Position Measurement & Control - Spring 1996 (SP96)

Contents

• Space-Qualified Units Unveiled
  
• SAE ‘96 Report: Dancing in Detroit
  
• Robert Yates Racing Pushing the Envelope
  
• Application Corner
  
• Potentiometer Resistive Characteristics: Overview
  

After two years of development, man rated/space-qualified position transducers from Firstmark Controls are now available. The compact units meet critical space vehicle requirements of small size, low weight, proven technology, and accurate measurement.

Series 160 products will be used on the International Space Station and in International Space Station experiments to be launched in 1997. The space-qualified products are manufactured to MIL-Q-9858A specifications and feature a unique cable redirection pulley. The pulley allows the low-profile transducer to be mounted at a 90 angle from the normal mounting direction. This enables mounting in the confined spaces of space vehicles.

We were pleasantly surprised at the response we received at the SAE ‘96 Exhibition held in Detroit, Michigan USA from February 26-29, 1996. When we counted all the visitors to our booth, we found people from over 10 countries and over 30 states had stopped by. At the show, we held a demonstration of the resolution and repeatability of our position transducers and also highlighted vehicle applications of the products. Firstmark Controls products were also featured in a number of other companies’ exhibits including:

Dateppli Inc. (Midland Michigan USA) Dateppli produces the DRIVE^TM in-vehicle data acquisition system based on the National Instruments LabVIEW system. One of the most popular demos at the show (over 800 exhibits!) was Dateppli’s Dancing Nash which featured their DRIVE^TM system in a 1957 Nash Metropolitan. The Nash was choreographed to "dance" by using DRIVE^TM, LabVIEW, hydraulic actuators, and various sensors and transducers including a Firstmark Controls Model 161-1283. Dateppli may be reached at 517-839-1040 (fax: 517-839-1042).

Sensor Developments Inc. (Lake Orion, Michigan USA) Sensor Developments specializes in force and torque sensors and systems. They have developed a broad range of strain-gage-based solutions for the automotive, aerospace, medical, nuclear, textile, and OEM industries. A Firstmark Controls Series 160 position transducer was featured as the displacement sensor on a truly unique instrumented pogo stick provided by Dateppli Inc. Force sensors and related instrumentation enabled the brave-at-heart to see how their jumping and falling looked when monitored in real time. Sensor Developments may be reached at 800-997-3676/810-391-3000 (fax: 810-391-0107, http://sendev.com.

Vector Research, Inc. (Milian, Ohio USA) Vector Research designs and manufactures anthropomorphic test devices targeted at the automotive, aerospace, military, and research arenas. At the show, Vector Research introduced an improved knee slider mechanism for crash test dummies that incorporates the Model 150-0121 position transducer. The new knee slider offers longer life, smoother action, and more significant side loading problems associated with linear potentiometers that can cause the displacement shaft to bend and the product housing to fracture. Vector Research may be researched at 419-625-5200 (fax: 419-625-5335).

If you watched the most recent Daytona 500 NASCAR Winston Cup race in February, you saw car #88 (Ford Quality Care/Ford Credit) of Robert Yates Racing get the check-ered flag. What you didn’t see were the long hours of development, testing, and finetuning that led to winning the race.

Part of the finetuning that made the difference in the race was the beefing up of the rear spoiler to reduce its deflection during high speeds. By mounting Firstmark Controls position transducers and acquiring data with an Edge data acquisition system from USA, it was determined that at high speeds, the rear spoiler was deflecting 1.5°. This deflection led to reduced spoiling effect ans a higher riding car which results in slower speeds. By reducing this deflection to virtually 0° with structual enhancements, the overall top speed of the car was increased.

Dave Kriska, Project Engineer at Robert Yates Racing used the Model 160-1285 position transducer with the Cable Guide, Potentiometer Cover, and Universal Base to determine the displacement change that was occuring. Mounted to the car’s rear bumper using the Universal Base and with the extraction cable attached to the spoiler using an eye bolt, Dave took data from the position transducers over 2 points on the spoiler. Data was collected over a series of three 2.66-mile test runs at Talladega, Alabama USA and analyzed.

Dave summarized his experience with Firstmark Controls products by saying, "We required the product ASAP and it got here a day early. The fast delivery combined with the transducer performance and ease of mounting make my job easier."

Robert Yates Racing uses Firstmark Controls products for a variety of of other measurement requirements including throttle position and suspension monitoring. The company is based out of Charlotte, North Carolina USA and has been developing and racing NASCAR vehicles since 1987. The company has two vehicles in this year’s NASCAR season:#28 Texaco?havoline driven by Ernie Irvan and #88 Ford Quality Care/Ford Credit driven by Dale Jarrett.

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, or mail.

Q. I’ve seen your sensor cover mentioned in your brochure. What is the purpose of this accessory?

A. The sensor cover (part number 160060), like its name implies, protects the sensor on Series 160, 161 and 162 products when used in dirty or hazardous environments. For example, sensor covers are used in applications where unpredictable events may cause an exposed potentiometer to be damaged. Note that if you have a Series 160, 161, or 162 product without a sensor cover, adding one at a later date requires a factory alteration. About 15% of our Series 160, 161, and 162 products are provided with sotentiometer covers.

Q. I am using a Model 160-1505 with a standard base and want the cable to exit straight down but the standard base is in the way. Go you make a mounting base that allows this?

A. The standard, universal, and Series 173/174/175 mounting bases can all be reversed to allow the cable to exit straight down. No additional bases are required.

Electronics tip: A short circuit on the output or an inadvertent connection of the excitation voltage to the potentiometer wiper mat pass excessive current through the wiper and element, causing a catastrastrophic failure of the potentiometer. Output short-circuit protection may be obtained by adding a current-limiting resistor in series with the potentiometer wiper. Call us if you need assistance in selecting the resistance value of the current-limiting resistor. Source: Specifications and Test for Potentiometric Displacement Transducers, ISA.

Firstmark Controls uses precision potentiometers as one type of sensing device in our position transducers. Historically, potentiometers used wirewound resistive elements that produced finite voltage resolution of 0.003% to 0.3% FS. With this type of performance, potentiometers gained a reputation of solid although limited accuracy devices. The development of hybrid and conductive plastic (thick film) resistive elements has resulted in potentiometers that can deliver infinite resolution and long life.

The table below summarizes performance characteristics of each of these resistive technologies. Unless otherwise requested by the user, Firstmark Controls potentiometer-based products use only conductive plastic (for single-turn products) or hybrid (for multi-turn products) potentiometers. Source: Handbook of Position Sensing Products, BEI Duncan Electronics.

ISSN 1527-5108