Reliable Protection of 24 VDC Load Circuits

When overloads and short circuits occur, there’s always a tradeoff between the power supply shutting down the entire 24 VDC supply and keeping load circuits that aren’t impacted by the failure continuing to run. The new SITOP PSE200U electronic diagnostic module from Siemens Industry Automation Division constantly monitors up to four 24 VDC load circuits for overloads and short circuits.

“Today’s switched-mode power supplies provide advanced functionality, by protecting 24 VDC loads against any kinds of overload. Unfortunately, it responds by shutting down the power supply to all load circuits even before a fuse or circuit breaker can trip on the circuit that is actually being overloaded. The result: Power is shut down to all 24 VDC load circuits, even those that aren’t affected,” says Kai Bronzel, product marketing manger, Siemens Industry. “The SITOP PSE200U electronic diagnostic module intelligently shuts down the current to the affected load circuit, without impacting the other load circuits that don’t have problems.” Furthermore, the SITOP PSE200U provides for sequential start up, which significantly reduces the total current required from the power supply during the start up phase of high inrush loads. This avoids the shutdown of the power supply when the total inrush current exceeds the current limitation of the power supply.
In order to more closely match the application, there are now two versions of the device with tripping current ranges of 0.5 to 3 and 3 to 10 amperes available. This is an improvement over the previous SITOP select model, which had a wide adjustment tripping current range of 2 to 10 amperes. Used as an additional component in switched mode regulated 24 VDC power supplies, the new SITOP PSE200U electronic diagnostic module detects not only slight overloads but also “creeping” short circuits on high-resistance cables. If an overload or short circuit occurs, the device switches off the current to the faulty path. This prevents the power supply voltage from dipping, thus ensuring that power continues to be supplied to all the other circuits not affected by the fault. Up to four load circuits per module can be protected. Additional electronic diagnostic modules can be connected to the power supply if the application requires the protection of more circuits.
The new SITOP PSE200U electronic diagnostic module has sealable potentiometer covers to protect the set tripping currents against unwanted changes. The three-color LED and signaling contact concept makes it simple to troubleshoot systems and get directly to the faults. Diagnostics data can be transmitted to a higher-level controller for remote diagnostics. The SITOP PSE200U allows fast commissioning due to switch on/off functionality by using individual reset buttons per circuit in front of the unit. In addition a remote reset from a higher level control system is also possible. In contrast to conventional miniature circuit breakers, which do not trip until the current rises to a multiple of the rated current, this new electronic diagnostic module already responds to an overload that is only slightly above the set tripping current. The device also differentiates between a sustained fault and a transitory, operational overcurrent. This enables short circuits to be detected even on high-resistance cables in which, for example, core cross-sections are small or there is a long distance to the load.

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