When do you need an Air Bearing LVDT Contact Measurement Probe?

When You Want to Increase the Quality Assurance of Your Metrology Department When quality assurance is your goal, measurement of a part feature must be performed by a measurement device that is capable of exceeding the part tolerance. Generally, in order to obtain statistical confidence in one's measurement, the measurement capability must exceed the feature tolerance by a factor of ten. For example, one cannot measure a .0001 inch feature with a .000050 inch resolution indicator with high statistical confidence. The high resolution capability of the Colorado Precision Air Bearing LVDT enables measurements with high statistical confidence. The probe is capable of high confidence measurements in the +/- .020 inch range and also demonstrates repeatable high confidence measurements at the atomic level (see examples).

When You Need High Resolution Over a +/- .020" Range In certain applications, measurement to high resolution over large indicator ranges is required. With the appropriate amplifier,as recommended by Colorado Precision, 1-microinch resolution is available over a +/-.020" range. When measurements taken are being performed over a +/-.020" range, the effect of varying stylus force becomes a critical concern, especially if microinch level accuracy is required. With a Colorado Precision Air Bearing LVDT, constant stylus forces over the total range of travel provides accurate high resolution measurements over relatively large ranges. Varying stylus force is not a concern.

When You Need to Make Very Accurate Contact Measurements With Very Light Stylus Forces in Order to Avoid Damaging Fragile Surfaces In certain applications, it is difficult to use spring-based mechanical indicators where fragile surfaces are being measured and care must be taken to not scratch, chip, dent or move the surface being measured. Often, for example, soft metals or plastics cannot be scratched, diamond edges or sharp edges cannot be chipped, and measurements of thin threads or wires cannot initiate deflections. The Colorado Precision Air Bearing LVDT has stylus force adjustable down to 1/10 of a gram and can be very realistically used at 2/10 of a gram stylus force. At Colorado Precision, we often use light stylus contact forces in the measurement of diamond turned glass and metal surfaces where we cannot use spring-based mechanical indicators.

When You Want to Avoid Direction Reversal Errors and Radial Loading Errors Associated With Spring-based Measurement Devices Measurements using spring-based electronic indicators are difficult when the direction of contact measurement is reversed. When the load direction is changed on a spring-based measurement device, often the measurement being taken jumps significantly and must be ignored as direction reversal error in the indicator. With the very light stylus forces available with an air bearing LVDT, and constant stiffness in different radial directions, reversal errors associated with measurement direction reversal have been extremely reduced. Direction reversal error with an air bearing LVDT is generally less than 0.1 microinch, negligible in most measurement applications.

When You Want Extremely High Resolution Contact Measurements Over Small Ranges, Such As .05 Microinch Resolution Over +/- 20 Microinch Range In certain applications it is difficult to make accurate contact measurements with spring-based mechanical indicators below 20 microinches. The stylus force in the Colorado Precision Air Bearing LVDT is controlled by differential air pressure between the front and back of the stylus shaft. In an air bearing LVDT, there are no spring mechanisms. As stylus force is not dependant on springs, the stylus force is constant over the total range of travel (.200 inches). Accurate measurements below 20 microinches are difficult to make using spring-based indicators which have varying stylus forces over the measurement range and low radial stiffness. The Colorado Precision Air Bearing LVDT has demonstrated its effectiveness and repeatability when making contact measurements of .05 microinch resolution over a +/-20 microinch range (see performance specification sheet). There are few, if any, contact indicator type probes, with the versatility and ease of use of the air bearing LVDT, that can compete with this level of accuracy and still operate in ranges as large as +/-.020 inches.