www.davidson.com.au - Honeywell Linear and Rotary Transducers

This page describes the performance factors that you will need to consider when selecting a position transducer. Answers to the following questions will help you focus on those parameters that will be most important in your selection.
As a specifier you must find the best cost versus performance trade-off for not only the transducer, but also the system. Usually you will take one of two paths to select a transducer.

Find a transducer that works with the power supplies and amplifiers, or controllers in your system.
Select the position transducer and then match your system components to it.

Either way, the following section can guide you to the best transducer for your needs.

What is the length to be measured?
What accuracy can I get?
How rugged does the transducer need to be?
What excitation should I use?
What mounting factors should I consider?
Does the transducer need to be compensated for temperature effects?

What is the length to be measured?
For potentiometers this is called the Theoretical Electrical Travel. For most applications this is straightforward, however, there are times where you may want to measure only a portion of the total travel of your system. For example, you may be interested in having the highest possible resolution at one end of the system's travel. Consider a 10" total travel, but by monitoring the last 1", you can increase your resolution tenfold.
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What accuracy can I get?
Accuracy can have several meanings. Do you mean how small a motion you can pick up (resolution), or how much error there is at any point along the electrical travel compared to a reference line (independent linearity), or is the output the same at a given point from one cycle to another (repeatability). These are not the same, but any one is often called "accuracy".

It is important to differentiate and prioritize these performance parameters. All of our MystRŽ conductive plastic position transducers have infinite resolution. The repeatability of any of our transducers is excellent and will rarely be more than the signal to noise ratio that will likely exist in your system. Our independent linearity, the error versus the reference line, is guaranteed to be less than 0.1% for many of our position transducers.
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How rugged does the transducer need to be?
The unit's ability to hold up under high levels of shock, vibration, moisture, dirt, oil or temperature extremes is sometimes more important than accuracy. What good is a high accuracy device if it won't last long in the application? The MystRŽ conductive plastic withstands many harsh chemicals and will work immersed in hydraulic oil.
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What excitation should I use?
For potentiometers, the excitation will be determined by the input of your signal conditioner or the controller you are using. You will need to decide whether to use regulated or unregulated voltage, depending on your conditioner or controller.
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What mounting factors should I consider?
These vary from application to application. Proper alignment of the shaft of the potentiometers is important for maximum life from the unit. Your mounting should allow for minor adjustment to minimize any misalignment. Rod ends or shaft couplings are an effective way to compensate for misalignment. Side load on a potentiometer will wear out the bearings long before the wiper or element fail, so careful mounting is to your advantage. If there is heavy hose down or spray from oil or water you should use a water resistant or waterproof potentiometer such as the AQ series.
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Does the transducer need to be compensated for temperature effects?
Potentiometers, while they have measurable temperature coefficients, will not usually require temperature compensation because they are being used as voltage dividers.
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