6 MM Features
Mk8 MM Manual Page | 128
6.3 Flame Detection Using Flame Switch
The Mk8 MM can utilise an external flame switch for the purpose of flame detection. To configure operation
with a flame switch, option/parameter 122 can be set to 1.
The operation of Terminals 85 and 86 will be as follows:
• When the flame switch indicates no flame, the voltage on Terminal 85 must be 0Vac, and the voltage
on Terminal 86 must be mains voltage (110/230Vac).
• When the flame switch indicates the presence of a flame, the voltage on Terminal 85 must be mains
voltage (110/230Vac), and the voltage on Terminal 86 must be 0Vac.
Terminal 85 is the functional input for detecting the flame.
Terminal 86 is solely for the purpose of checking that Terminal 85 is operating correctly.
Terminal 86 must be seen to be the inverse of Terminal 85, i.e. if Terminal 85 is at 0Vac, Terminal 86 must
be at mains voltage and if Terminal 85 is at mains voltage, Terminal 86 must be at 0Vac.
If Terminal 86 does not follow the inverse of Terminal 85 ‘Terminal 86 inverse’ error will be triggered.
Important notes:
• High purge interlock (parameter 92) will not operate with flame switch.
• Within the Mk8 MM there is a latency of 250 milliseconds on the monitoring of Terminal 85. To
ensure a 1 second overall flame failure response time, it is essential that the response time of the
flame switch is set to no more than 750 milliseconds.
• Flame switches often provide a volt free changeover contact to indicate the flame status.
Alternatively, they may provide a pair of `inverse’ outputs. If the flame switch only provides a single
output terminal, a relay will have to be installed between the flame switch and the MM to provide a
set of volt free changeover contacts.
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