ABB ETL600, Instruction Manual

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ETL600 1KHW001489-EN
ABB Switzerland Ltd
•
the non-flat frequency response of the transmission channel,
•
noise and non-linear distortion on the transmission channel,
•
implementation losses of the modems.
When the data signal satisfies certain conditions, isochronous
distortion can be reduced using nonlinear processing. This is called
regeneration. The regenerator – in addition to the regenerated data
signal – also produces a clock signal that may be used by the
receiving data terminal to sample the data signal.
Note:
FSK modem data regeneration is only possible when
data transfer rate corresponds to the configured
nominal datarate.
Regeneration requires that the time between transitions of the data
signal is an integer multiple of a fixed time interval. This interval is
called “Nominal bit length”. SCADA protocols usually pack the data
into telegrams. Inside telegrams, no pauses are allowed between
characters, so that the above condition is fulfilled. However, between
telegrams, a pause of some minimum length is required. If the
regenerator is capable of recognizing these pauses, regeneration can
also be used for SCADA protocols.
In order to save transmission bandwidth, polling of multiple RTUs over
PLC is often done using one single communication channel. Only one
RTU is allowed to transmit at any moment. In such cases, the data
carrier detector handshake line (DCD) can be used to recognize the
pauses between telegrams.
Generally, regeneration brings an advantage only if several FSK
channels are connected in tandem. As a rule of thumb, isochronous
distortion at the input of any FSK channel should be lower than 25%.
The regenerator in the receiver of the preceding FSK channel should
be enabled if this condition is not met.
NSK600 modems offer data regeneration as a parameter: refer to
“Receive clock recovery” in section
5.3.5.4
for details.
3.5.1.2. Required data transmission format parameter for DAPSK
Opposed to transparent transmission with FSK, modems using
DAPSK modulation do not provide transparent transmission.
DAPSK modems are based on transmission of characters. Therefore,
when using NSK600 modem with data transfer rates of 2’400, 4’800 or
9’600 bps, the exact data format of the DTE connected to the interface
has to be configured for the V.24 port in terms of amount of data bits,
stop bits and parity: Refer to section
5.3.5.3.3
for details.
3.5.2. MOD600 Modem
The MOD600 modem converts digital data to an analog signal in the
DPLC channel and vice versa. The supported data transfer rates are:
Structure and Function November 2005 3-47