1) Heat blanket amperage requirement. This can be determined by dividing the rated wattage by the rated voltage. For example, If I am using a heat blanket rated at 1280 Watts, and 120 Volts, the amperage calculation is Watts = (1280/120) = 10.67 Amps.

2) Input plug amperage limitation. The cables that Delta has purchased from us most frequently have a HCS1201 input plug rated at 15 amps. The amperage is always limited by the input plug. If the input plug on your bonder looks like a standard 120Volt household plug, you are limited to 15 amps. If a higher amperage is required we can supply a 30 amp input plug.

3) Output receptacle amperage limitation. Again, the cables that Delta has purchased most frequently have two 15 amp receptacles in the output cable. These look like a household 120V configuration. The maximum amperage of each heat blanket plugged into the output receptacle must not exceed 15 amps. The maximum combined amperage of the heat blankets plugged into the output cable must not exceed the amperage rating of the input cable (15 amps).

4) Service power limit. Many shop environments also use 15 amp, 120 V
receptacles. When this is true, your input power will be limited by the service power available. If you had a 30 amp input cable to the bonder, and only had a 15 amp power receptacle available, you would still be limited to 15 amps. If you do decide to use a 30 amp input power cable, make sure that 30 amp service power is available (These are usually twist-lock style receptacles).

In conclusion, all you need to remember is Service power rating, Input power rating, Output power rating. Pick the lowest of the three and this is the limit of the heat blanket you can use. Calculate the amperage of the heat blanket using the Watts/Volts formula and compare it to the lowest rating. If it exceeds the lowest rating, you cannot use the blanket with the existing power configuration. If it is under the lowest rating, you are in good shape.

The thermocouples sold by Heatcon Composite Systems are designed and manufactured for aerospace application, using the highest quality material. The type of thermocouple wire used is known as "instrument grade" wire, with a specified measurement tolerance of +/- 2 degrees F, (1.1 degrees C). This is as opposed to other products available that are constructed of "extension grade" wire, with a specified tolerance of 4 degrees F, (2.2 degrees C). The insulation on the wire is Kapton. This material does not melt, and has excellent abrasion and moisture resistance. The specified maximum service temperature is 500 degrees F. The actual thermocouple junction, (temperature sensor), is welded to provide mechanical integrity and stable temperature output readings.

Background

A thermocouple is temperature measuring device consisting of two conductors of dissimilar metals or alloys that are connected only at the ends, called junctions. When the ends are at different temperatures, a small voltage is produced in the wire that is directly related to the temperature difference between the ends. If the temperature at one end is known, the temperature at the other end can be determined by the measured voltage. The accuracy of the thermocouple is determined by several factors. The major factors are the quality and uniformity of the wire, and the type and condition of the junction. The quality of the wire is specified by Heatcon and controlled by the manufacturer. The junction is probably the most important factor of which the user has control. Other factors would be shunt impedance, galvanic action, series resistance, and decalibration due to annealing when exposed to excessive heat. Shunt impedance and galvanic action are minimized by the use of the Kapton insulation, which prevents moisture intrusion. Series resistance becomes a factor only at very long lengths or if very small diameter wire is used. The Heatcon Composite Systems thermocouples are made of 24 AWG wire, that is useable up to hundreds of feet. The temperature ranges the wire is subjected to, under composite repair conditions, is well below the annealing point, and is not considered a problem factor.

Application

A point to consider is that the thermocouples have a finite service life, and require periodic inspection and re-termination. As the thermocouple is used in the repair process, foreign material can contaminate the junction, and the junction material will oxidize when exposed to heat and moisture. These factors will affect the temperature as sensed by the repair equipment. The junctions are welded during the manufacturing process, which minimizes the effects of contamination and oxidation. Simply twisting the wire ends together is not considered a satisfactory junction. This type of junction will degrade very quickly under heat and pressure, resulting in false temperature measurements. The junctions can be reworked in the field with the use of a portable thermocouple welder. The original junction is cut off, wires stripped, and a new junction is formed by fusing the bare wires together with the welder. The change in length caused by the re-termination process does not affect the temperature reading, due to the relatively large wire size used in the construction of the thermocouples.