Relay Contact Protection And Interference Suppression - ABB AX416 User Manual

Single and Dual Input Analyzers for pH/Redox (ORP)
AX416, AX436, AX460, AX466 & AX468 6 INSTALLATION

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/0.022µF 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 (600V peak inverse voltage at 3A).
Note. For reliable switching the minimum voltage must be greater than 12V and the minimum current greater than 100mA.
NC C NO Relay Contacts NC C NO Relay Contacts
Diode
R
C
Load Load
External External
L N + –
AC Supply DC Supply
A – AC Applications B – DC Applications
Fig. 6.6 Relay Contact Protection
48 IM/AX4PH Issue 9