ABB ETL600, Instruction Manual, Page: 163 / 382

ETL600 1KHW001489-EN
ABB Switzerland Ltd
5.3.4.2. Level settings of teleoperation ports, introduction
A little background is useful when configuring a teleoperation port to
understand structure and the various tuning possibilities. Physical
basics are explained in section 5.2.
In Fig. 5-1, the line of life of an input signal is shown, entering at the
terminal of AF interface O4LE through the ETL600 up to the RF
terminal, which is connected to the coupling device. Only the input
path of one teleoperation port is depicted. A non transit application is
assumed. Settings which can be done in HMI600 are marked with a
finger symbol.
Level in dBm
(600 Ohm)
AF terminal (600 Ohm)
System Level in dBm0
ETL600 signal processing
Re
la
ti
v
e
Input
le
v
e
l
Adder
sum signal
20 l
o
g
(S
-val
u
e
)
RF terminal (75 / 125 Ohm)
Amplifier
Level in dBm
(45 / 75 / 125 Ohm)
Ma
x
. P
o
w
e
r (P
E
P
) i
n
d
B
m
max. input level
System Level of the input signal
is determined by selection of
'Reference signal' in HMI600
Terminal ..
.
: Configuration in HMI600
Input l
evel
dBm (PEP)
dBm (RMS)
Terminal
to RF
coupling
device
Legend:
: Selection inHMI600
0
other
signals
0
Fig. 5-1 Signal levels from AF terminal to RF terminal
An external device, which is not shown, sends an input level, which
can be configured in by HMI600. The signal passes the terminal of the
AF interface and is present in the internal ETL600 system. Levels of
external AF devices are mostly given in dBm
(600
Ω
), dBm,
‘dB at 600
Ω
’ or dBm (RMS), which means all the same. In what
follows, the unit dBm (RMS) is used. It is the average power level. A
standard true rms volt meter is measuring dBu (RMS) with a high
impedance and calculating the dBm(RMS) value considering a
reference impedance, e.g. 600
Ω
, 75
Ω
, … .
For the system ETL600, the RMS levels have to be converted to
P
eak
E
nvelope
P
ower (PEP) levels expressed in dBm (PEP). With these
PEP levels, the peak voltage at any point in the system can be
determined and compared to the allowed maximum to avoid clipping.
For conversion of RMS to PEP levels, the peak to average ratio must
be known, which is characteristic for a specific type of signal:
)
U 2
U
log( 20 ) RMS ( dBm ) PEP ( dBm
rms
peak
×
× + =
valid for 600
Ω
For each type of signal, an associated system power level expressed
in dBm0 is defined as explained in section 5.2.10. System levels and
Configuration and Set-up November 2005 5-19