Safe speed monitor

The Wieland SNS 4084K standstill monitor enables machinery operators in process industries to safely monitor two input signals in the 0.1 to 99 Hz frequency range.

The 45 mm housing fits into standard racks and operates on 24 VDC nominal power. The unit provides four semiconductor outputs with automatic or manual start and can operate in the -25 to +55 °C range.

The unit’s main function is safe monitoring of the frequency of pulses on the inputs I1 and I2 of the device. If the frequency of the pulses is higher than the adjusted frequency, the outputs Q1/Q2 are switched off. This monitoring function is used for detecting a standstill or limited machine speed.

The signal can then be used to ‘inch’ the machine at low speed or unlock solenoid locks at zero speed.

The sensors for monitoring the standstill can be, for example, two inductive proximity switches connected on I1, I2, or an incremental sensor with HTL outputs connected on I1-I3.