Safety Information; Relay Contact Protection And Interference Suppression - ABB 4690 User Manual

4690 Series
Turbidity systems

4.2 Safety Information

Warning. The power supply earth (ground) must be connected to ensure safety to personnel, reduction of the effects of RFI and
correct operation of the power supply interference filter.
Note.

Stud terminal(s) is (are) fitted to the analyzer case for bus-bar earth (ground) connection – see Figs. 4.1, 4.4 and 4.5.

The cable length between the turbidity sensor and the 4690 / 4695 analyzer is provided as ordered and terminated at the
sensor. Shorten or lengthen the cable as required for the installation.

Always route the signal cable and mains-carrying/relay cables separately, ideally in earthed (grounded) metal conduit.
Ensure that the cables enter the analyzer through the glands nearest the appropriate screw terminals and are short and
direct. Do not tuck excess cable into the terminal compartment.

Ensure a moisture-tight fit when using cable glands, conduit fittings and blanking plugs/bungs (M20 holes). The M16 glands
ready-fitted to wall-mount analyzers accept cable of between 4 and 7 mm diameter.

The relay contacts are voltage-free and must be connected appropriately in series with the power supply and the
alarm/control device that they are to actuate. Ensure that the contact rating is not exceeded. Refer also to Section 4.2.1 for
relay contact protection details when the relays are to be used for switching loads.

Do not exceed the maximum load specification for the selected current retransmission range – refer to Section 11,
page 37.
The retransmission output is isolated therefore the –ve terminal must be connected to earth (ground) if connecting to the
isolated input of another device.

4.2.1 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) that can cause analyzer malfunction 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. On 4690 / 4695 analyzers, fit the RFI
components to the relay terminal block together with the supply and load wires – see Fig. 4.3.
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 (part no. B9303) as shown in Fig. 4.3A. If the analyzer malfunctions (incorrect readings) or resets
(display shows 88888) the value of the RC network is too low for suppression – use an alternative value. 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. 4.3B. For general applications use an IN5406 type (600 V peak inverse voltage at 3A
– part no. B7363).
Note. For reliable switching, the minimum voltage must be greater than 12 V and the minimum current greater than 100 mA.
NC C NO
External L
AC Supply
A – AC Applications
Fig. 4.3 Relay Contact Protection
IM/4690–EN Rev. A
Relay Contacts
R C
Load
N
NC C NO
External + –
DC Supply
B – DC Applications
4 Electrical Connections
Relay Contacts
Diode
Load
13