Strain gage type [ 應變規式位移計 ]
LVDT [ 線性可變差動位移計 ]
This is the simplest mechanical configuration, where the armature fits loosely in the bore of the LVDT, being attached to the moving point by a male thread. It can be completely separated from the transducer body without demounting either part.
Proper installation of this type of LVDT requires that the armature and LVDT body be separately supported so as to ensure relative movement along a common axis. When properly aligned, this noncontact arrangement allows essentially frictionless movement with zero wear, and ensures continued repeatability with infinite resolution. With no internal springs or bearings, the unit has virtually unlimited fatigue life.
A free unguided armature
is most suitable for short-range, high-speed applications (such as
mechanical vibration measurements) or applications with a very high number
of cycles. It is also recommended for applications in which the target
being measured moves parallel to the transducer body.
This configuration can be used for both static and dynamic applications, including applications where the target being measured moves in a direction transverse to the transducer body.
Here, the armature is both restrained and guided by a low-friction bearing assembly. This allows all units to be mounted vertically between optional self-aligning bearings, if desired. Units measuring ranges of 3 inches (76 mm) or less can also be mounted horizontally. Units with a range greater than 3 inches, however, may require additional support along the transducer body, to prevent flexing.
are suitable for applications with a longer working range, where the
transducer is to be mounted by its ends only, or where misalignment might
occur if the armature were unguided.
In this configuration, the armature is both restrained and guided by a low-friction bearing assembly (as with the "captive" armature, above). In addition, it has an internal spring to continuously push the armature to its fullest possible extension, thereby maintaining light yet reliable contact with the measured object. This feature is appropriate where the contact surface moves periodically beyond the range of the transducer (as, for example, when multiple separate parts are being gaged on a production line).
Spring-loaded LVDT's only
require a fixing point for the transducer body, and are most suited to
static or relatively slow-moving applications. The probe end of the
armature is normally tipped with a ball, although optional flat or roller
ends are also available .
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