Ntron SIL O2, User'S Operation Manual, Page: 13 / 56

13 | P a g e R e v . 1 . 1
I s s u e 3 0 - 1 1 - 2 0 1 8
2.3.3 Typical Relay Configuration
Power to the Analyser Relay
Contact 1
Relay Contact
2
Relay Contact
3
Comments
Power Off
(All relay contacts in Fail
Open condition) Relays
De-energised
Power on and system
good/healthy ** ** All Relays
Energised
Power on and O2 alarm
level(s) reached * * Relays 1 & 2
De-energised
Power on and System fault ** ** All Relays
De-energised
These relays are programmed to respond to the measured Oxygen level setpoints (Alarms), rising or falling in
the range 0-25% Oxygen. These are pre-set to the customer’s requirements.
They operate in ‘Fail Safe’ mode which means that they are energized (under current), presenting a closed
contact to the customer/user when the SIL O2 module is under power and the status is healthy/good.
When at a level setpoint (Alarm) or when the SIL O2 module is not-powered, the relays are de-energised (not
under current), presenting an open contact to the customer/user. This is also known as ‘Fail Open’ (FO)
condition.
Transisitor (DO)
This is an NPN device that can switch 24VDC and can be configured to be normally open or normally closed.
Analogue 4-20mA
This is an active output and requires connection to a passive external circuit suitable for proper operation.
It is set to the range 0-25% Oxygen / 4-20mA (0% Oxygen = 4mA, 25% Oxygen = 20mA.)
This range can not be adjusted.
If the 4-20 mA output is not used, the SIL O2 terminals T11 and T12 must be wired by the user. This output is
internally connected in series with the SIL O2 Analyzer digital display, which will not work if the
aforementioned terminals are in open circuit!