July, 2015


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Optical Encoders Help Measure Material Fatigue Continued from page 61


designs. While suitable for position control, an LVDT suffers from rela- tively poor signal stability. This lack of signal stability makes it difficult for LVDT-based systems to achieve accurate velocity measurements. LVDT-based systems are also sus- ceptible to the effects of magnetic fields produced within a linear motor and exhibit increasing nonlinearity over longer axes.


Optical Encoders In contrast to LVDTs, optical


encoders have intrinsically better signal stability and higher accuracy, making them superior for achieving the requirements of these material measurement systems. The engi- neers at Instron determined that an absolute optical encoder, capable of providing absolute position informa- tion without homing, would be the best solution for their E10000 and E3000 biaxial systems, offering a


EMI Shielding Caulk Cures Quickly and Is Paintable These results, along with those


Continued from page 60


from environmental and SE testing, indicate that both PTE-based com- pounds are superior to the incum- bent materials. The Ag/Al PTE com- pound was the "standout" with its 80dB shielding and would be the preferred replacement for any exist- ing EMI shielding caulk. The Ni/C PTE compound exhibited moderate shielding compared to the Ag/Al compound. Both PTE compounds showed no signs of galvanic corro- sion between the compound and the aluminum panel after 1000 hours of salt fog exposure. Both PTE materi- als have a wider application temper- ature range than their predecessors, are paintable 24 hours after applica- tion, and do not require a polysulfide paintable sealant. They will save application costs and field repair costs while delivering equal or bet- ter operating performance than cur- rent industry favorite EMI shielding materials. Chomerics continues to search


for filler-resin combinations that will deliver


the performance


improvements necessary for the lat- est application requirements. As part of these efforts, Chomerics ben- efits from its proximity to the University of Massachusetts-Lowell (UML) and its internationally recog- nized


Plastics Engineering


Department as well as Harvard Medical School’s Core Facilities. Harvard and UML offer polymer research experience and test facili- ties to complement Chomerics’ prod- uct development capabilities in the development of new types of poly- mer and conductive particle combi- nations for improved EMI shielding. Contact: Parker Chomerics,


Division Headquarters, Woburn, MA 01801 % 781-935-4850 fax: 781-933-4318 E-mail: chomailbox@parker.com Web: www.chomerics.com


number of advantages over servo mechanisms employing optical linear incremental encoders in conjunction with an LVDT. Graham Mead, Principal Mech -


anical Engineer for Instron Electro - Puls, at Instron’s United Kingdom- based European headquarters, offers: "We previously used an LVDT to provide the absolute position feed- back needed to commutate a linear motor, and an incremental optical encoder to provide the required measurement and control accuracy." Mead adds: "With the RESOLUTE absolute linear encoder, we are able to get all the functionality and accu- racy from one device. The reduced assembly complexity and number of parts allows much simpler setup and maintenance-free operation. The use


of the RESOLUTE ring encoder for the rotary axis perfectly comple- ments the linear encoder. It provides superior resolution, accuracy and mechanical simplicity over our previ- ous belt driven, conventional rotary encoder." The ElectroPuls E3000 linear-


torsion machine requires both linear and rotary absolute encoders for its linear and rotational axes, respective- ly. The linear position is provided by a RESOLUTE read head and range and training land assessment (RTLA) tape scale with ±5µm/m accuracy and 5-nm resolution. A second RESOLUTE encoder reading a 115mm diameter RESA ring determines angular posi- tion, offering an impressive resolution of 0.019 arcsec and an encoder accura- cy of ±2.5 arcsec.


Page 65


Advanced Bi-Axial Variant The company recently launched


an advanced bi-axial variant of its ElectroPuls E3000 all-electric test instrument. The E3000 is a compact tabletop instrument comprised of a load frame, crosshead with combined linear/torsion actuator, Dynacell load cell, and T-slot table for fixing sam- ples. The new E3000 linear-torsion model is a smaller-scale equivalent of the E10000 linear-torsion system, and includes a rotation axis with a standard range of ±135° as well as optional multiturn capability for applications such as orthopedic bone- screw testing. An ElectroPuls bi- axial linear-torsion test can be con- ducted on most materials and has found applications in testing inter-


Continued on next page


See at SEMICON West Booth 5679


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