Position Measurement & Control - Fall 1997 (S018A)

Contents

• Application Corner
  
• Mounting Position Transducers
  
• Thirty Years of Position Measurement
  
• Series 174 and 175 L-Base Now Available
  

Q. How do I crimp the small-gauge electrical wire on your Series 17X and 150 products? When I try to strip the wire, I always end up breaking it.

A. Due to their small size, these products use 30-gauge (0.010-inch (0.254-mm)) diameter) electrical wire. When crimping the wire to connector pins, use a thermostripper such as HotWeezers and not a mechanical stripper.

Q. What type of meter and power supply do you recommend for your products?

A. Firstmark Controls does not typically provide meters, power supplies, data acquisition equipment, or other instrumentation. However, we can provide referrals to other companies with suitable products once we know more about your application. If you have questions on what type of instrumentation is compatible with our products, please contact us with your application details.

A general-purpose digital meter and power supply that are compatible with our products can be obtained from these sources:

Texmate The DI-45U digital meter is priced around US $170.00. While you can get more affordable meters, this one is programmable, takes a variety of electrical inputs, and can read up to 32,753 counts. You can get more information on this and other meters from:

Calex The Calex CM1.24.240 power supply is priced around US $160.00. You can get more information on this and other meters from:

Q. I am preparing to install my position transducer. Do you have any recommendations on how to provide an electrical cable strain relief?

A. For Series 160, 161, and 162 products, two ways to provide an electrical cable strain relief are shown below.

Q. Sometimes our instrumentation installers wire the position transducer with power to the wiper. This burns out the potentiometer. How do I prevent this?

A. You can either severely discipline the installer or install a current-limiting resistor. Installing a current-limiting resistor is probably the easiest thing to do.

A current-limiting resistor provides protection in case power is applied to the wiper. If a short condition should occur between the wiper (white) and the common (black) while the wiper is at the CW (red), full available current from the power source would be dumped into the wiper. Depending on the the available current, this could burn out the potentiometer.

To limit current to 0.005 A (5 mA), use the following equation to determine the value of the current-limiting resistor:

resistor value (ohms) = (input voltage/5) x 1000

Please contact us if you have any questions on potentiometer protection.

Q. What is the temperature coefficient of your standard displacement cables? How do they vary in length over the operating temperature range of your products?

A. Our standard cables are constructed of Type 304 stainless steel and have a temperature coefficient of 9.6 ppm/° F (17.82 ppm/° C). The equation for change in length due to thermal expansion is delta l = a * l * delta T. Over a nominal 10-inch range (254.00 mm) (assuming a total of 15 inches (381.00 mm) of cable being used to attach to the application), the cable would increase approximately 0.05 inches (1.27 mm) in length in going from -85° F to +257° F (-65° C to +125° C).

Mounting transducers, sensors, and related instrumentation can be quite a challenge in many applications. Size, performance, rigidity, weight, and other constraints often cause for creative solutions in attaching the instrumentation to the application.

Over the last three decades, Firstmark Controls position transducers have been mounted to applications using everything from hardened bases to specialty screws and from dental cement to duct tape.

If you have a mounting challenge facing you, you may want to consider a few of the ideas below for mounting both the position transducer and attaching the displacement cable.

High-adhesion tape Double-sided tape and other tape-based adhesives can be used to quickly and effectively mount the position transducer with a minimum of effort

Suction cups Suction-based devices provide a reusable, easy-to-install, easy-to-dismantle solution for temporary mounting. While not as stable as other mounting solutions, they are quite usable for those applications requiring moderate accuracy.

Magnets For applications involving attachment to ferrous metals, magnets can provide a removable, stable, and flexible solution.

Clamps C clamps or other clamping devices can be used for testing, prototyping, and other temporary uses.

Bases Firstmark Controls has developed a number of bases including those shown below.

Screws Series 150, 173, 174, 175, and 180 products come with 2-56 screw holes for mounting the transducer to the application via screws.

Custom mounts Specialty mounting hardware provided by the user or Firstmark Controls can be designed and fabricated. If you would like assistance creating a design, please contact us.

Attachment of the displacement cable to the application is often easily performed using Firstmark Controls provided swivels, line connectors, and crimped balls.

Other methods of attachment include looped cables, screw connectors, magnets, and clamps.

If you require sources for the above mounting methods, you may want to try these vendors:

In June 1997, Firstmark Controls entered its 30th year of operation. Over the past three decades, the company has focused on meeting exacting position measurement requirements as well as developing innovative products offering high accuracy, small size, flexibility, and durability.

Started in June 1968 by NASA researcher Norm Foster, the company's first products were control devices for space instrumentation. Shortly thereafter, the company produced a unique position transducer to measure flight control surfaces on NASA's F-8 supercritical wing research aircraft. This position transducer formed the basis for a complete line of products targeted at high-performance, high-accuracy applications. Building on a strong aerospace base from the 1970's, the company has expanded to provide position measurement solutions for the automotive, industrial control, and OEM markets. Today, the company is a supplier to a broad range of industries ranging from automotive safety product manufacturers to space and missile companies to testing labs.

Thank you to all our customers, suppliers, and employees who have helped us achieve this milestone. We look forward to serving you in the future.

Several customers have requested we develop a mounting base like the Series 173 and 180 L-base (part number 173015) for the Series 174 and 175 products. This base is now available and can be ordered as part number 174015.

ISSN 1527-5108