Monitoring device for computers with connected peripherals such as monitors, printers or the like

The present invention relates to a monitoring device for computers with connected peripherals such as monitors, printers or the like, wherein all peripherals are respectively connected with the computer by at least one ground line. At that, each ground line includes a sensor device looped in between the peripheral and the computer for monitoring a continuous ground connection, and an alarm device actuated by the sensor device, when a deviation is recorded, for signaling an interrupted ground connection. Thereby, a simple and operationally reliable monitoring of one or more computers with connected peripherals is achieved.

The invention relates to a monitoring device for computers with connected 
peripherals such as monitors, printers and the like, wherein all 
peripherals are connected with the computer by at least one ground line. 
One such monitoring device is disclosed in DE-GM 91 10 174. In this 
monitoring device, which is called an anti-theft device, there are 
provided a light signal emitted transmitter and a receiver associated with 
the light signal transmitter for receiving the light signals emitting by 
the transmitter. In addition, a light waveguide, which connects the 
transmitter and the receiver and is formed as a locking element, is 
provided. The light waveguide is formed of several parts releasably 
connected with each other with couplings and counter couplings. In this 
way, a plurality of apparatuses such as computers with connected monitors, 
printers and the like can be connected with each other with a light 
waveguide formed as a locking element, i.e., they become interlinked and, 
thus, protected against theft. Thus, as soon the multi-part light 
waveguide is interrupted by an unauthorized release of a coupling from its 
counterpart or is manipulated in a similar way, no signal or a changed 
light signal is transmitted from the transmitter to the receiver. A 
computer anti-theft device with a sensor unit, which includes a computer 
side and stationary sensor devices operationally electrically connected 
with each other, is disclosed in DE-GM 93 11034. The stationary sensor 
device is advantageously formed as conduit having, on one side, a contact 
point and, on the other side, a loop wound around a stationary part, e.g., 
a desk leg or a shelf rail. The severing of the conductor, loosening of 
the plug connection or the like generate an alarm signal. 
The known devices are adapted more or less only to monitoring computers, 
while the conventionally connected peripherals such as monitors, printers 
or the like are not monitored and can be sealed (please see DE GM 93 11 
034). On the other side, the known conventional monitoring devices formed 
as multi-part light waveguide locking elements are very-expensive. Here 
lies the invention. 
U.S. Pat. No. 3,423,747 discloses a monitoring device for, e.g., a TV-set 
in which each ground line between a respective peripheral and, e.g., the 
TV-set has a looped-in common sensor device for monitoring the continuous 
ground connection. The sensor device is set for recording deviations of an 
electrical potential from a ground potential at a respective looped-in end 
of the sensor device. There is provided an alarm device, which is actuated 
by a sensor device upon recording of a deviation, for signaling ground 
connection interruption. 
The subject of the invention is a monitoring device of the type described 
in the beginning which is simple and operationally reliable. 
This object is achieved by a monitoring device having features of claim 1. 
These features of the invention insure a simple and operationally reliable 
construction of the monitoring device because the invention is based on 
already available connections between the computer and usually connected 
therewith peripherals-such as monitors, printers and the like. Each such 
connection necessarily includes a ground line. The invention recognized 
that a computer with a connected peripheral can be monitored by monitoring 
the ground connection between the computer and the peripheral. This is 
effected with a sensor device looped in between the computer and the 
peripheral for monitoring a continuous ground connection therebetween. In 
this way, monitoring can be effected without any interference with the 
peripheral and without disturbing its function. Simultaneously, the 
monitoring device can be used even with any type of a peripheral and a 
computer. Overall, neither the operation of the computer nor that of a 
peripheral is disturbed because the measured ground connection does not 
have any active potential and, consequently, no disturbance in the data 
flow between the peripherals or between the computer and the peripherals 
occurs. The sensor device is set for recording, i.e., for measuring and/or 
storing (staging) of the deviations of the operation of the computer nor 
that of a peripheral is disturbed because the measured ground connection 
does not have any active potential and, consequently, no disturbance in 
the data flow between the peripherals or between the computer and the 
peripherals occurs. The sensor device is set for recording, i.e., for 
measuring and/or storing (staging) of the deviations of the electrical 
potential from a ground potential at a respective looped-in end of the 
sensor device. In this way, a successful monitoring can take place even if 
the connection between the sensor device and the alarm device is 
disturbed. In any case, a reliable monitoring of one or several computers 
with respective connected peripherals in a simple and operationally 
reliable manner becomes possible. 
