The Signal Isolation Card ‘SIC’ powers the Ultrasonic Sensor. The Ultrasonic Sensor measures the diameter of the roll in order to keep tension constant as the roll size changes and sends a 0-10 VDC signal to the ‘SIC’. The SIC's 0-10 VDC output signal controls a Placid Industries PST power supply. Web tension is adjusted by the Tension Adjustment Potentiometer.