The Retarding (also called DRED), is a device capable of applying or removing the power supply to a relay connected to its output, after a pre-set time.
The DRED guarantees a high level of reliability in typical railway signalling environments (sentry station, station) taking into account different sources of environmental stress (vibrations, temperature range, over voltages, etc.) according to the IS 402 Railway Regulation (Installation environment A5). This product complies with the IS 718 Italian Railway Specification.
There are two types of delay devices and they can be classified according to the following functions:
- Those of which (ie. DRE) are intended to apply, after a pre-set time has elapsed, the power supply to a neutral DC relay, for FS 58 counterplate: cat/prog 825/647; for FS 80 counterplate: cat/prog 825/649. (It occupies two FS 80 modules).
- Those of which (ie. DRD) are intended to delay, after a pre-set time, the removal of the power supply to a neutral DC relay, for FS 58 counterplate: cat/prog 825/648; for FS80 counterplate: cat/prog 825/650. (It occupies two FS 80 modules).
Such devices are housed in a plastic box of equal dimensions of a FS 58 neutral relay. They are equipped with auto diagnostics LED, which simplify its maintenance.
These delay devices are realized with a safety architecture that ensures a SIL4 safety integrity level, according to the Cenelec EN 50129 and EN 50126 regulations.
The device delay functions are continuously tested by a 2oo2 logical architecture and in case of safety failure, the device brings itself into an irreversible safe state. It powers down its external relay and also its own internal logic.
The delay is set via an opportune rotary thumbwheel lodged in the shell of the device, it enables the operator to see the time set.
The device is equipped with a special transparent sealable protection, and it can prevent the accidental variation of time that has been set by the rotary thumbwheel.