A thermocouple
is a pair of dissimilar wires so joined as to produce a thermally
generated emf when its ends are at different temperatures. Several
combinations of dissimilar pairs have become standardized and
used in temperature instrumentation. T, J, E, K, N, R, S, B are
letter codes designating some popular thermocouples that are readily
available. Each combination has its own unique emf output and
its own properties that make them more applicable for a particular
use. Thermocouple theory allows the extension of the thermocouple
without affecting its emf output when the extension wire and connectors
have the same thermoelectric characteristics. For example, when
a type "K" thermocouple is being used the wires and connectors
used to extend it should also be type "K". The different types
have color codes, for instance type "K" is yellow, assigned to
them for easy identification so as to help prevent mismatching
of extension wire connectors and thermocouples. For example in
the yellow color code of the type "K" circuit, a blue type "T"
connector would be an obvious improper component.
The generalized
thermocouple system may be divided into five basic areas: Hot
Zone/Gradient Area/Extension Region/Reference Junction/ and Readout.
The extension region is generally where thermocouple connectors
are used to facilitate thermocouple-to-readout hook-up. In a simplistic
and isolated system the thermocouple will perform to specifications.
Unfortunately, these low voltage thermocouple signals can be interfered
with from power lines, relays, motors, transformers and all other
power associated appliances. This electrical noise can be reduced
by the correct application of shields and grounding techniques.
3-pole
thermocouple connectors provide a shield terminal that
maintains the shield circuit from metal sheathed thermocouples
to extension wires or from wire to wire hook-ups. Grounding must
be done at one point and only one point.
Thermocouple
connectors and panels are polarized making them virtually impossible
to mismate. Marlin's connectors and panels are molded from glass
filled thermoset compounds for high strength. They will not melt
and are rated for continuous use to 400°F (205°C) and 500°F (260°C)
intermittently. They are color coded and letter coded for type
and polarization identification. Current carrying metal parts
are made of alloys matching the characteristics of the thermocouple
type with which they are intended to be used. Contact springs
are non-magnetic, non-corrosive, and are specially selected and
processed to withstand the rated operating conditions.
An exception
to the color code is the red colored high temperature version
of these connectors and panels which are rated for use to 800°F
(425°C) continuous duty and 1000°F (540°C) intermittently. They
are molded from a highly stable and inert silicone-based thermoset
compound filled with glass fibers for strength. These high temperature
units are color coded red for
all thermocouple types but do retain the letter and polarization
identification. The premium materials of which Marlin's high-temperature
products are made, make them unusually suitable for harsh environments,
even where extreme temperature tolerance may not be a factor.
In particular, these high temperature units have proven durable
in the presence of radiation, and their low-outgassing properties
also make them highly satisfactory for use under vacuum. Marlin's
high temperature connectors are fully compatible, mechanically
and electrically, with normal-temperature connectors, and share
the same accessories and hardware. Regular and high-temperature
connectors of like kind will fully intermate.
For
more information regarding 3-Pole Connectors
Consult your Marlin Catalog, Pages F-19 to F-33.
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you do not have a Marlin Catalog - Click
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