hardware knows which data is of interest, it can be programmed to perform other task on events that cause data storage such as generating interrupts and triggers. C&H Technologies has a number of products that fit the descriptions of data extraction and transient data acquisition. An overview of those products can be found here.

Finally, an A/D converter module is only as good as its analog front end. Like the aperture feature, this will be the topic of a future post in this series but it merits a brief description in this post. The M228 has a highly flexible, software-configurable analog front-end including the selection of a programmable Elliptic anti-aliasing filter, a programmable Bessel anti-aliasing filter or a direct (filter bypass) mode. In addition, programmable amplifier and divider circuits allow for sampling of differential analog signals of up to +/-60V. Further, calibration adjustments and a storage EEPROM for calibration values allow system level calibration to ensure precise measurements.

As you can tell, the M228 is a highly capable data acquisition module. With the flexibility of the M-Module format, it can answer many data acquisition challenges, regardless of the environment. Stay tuned for parts 2 and 3 where I will discuss more details about the unique features of this card.