A heating solution for creating the desired temperature gradient in long metal pipes.

In order to perform experiments, scientific research institutes require a precise temperature gradient on long metal objects, usual pipes with a 6-18 inch diameter. Temperatures can go up to 1000°C and must be accurate within 1°C.

Libratherm offers a multi-zone heating system with up to 20 individually controllable zones. These zones are used to heat up a specific section of the object to a specific temperature. Each zone is individually controlled with a closed-loop system.

Heaters in each zone are connected to a Thyristor Power Controller (POW-1-PA) which controls the power delivery proportional to the control signal. This power controller receives its control signal from a Temperature Controller (PID-723/PID-966), which uses a robust control algorithm to achieve precise temperature control. The temperature controller takes the temperature feedback from the zone using a K-Type thermocouple thereby forming a closed loop. When several such zones are brought together in a heating system, a temperature gradient can be achieved across the object by setting the desired temperature of each zone.

Additionally, current meters are provided to monitor the current drawn by each zone. An Auto/Manual selection along with manual heater control is also provided for each zone. Keeping in mind the ergonomics of a laboratory setup, the control panel is designed in the most compact way possible.

When to select Phase angle control thyristor power regulator and when to select zero cross over thyristor power switch?

It all depends on the user’s application. If the requirement is just the temperature control and the KW ratings of heaters are within 25KW, and frequent turning ON-OFF operation does not put the burden on the power lines, the power factor is of concern then thyristor switches are recommended. Many heating applications using higher KW of heating elements of the order to 500A, also use 2 leg or 3 leg control thyristor power switches as a cost-effective solution.

However, if the concern is electrical power savings, if the system is going to remain ON for 365 x 24 hours, consistency and stability in temperature control is utmost important, not to put the burden on power lines, the incoming voltage is not stable, want to enhance the life of heaters, then in such applications, always, thyristor power regulators are preferred.

Main users of thyristor power switches have been AHU manufacturers where heater power is required to be controlled to maintain the desired level of Humidity in the treated delivery air. If the Moisture contained in the air increases, the temperature is required to be increased to evaporate the moisture. The PID controller is used for such automatic humidity control in conjunction with thyristor power switch or thyristor power regulator.