Electronic gaging probes are commonly used in the dimensional gaging of manufactured parts, serving as an important component of a quality assurance system. Typically, gaging probes are cylinders with diameters of 8 mm or 9.5 mm (5/16 in. or 3/8 in.) and lengths ranging from ~ 0. 65 mm to 100 mm (2.5 in.-4 in.).
Gaging probes, also referred to as gage heads or spring-loaded LVDTs, incorporate a non-contact inductive position sensor, either an LVDT or half-bridge, that uses a spring-loaded movable armature coupled to a shaft that is supported in a high-precision linear bearing. Most gaging probes have a maximum gaging range of ±0.25 mm to ±2.5 mm (±0.010 in. to ±0.100 in.), with resolutions of fractions of microns.
In the harsh environment of the shop floor, however, these probes can encounter serious problems. For example, the zero-clearance linear ball bearing must be protected from even the slightest contamination or it will jam up and fail. The small diameter and slenderness of the probe body make it susceptible to accidental damage. And if its cable is pulled out or severed, the entire probe must usually be replaced.
Rugged and robust probes, such as Macro Sensors’ GHS Series of Hermetically Sealed Gaging Probes, can solve many of the problems associated with dimensional gaging in harsh environments. These units feature a ¾” diameter hermetically sealed stainless steel probe with integral connector, a clearance-fit sleeve bearing, and gaging ranges up to 2”. Units can survive heavy shocks as well as the effects of dirt, water, steam and other corrosive elements without effecting performance.
Internal construction consists of a spring-loaded shaft running in a precision sleeve bearing connected to the core of an LVDT. The sleeve bearing offers nearly the repeatability of a zero-clearance linear ball bearing, but is less susceptible to jamming. An outflow of air through the probe’s bearing inhibits the ingress of grit, dirt, dust, oil, solvents or other contaminants, increasing reliability and probe life.
The probe shaft of the position sensors is fully extended by a spring exerting a nominal force of 6 to 20 ounces depending upon total range. Known as pressure-extend/spring-retract probes, these units can spring retract out of the way during loading/unloading operations in a gaging fixture or inspection jig, but extend immediately when pressurized by air.
While Macro Sensors offers its Spring Loaded LVDT Position Sensors in both AC- or DC-operated versions, DC-operated units incorporate integrated electronics that provide a 4-20mA, single ended or bipolar DC output compatible with most standard PLCs, digital indicators, and data acquisition systems. Macro Sensors also offers metric calibration options for all Spring-Loaded LVDT Position Sensors.
Macro Sensors
www.macrosensors.com