SD memory cards are not created equal. Because an SD memory card works in your digital camera, doesn’t necessarily mean that it will work with your stand-alone data logger. When used in a digital camera, the rate at which data is written to the SD card isn’t critically important. Sure, if you’re using a slow SD card, you may have to wait a second or two before taking another picture, but ultimately you’ll capture an image. When acquiring data however, the flow of information is constant, and the faster you sample, the faster data must be written to the SD card. In addition, because the data logger is anticipating a steady stream of data, when an interruption occurs, the whole process comes to a screeching halt.
Determining which SD card to choose is complicated by the fact that most manufacturers do not strictly adhere to industry standards. An SD card produced by one manufacturer can have completely different characteristics than a card manufactured some place else.
In most instances, speed and capacity are key. Take DATAQ Instruments line of stand-alone data loggers, for example. Regardless of the manufacturer, cards must be Standard SD (not SDHC, SDXC, etc.), with a capacity no greater than 2 Gigabytes. Further, a new breed of SLC (Single Level Cell) memory cards promises performance at the maximum rate of our hardware (see the nearby picture).
To avoid the hassle and get an SD card that’s guaranteed to work at the sample rate you require I’d recommend purchasing SD cards directly from the manufacturer of your data acquisition equipment. DATAQ Instruments’ part number 101014-2G is a high-speed SLC SD memory that’s sold as an accessory to any product that operates stand-alone using an SD memory card. It’s also included in all discounted Bundle versions of hardware and software combinations.