Position Transducers for Zero-G Plumbing?

Position Measurement & Control - Issue 48

PRODUCT FOCUS

Position Transducers for Zero-G Plumbing?

Firstmark Controls Custom Products Can Fulfill Even the Obscurest of Applications

You never know when a good position transducer can come in handy -- that's why Firstmark Controls's customizable orders provide a little bit of measuring precision no matter what the situation. How extreme can these situations be? Ask NASA. In the zero-G environment of space, a lot of things are mission critical, but what about the human aspect of things? Just because astronauts are performing experiments in outer space doesn't mean that things like washing up aren't still important -- and to keep those types of things running, NASA called in Firstmark Controls.

Inside the pressurized system of NASA's outer space wastewater tank, the tank's bellows have a conspicuously high-tech component to them: a Firstmark Controls position transducer. The transducer offers precise measurement of movement within the wastewater tank -- a critical piece of monitoring to keep the system optimally running while ensuring that astronauts can take care of the day-to-day logistics of hygiene.

What was so customized about this part? While the core component -- the position transducer -- is essentially standard in terms of functionality, there's always the question of mounting, accessibility, and positioning. In the case of the wastewater tank part, a picture is worth a thousand words:

Figure A1: A Firstmark Controls custom-design position transducer allows for water tank measurement on the International Space Station.

Firstmark Controls custom products grab whatever is applicable from pre-existing designs to keep development costs down; approximately 50% to 70% of most designs are taken from off-the-shelf products. With nearly 40 years of development experience, our inventory of off-the-shelf product design is substantial! Let us know what your custom design requirements are by making a custom solution request.

APPLICATION FOCUS

Position Transducers Replace Duct Tape and Rubber Bands

Rotary Wing Researchers Turn to Firstmark Controls Position Transducers to Replace Makeshift Measurement Tools

In the line of duty, desperate measures are sometimes needed to get the job done. Sometimes, that means using nothing more than rubber bands and paper to create measuring devices that would make television action hero MacGyver proud. When necessary, the user's need for making yoke and throttle measurements came down to creative -- and not necessarily accurate -- methods.

In one instance, yaw was measured using a contraption built from duct tape and a protractor. In another case, yoke measurements were performed using a chain of rubber bands and a ruler. For pedal measurements, the user used the same trusty combination of rubber bands and a ruler.

Figure B1: A ruler and rubber bands don't quite have the same accuracy as a Firstmark Controls position transducer.

Figure B2: The user's duct tape/fishing wire/protractor makeshift measuring device.

Why use these household items for intricate military calculations? In some cases, it was necessity. In other cases, it was convenience. But these rigs come with a price -- inaccurate data, unreliable measuring subject to human error, and the loss of critical time spent creating these devices and deciphering the data. Firstmark Controls offers a simple and effective alternative to these makeshift devices.

Firstmark Controls position transducers, with time-proven reliability and test-proven repeatability, are the ideal solution for the flight control and pilot control measurement needs. Instead of wasting time creating a chain of rubber bands and squinting at a ruler taped up in the cockpit, engineers can get a quick, accurate, and repeatable digital reading for yokes, pedals, brakes, and other critical aircraft controls. In addition, Firstmark Controls position transducers are affordable, durable, and easily mounted and moved. With all things considered, it's no wonder the military switched over to Firstmark Controls products on this project in 2005.

TECHNICAL FOCUS

Methods for Zeroing Position Transducers

Multiple Electrical and Mechanical Techniques Are Available

Accuracy is critical to the performance of any measuring device. If sensor readings are off, users risk everything from faulty data to potentially dangerous situations. In the case of position transducers, zeroing the analog output allows users to map the mechanical input (mechanical position) to a specific electrical output. How can users adjust the zero point of the electrical output to meet the requirements of their application?

Fortunately, Firstmark Controls position transducers are flexible enough to accommodate "zeroing" with just a little tweaking. A number of methods exist, both mechanical and electrical, to get data properly set:

Adjustable Displacement Cable Termination	With a turnbuckle, (threaded plug), or similar device, users can adjust the cable length until the right output is achieved.
Precision Displacement Cable Leader	Zeroing can be achieved by using leaders that are manufactured to meet application specifics. For moderate quantities, you can produce the leaders yourself using the 160001-01 installation kit. For larger quantities, Firstmark Controls may be able to provide a suitable configuration.
Shims	Thin layers of material known as shims can be added as required on the mounting base or displacement cable termination to zero the unit. The shim material can be metal, plastic, or other durable, rigid material compatible with the application.
Rotating the Potentiometer	For position transducers with cam locks, the cam locks can be loosened and the potentiometer rotated to achieve the desired output. For units with multi-turn potentiometers, extra caution must be exercised to ensure the spring torque is not applied to the fragile potentiometer wiper tracking mechanism.
Trimming Potentiometer	Trim potentiometers can be added to the voltage divider circuit to control the zero point.

For information about accuracy and Firstmark Controls devices, see the Draw Wire Transducer Accuracy application note. Firstmark Controls welcomes user ideas on zeroing position transducer output. If you have an effective technique, please contact us.

ISSN 1527-5108 • Document Number S050AH(060815)