Note: Descriptions are shown in the official language in which they were submitted.
CA 02290927 1999-11-29
' Eh 354 US
November 4, 1999
Transmitter housing
The invention relates to a transmitter housing.
Transmitters are used in virtually all areas of
measurement and control technology. There are a
multiplicity of possible uses, both in stockkeeping and
in processing industry, e.g. in the chemical industry,
in the foodstuffs industry and in the oil industry.
Sensors, e.g. pressure, differential pressure, filling
level and/or flow rate measurement sensors, are
typically used, said sensors detecting a physical
quantity and feeding a sensor signal proportional
thereto to a transmitter. The sensor and transmitter
are frequently combined in one apparatus comprising
both the measurement sensor and the transmitter
electronic unit. In the transmitter, the measurement
signal is converted into a measurement signal which can
be transmitted over relatively large distances. Often
the sensor signal is additionally subjected to signal
processing in the transmitter, said signal processing
serving, e.g. to determine the desired measurement
quantity, to eliminate or compensate for measurement
errors and/or to improve the signal quality, e.g. by
means of noise filters.
Cable lead-ins are regularly provided; external lines
can be led into the transmitter through said cable
lead-ins and the latter project beyond the transmitter
housing. Conventional transmitter housings are in one
piece and have a cover. When the cover has been opened,
the lines led in through the cable lead-ins are
accessible. The electrical connection of the
transmitter, e.g. to a supply, to unidirectional signal
lines and/or to bidirectional communications lines, is
effected when the cover has been opened. In doing so,
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an electronic unit arranged in the housing is exposed to the
influences of the surroundings without any protection.
There is the risk, e.g, o.f moisture attacking the electronic
unit and/or c>f the electronic unit being mechanically
damaged. These risks are particularly high when
transmitters are installed in the open, e.g. in the event of
rain or snow, or when they are used in installations in
which aggres:~ive, abrasive or caustic materials are used or
processed.
J.0 An object of the invention is to specify a
transmitter housing in which the transmitter electronic unit
is protected against ambient influences even during the
electrical c~~nnectiorn of the transmitter.
Fo:r this purpose, the invention consists in a
:l5 transmitter :housing, comprising: a housing configured to
receive a transmitter electronic unit; a connection housing
configured to provide an opening to receive at least one bus
line; the connection housing including an electrical
connector connected l:o a branch :From each bus line; a plug-
20 in connection between the housing and the connection housing
to connect the transmitter electronic unit to the electrical
connector; a.nd a releasable connection configured to connect
the connection housialg to the housing whereby the housing is
removable from the e:Lect.rical connector without interrupting
25 the at least. one bus line.
In accordance with a further development of the
invention,
- the transnnitter ca:n be addressed via a bus line,
- the bus lines pass through the connection housing, and
30 - branches f-_rom eactl. bus line to the plug-in connection are
provided in the connection housing.
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November 4, 1999
In accordance with a preferred embodiment of the
invention, a seal for protection of the plug-in
connection is provided between the housing and the
connection housing.
In accordance with a further preferred embodiment, a
flame penetration barrier is provided on the housing.
In accordance with a further preferred embodiment, the
connections are arranged inside the connection housing
and the connection housing has an openable cover
through which the connections are accessible.
In accordance with a further preferred embodiment, a
cavity remaining in the connection housing is filled
with a potting compound.
In accordance with a further preferred embodiment, the
transmitter can be addressed via a bus line, the bus
lines pass through the connection housing, and a bus
driver circuit is arranged in the connection housing.
One advantage of the invention is that the housing
together with the transmitter electronic unit can, as
required, be exchanged without the transmitter having
to be electrically connected anew. This can bring about
considerable cost savings, e.g. in the context of
exchanging defective apparatuses or during conversion
to more modern transmitters.
Regular servicing of the transmitters is necessary in
some cases. This is particularly laborious and costly
when transmitters are used at poorly accessible
locations or in harsh surroundings. In the case of the
transmitter housing according to the invention, the
housing together with the transmitter electronic unit
can be separated from the connection housing in a
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_ - 4 - Eh 354 US
November 4, 1999
simple manner and be serviced at a location which is
better suited to this purpose.
The invention and further advantages will now be
explained in more detail with reference to the figures
of the drawing, in which two exemplary embodiments are
illustrated; identical elements are provided with the
same reference symbols in the figures.
Figure 1 shows a transmitter housing according to the
invention,
Figure 2 shows individual parts of the transmitter
housing of Figure 1 in an exploded
illustration, and
Figure 3 shows a further transmitter housing, in which
housing and connection housing are
connected by means of clamping clips.
Figure 1 illustrates a transmitter housing for a
transmitter. It has a housing 1 for accommodating a
transmitter electronic unit (not illustrated in Figure
1). The housing 1 is connected to a connection housing
3. The housing 1 and connection housing 3 together form
the transmitter housing.
The connection housing 3 has openings 5, through which
external lines can be passed into the connection
housing 3. Examples of external lines are supply lines
via which the transmitter can be connected to an
external voltage supply, unidirectional communications
lines, bidirectional communications lines and/or bus
lines via which data, information, measured values,
alarm signals, etc., can be transmitted in accordance
with bus-specific transmission protocols, e.g. CAN bus,
Fieldbus or Profibus transmission protocols. In
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November 4, 1999
addition, supply of the transmitter as well as
communication can be effected via two conductors.
