Thermocouples
A thermocouple is a temperature measuring device consisting of two conductors of dissimilar metals or alloys that are connected only at the ends. When the ends are at different temperatures, a small voltage is produced in the wire that can be related directly to the temperature difference between the ends. If the temperature at one end is known, the temperature at the other end can be determined. Thermocouple wire or extension grade wire is used to connect the thermocouple to the sensing or control instrumentation. The conditions of measurement determine the type of thermocouple wire and insulation to be used. Temperature range, environment, insulation requirements, response, and service life should be considered when selecting a wire type. There are two common types of thermocouple wire, Type J and Type K.
TYPES OF THERMOCOUPLES COMMONLY AVAILABLE?
Thermocouples are available in different combinations of metals or calibrations. The most common calibrations are "J" and "K".
● Type “J” (Iron/Constantan™)
Type "J" thermocouples are used in vacuum, oxidizing, inert or reducing atmospheres. Iron element oxidizes rapidly at temperatures exceeding 1000 F (538 C), and therefore require heavier gauge wire to withstand these temperatures. Typically the two wires are red and white. When connecting to the control, the red wire is the negative terminal and the white is the positive terminal. The white wire is also the magnetic wire.
● Type “K” (Chromel™/Alumel™)
Type K thermocouples are used in oxidizing, inert or dry reducing atmospheres. Exposure to vacuum is limited to short time periods. Type "K" thermocouples must be protected from sulfurous and marginally oxidizing atmospheres. This type is reliable and accurate at high temperatures. Typically the two wires are yellow and red. The yellow wire is the positive terminal connection, and the red is the negative terminal connection. In this case, the red wire is the magnetic wire.
● GROUNDED THERMOCOUPLES
With a grounded thermocouple, the junction is connected to the tip of a metal enclosure. Being connected to the sheath of the enclosure affords protection to the thermocouple and excellent response.
● UNGROUNDED THERMOCOUPLES
The thermocouple is isolated from the metal sheath and for this reason gives up a little response time. By being electronically insulated, this design is not subjected to picking up electrical noise. Most newer Van Dorn/Demag, and some other machines, require ungrounded thermocouples.
SS Flexible Armor
CSS Overbraid
Adjusting Spring
Armor & Spring Adjustable Thermocouples
Adjustable Depth Thermocouples can easily adjust to any immersion depth -- saving time and money. Simply insert the adjustable thermocouple probe into the thermocouple adapter well. Then the thermocouple's locking cap is rotated up or down to the proper immersion depth and locked onto the adapter. Spring compression acts to keep the probe firmly seated in the well. This assures for rapid heat transfer and accurate sensing. The "AO" series has the bayonet cap on an 8" spring and allows for 7" of adjustable immersion. The "AA" series has the bayonet cap on the flexible armor and allows for full 8" length adjustable immersion. Both series have leadwire rated to 900°F maximum temperature.
● AO Series - Type J, 20-gauge stranded wire, single element, grounded, with stainless steel overbraid.
● AA Series - Type J, 20-gauge solid wire, single element, grounded, with flexible armor.
Click Here to View Part Number and Specifications for AA Series Adjustable Depth Thermocouples
Click Here to View Part Number and Specifications for AO Series Adjustable Depth Thermocouples
Fixed Bayonet Thermocouples
Bayonet Thermocouples are a fixed immersion thermocouple with compressible spring and locking cap. Bayonet TCs are well suited for applications requiring longer immersion depths. The probe of the bayonet TC is more rigid and provides a more positive contact in the deeper well. The compressible spring outer covering and its locking cap hold the probe securely in place. 90° bayonet TCs are often selected for use where space is at a premium and the 90° bend allows for a tighter, neater installation. All bayonet TCs have flexible extensions (overbraid or armor), ideal for connection to near or distant junction boxes.
● BA Series - Type J, 20-gauge solid wire, single element, grounded, with flexible armor.
● BO Series - Type J, 20-gauge solid wire, single element, grounded, with stainless steel overbraid.
