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.
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 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 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."
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Number of Elements
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Many sensors can accommodate two elements – called dual element. Dual element construction is restricted by wire size and tube size. |
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Junction Style
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Junction style specifies whether the tube end is open or closed, and if the element is grounded to the tube. |
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Probe Configuration
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Specifies the angle of the sensor probe relative to the attaching device. Sensors are available straight in line, or 45° or 90° off the mounting plane. |
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Length of Components
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Components with meaningful linear dimensions are the rigid tube (or probe), flexible tube, including stainless steel overbraid and Fiberglass insulation only, and extended lead (considered part of the cold end termination). Code designations for each of these dimensions are as follows:
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X= |
Rigid length (probe). Typically applies to sensor with adjustable attaching device. |
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Y= |
Flexible length (flexible armor, SS overbraid, Fiberglass) |
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Z= |
Locating depth for fixed bayonet lock. Frequently, but not always, replaces X. |
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L= |
Extended lead. In addition to the standard lead length provided on the sensor. |
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The sensor probe can be mounted to the workpiece with any of the following attaching devices. All attaching devices are not applicable to all sensors. Each sensor illustration on the following pages lists only the attaching devices appropriate for that sensor.
