All-in-one models

Phase control: Thyristors are ignited during each half-wave, resulting in constant temperature control through fast clocking.

© System technology Leber

Pulse packet control: Complete sine waves of the mains voltage are switched through or blocked.

© System technology Leber

Many of the thyristor controllers on the market now offer an average of two of these functions in combination, for example phase control, pulse width modulation, pulse packet control, soft start, load monitoring, wire break detection, power failure detection, zero switching and bus control.

However, as processes and systems become increasingly complex, and therefore precise control is becoming more and more important, the functions of these controllers are often not sufficient. If additional functions are required, these must be retrofitted in the form of additional modules. In addition to money, these cost additional space in the control cabinet. The additional modules often require even more space in the control cabinet than the actual thyristor controller. For example, up to 100 thyristor controllers are now used to control the temperature of halogen or infrared radiators in a painting line in the automotive industry. In the area of bonding point attachment in dashboard production, there are up to 60, as the number of so-called holding points for airbags, sockets, etc. has almost tripled in recent years. These holding points are attached using the melting process, with each heating element requiring its own controller. And almost 100 thyristor controllers are also installed in modern stretch blow molding systems. As a result, the control cabinets are gradually becoming cramped.

The soft start dampens the high rate of current rise.

© System technology Leber

So-called all-in-one thyristor controllers such as the 'SHP controller' from Systemtechnik Leber offer a solution to this dilemma. Here, common functions are stored in a single device via software and can be selected by the user using DIP switches. If it turns out during the project planning phase that parameters such as the response behavior of error messages or the characteristic curve of the soft start need to be changed, this can also be done by changing the firmware.

If you want it to be even more precise

In some applications, even the thyristor solution is not the optimum solution - especially when network fluctuations affect the production process and, in particular, the production result.

Fluctuations in the mains voltage always lead to fluctuations in the electrical energy supply. If the mains voltage changes by 5 %, the power supply also changes by 5 %. As a result, the output changes by 10 %. And while the resulting heat changes by 10 % for pure resistance heating elements, complex loads such as NIR radiators result in considerably greater changes in the process energy. Such radiators do not have a linear relationship between electrical energy and process energy. The NIR radiation is only emitted in a certain electrical window and the characteristic curve has a high gradient towards the end. So if the electrical energy changes by 10 %, this means a change of around 20 % for the process energy.

For applications in which such fluctuations cannot be tolerated, the use of a power controller instead of a thyristor controller is recommended. Systemtechnik Leber offers 'UP power controllers', for example, which can be used with a supply voltage of 230 V(AC) as well as 400 V(AC) and for a load current of 16 to 75 A. These devices also regulate network fluctuations. These devices also regulate network fluctuations.

A concrete example: A control signal of 70 % results in an effective load voltage of 280 V at 400 V mains voltage. Regardless of whether the current supply voltage is 360 V or 400 V, the power controller ensures a constant load voltage of 280 V. It is particularly effective if the load voltage can be measured very quickly and corrective measures are initiated after each sine half-wave if deviations are detected.

The control

A common method for controlling solid state relays, power controllers and regulators is analog control with 0 to 10 V via a PLC. This requires an analog output for each individual switching element and an additional digital enable output for the entire system. Another option is control via industrial buses such as Profibus or Modbus. Both methods are relatively complex or oversized and usually incur considerable costs.

An alternative is to transmit the analog control values by means of a serial data telegram via digital outputs. Digital outputs of a PLC are less expensive than analog outputs and reduce the overall costs of the system. Most of Systemtechnik Leber's power controllers and regulators are designed for the use of this telegram. A free driver is available for 'Simatic' controllers from Siemens; a customized solution can be developed for controllers from other suppliers.

Author:
Denny Vogel is an expert for power supplies and power controllers at Systemtechnik Leber in Schwaig near Nuremberg.