This invention relates to mains interface modules.
US patent US 5340944 discloses a mains interface module, comprising
a screened casing having a mains inlet connector and at least one mains outlet
and containing EMI filters operative to protect the outlet(s) from interference
from a mains supply when connected to the inlet connector.
The present invention is characterised over the disclosure of US 5340944
in that there are at least two mains outlets of which one or two mains outlets
is/are controlled by a thermostat internal to the interface module for connection
to a respective heater, and the mains inlet connector is weatherproof.
The screening prevents radiation of interference within the enclosure.
The weather proof mains inlet, e.g. to IP65, allows the equipment to be used and
installed outside. The EMI filters prevent interference from being conducted through
In one application to mobile cellular telecommunication base stations
which are required to operate in extremes of temperature, it is necessary to provide
heating which is controlled by a thermostat. In a preferred form the interface
module includes at least two mains outlets one controlled by a thermostat internal
to the interface for connection to a heater. Conventionally, a thermostat would
be placed with the heater it controls.
The or each mains outlet may include a manually operated switch.
A fuse may be provided to protect all outlets.
A mains voltage detector may be provided with an indicator, responsive
to the detector, to indicate presence of mains voltage.
An indicator may be provided responsive to an input from a unit powered
by said interface module by which a fault diagnosed by the powered unit may be
One embodiment of the invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
- Figure 1 is a section through base station equipment for a mobile cellular
- Figure 2 is a side view of a mains interface module of the equipment of Figure
- Figure 3 is an underneath plan of the unit of Figure 3;
- Figure 4 is an end view of the unit of Figure 2;
- Figure 5 is a top plan of the unit of Figure 2;
- Figure 6 is a schematic circuit diagram of the unit of Figure 2;
- Figure 7 is a cross section through a heater of the equipment of Figure 1;
- Figure 8 is a plan view of the heater of Figure 6.
Referring to the drawings, a base station for a cellular mobile telecommunications
network comprises a radio unit contained by an external enclosure 2. For use,
electronic units such as RF screened transmitter receivers 3, RF screened power
amplifiers 4, a processor board 5 (mounting components not shown) and duplexers
6 are environmentally sealed within the enclosure 2. The processor board 5 is
mounted on protuberances 7a from a wall 7 of the external enclosure. The transmitter/receivers
3 are mounted by protuberances 9 over the processor board 5. Two transmitter receivers
3 are mounted side by side in the enclosure 2 so that only one is visible in Figure
1. Similarly, two duplexers 6 are mounted side by side so that only one is visible
in Figure 1.
In order to supply power to a power supply (not visible in Figure
1), a mains interface module 10 has a weather proof mains inlet connector 12, e.g.
to specification IP65. The interface module 10 has a conductive housing 13 which
acts as a screen against electromagnetic emissions from the unit.
The unit has three mains outlets terminated by connector sockets
14, 16 and 18. Connectors 14 and 16 are recessed so that interference is not transmitted
through the unit to the outlets, between the inlet 12 and the outlets 14, 16 and
18 is an EMI filter 20. The outlets may be isolated by a two pole on/off switch
22 and are protected by a fuse 23. A monitor circuit 24 contains a mains monitor
26, a fuse fail monitor 28 and an on/off switch monitor 30. The monitors have
open collector outputs driving an LED indicator 32 such that the indicator shows
green when all three units detect mains voltage at the appropriate points in the
The connector 14 is used to supply power to the power supply of the
The enclosure 2 is mounted outside within an external housing (not
shown). The enclosure is cooled normally by natural convection and to this end
is provided with fins or extended surfaces of which only two are visible in Figure
1. In very cold environments it is possible that the internal temperature of the
enclosure would become too low for the electronic units to function. In order to
allow the base station to function at such low temperatures, two heaters 36 are
provided, one being shown in Figures 7 and 8. The heater 36 has a commercially
available trace heating element 38 which comprises a Nichrome foil resistor pattern
6, seen only in section in Figure 7, sandwiched between two layers of flexible
rubber dielectric 42.
The element 38 is bonded by a layer of double sided adhesive tape
44, to an aluminium sheet 46 of similar dimensions, which acts to disperse any
potential hot spots in the assembled heater.
Two set screws 48, screwed into the enclosure, provide shoulders
spaced a distance from the internal surface 50 of the enclosure 2. A leaf spring
52 is formed with notches 54 to receive the shanks 56 of the set screws 48 so
as to be retained by the heads 58. The heads are positioned so that the underside
of the spring 52 is spaced from the surface 50 of the enclosure 2 by a distance
approximately equal to the combined thickness of the heating element 38 and the
The leaf spring 20 is curved when relaxed. At its end remote from
the notches 54, the leaf spring 52 has a step providing a shoulder 60 leading to
a tang 62. The step is approximately the size as the combined thickness of the
heating element 38 and sheet 46. When the tang 62 is fastened to the surface 50
of the enclosure 2 by a screw 64, the leaf spring clamps the heating element with
a uniform pressure against the surface 18 of the enclosure 2.
Each of the heaters has a supply lead 66 by which it is connected
to a respective on of the connectors 16 or 18. As may be seen from Figure 6, a
thermostat 68 having contacts 70 is contained within the housing 14, to control
the supply to the two heaters. When the temperature falls below a predetermined
level the thermostat contacts 70 close to operate the heaters. When the temperature
rises above a predetermined level, the thermostat contacts open 70 to switch off
A connector 72 provides inputs to operate LEDs 74 and outputs for
signals from and to the processor board 9. These may indicate normal operation,
various start-up processes, fault conditions detected by internal diagnostic processes
in the processor board and the condition of a data link to a switching centre.