Click Here to View Part Number and Specifications for BA Series Adjustable Depth Thermocouples
Click Here to View Part Number and Specifications for BO Series Adjustable Depth Thermocouples
Melt Bolt Thermocouples
Melt Bolt Thermocouples are immersed directly into the melt for a more accurate reading. They mount in the extruder barrel neat the head. The closed end sensitive portion of the tip is immersed directly into the plastic. There are two styles available. The Fiberglass type has a fiberglass insulated thermocouple element in a stainless steel probe. The MgO type obtains its insulation from magnesium oxide which is tightly compressed between the thermocouple wires and the stainless steel sheath.
● MB Series - Type J, 20-gauge stranded wire, single element with closed end, grounded, with flexible armor.
● MMB Series - Type J, 24-gauge stranded wire, single element with closed end, grounded, with 316 stainless steel rigid tube. Tip has MgO insulated element.
Click Here to View Part Number and Specifications for MB Series Melt Bolt Thermocouples
Click Here to View Part Number and Specifications for MMB Series Melt Bolt Thermocouples
Pipe Clamp Thermocouples
Pipe Clamp Thermocouples are attached to an all stainless steel worm gear hose clamp and are convenient where drilling or tapping is impractical.
● PC Series - Type J, 20-gauge wire, single element, grounded. Also available in Type K, solid or stranded wire, and with stainless steel overbraid or flexible armor.
Click Here to View Part Number and Specifications for PC Series Pipe Clamp Thermocouples
Rigid Tube Thermocouples
Rigid Tube TCs have an adjustable attaching device that eliminates the need for an adapter. Compression TCs allow for the final adjustment of immersion depth to be made at the time of installation. They are ideal for the monitoring of liquids or gasses since they seal the process from the atmosphere.
● CA Series - Type J, 20-gauge solid wire, single element, grounded, with flexible armor.
● CO Series - Type J, 20-gauge solid wire, single element, grounded, with stainless steel overbraid.
Click Here to View Part Number and Specifications for CA Series Adjustable Depth Thermocouples
Click Here to View Part Number and Specifications for CO Series Adjustable Depth Thermocouples
Ring Thermocouples
Ring Thermocouples also measure surface temperature, but are bolted to molds, platens and nozzles. They are often connected in parallel with another thermocouple to control at an average temperature. An example would be the connection of a ring thermocouple, measuring the surface temperature of the barrel, and a bayonet thermocouple, measuring deep inside the barrel's wall. The resulting reading would enable closer control for a more uniform temperature of the plastic melt. Note that the connected thermocouples must be of the same type and resistance..
● RT Series - Type J, 20-24-gauge stranded wire, single element, grounded, with stainless steel overbraid.
Click Here to View Part Number and Specifications for RT Series Ring Thermocouples
Spade Thermocouples
Spade Thermocouples measure the surface temperature by being slid underneath heater bands or held in place with a strap. They are very flat and can be placed in the gap where the two halves of a heater band come together. The heater's locking mechanism secures it in place. When used under heater bands in the nozzle area, it is relatively safe from damage by plastic back-up.
● ST Series - Type J, 20-gauge stranded wire, single element, grounded, with stainless steel overbraid.
Click Here to View Part Number and Specifications for ST Series Spade Thermocouples
Spark Plug Gasket Thermocouples
Spark Plug Gasket Thermocouples is a simple effective method to monitor the cylinder head temperature on a variety of single and mulitiple cylinder engines. The spark plug is inserted through the sensor and then torqued into the head as usual. The unique one piece design allows the use of the standard spark plug and eliminates the need for machining of the cylinder head.
● SPG Series - Type J, 24-gauge stranded wire, single element, grounded, with stainless steel overbraid.
Click Here to View Part Number and Specifications for SPG Series Spark Plug Gasket Thermocouples
Threaded Nozzle Thermocouples
Threaded Nozzle Thermocouples measure the temperature of the nozzle, when placed in a threaded shallow drill hole on the injection nozzle. There is no direct contact with the material flow. These TCs are a must for nozzles with minimal wall thickness between the inside bore and hex flat. Threaded Nozzle TCs come with a threaded rotatable sleeve bolt, which turns independently of the extension leads for easy installation or removal.
● TN Series - Type J, 24-gauge solid wire, single element, grounded, with stainless steel overbraid.
Click Here to View Part Number and Specifications for TN Series Threaded Nozzle Thermocouples
Click Here for technical information about Thermocouples