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Thermocouple Technical Data

Junction Types

Grounded

Exposed

Ungrounded

Measuring Junctions

An exposed junction is recommended for the measurement of static or flowing non-corrosive gas temperatures where fast response time is required. The junction extends beyond the protective metallic sheath to give accurate fast response. The sheath insulation is sealed where the junction extends to prevent penetration of moisture or gas which could cause errors.
An ungrounded junction is recommended for measurements in corrosive environments where it is desirable to have the thermocouple electronically isolated from and shielded by the sheath. The welded wire thermocouple is physically insulated from the thermocouple sheath by MgO powder (soft).
The grounded junction is recommended for the measurement of static or flowing corrosive gas and liquid temperatures and for high pressure applications. The junction of a grounded thermocouple is welded to the protective sheath giving faster response than the ungrounded junction type.

Material	Maximum Temperature	Application Atmosphere				Applications
		Oxidising	Hydrogen	Vacuum	Inert
304 SS	900°C(1652°F)	Very Good	Good	Very Good	Very Good	Recommended for general chemical applications, food applications, oil refinery use, and steam lines.
Inconel 600	1150°C (2102°F)	Very Good	Good	Very Good	Very Good	Recommended for gas furnaces, lead baths, and bath mixtures containing cyanide. Do not use in salt baths contaminated by sulphur.

SPECIFICATIONS Diameters: standard diameters. 1.5 mm, 3.0 mm, 4.5 mm and 6.0 mm with two wires. Length: standard thermocouples have 30 cm immersion lengths. Other lengths available. Sheaths: types 304 and 321 stainless steel and Inconel are standard. Other sheath materials available; call for price and availability. Insulation: Magnesium Oxide is standard. Minimum insulation resistance wire to wire or wire to sheath is 1.5 megohms at 500 volts dc in all diameters. Calibration: Iron-Constantan (J), CHROMEGA-ALOMEGA (K), Copper-Constantan (T) and CHROMEGA-Constantan (E) are standard calibrations. Bending: easily bent and formed. Bend radius should be not less than twice the diameter of the sheath.

Delivery: off-the-shelf, other sheaths available; write for price and delivery. Dual Elements: thermocouples with a sheath diameter of 1.0 mm (0.040") through 6.0 mm (1/4") are available in dual element. Accuracy: the wires used in OMEGA thermocouples are selected and matched to meet ANSI Limits of Error. Special limits of error thermocouples can be made from all 1.5 mm OD or larger. Polarity: in the thermocouple industry, standard practice is to colour the negative lead red. Other standards that OMEGA uses are: the negative lead of bare wire thermocouple is shorter than the positive lead, and the large pin on a thermocouple connector is always the negative conductor. Extension Wire: thermocouple alloy wire must always be used to connect a thermocouple sensor to the instrumentation to assure accurate measurements.

Symbol	Recommended Thermocouples
	Calibration and Use	Positive (+)	Negative (­)	Colour Code—ANSI
T	Copper-Constantan (very low temperature)	Copper (yellow metal)	Constantan (silver metal)	Blue
	Suitable for subzero temperatures. Can be used in oxidising, reducing, inert or vacuum atmospheres up to 350°C (662°F).
K	CHROMEGA-ALOMEGA (Oxidising atmosphere)	CHROMEGA (Non-magnetic)	ALOMEGA (Magnetic)	Yellow
	Recommended temperature range is -200 to 1250°C (-328 to 2282°F). Should not be used in reducing or sulfurous atmospheres. Can only be used in vacuum for short time until calibration shifts.
J	Iron-Constantan (reducing atmosphere)	Iron (Magnetic)	Constantan (Non-magnetic)	Black
	Recommended temperature range is 0 to 750°C (32 to 1382°F). Can be used in oxidising, reducing, inert or vacuum atmospheres.
E	CHROMEGA-Constantan (High output)	CHROMEGA (Non-magnetic)	Constantan (Non-magnetic)	Purple
	Recommended temperature range is -200 to 900°C (-330 to 1600°F). Can be used in oxidising or inert atmospheres. Should not be used in reducing or vacuum atmospheres.