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Speed monitor can retrofit safety

18 May, 2011

A new speed monitor from Pepperl+Fuchs allows safety functions up to SIL3/PLe to be retrofitted to existing installations without needing safety PLCs or relays, or a second sensor. The simplest version of the modular system consists of a safety control, a speed monitor and a safe 58mm, 1,024 pulse/rev sin/cos encoder.

A custom chip continuously verifies signals from two encoder tracks offset by 90 degrees, as well as monitoring the supply voltage, temperature and calibration data. An additional absolute track provides information about the exact position of the shaft.

The system provides safe stop, safe speed, and safe acceleration/deceleration ramps for monitoring drive shafts via two safe outputs. If a condition is broken – for example, the allowed speed is exceeded – the system initiates a measure such as an emergency stop. The ramp-monitoring function can determine the minimum deceleration path required by referring to speed and position data or deceleration ramps. If the system risks losing control, the monitor raises an alarm and prevents a potential crash.

The monitor is said to be easy to set up using PC software. A teach-in function can “learn” the current speed at the press of a button. The configuration can be transferred to another monitor using a memory card.

Four safe inputs are provided for connecting standard or safety peripherals.
Using extra speed monitor modules, the decentralised system can be upgraded to protect up to 40 axes. The monitor for a second axis is already built into the basic device, which can be linked to other systems via Profibus DP or Profinet.

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