Position Measurement & Control - Summer 1996 (SU96)

Position Measurement & Control is published for the customers of SpaceAge Control and the engineering and instrumentation community. Subscriptions are free. To subscribe at no charge, submit a Newsletter Subscription Request.

Contents

• Big Foot Base Now Available
• Product Highlight: Model 180-0803
• Southwest Research Institute: Explosive Test Results
• Application Corner
• ISA Displacement Transducer Standard

Summer 1996

The Big Foot Base (P/N 160015), a larger footprint mounting base for Series 160, 161, and 162 position transducers, is now available. Featuring an expanded mounting area, the Big Foot Base allows for easier mounting when compact size is not paramount. The unit also features larger throughholes (0.193 inch (4.90 mm) diameter) that accept No. 10 mounting hardware.

Developed originally for quick installation and removal in the auto industry, the Big Foot Base has found increased use in other industrial and test & measurement applications. Please contact us for more information on this product or for a 30-day evaluation unit.

Over the last 28 years, we have designed a broad range of application-specific position transducers for unique measurement challenges. An example is the Model 180-0803 position transducer designed for aerospace ordnance testing use.

The Model 180-0803 offers 10 inches (254 mm) of displacement measurement in a size somewhat wider than the standard Series 173 position transducer. Available with 1K or 5K ohm resistance potentiometers, this product has a bearing-mounted shaft. Due to its small size, high cable tension is not available.

If you would like more information on the Model 180-0803 or have unique measurement challenges not met by our standard product lines, contact us.

Ever wonder how a building reacts when an explosion occurs inside of it? Southwest Research Institute (SwRI) now knows after recently completing a study to evaluate the performance of a vapor and blast containment structure (VCS). The structure, 16 feet high, 30 feet wide and 60 feet long and fabricated of corrugated metal panels, is used to contain blast pressures, fragments, and chemical vapors during ordnance excavation and disposal. SwRI was tasked with evaluating the effects of blasts on the building's structural integrity.

Kirk Marchand of SwRI headed up the project and first modeled the building and blast numerically. SwRI then instrumented the structure with position transducers, strain gages, and pressure gages and conducted an actual blast experiment with up to 1.2 pounds of explosive. SpaceAge Control Model 160-1505, 160-0963, and 160-0321 position transducers with 48 oz. of cable tension and Cable Guides were used to measure displacement of the building doors, walls, and roof.

Marchand selected SpaceAge Control position transducers for their ability to function with multi-dimensional displacements, high frequency response, and low inertial resistance.

It was paramount that the position transducers be mounted rigidly to ensure the blast itself did not move the position transducers. Door and wall position transducers were mounted on 4 by 4 inch steel tubes sunk into concrete and located 2 feet from the structure. Roof position transducers were mounted to a steel joist that was suspended by two telephone poles. All position transducers were located outside of the structure. Data was collected over two seconds with NIC Windows software and Nicolet MultiPro hardware.

Were there any surprises from the test? "Not really", replied Marchand. Our model indicated that the back wall was the weak point of the structure, even though the front roll-up door was the most flexible component. The position transducer confirmed those presumptions by indicating a maximum displacement of 15-17 inches on the roll-up door with no damage, while the rear wall saw damage at about 6-7 inches.

Marchand noted that the position transducers' frequency response exceeded his expectations. "After we analyzed the data, we determined that the transducer was tracking movements travelling in excess of 20 feet per second."

Founded in 1947, SwRI is a non-profit research and development organization with more than 2,600 scientists, engineers, technicians, and support personnel who conduct about 1,500 nationally and internationally sponsored projects a year. Gross revenues in 1995 exceeded $243 million. SwRI operates from almost 2 million square feet of laboratory and office space in facilities located on 1,200 acres. SwRI has a unique intellectual property policy. All patents and licenses resulting from client-sponsored research belong to the client.

SwRI has a wide range of technical competency and breadth. Its staff members in 13 technical divisions have expertise in such areas as chemistry, space sciences, nondestructive evaluation, automation, engine design, mechanical engineering, electronics, and more. The Institute can assemble a multidisciplinary team of experts required by any technical project, giving SwRI a teaming flexibility hard to find at other R&D organizations.

For more information on this application or SwRI, please contact:

The Application Corner is dedicated to answering your questions about using position transducers in specific applications. If you have an application question you would like answered, please let us know by phone, fax, mail, or the reply card in this newsletter.

Q. Your standard displacement cable connector, the Swivel, is not right for my application. How else can the cable be connected?

A. Other choices for terminating the displacement cable include:

• Line Connector - similar to the swivel in appearance but with no rotatable part and with a breaking strength that exceeds the cable
• Crimped Ball - an 1/8 inch (3.175 mm) diameter Stainless Steel ball fitting that can be inserted into a fixture that you supply or that we fabricate
• Custom Connector - we have developed custom connectors for a broad range of applications or you can devise your own

Note that all standard products come with an uncrimped swivel. This allows you to place the swivel where you would like or to replace the swivel with your own cable connection design.

Q. I have two of your position transducers. One of the displacement cables has a larger diameter than the other one. Why did you change your cable size?

A. Unless specified differently by the user, all displacement cables are either 0.018-inch (0.4572-mm) or 0.027-inch (0.6858-mm) diameter and of 7x7 stranded, stainless steel construction. The smaller diameter cable is used on all products except ultra-high tension Series 160, 161, and 162 products. One of your position transducers probably has ultra-high tension. If you would like the 0.027-inch (0.6858-mm) diameter cable on your position transducer, please specify this on your purchase order.

Q. Which resistance value should I order for the potentiometer?

A. The selection of the resistance value is solely dependent upon the requirement of your data acquisition or control circuitry. Accuracy and resolution is independent of the actual resistance value. Source: JDK Controls, Inc., 424 Crown Point Circle, Grass Valley, CA 95945 USA, 916-273-4608, Fax: 916-273-0769.

ISA, the international society for measurement and control, is currently reviewing and revising its S37 Measurement Transducer Standard. This Standard incorporates a broad range of transducer types including:

• displacement (position)
• strain gage
• pressure
• acceleration
• level
• flow
• vibration

The purpose of the standard is to create uniform specifying and testing characteristics for instrumentation transducers. By adhering to the Standard, users and manufacturers will benefit from reduced design and procurement lead times and reduced material cost. A major factor in these reductions is the reduction of qualification tests resulting from the use of commonly accepted test procedures and uniform data representation.

The original SP37 Standard was initiated in the early 1960's with several revisions made since the original publication of the first Standard. The displacement transducer standard, SP37.12 presently covers only potentiometric displacement transducers. However, the next Standard will provide more complete coverage of displacement transducers by not referencing a sensing technology.

If you would like more information on the SP37 Standards or would like to participate on the Committee, please go to the SP37 Web page at http://www.isa.org

ISSN 1527-5108