Dependability - ABB ETL600 Instruction Manual

ETL600
All security measurements were performed according to the
procedures prescribed in IEC 60834-1.
Security is determined by coupling bursts of white noise of high
amplitude into the communications channel. The number of bursts
injected and the number of false commands they cause at the
receiving end are counted.
The probability of unwanted commands is then calculated according to
the following relationship:
P = probability of an unwanted command
uc
N = number of unwanted commands received
uc
N = number of noise bursts injected
B
3.6.6.4.

Dependability

For analog channels dependability is expressed as the signal-to-noise
ratio (SNR) for a noise bandwidth of 4 kHz, which must be maintained
during the transmission of a tripping signal to enable that it can be
received within 1.3 times the nominal transmission time T0 (probability
of missing a command P
Dependability Measurements
All dependability measurements were performed according to the
procedures prescribed in IEC 60834-1.
Dependability is determined by sending a large number of commands
to the remote station. The number of commands transmitted and the
number of commands received within a specified time (normally 1.3 x
T0, 1.5 x T0, 2 x T0 and 3 x T0) are recorded. The lower the signal-to-
noise ratio at the input of the receiving NSD600, the fewer the
commands which will be received in the prescribed time.
The following applies for a sufficiently high number of transmitted
commands:
Structure and Function
1KHW001489-EN
Noise/bit error burst
Duration of pause
Noise bandwidth
SNR
P = N
uc
< 1%).
mc
Command duration
Duration of pause
Noise bandwidth
SNR
November 2005
ABB Switzerland Ltd
200 ms
200 ms
4 kHz
0 dB ... -30 dB
/ N
uc B
3 × T0
2 × command duration
4 kHz
-10 dB ... +20 dB
continuous noise
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