The EDL series of Platinum reference thermocouples are offered for use from 0°C to
1450°C and for short-term intermittent measurements up to 1700°C. Our thermocouples are designed and built to be used as precision standards and are not meant to be left in the case lying on a shelf. Our construction method and superior materials result in a highly durable and reliable reference sensor.

EDL offers three different sheath materials for our line of Platinum reference sensors; a high purity ceramic, Inconel 600, and quartz sheaths are available in three standard lengths of 10", 16", and 22" long. Our sensors are also available in three different diameters as a standard part number. These standard sizes are .187", .250", and .375" diameters.

A specific combination of diameter and length can be chosen to fit your calibration furnace or fixed point cells. These probes may also be used to verify processing readings in virtually any type of processing equipment from semiconductor wafer fabrication to high temperature sintering furnaces.

Imperial Units

Metric Units

EDL Platinum reference sensors are available with either a cold end compensation junction or with standard type R/S extension wire of 48 inches long. Our cold junction connection is made within a .250" diameter Stainless Steel sheath that may be placed in a standard Dewar type flask or in an artificial ice point. The lead length from the sensor to the compensation probe is 24 inches; the compensation probe has 48 inches of flexible stranded copper ready for attachment to your instrument. The option code for this feature is a "C" at the end of the part number.

The lead material for all sensor styles is a Teflon insulated wire inside of a Stainless Steel armored cable. This construction is well suited for both the laboratory and shop floor environment. Lead termination may be added at your facility or we can supply most terminations for your convenience. To assure an integral seal we use only pure Teflon glands in the compression-fitting end of the handle to connect the protection tube to the handle.

General considerations regarding the use of Platinum Rhodium/Platinum thermocouples:

The thermoelectric power of these thermocouples is relatively low, but their other physical characteristics generally prove more valuable to the industrial user. Primarily the behavior of the EMF is quite good and is considered one of the best for binary alloy thermocouples. The Platinum is also quite inert and resistant to oxidation that proves beneficial for many gaseous environments at elevated temperature. The melting point of Platinum is 1772°C, which makes this thermocouple useful up to almost 1700°C. Caution must be used above 1450°C as even short excursions above this temperature will cause premature grain growth which will promote contamination at the grain boundaries and will also cause a reduction of tensile strength of the thermo element. Environmental conditions will also affect long-term stability, requiring careful consideration of construction materials.

The thermo element will perform well in vacuum, oxidizing, reducing and inert atmospheres for extended periods provided it is sufficiently protected by the protection tube. The predominant contributor to drift will be caused be contamination originating from the sensor itself. All components of our sensor are well cleaned and carefully assembled to reduce contamination. We also use only gas tight protection tubes and 99.8% pure Alumina insulators to reduce cross alloy contamination. This is an overview of considerations and further discussion may be required depending on your specific application.

Sheath Material Specifications:

Alumina
Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99.8% (Al2O3)
Impenetrability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gas Tight
Maximum Working Temperature . . . . . . . . . . . . . . . . . . . . 1800°C
Unsupported Sag Temperature . . . . . . . . . . . . . . . . . . . . .1600°C
Volume Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .>1014
Thermal Conductivity:
@24°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67.4 WmK
@800°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17.6 WmK

Quartz 214
Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99.995% (SiO2)
Impenetrability . . . . . . . . . . . . . . . . . . . . . . . . . . .Gas Tight
Softening Point . . . . . . . . . . . . . . . . . . . . . . . . . . 1683°C
Anneal Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1120°C
Recommended max use temp. . . . . . . . . . . . .1250°C (15 Min.)
Electrical Resistivity . . . . . . . . . . . . . . . . . . . . . .7x109 Ohms/Cm@350°C
Thermal Conductivity:
@24°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1.6 WmK
@800°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9 WmK

Inconel 600
Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ni76Cr15 (approximate)
Impenetrability . . . . . . . . . . . . . . . . . . . . . . . . . . . .Gas Tight
Melting Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1350°C to 1425°C
Recommended max use temp. . . . . . . . . . . . . .1000°C (15 Min.)
Electrical Resistivity . . . . . . . . . . . . . . . . . . . . . . . 103: Ohms/Cm@350°C
Thermal Conductivity @24°C . . . . . . . . . . . . . . ..14.8 WmK

Alumina
The EDL Alumina sheath is 99.8% pure and will withstand temperature above the melting point of Platinum. This material is impervious to most chemicals and will not contaminate the working environment due to evaporation at elevated temperatures. It is more fragile than the Inconel 600 and will not tolerate shock or side loading. Alumina does have very high compressive strength. Replacement protection tubes are available.

G.E. Quartz 214
Our quartz protection tubes offer the most effective solution for environments requiring virtually no contamination from external sources. Quartz is an excellent choice for minimizing both hydrocarbon and metallic ion contamination. The quartz is easily cleaned with alcohol to remove any contaminants; this is difficult to accomplish with Inconel and Alumina. In addition due the very high melting point of Platinum there is virtually no ion contamination potential from the sensor in spite of the transparent nature of quartz near 1200°C. The quartz is the most fragile protection tube and will not withstand mechanical shock; it is resistant to thermal shock. Quartz will also sag as a function of both time and temperature as it is technically a viscous fluid. This will begin at about 1200°C after 15 min. and accelerates from this time and temperature. Replacement protection tubes are available.

Inconel 600
All sheath materials are supplied as gas tight assemblies and can be used with a vacuum wall feed through. It is recommended that the Inconel 600 be used for slightly lower temperature applications where durability is the primary requirement. This material resists oxidation and is also quite chemically resistant. Consideration should be given to potential electrical shock should the probe come in contact with any electrical source, such as a furnace or set of kiln elements. Replacement protection tubes are quite inexpensive and easily replaced.

Calibration: Platinum 10% Rhodium vs. Platinum

According to the NIST Monograph 175, the temperature to voltage relationship for Type S thermocouples is described by an eighth order polynomial and is available in the NIST Monograph 175. The defined range extends from -50°C to 1768°C. It should be noted that drift is considerable above 1450°C. In each sub range there is less than 0.75:V of fit error for the assigned polynomials and their respective coefficients.

The EDL Platinum sensors are calibrated by comparison at the ITS90 defined fixed points. The overall achievable uncertainty for these thermocouples is ±1.0°C. In limited use ranges ±0.5° is an obtainable accuracy. Calibration tables can be supplied for the sensor ensuring accurate results and eliminating the need for linear interpolation between calibration points. Please inquire about this option when placing your order.