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...2 INSTALLATION
2.7 Relay Contact Protection and Interference
Suppression – Fig. 2.6
If the relays are used to switch loads on or off the relay
contacts can become eroded due to arcing. Arcing also
produces radio frequency interference (r.f.i.) which can cause
instrument malfunctions and incorrect readings. To minimize
the effects of r.f.i., arc suppression components are required;
these are resistor/capacitor networks for a.c. applications, or
diodes for d.c. applications. These components can be
connected either across the load or directly across the relay
contacts.
For a.c. applications the value of the resistor/capacitor
network depends on the load current and inductance that is
switched. Initially fit a 100 R/0.022 F RC suppressor unit
(part number. B9303) as shown in Fig. 2.6A. If the instrument
malfunctions the value of the RC network is too low for
suppression and an alternative value must be used. If the
correct RC suppressor unit cannot be obtained, contact the
manufacturer of the switched device for details of the RC unit
required.
For d.c. applications fit a diode as shown in Fig. 2.6B. For
general applications use an IN5406-type (600 V peak inverse
voltage at 3 A – part number 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
R
L
N
External
a.c. supply
A – a.c. Applications
NC
C
NO
+
–
External
d.c. supply
B – d.c. Applications
Fig. 2.6 Relay Contact Protection
8
Relay Contacts
C
Load
Relay Contacts
Load
3 SETTING UP
Note. Before proceeding any further, ensure that
the HOLD switch is ON; all other switches are set to OFF
on the right hand side of the electronics unit – see Fig. 1.1.
a) Ensure
that
all
external
connections have been made correctly.
b) Fill reagent and standard solution bottles (see Section 8.1
for details of these solutions).
c) Connect the reagent float switch to the plug (Fig. 3.1)
routing the lead through the far left hand grommeted hole in
the bottom of the enclosure.
d) Connect the electrical supply and switch on.
Note. The temperature controlled reaction block
and optical block require up to one hour to reach the
normal
control
temperature.
'Temperature Stabilizing' is indicated on Programming
Page 1.0 – see Section 6 (or Appendix A for multi-stream
programming). Any calibrations are prevented by the
microprocessor during this time.
e) Verify that there is an adequate supply of sample to the
monitor constant head unit.
f) Fit the cuvette drain tube into the pinch valve. Press in the
central plunger and ensure that the tube is fully inserted
into the valve. This ensures that no leakage from the
cuvette occurs.
Pump Motor
Fig. 3.1 Reagent Float Switch Connector
electrical
and
plumbing
During
this
time,
Reagent
Float Switch
Connector
Solenoid Valves
SV1
SV2
Out of Sample
Float Switch
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