19
5 Connecting to power supply
MINITRAC 31 • 4 … 20 mA/HART - four-wire
40447-EN-130430
5 Connecting to power supply
5.1 Preparing the connection
Always keep in mind the following safety instructions:
•
Connect only in the complete absence of line voltage
•
If overvoltage surges are expected, overvoltage arresters should
be installed
In this case, the instrument is designed in protection class II. To main-
tain this protection class, it is absolutely necessary that the ground
conductor be connected to the internal ground terminal. Take note of
the general installation regulations.
Supply voltage and current signal are carried on separate connection
cables if reliable separation is required. The supply voltage range can
differ depending on the instrument version.
The data for power supply are specified in chapter "
Technical data
".
For power supply, an approved installation cable with PE conductor is
required.
The 4 … 20 mA current output is connected with standard two-wire
cable without screen. If electromagnetic interference is expected
which is above the test values of EN 61326-1 for industrial areas,
screened cable should be used.
Use cable with a round wire cross section. An outer cable diameter
of 6 … 12 mm (0.24 … 0.47 in) ensures the seal effect of the cable
entry. If cable with a different diameter or wire cross section is used,
exchange the seal or use an appropriate cable connection. Free cable
glands have n sufficient protection against moisture and must be
replaced by blind stoppers.
Generally provide all unused cable entries with suitable blind plugs.
The thin foam rubber wahsers int he cable glands are only used as
dust cover during trasport.
In the case of instrument housings with self-sealing NPT threads, it
is generally not possible to have the cable glands screwed in at the
factory. The openings for the cable glands are therefore covered with
red protective caps as transport protection.
You have to replace these protective caps with approved cable glands
before setup or cover them with suitable filler plugs. Unused cable
glands do not provide sufficient protection against moisture and must
be replaced with filler plugs.
The suitable cable glands and blind plugs come with the instrument.
If screened cable is necessary, connect the cable screen on both
ends to ground potential. In the sensor, the screen must be connected
directly to the internal ground terminal. The ground terminal on the
outside of the housing must be connected to the potential equalisa-
tion (low impedance).
Safety instructions
Voltage supply via mains
voltage
Select connection cable
Cable entry
Cable gland ½ NPT
Cable screening and
grounding
