20
+
-
5.3 Signal wiring notes
An earth current loop is created if a wire or screen is connected between two earth points
that are at different potential (voltage). If the wiring diagram is followed correctly, the screen
will only be connected to the earth at one end.
The earth terminal is a functional earth rather than a protective earth.
A protective earth provides protection from electric shock under a single fault condition. This
product has double insulation and therefore does not require a protective earth. A functional
earth is used in order for the product to operate. In this application, the earth is used as a
sink or drain for any electrical interference. The earth terminal must be connected to a local
earth in order to conform to the EMC directive.
5.4 Probe wiring
The maximum cable length for all transducers is 100 m (328 ft).
Note: It is essential to select the correct sensitivity on the PA20 preamplifier,
(see the PA20 Installation and Maintenance Instructions for details).
Back
Front
Notes:
Do not connect terminal 54 to any other earth
Ensure that the resistance from the probe body to the pipework / boiler shell is less than 1 ohm.
E = Functional earth - connect these pins to a clean earth local to the panel.
Fig. 6 Signal circuit
Signal circuit
(view from the top)
50
51 52 53 54 55
6256 57 58 59 60 61
Open
Close
+24 V SCNVin Iin COM SCN
Level input(s)
Feedback Pot
COMRin
4 - 20 mA
output
Capacitance probe
(See PA20 IMI for
sensitivity selection)
Connect to
a clean local
earth in the
panel
4 - 20 mA
valve positioner
Screens
1 2
E
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