© Brüel & Kjaer Vibro ● S1079330.002 / V04 ● █ Page 39 of 188
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Brüel & Kjaer Vibro │ Instruction
VC-8000 MPS
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6.9.3 Can I Bypass “the Rack” to Avoid a False Trip? No.
No. You cannot bypass “the rack”. The bypass function is often misunderstood. Most of the time the
phrase “bypass the rack” means “isolate the rack from external systems”. The rack bypass function is
a “self-governing” feature; whereas “isolation” is external to the rack.
An analogy will help. You can ask a child to stop yelling (alarming). If the child obeys, he is self-
governing. Or you can isolate the child by placing him in another room. The child can yell (alarm) as
loud as he wants – but it does not matter because you can’t hear him.
Channel Bypass and Rack Inhibit are self-governing features in the rack. The rack needs power and
must be running normally for self-governing to occur.
The rack cannot “self-govern” during maintenance activities such as re-configuration, card removal,
power cycles etc. The rack needs to be isolated with circuitry (or systems) external to the rack. If the
rack is isolated externally, it can alarm (yell) as much as it wants while the maintenance takes place.
6.9.4 Every Card is a Relay Card
By design, every monitoring card in the VC-8000 system is also a relay card. If you ‘Send’ a
configuration to a UMM module, you are configuring a relay card; If the relay channels are Normally
Energized, the relays will change state.
Any monitoring system connected to a running machine (in production) should be externally isolated
before any maintenance takes place. In many places and industry this is even mandatory. When the
rack is externally isolated it will not matter if the card reboots, or if the relays change state.
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