30/07/04 - Information - AS-Interface networks with double masters, bus termination and tuner: More flexible, more reliable, less expensive
Today Bihl+Wiedemann
is no longer just the "AS-i-Master Company" but the specialist for all
intelligent AS-Interface solutions. It supplies the whole range of masters,
double masters, gateways and links, repeaters, power supplies, circuit
extensions, the tuner and the analyser, analogue slaves, special solutions for
frequency converters and balance controllers etc.
In practice, this leads to
many possible configurations of AS-Interface networks, which may be especially
simple, flexible, reasonable or tricky. Here you get an overview of some
possibilities concerning multiple networks, networks extension and
tuning.
A) Single and multiple masters
Nowadays, AS-Interface networks are the standard technology for applications with up to 31 (62) participants and a length of up to 100 m (configuration A1). Their benefits are low costs, simple installation and a reliable operation. For the single network configuration, Bihl+Wiedemann offers different masters, gateways and links in IP20 und IP65 including some useful application functions1, as well as a power supply (4 A) and a diversity of analogue slaves.
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| Config. A1: The standard: Single network, often with coupling to a higher level network, e.g. to PROFIBUS |
If more than 31 (62) slaves, cables longer than 100 m, more flexibility, or more flexibility in the network are needed, formally the answer to these cases was "duplicate all". The standard AS-Interface single network with up to 31 slaves and 100 m in length used to be the biggest unit (configuration A2). The rest was a matter of multiplying.
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| Config. A2: Multiple networks simply duplicating the standard single network |
Today there are
several alternatives. A first step to more intelligent solutions is to install
a double master, which is more cost effective than two single masters and saves
one connection with a higher system (configuration A3). Thus the (cost)
threshold to use multiple networks is lowered. Not only the number of slaves
can require a second network, but also the higher rate of flexibility in
designing a plant may make them appear desirable.
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| Config. A3: Two networks are served by one double master. |
As a second step, Bihl+Wiedemann now offers a double master which also saves one of the power supplies. In this case the data decoupling is inside the master. The power supply (4 A or 8 A) meets all additional requirements of the AS-Interface specification.
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| Config. A4: The second step: Using a double master in the version "1 power supply for 2 AS-Interface networks". |
The identical power
supplies can be used together with external data decoupling units of an
"AS-Interface Power Extender" to feed several separate networks. As the leads
between the power supplies and the data decoupling do not count in the 100
m-limit, these networks may be placed separately from each other (configuration
A5).
If IP65-masters are used no service cabinets are required. The power
supply may be placed in a central switch box (but mind the voltage drop). This
configuration is of special interest in large and spacious
applications.
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| Config. A5: External data decoupling (so-called AS-Interface power extenders) can be used to feed several masters from 1 power supply. |
B) Circuit extension by repeater
Today's standard for networks over 100 m is to supplement one or several repeaters and as many power supplies (configuration B1).
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| Config. B1: Conventional solution using repeaters and additional power supplies to realise networks with more than 100 m. |
An alternative is the IP20 repeater that is placed in a service cabinet together with the power supply, the main advantage being easy mounting of the repeater in the cabinet (configuration B2). The IP20 repeater has been designed with this intention.
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| Config. B2: Simplifying the mounting by using the IP20 repeater inside the service cabinet |
C) Optimizing the energy distribution with repeaters
Repeaters may also be used to isolate parts of a network from each other or to feed several segments of a network by separate power (configuration C1).
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| Config. C1: Separation of 1 network into 3 galvanically isolated segments, e.g. to feed a network that demands 12 A by 3 separate power supplies. |
D) Circuit extension by bus termination plug or by tuner
If a network of more
than 100 m is needed, the answer is no longer "add a repeater and a power
supply (for each 100 m)" (configuration B1). Bihl+Wiedemann now offers two more
intelligent solutions: The (passive) bus termination and the (active) tuner,
both with a protection degree of IP65.
The passive bus termination permits
an extension of up to ca. 200 m. However, Bihl+Wiedemann recommends to
carefully check the number of repeated telegrams in each installed network (use
the error counter in B+W masters or a B+W analyser2). If the
compensation of the network's impedance is successful, this configuration is
the most cost-effective one for an extension (config. D1).
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| Config. D1: The passive bus termination permits networks up to ca. 200 m (check the repetition rate, please) |
In networks of up to
ca. 300 m, it is more secure and feasible to use the Bihl+Wiedemann
tuner3. This is an active bus termination which adjusts itself
automatically to the situation found in the particular network. Thus it reaches
farther and works in more conceivable configurations (configuration
D2).
Additional benefit: The tuner shows continuously whether compensation
has been reached well enough. Three LEDs (green, yellow, red) signal "normal
communication", "functioning but with a remarkable amount of repetitions", or
"too many repetitions or (sporadic) loss of at least one slave". As opposed to
a fixed bus termination, the alignment of the tuner can easily be repeated at
any time if the plant is changed.
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| Config. D2: The active bus termination by a tuner permits networks up to ca. 300 m. In addition it checks and signals communication quality. |
For even bigger networks, tuners or bus terminations and repeaters can be combined. As up to two repeaters may be used in series, one can achieve lengths of up to 600 m (with passive bus termination) or 900 m (with tuners), respectively. This is shown in configuration D3 with two segments.
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| Config. D3: 600 m-network with tuner plus repeater. May be extended up to 900 m. |
E) Tuning of AS-Interface Networks
Please note: There is
no decrease in date security when using the AS-Interface tuner. The high level
measures of data security and error detection are NOT affected. Thus the tuner
may also be used in Safety-at-Work networks.
Apart from extension the tuner
can even be used to correct an unstable network if the instability is caused by
a faulty impedance. Thus networks can be run properly and with a high degree of
availability even if their components misfit the specifications to some extent.
This effect is due to the active adjustment and the continuous monitoring by
the tuner. Especially if a network has to be extremely reliable (e.g. in plant
automation or with AS-Interface Safety-at-Work), optimising the impedance of
the individual network may be of advantage.
It should be emphasised,
however, that this tuning is not necessary for standard networks if built with
perfect (certified) components. "Tuning" of AS-Interface networks up to 100 m
should be the exception and used only in an emergency.
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Article as PDF file |
Literature
(1)
The new master generation of B+W:
Double addresses? - The problem has been solved!
(2) An Analyser for
AS–Interface
(3)
AS-i XXL with the AS-i
Tuner