Articlets

IST Hardware tech tip 
January 2000 
Daniel R. Burk 
IST Applications Engineering 
mailto: support@isthq.com

Hello from IST Applications Engineering!

Here we are, in the cusp of the millennium. Some say that we in the beginning whereas some say 2000 is the last year of the millennium. I personally like to think of it as the apex, or peak of the event.  Only once in modern history has civilization experienced a year that ended in three zeroes.  The year 1000 was met with probably even more fear and trepidation than our own 2000: People were sure that the end of the first millennium spelled the end of the world. As for us, we had our own fears that "The Y2K bug" was going to spell doom for modern civilization. Well, it didn't.

Unfortunately for IST, though, the Y2K bug did present a bit of a headache. Our supposedly Y2K compliant compiler software wasn't. So, we built our latest windows software with these development tools, just to find that on January 3rd, the new software was reporting the date as June, 2005. This is a big problem, especially when you are trying to set up a data recorder. Luckily, the problem turns out to be external to our program code. It is a single, compiler supplied DLL file, located in the system directory. Therefore, we were able to get a Y2K compliant DLL, and build it into a self extracting file for easy download. If you are suffering from these date problems, just go to the Y2K page, download the appropriate file, and execute it once. The program will find the bad DLL and replace it. We apologize for any inconvenience. 

Understanding the Autozero Correction circuit. 
Do you have interest in acceleration information below 1 Hz? If so, you probably need to know more about the Autozero correction circuit(AZC). I've recently completed a study on the little known effects of the AZC, and this white paper is now on-line. Find it under the technical notes section of our web site, or click on AZC Revealed.
One story that I didn't include in the white paper involves a customer on the east coast who launches sub orbital rockets. They use our data recorders for measuring the acceleration forces during the flight. When they received some systems from another office, they forgot about autozero correction. These rockets experience 9 g of acceleration for close to two minutes of flight time, at which time the engines are shut down, and the rocket then experiences -1g of acceleration due to wind drag. The systems that they borrowed had the AZC enabled, and after a minute, the data showed acceleration levels dropping back to zero. Then, when the rocket engines were shut down, the acceleration dropped to -10g! This example shows how a constant, near-DC acceleration is affected by autozero correction circuitry. The purpose of this circuit is to correct for DC offsets from orientation change, or temperature drift. As a consequence, the DC offset caused by the acceleration of a rocket engine is also corrected out. When the rocket acceleration was suddenly replaced by aerodynamic drag, the new reference was shifted by 10 g.

What other types of applications could be affected by AZC?

vehicle dynamics, such as measurement of lateral acceleration
Hard braking maneuvers, such as panic stops
Skid tests on astronautic reentry vehicles, such as shuttle escape modules
Drop tests with 100g accelerometer equipped systems
Roller coaster ride analysis

In all cases, the primary frequency of the acceleration will be less than 1 Hz. If your application fits into this category, then check out the white paper. It also gives some ideas on how you can correct for the effects of AZC by building a virtual recorder in DynaMax Suite.

One final note: The EDR3C system has the ability to turn off the AZC during triggered events whereas the original EDR3 does not. In most cases, the AZC will not affect your measurements, and should be left enabled.