Flame Supervision With Ionization Probe; Measuring Circuit; Figure 6: Measuring Circuit: Ionization Probe - Siemens LME39 Series Basic Documentation

Detector voltage between ionization probe and ground
(AC voltmeter Ri  10 M)
Switching threshold (limit values):
Switching on (flame on) (DC ammeter Ri 5 k)
Switching off (flame off) (DC ammeter Ri 5 k)
Detector current required for reliable operation
Switching threshold in the event of poor flame during operation
(LED flashes green)
Short-circuit current between ionization probe and ground
(AC ammeter Ri 5 k)

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Building Technologies Division

6.4 Flame supervision with ionization probe

Table 3: Data ionization probe
¹) For applications outside the European Union, operation at mains voltage AC 120 V/AC 230 V ±10% is
ensured
Flame supervision with ionization is accomplished by making use of the conductivity and
rectifying effect of the flame.
The DC current that flows in the presence of a flame (ionization current) is largely
proportional to the flame quality. This current is measured in the flame signal amplifier.
The amplifier is designed such that it only responds to the DC current component of the
flame signal. This ensures that a short circuit between the ionization probe and ground
cannot simulate a flame signal (since in that case AC current would flow).
Note!
The ignition (ignition spark) can have a negative effect on the ionization current
formation during startup.
To minimize the impact

the positioning of the ionization probe must be checked and optimized

it may be beneficial to replace the electrical connections (phase / neutral) on the
primary side of the ignition transformer
A short-circuit between ionization probe and ground initiates a non-alterable lockout.

6.4.1 Measuring circuit

M
+
+
LME39...
1
C
7106v01/0405

Figure 6: Measuring circuit: Ionization probe

For detector currents, see General unit data.
Basic Documentation LME39...
6 Technical data
UN = AC 120 V ¹)
AC 50...120 V
DC 1.5 µA
DC 0.5 µA
DC 3 µA
Approx. DC 5 µA
AC 50...150 µA
Legend
-
C Electrolytic capacitor 100...470 µF; DC 10...25 V
ION Ionization probe
Microammeter, Ri max. 5,000 
M
ION
At mains voltage
UN = AC 230 V ¹)
AC 115...230 V
DC 1.5 µA
DC 0.5 µA
DC 3 µA
Approx. DC 5 µA
AC 100...300 µA
CC1P7106en
08.12.2017