Ionization probe
Microammeter DC
uA > 2-3 times the minimum one
Example with 0,5 μA: μA>1,5 μA
+
-
μA
■ Disconnect the terminal of the flame control electrode as shown in ;
■ Connect the multimeter in series as described above by means of the two cables with the crocodile
clamp to one of the flame control electrodes and to one of the internal metallic part of the terminal of
the cable, as shown in ;
Ionization current measurements
The ionization flame detection device makes use of the rectification property of the flame (ionization), as
shown in Figure 19. The control system is more sensitive to the flame at starting or during waiting/prepurge
time (negative differential switching).
Figure 19
Ionization flame scheme
The ground terminal of the control system, the metal frame of the gas burner and the ground on the main
supplies must have a good connection. Avoid putting the detection cable close to power or ignition cables.
In case of “partial” short circuits or bad insulation between signal and ground the voltage on the detection
electrode can be reduced making it impossible to detect the flame signal, resulting in a lockout of the
control system. In order to measure the ioniziation current, the multimeter has to be connected in series
between the flame control electrode and the flame control board. The value of the current measured
should be in the range of 1.5 - 10 μA.
Figure 20
Flame control plug and flame control plug cable
Figure 21
Multimeter connection to the flame control plug
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