Single and dual input analyzers for pH/Redox (ORP)
AX416, AX436, AX460, AX466 & AX468 6Installation
48 IM/AX4PH Rev. P
6.3.1 Relay Contact Protection and Interference Suppression
If the relays are used to switch loads on and off, the relay contacts can become eroded due to arcing. Arcing also generates radio
frequency interference (RFI) which can result in analyzer malfunctions and incorrect readings. To minimize the effects of RFI, arc
suppression components are required; resistor/capacitor networks for AC applications or diodes for DC applications. These
components must be connected across the load – see Fig. 6.6.
For AC applications the value of the resistor/capacitor network depends on the load current and inductance that is switched. Initially,
fit a 100R/0.022 µF RC suppressor unit (part no. B9303) as shown in Fig. 6.6A. If the analyzer malfunctions (locks up, display goes
blank, resets etc.) the value of the RC network is too low for suppression and an alternative value must be used. If the correct value
cannot be obtained, contact the manufacturer of the switched device for details on the RC unit required.
For DC applications fit a diode as shown in Fig. 6.6B. For general applications use an IN5406 type (600 V peak inverse voltage at
3A).
Note. For reliable switching the minimum voltage must be greater than 12V and the minimum current greater than 100mA.
Fig. 6.6 Relay Contact Protection
NC C NO
External
DC Supply
+
Relay Contacts
Load
Diode
NC C NO
External
AC Supply
LN
Relay Contacts
C
R
Load
A AC Applications B DC Applications
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