The housing 1 can be mechanically releasably connected
to the connection housing 3. In the case of the
exemplary embodiment illustrated in Figure l, the
mechanical fastening is effected by means of screws 7,
which are screwed through the connection housing 3 into
the housing 1.
In the case of the exemplary embodiment illustrated in
Figure 3, the fastening is effected by means of
clamping clips 8. The clamping clips 8 are fastened to
the housing 1 such that they can pivot about an axle
and each have a hook at their free end. Projecting lugs
10 are provided on the connection housing 3, behind
which lugs the hooks engage in the assembled state, as
illustrated in Figure 3.
Other types of mechanical fastening can likewise be
used. Thus, the mechanical connection can be effected
by means of latching devices, for example.
Electrical connections that can be connected to the
external lines are provided in the connection housing
3.
Two variants are possible for this purpose. On the one
hand, the connection housing 3 may have an openable
cover through which the interior space of the
connection housing 3 is accessible. When the cover has
been opened, the external lines can then be connected
to the electrical connections. On the other hand, the
connection, when the housing 1 and connection housing 3
are separated from one another, can be effected through
an opening in the connection housing 3, said opening
facing the housing 1.
_.~ __
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It is preferable for a cavity remaining in the
connection housing 3 to be filled with a potting
compound. This potting compound affords protection
against moisture which might otherwise penetrate the
connection housing 3 and might pass through the
connections and the plug-in connection 9 to the
transmitter electronic unit. For this purpose, e.g.
after the external lines have been electrically
connected to the connections, potting compound is
introduced in the liquid state through the cover or the
opening into the connection housing 3, where it
hardens.
A plug-in connection 9 is provided between the housing
1 and the connection housing 3, via which plug-in
connection the transmitter electronic unit can be
connected to the connections. The plug-in connection 9
has a plug and a socket. In this case, it is entirely
unimportant whether the plug is arranged on the housing
1 and the socket is arranged on the connection housing
3, or vice versa. It will be assumed in the description
below that the plug is arranged on the connection
housing 3 and the socket is arranged on the housing 1.
In the housing l, the transmitter electronic unit is
electrically connected to one pole and/or a plurality
of poles of the socket. In the connection housing 3,
the individual connections are electrically connected
to the corresponding poles of the plug.
In the case of transmitters which can be addressed via
bus lines, the bus lines preferably pass through the
connection housing 3 and branches from each bus line to
the plug-in connection 9 are provided in the connection
housing 3. That affords the advantage that the housing
1 can be removed, e.g. for the purpose of servicing,
without the bus line thereby being interrupted. The
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November 4, 1999
function and operation of downstream apparatuses
connected to the same bus lines are not disrupted or
impaired at all. In particular, the user is spared the
need to install a branch or bypass for the bus lines,
this installation being necessary in the case of
conventional transmitters.
A bus driver circuit is preferably provided in the
connection housing 3. The transmitter communication via
the bus takes place via the bus driver circuit. The bus
driver circuit may contain a DC isolation between
transmitter and bus and amplify signals to be
transmitted via further paths via the bus lines.
In order to protect the plug-in connection 9, a seal 11
is provided between the housing 1 and the connection
housing 3. As illustrated in Figure 2, this is, e.g. a
shaped seal having a peripheral lip 13, which, for the
purpose of prefixing, can be introduced into an
identically shaped groove in the connection housing 3.
When the housing 1 and connection housing 3 are
mechanically connected to one another in the assembled
state, an end face 15, opposite the lip 13, of the seal
11 bears on a shoulder area 17 in the housing 1. The
seal 11 is clamped in between groove and shoulder area
17 by the mechanical fastening of the housing 1 and
connection housing 3, that is to say by the screws 7 in
the exemplary embodiment shown, and thereby seals off
the interior space between the housing 1 and the
connection housing 3 in which the plug-in connection 9
is situated.
A flame penetration barrier is preferably provided in
the housing 1. The flame penetration barrier serves to
prevent a spark occurring inside the housing 1 and/or a
flame from penetrating to the outside. A flame
penetration barrier is necessary, e.g. whenever the
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November 4, 1999
transmitter is used in areas where there is a risk of
explosion. In such areas, even a small spark can lead
to an explosion that may have disastrous consequences.
In most countries there are safety regulations which
specify constructional regulations for flame
penetration barriers, depending on the type of danger
zone. An example of such a regulation is the German
Standard DIN EN 50018 from 1994. It contains
regulations for electrical operating equipment for
areas where there is a risk of explosion with the class
of protection: Explosion-proof enclosure. It includes,
inter alia, constructional regulations for widths of
joints, widths of gaps, threaded joints and seals.
In the present case, the flame penetration barrier may
consist, e.g. in routing all the lines from the
transmitter electronic unit through bushings which are
arranged directly in front of the socket and are
dimensioned in accordance with the abovementioned
regulations. Equally, the socket could be designed in
accordance with these regulations, so that no spark
and/or no flame can penetrate to the outside through
the socket.
