The ac drives manufacturer, Vacon has developed an ATEX-certified thermistor input which is fully integrated in the drive. Certified and compliant with ATEX 94/9/EC, the integrated thermistor input is specially designed for the temperature supervision of motors that are placed in potentially hazardous areas.
In contrast to a typical system with a separate thermistor relay and contactor, a thermistor input can be fully integrated in the Vacon NXP drive. This unique feature simplifies the use of drives together with Ex motors, i.e. motors that are designed and certified for use in potentially explosive environments. If overtemperature is detected, the drive immediately stops feeding energy to the motor and thus further heating of the motor is avoided. As no external components are needed, the cabling is kept to a minimum. This improves reliability and saves both space and costs.
"As usual, designing an ATEX-certified thermistor input started from a customer need," says Mr Heikki Hiltunen, Executive Vice President, Vacon. Explosive atmospheres where supervision of motor temperatures is required are widely found in the chemical, petrochemical, marine, metal, mechanical woodworking, mining and oil drilling industries.
The thermistor input is available for the Vacon NXP drives in the power range of 0.75 kW - 5 MW in voltages 380-500 V and 525-690 V. This function is now certified to comply with the ATEX requirements. "However, the drives as such cannot be placed in a hazardous area," emphasizes Mr Hiltunen.