WorldWide Drilling Resource

Responding toVarious Conditions by Britt Storkson Owner, P2FlowLLC Often, we humans must respond to various conditions we encounter. If we’re driving a car in winter, and we notice ice on the road, most responsible drivers will reduce their speed to match the conditions. Computers can do it too. We don’t have computers capable of independently driving a car...yet. The reason we don’t is because computers are not able to make decisions intuitively. Intuitive means having the ability to understand or know something without any direct evidence or reasoning process. Or we could add: without any programmed reference. A computer must be pro- grammed to respond to every condition it will encounter during its lifetime. If there is no “reference” for the computer, it will either simply not respond or respond incorrectly. For example, with our variable speed water pump control unit, we need to define in the software how fast it responds to changes in pressure. We have the target desired pres- sure we want to maintain and the system pressure...the pressure the system currently measures. Even though our goal is to keep the “target” and the “system” pressures the same, often they are not the same because of water usage increasing or decreasing the pres- sure relative to the speed of the pump motor. The higher the pump motor speed, the more pressure and volume the pump delivers - and vice versa. This is also a nonlinear relationship...meaning doubling the pump motor speed does not necessarily double the pump pressure and volume. This is because the pump efficiency is different at different pump motor speeds and fluid flow rates. We will call the difference between the target pressure and system pressures the “Delta P”. If the system pressure is lower than the target pressure, we cannot simply increase the speed of the pump motor. This increase in speed must be timed so we don’t overshoot the target pressure and get a rapid cycling condition...violently speed- ing up and down, up and down. This is not good. Not only that, how fast we need it to respond depends on the Delta P we have. If there is a large Delta P...like when the pump is starting from zero pressure...we don’t want slow ramp up times because it would take a long time to achieve operating pressure. Likewise, we do not want fast ramp up times because the system pressure will overshoot the target pressure and will keep going. We need the best of both worlds. The trick is defining this in software and utilizing other computer tools to make this happen. One way we can do it is by making a lookup table and storing it in memory. For this task, we need to read the Delta P and then lookup the corresponding time delay value that works best for that particular pumping system. Generally, the smaller the Delta P value, the shorter the delay time should be. This is because you want the pump to respond quickly when near the target pressure to quickly zero in on the target pressure. The larger the Delta P value the longer the delay time should be to minimize the effects of inertia when pump motor speeds up or slows down for smoother operation. With this method, different timing de- lays can be programmed for ramp up and ramp down routines. This, combined with the fact all of these values are fully adjustable and stored in nonvolatile memory (memory that retains its values even after the power is turned off), gives us the ability to fine tune the pump operation for best results. The cost for all of this computing power? Literally pennies. All of these functions can be implemented with a microprocessor costing just a few dollars, and it can execute literally hundreds of other computer control functions at virtually the same time. People wonder why we have computers running nearly everything nowadays...that’s why. Britt Britt may be contacted via e-mail to michele@ worldwidedrillingresource.com 326()6 2,341(6/32 +43: 33*532 .32+ (9 # $ " % # & 1(/0 33*532 68)( 34- 888 6-8( 34- ! !!& # " ! " ! "4(*+ !.38 8 *7)(6/32 *7) 3 30, 380/2- "3742(1+26 4 7)6/32 34+ " $ " " " " & ! # % " " % " % #!" ' 337.332.0239 DRILLPIPESUPPLY.COM 10 ACRES OF: Drill Pipe Drill Collars Stock for Tooling Tubular Machine Shop IN STOCK: 6 5/8” OD X 5” ID DRILL PIPE 5 7/8” OD X 5” ID DRILL PIPE 10” OD X 5 1/4” ID COLLARS 11” OD X 5 1/4” ID COLLARS 23 WorldWide Drilling Resource ® DECEMBER 2015