WorldWide Drilling Resource

Active vs. Passive by Britt Storkson Owner, P2FlowLLC In computer controls/electronics, we have two basic com- ponent operations: active and passive. Active means “doing something”. The part does not just sit there. It is actively engaged in monitoring or impacting the circuit in one way or another. Passive means “not doing something”, but it is there to affect/impact the circuit in a positive way. An active device actively operates to prevent this or that problem, or adds value to the product in one way or another. A good example is airbags found in many cars on the road today. A sensor called an accelerometer constantly meas- ures the g-forces acting on the car, and triggers the air bag if sufficient force is sensed in one or more directions, deploying the airbags to cushion the car occu- pants during a crash. A passive device is put there to prevent any problems. One good example of this is seat belts in a car. They are there because many studies have shown car occupants have a much better chance of survival if they stay in the car during a crash. The advantage of passive devices is they require very little, or zero, power to operate. The disadvantage is they don’t have any “smarts” and they don’t make any decisions. While passive components are more reliable, they are more limited. Sometimes it is wise to substitute active devices for passive devices, or vice versa. One time, I was asked about a water pump that would vibrate when starting up when it reached a certain RPM (revolutions per minute). This was only obvious at about one-half of the full-speed RPM, but the pump motor had to travel through the vibration zone when ramping up on start-up or ramping down on shutdown, and the customer was concerned the vibration could be a problem over time. The pump supplier came up with a partial fix for this condition, which was to skip through the problem RPM band. When the pump reached the problem RPM areas, a program was written to quickly skip over this band and get into the non- problem RPM band as soon as possible. This was a simple and inexpensive fix, but did not take into account the fact these pump characteristics often change over time and wear. This vibration condition was a dynamic (changing) condition, while the program was a static (unchanging) solution and was incapable of adjusting to any changes which could happen over the life of the pump. A better solution would be to install an accelerometer which would detect the vibration level, and if the vibration exceeded a certain level, then quickly ramp up the pump speed if it was accelerating or ramp down the pump speed if it was decelerating. This makes it self-correcting and able to change as pump conditions change. This approach also has the advantage of detect- ing a major problem condition, like a rotating part coming loose or breaking off and resulting in a very destructive vibration. The computer control can be programmed to shut off the machine immediately and generate an alarm if this happens. Accelerometers are now relatively in- expensive and widely available, and are useful for detecting vibration or motion. A simple computer control can read the accelerometer and make decisions re- garding what to do about the condition. Oftentimes, this can mean the difference between a minor shutdown or an expen- sive repair. Britt Britt Storkson may be contacted via e-mail to michele@ worldwidedrillingresource.com 302-684-3197 FAX: 302-384-0643 142 Broadkill Rd. • Milton, DE 19968 www.atlantic-screen.com email: atlantic@ce.net Manufacturers of Slotted & Perforated Pipe ranging from ½” to 24” diameter Atlantic Screen & Mfg., Inc. • Well Rehab. Products • Manholes • Bentonite • Filter Sock • Inline Chemical Mixers • Sampling Bailers • Clear PVC Pipe • Locking Caps 23 WorldWide Drilling Resource ® FEBRUARY 2018