WorldWide Drilling Resource

WorldWide Drilling Resource ® 16 JANUARY 2015 Making a Silk Purse Out of a Sow’s Ear by Britt Storkson Owner, P2FlowLLC In the early days of electronics, much time and research was spent studying the thermal stability of semiconductors. All materials’ properties change with temperature, and electronics materials are no exception. Most materials expand when heated and contract or solidify when cooled, which can cause all sorts of problems when proper clearances must be maintained. Not only did the semiconductor material (in most cases the element silicon) need to be able to withstand thermal cycling (repeated heating and cooling), but the wire bonds connecting the silicon to the leads needed to be maintained or the internal connections would break off. That’s not a good thing, as it’s likely the part would be rendered useless if even one connection broke off. To be useful, electronic parts must have a very little temperature “drift”. It’s not possible to get zero drift, but small amounts are acceptable. Microproces- sors can also compensate for tempera- ture drift by measuring the temperature, then adjusting calibration values to cor- rect for temperature variations. With electrical resistance, when the resistance of a material goes up with increasing temperature, it’s called a positive temperature coefficient. Con- versely, when the resistance of a material goes down with increasing temperature, it’s called a negative temperature coef- ficient. Copper wire has a positive tem- perature coefficient...meaning the resist- ance of the wire goes up with increasing temperature. This is why copper wire must be “derated” for use in high-tem- perature applications. It means larger diameter wire than normal must be used because the electrical resistance is high- er at higher temperatures. While temperature changing the property of materials may be viewed as a negative, there is another aspect we need to consider: Repeatability. If the material always exhibits a certain re- sistance at a given temperature, we can make a temperature sensor out of it. This is what thermistors are. While the material’s resistance changes, it exhibits a known resistance at a given tempera- ture, so it’s useful for temperature meas- urement. And there is yet another aspect we need to consider: Linearity. Linear means “straight line,” and it can be graphed as a 45-degree straight line. Simply put, it means if you double a value, then anoth- er value will also double. If you double the voltage in an electrical circuit through a fixed resistance, then the current (am- perage) will also double. This is a “linear” relationship. While the thermistors are great for temperature measurement, they are nonlinear...meaning when the temper- ature doubles, the resistance does not change in a linear fashion. For exam- ple, doubling the temperature does not double the resistance. However, it is repeatable. So it is useful for tempera- ture measurement. We connect a known resistance to it with a known voltage feeding it, and we will get a predictable voltage at the voltage divider it created. By measuring this voltage and “looking up” the corre- sponding temperature in a table stored in memory, we can determine the tem- perature at a certain point cheaply and reliably. Software is cheap and reliable, so it is well suited for this task. So while certain materials may not have desirable properties upon initial examination, they may have other prop- erties which can be utilized to make a less costly, yet very usable and reliable product. Yes, you can make a silk purse out of a sow’s ear. Britt Britt Storkson may be contacted via e-mail at michele@ worldwidedrillingresource.com Focus on UCT Celebrating its 20-year anniversary, UCT (Underground Const ruct ion Technology) International Conference & Exhibition will again be held at the George R. Brown Convention Center in Houston, Texas. The 2015 dates are January 25-30. Adding up the numbers, UCT offers 10 training courses for industry certifi- cation, both before and after the event. Primary program tracks - 14 of them - will ensure you have what is most rele- vant to your business. These include horizontal directional drilling operations, productivity, and fluids management; along with sewer construction and reha- bilitation. Plus, UCT has more than 90 information-packed sessions to help you understand the new technologies and products showcased in the exhibit hall to stay on top of the latest safety, regu- latory, and operational issues impacting the way you do business. Nearly 200 companies, including WWDR , will have displays in the exhibit hall January 27-29. There’s something for everyone who deals with sewer, water, gas/electric utilities; pipeline construc- tion, maintenance, or rehabilitation; or telecommunications. Contact kfrancis@uctonline.com or go to www.uctonline.com for more information. The WWDR camera found the T&T Carbide Team ready for business during the last uCT.