The typical plastics industry sensor assembly consists of four components:

• Attaching device
• Element
• Element protection
• Cold end termination

The sensor is further defined by its physical attributes:

• Number of elements
• Junction style （hot end）
• Probe configuration （straight, 45°, 90°）
• Length of components

Some sensors are designed for specific applications and have a unique attaching device; others are designed for general application and have a common attaching device.

Some sensors are designed for specific applications and have a unique attaching device; others are designed for general application and have a common attaching device.

• Melt bolt
• Nozzle melt
• Ring or Lug

The melt bolt sensor is used on extruders and injection molding machines. A melt bolt "blank" with a hole through its length is welded to the rigid tube.

The nozzle melt sensor is designed for injection molders. Two types are available: immersion type and non-immersion type. The immersion type is a bolt "blank" with a hole through its length on the sensor tube. The sensor tip protrudes through the workpeice and seats in a beveled hole in the work piece. The attaching bolt is threaded into the workpiece and tightly seals the tip to the workpiece.

The non-immersion type is an attaching bolt with a center hole. A short tube seats in the bolt hole and supports the thermocouple junction against the bottom of the hole in the workpiece. Or, if the sensor is an RTD, the tip is potted in the hole in the bolt.

Ring type and lug type sensors measure surface temperature – such as a barrel or a mold. The sensor leads are joined at the ring or lug （hot junction）. The sensor attaches to a threaded stud on the workpiece and must be secured with a nut.

General application sensors are commonly called tube style sensors and are mounted with:

• Bayonet lock, or
• Threaded bushing.

These devices are secured to the rigid tube portion of the sensor assembly.

Varidepth® sensors have no rigid tube （other than the tip）. The element of a Varidepth sensor is protected by either a flexible tube or spring. Both of these components are compressible. Varidepth sensors are equipped with a bayonet style lock cap directly on the tube or spring.

Two types of bayonet locks are available: fixed or adjustable. The fixed bayonet lock is secured to the tube between two rings formed on the tube surface. The adjustable bayonet lock is held on the tube with a compression ring and nut.

Two types of threaded bushing mounts are available: fixed or adjustable. However, the more common, by far, is the adjustable bushing held on the tube with a compression ring and nut. The fixed bushing is brazed to the tube.

Both the Varidepth sensor and the bayonet lock require a mating adapter to mount it to the workpiece. The threaded bushing mounts directly into a tapped hole in the workpiece.

Element: The thermocouple element is defined by its calibration （type）, wire size （gauge）, construction （solid, strand, insulation）. The resistance temperature detector （RTD） is defined by its resistance coefficient.

Element Protection: Element protection is defined by its construction: rigid tube, flexible armor （or flexible tube）, stainless steel overbraid, spring, or insulation only. Rigid length is identified as dimension "X." Flexible length is identified as dimension "Y."

The depth of the fixed bayonet lock attaching device is identified as dimension "Z." Since the location of the bayonet lock on most assemblies （but not all） is near the transition point （from rigid to flexible）, the "Z" dimension is equal to the length of the probe. Therefore, there is no "X" dimension.

Cold End Termination: Cold end termination is defined by the device with which the sensor leads are terminated: stripped ends, spade lugs, plug, and/or jack. It is further defined by the extended length of the leads – that is, leads in addition to the standard length normally provided with that sensor. Extended lead length is identified as dimension "L."