38477BA2B
2 – 190 25.5.09
3 Electrical Installation Volume 2
1. Capacitor-buffered real-time clock
2. Slide switch for current output
With this slide switch you can choose whether power is gener-
ated by the current output or supplied by an external source.
Move slide switch to the left: current output is passive Move
slide switch to the right: current output is active Versions with
intrinsically safe current output may not be switched over, since
the connected buffer amplifier serves as current output to the
control system. See chapter "3.5 Uni-Probe with Ex i Current
Output".
3. Slide switch for the termination resistor in a RS-485 connec-
tion.
The RS-485 connection is used in multi-detector systems to
connect the Main Unit with the Auxiliary Units. Always at the
beginning and at the end the RS -485 has to be terminated with
120 Ohm, i.e., at the first and the last detector the resistor has
to be enabled.
Down: resistor is enabled
Up: resistor is disabled.
4. RS-232 interface
Used to update the embedded software in the Uni-Probe. See
chapter "4.13 Updating the Embedded Software in the
Uni-Probe".
5. Slide switch for communication
If the slide switch is set to “Auto”, the bus module (Profibus PA
or FOUNDATION
™
Fieldbus) is identified automatically and
communication is switched over to the bus module. If the bus
module is not plugged in, HART
®
is automatically enabled.
If the slide switch is set to “forced HART”, then only communi-
cation via the HART
®
interface is possible, regardless of
whether the bus module has been installed or not.
up: HART
®
fixed
down: automatic detection
6. Reset button
Push the Reset button to reset the Uni-Probe. The effect is the
same as if the power supply has been turned off for a short
time and turned on again.
Signal cable with shielding We recommend using a screened cable for the HART
®
current out-
put and also for Profibus and fieldbus signal outputs.
The screen has to be connected to the grounding screw in the con-
nection box of the Uni-Probe. If potential differences can be ruled
out, the screen can be connected on both sides. In the multi-detec-
tor mode, the screen for the RS-485 connection cable has to be
connected to terminal 56.
Terminal resistance In case of cascading several detectors (multi-detector mode), the
first and the last Uni-Probe that is connected to the Uni-Probe
RS-485 interface has to be terminated by a resistor (see Figure 3-3
and Figure 3-4).
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