Small industrial servomotors are typically electronically commutated brushless motors. Copulas have been used for quality ranking in the manufacturing of electronically commutated motors. Voltage sourced converters generally produce lower intensity harmonics than line commutated converters. DC stands for Direct Current and EC stands for Electronically Commutated. These are driven using high efficiency EC (electronically commutated) motors with built in speed control. They are commutated direct frequency converters that are synchronised by a supply line. An original Mendocino Motor is a light commutated motor. Converters using thyristors or mercury-arc valves are known as "line commutated converters". In the inversion mode, a controlled rectifier circuit operates as a line commutated inverter. In recent years, quiet, electronically commutated motors with increased energy efficiency have been finding use. This minimum delay is called the circuit commutated turn off time ("t"). Commutated electric motors, such as universal motors, will run at reduced speed or reduced torque. Both line commutated converters (LCCs) and voltage source converters (VSCs) have been considered for this.