#button heater

[thermicedgeltdengland-blog]

THERMOCOUPLE NOISE

Thermic Edge have years of expertise when it comes to temperature measurement. Within each of our systems from Laboratory Vacuum Furnaces to Sample Heaters, thermocouples play a central role in the safe and accurate operation of these Substrate Heating systems. All thermocouples used in our substrate heating applications are made in house, with specialist sheathed thermocouples available from UK manufacturers, such as those found in our Laboratory Furnace range.

One of the key items that make Thermic Edge systems so accurate is the combination of the thermocouples with our controller systems. One of the greatest problems with thermocouple accuracy at temperature. Discrepancies within temperature measurement is found when electrical noise is generated in the thermocouple signal. This noise may not be an issue for applications where a wide temperature range within the system can be accommodated. However in areas where fine controlling of the temperature of the system is required, this noise can cause serious adverse effects on the accuracy of the process being carried out.

It is a low frequency noise (i.e. less than 1hz) that is caused by a change in the dielectric properties of alumina at high temps (>1000C).  Alumina is one of the most common sheath materials used at high temperatures, therefore this can be a very common problem.

 The solution to this issue is to use a controller specifically designed for furnace control. These units, which Thermic Edge supply with each of our controllers, have a filter within the system to remove this noise. Coupled with an input impedance of about 10M, which suppressers the larger peaks seen in the noise, the accuracy of the temperature readout is vastly improved.

Another source of electrical noise occurs when a system is connected to an AC circuit. The alternating current within the element creates a magnetic field within the vicinity of the heater. This alternating field then has the propensity to induce a current within the thermocouple tip. This current will affect the signal read by the controller.

The solution to this is to use a DC power supply. Thermic Edge have a range of power supplies up to 6 kW as standard, and up to 30kW available on request. These powers supplies are used widely within all of Thermic Edge’s range of systems from Sample Heaters and Heater Stages up to our vacuum Furnace range.

For more information or to seek assistance with any issues you may have with your current thermocouple arrangement, contact Thermic Edge and a member of our team will be more than happy to assist you in choosing a system to meet your exact requirements

[thermicedgeltdengland-blog]

VAPOUR PRESSURE

One of the greatest challenges with high temperature Substrate Heating, is the effect of vapour pressure of materials on the ability of the system to achieve the required targets and survive.

The vapour pressure is defined as the pressure at which the molecules of a certain solid material will escape from that substance to form a separate vapour phase above the solid phase.Vapour pressure is a measure of the molecules ability within the material to be able to bond with each other. Materials with a low vapour pressure have strong bonds while those with a high vapour pressure will have weak bonds. The normal boiling point of a liquid is defined as the temperature at which the vapor pressure of the liquid is 1 atmosphere. The effect of pressure and temperature on the boiling point of water can be seen when water is boiled at altitude. The boiling point is reduced.

The effect of pressure is similar for solids used within a UHV Heater. At these extremely low pressures, the temperature point at which the liquid phase becomes unstable the solid vaporises is reduced. Therefore, materials which would have been able to withstand high temperatures at atmospheric pressures are no longer effective as a material to be used within Ultra High vacuum (UHV). Even the change from High Vacuum (HV) to UHV can cause extremely detrimental effects to the materials within a Sample Heater. The process by which a solid transforms directly to a vapour is known as sublimation.

To combat this possible problem, Thermic Edge ensure that the vapour pressures of all materials are identified prior to being used within a heater. This can be determined through simple research into a material, assessment of the material specification, or through direct testing in our test facilities.

Each one of our Substrate Heating solutions, be it from our Heater Stage or Button Heater range through to our Laboratory Furnace range has been rigorously tested with each component used assessed for both its ability to withstand ultra high temperatures up to 3000 degrees Celsius, through to the ability to survive within HV and UHV environments.

For more information on how our Substrate Heating technology can assist in your applications, please contact us and one of our team will be more than happy to assist you in identifying the best solution for your requirements.