Table of Contents
Advertisement
...6.5 Electrical Connections
6.5.1 Relay Contact Protection and Interference Suppression – Fig. 6.8
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) that can result in monitor 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 can be connected either across the load or directly across the relay contacts. The RFI components must be fitted to the
relay terminal block along with the supply and load wires – see Fig 6.8.
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. 6.8A. If the transmitter 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. 6.8B. 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.
External
L
N
AC Supply
A – AC Applications
NC C NO
Relay Contacts
R
C
Load
Fig. 6.8 Relay Contact Protection
NC C NO
External
+
–
DC Supply
B – DC Applications
6 INSTALLATION...
Relay Contacts
Diode
Load
39
Advertisement
Table of Contents
