The Miniature, Rugged Alternative to LVDTs and Linear Potentiometers
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The Miniature, Rugged Alternative to LVDTs and Linear Potentiometers
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Rotary Transducer, Crack Displacement Sensor, Voltage Divider Calculator |
Position Measurement & Control - Issue 45
PRODUCT FOCUSSeries R: A New Angle On Rotary Transducers New Series R Rotary Transducers Offer Maximum Flexibility And Reliability Flexibility-it's the key to the success and market longevity of any mechanical device. It is also one feature that we try our best to introduce when we design our products. Rotary transducers can be used for a variety of purposes across a number of different industries. Each usage puts the transducer in a different situation, making the flexibility of the rotary transducer that much more important. SpaceAge Control's Series R rotary transducer features many customizable options while maintaining the integrity and durability synonymous with the SpaceAge Control name.
Figure A1 - The New Series R Rotary Transducer The Series R rotary transducer can handle up to 150 turns (54,000° rotation) giving a broad range of rotational measurement. Different situations require different signal output types; the Series R rotary transducer accommodates this with SpaceAge Control's exclusive FlexSignal™ signal conditioning pack, offering users the choice of a transducer with voltage divider, low-level bridge, voltage conditioner, or 4-20 mA (current loop) analog output options. To further user customizability, SpaceAge Control offers six mounting styles and five shaft choices. The schematic for a Series R rotary transducer with mounting style C1 is shown in Figure A2.
Figure A2 - The New Series R Rotary Transducer SpaceAge Control's design emphasizes repeatability and durability in addition to the Series R's customizable features. The Series R minimizes error by directly connecting the sensor to the shaft with SpaceAge Control's proprietary screw-driver technology. Independent linearity error can be as low as ±0.50% ensuring users high levels of accuracy. With a minimum shaft rotational life of 5 million revolutions and operational temperatures ranging from -40° to 185° F (-40° to 85° C), the Series R rotary transducer is designed for a long life in the most extreme thermal conditions. Lightweight (11 oz (312 g) nominal), customizable, and durable, the Series R transducer is designed for a long life of repeatable, accurate data collection. For more information, see the Series R data sheet or contact us. APPLICATION FOCUSCrack Position Transducers Series 150 Position Transducer Exceeds LVDT Performance for Crack Monitoring Task When is a crack not just a crack? When it expands and grows over time due to temperature, wind, humidity and other environmental factors, threatening the structural integrity of buildings and the safety of those involved.
Figure B1 - A Sensor Node / Potentiometer System Designed For Structural Crack Detection. This was the focus of Hasan Ozer's Master's thesis for Northwestern University's Department of Civil Engineering. Hasan proposed implementing modern wireless technology instead of traditional wired crack monitoring technology. This proposed wireless system consisted of sensor nodes (complete with operating system capable of online monitoring) wired to potentiometers. While traditional wired crack monitoring systems use LVDTs, Hasan wanted to use potentiometer-based cable position transducer because of their low power consumption (0.5 mA) -- a crucial aspect of uninterrupted operation for a system that was powered by only two AA batteries.
Figure B2 - Short-Term Dynamic Test Using Aluminum Blocks and the Series 150 Position Transducer To verify that his wireless position transducer system could provide the same data as a wired LVDT, Hasan created two tests: one for long-term monitoring under controlled environmental conditions and one for constant monitoring of dynamic disturbances. For his tests, Hasan used a SpaceAge Control Series 150 position transducer and a Macro Sensors DC-750-050 LVDT. For the long-term test, both sensors underwent a temperature cycle using different materials. This test used regulated, linear ±15 VDC power. Temperatures and materials were selected to expand and collapse the crack over the cycle. For the short-term dynamic test, the two sensors were wired to two separate aluminum blocks subject to impact loading. A small weight of 0.1 kg was dropped from various heights to impact the block and produce vibrations, causing the separation of the two aluminum blocks to change.
Figure B3 - Thermal Expansion Test Setup Hasan Ozer's project relied on the performance of SpaceAge Control position transducers. LVDTs sensors simply sucked up too much power to make his wireless system work. The results of the two tests proved the acceptability of the Series 150 position transducer for the task. The Series 150 units gave similar drift and hysteretic responses compared to the LVDTs. Long-term test responses indicated reliability with consistent linear displacement readings, while the dynamic displacement test responses generally matched those of the LVDT sensors. The potentiometers operated with acceptable noise levels of 0.5 mm peak-to-peak. More importantly, the potentiometers required no warm-up period and operated with only two AA batteries for power. Hasan Ozer's idea proved to be a success, and with the help of the Series 150 position transducers. He demonstrated to the world that performing crack detection with wireless technology is something the civil engineering world should seriously consider in the near future.
Figure B4 - The Series 150 Unit and the LVDT Glued on the Ceiling Crack of the Test House in Milwaukee, Wisconsin USA TECHNICAL FOCUSCalculating Power Draw And Voltage Division Online Voltage Divider / Power Draw Calculator Outputs Maximum Current and Voltage Potentiometers can have a variety of functions across many different applications. However, many potentiometers act as simple voltage dividers: voltage goes in, voltage drops by a certain ratio across resistance or impedance, voltage goes out. Determining the voltage divider, or the ratio that the voltage drops by when it travels across the resistance or impedance, can come from a simple analysis of the system being used. In essence, it all comes down to the output voltage (Vout) accounting for a certain percentage of the input voltage (Vin). Vin is affected by either resistance or impedance; the total resistance or impedance gives the user the voltage divider, or Vout / Vin.
Figure C1 - A Voltage Divider Schematic SpaceAge Control has provided an online calculator (http://spaceagecontrol.com/calcvd.htm) for users to determine the output of their voltage divider and power draw under specific circumstances. To use the calculator, you'll need to know the following values:
The calculator determines the Vout with the related voltage divider (ratio) determined simply by calculationg Vout / Vin. In addition, the calculator determines the current across the potentiometer. Why are these values important? Every device that has electricity flowing through it is in danger of failure when device limits are exceeded. The SpaceAge Control voltage divider/power draw calculator also determines the maximum recommended current and power supply voltage for the specified conditions. With this information, the users can identify just how far they can push the boundaries without harming the device. ISSN 1527-5108 • Document Number S050AE(060125) |
