Silicon Carbide is a semiconductor material, and has a much higher resistivity than metallic resistance materials. Room temperature resistivity is fairly high, and falls with increasing temperature to a minimum value at about 600-900°C. At elements temperature above 900° C. Resistivity increase with rising temperature, as shown in figure.
All silicon carbide elements gradually increase in resistance during their life in operation and the rate at which this occurs is affected by the following factors:
a) Element Specific Loading
b) Operating Temperature
c) Process Atmosphere
d) Mode of Operation (continuous or intermittent)
e) Power Supply Type used
f) Element Type
To optimize element life, the right type of element should be selected and the lowest specific loading consistent with the fournace design should be used. To compensate for the gradual increase in element resistance (ageing), a variable voltage power supply is usually provided, to enable the design power to be maintained throughout the life of the element.
SiC Touch Panel
CD Automation has developed many applications dedicated to drive particular loads and one of these application is for Silicon Carbide. The Philosopy is to use standard Thyristor units with serial communication and to implement the control strategy inside the intelligent panel. This Touch Panel in addition to a CD Automation universal unit able to work with all firing and control mode removing all application risks due to the control type selection.
This Solution gives many Advantages
- The Thyristor Units are standard and easy to be found everywhere
- An external port is available to connect your normally used PLC
- One Ethernet port is available on 8″ touch panels
- The Human interface is friendly and just feeling few data of thermic project is possible to achive.
Two different modes to drive SiC:
- Burst Firing with automatic adjustment of Power Limit
- Phase Angle with transfer from voltage to Power control mode.
- Automatic configuration and tuning of the thyristor unit
- Automatic tuning of Power Control mode VxI
- Message on when to change the elements because are at the end of their life
- Automatic switch from Voltage to VxI control mode when the element temperature is the correct one
- Automatic tuning procedure of Heather break alarm to diagnostic partial or total load failure
- Diagnostic of fuse failure and Thyristor in short circuit
- Recent and Historical Curve of following process variable
- Power density W/Cm2
- Load Voltage
- Load Current
- Power to the load
- Resistance value curve with new element
- Time elapsed from start to actual resistance value