Technology and application

Control types

ON/OFF: The easiest way to switch a load is to switch it on or off. Thereby the power controller overtakes the synchronization of the zero-crossings of the net. It switches on when the voltage passes through zero and switches off during zero-crossing of the electrical current.

The pulse width modulation (PWM) defines the efficiency through the ratio of duty cycle to pause duration during a fixed period and is the most applied controller mode. This controller mode is ideal for inert processes.

The burst firing – as a sub category of the PWM – provides precise switch of single full waves of the net with the aim to avoid long on- or off-phases. However, this mode requires a certain thermical inertia of the load.

In a phase angle each single half-wave is cut directly. Thereby electricity flows from ignition timing to the next zero-crossing at which the thyristor switches off automatically. With this the required capacity can be set almost continously. It is the most accurate and fastest mode of control. Thus, an optimal power support for processes with a high processing speed and high requirements for a stable output is possible.

Control of Power Controllers

Analogue 0-10V: The analogue control with 0-10V over a SPS is a common method for the control of power controllers or solid state relays. Therefore an analogue output for each single power controller as well as a digital release-output for the whole system is needed.

Serial data telegram: The serial data telegram needs for each single power controller a digital output for the data as well as for the whole system a digital output for the tact. The serial transmission of the analogue values requires a protocol which can be understood by the power controller and be outputted over a SPS. For the SPS-family S5 and S7 a free driver can be downloaded under www.powercontact.de.

Bus: The most elaborate option of control is the application of an industrial bus as for example Profibus DP. Thereby, the controllers can be optimal integrated in an existing bus-infrastructure. Moreover, additional options for reading-in and reading-out are available. For power controllers up to 75 A due to cost reasons the usage of a common Profibus switch – by which several participants can be controlled – is recommended. For controllers above 150A an alternative intergated Profibus-board is available.

Monitoring functions

The power controllers have a wide range of diagnostics to be able to detect for example safety case, wire breaking, load interrupt, undervoltage, failure in load voltage or auxiliary voltage and to report it over an alarm output. Moreover the power controller is monitoring itself (failure, partial failure).

Special functions

For difficult loads power controllers with special functions are available including control modes as voltage control (constant level of load e.g. in case of line variations), current control (for complex loads) or the power control (exact energy output independent of voltage- and current fluctuations). For applications in which loads are connected in parallel a power controller with partial load failure recognition can be recommended. Thereby, several loads can be controlled with only one controller (cost savings) without renouncing an error message in case of failure load. Controllers with current limiting protect the load and ensure a safe operation.

Circuit protection with power controllers

For the application of power controllers in a load circuit the whole load circuit has to be protected with a saftey mechanism. Typically, by this not only the load circuit but also controller is protected in the event of short-circuit. For this purpose the relevant literature recommends the application of (expensive) semi conductor fuse. The power controllers from Systemtechnik LEBER are designed to be protected with standard (low priced and easily available) automatic circuit breaker. We would be glad to assist you in the dimension.