The BNS/AES non-contact machine guard monitoring system from Schmersal
includes sensors that are operated by a coded and tamper-proof magnetic
field with a special polarisation and field strength. The sensor also
feature two-pole reed elements with a normally open and normally closed
circuit, minimising common mode causes of failure such as welding of the
normally closed contact. BNS/AES conforms to the new classification,
PDF-M (self-monitoring) described in IEC60947-5-3.