The further important features of the invention will be discussed bellow. 
Advantageously, the sensor device is formed as a plug-in coupler provided 
between the computer and a respective peripheral, e.g., as a plug adapter 
pin up on an associated output of the computer. Here, the invention is 
based on a knowledge that the monitored computer is generally connected 
with the connectable peripheral by a standard cable, so that respective 
endside and peripheral side standard plug and socket with a standard 
number of poles (e.g. 9-, 15-, 25-, etc. poles) are used for a series or 
parallel data transmission. In any case, there exists a possibility to 
form the sensor device as a plug adaptor between the computer and the 
connecting cable for the connectable peripheral. The sensor device is 
advantageously provided at a respective looped-in end with a computer side 
input and a peripheral side input, and is set to record deviations of the 
ground potential at one input or both inputs. Additionally, there is 
provided at least one other ground connection, which serves as a reference 
potential, and an operational voltage connection for feeding the sensor 
device with current. There is also provided an output connection leading 
to the alarm device for signaling an interrupted ground connection. In 
case the sensor device is formed as a plug adaptor, the output connection 
to the alarm device is formed as a cable leading from the plug adaptor. 
This multiwire cable can also be used for feeding current to the sensor 
device via the alarm device. It is also possible to establish a computer 
side operational voltage connection and a ground connection with a 
connection socket or plug provided on the computer and a plug adaptor. 
Independently of this, for providing a network-independent power supply, 
an accumulator, which is buffered during the operation of the computer, 
can be provided. This accumulator, naturally a plurality of accumulators 
can be provided, can be arranged e.g., together with the alarm device in 
the same housing. In this case, the power supply of the sensor device is 
effected from that housing. Such a network-independent power supply proved 
to be advantageous when monitoring of a computer with connected 
peripherals is necessary also with a pulled-out main plug. 
Preferably, the sensor device for monitoring a continuous ground connection 
comprises an analog idle current loop monitor or a digital signal shape 
monitor of a square wave signal which is communicated to an additional 
signal input of the sensor device and phases of which are shifted, in 
particular, which is negated at a continuous ground connection. The use of 
a digital signal shape monitor of a (negated) square wave signal enables 
to reduce power consumption of the sensor device by using a CMOS-element. 
Generally, no alignment of a signal shape monitor is necessary, and no 
displacement of the operating points due to a temperature drift occurs, so 
that a continuous ground connection can be definitely ascertain 
independently therefrom. Both the idle current loop monitor and the signal 
monitor can be incorporated in the plug adaptor when the sensor device is 
not any more accessible. It is particularly the case, when the plug 
adaptor has a cast sheathing and cannot be open. In any case, manipulation 
of the sensor device is successfully prevented. This applies also to the 
alarm device when it is formed as an alarm card insertable into a computer 
and has an adjustable duration. Then, the alarm device with a closed 
computer housing is also unaccessible. The data flow between the computer 
and separate peripherals and between separate peripherals is not affected 
by the alarm card because the alarm card cooperates with the power supply 
and ground contacts and not with data or control contacts when inserted 
into the computer. If no free slot is available, the alarm device can be 
arranged in an external housing. In this case, the alarm device can be 
monitored from a location remote from the computer and connected therewith 
peripherals and be connected with the sensor device, e.g., by a telephone 
line. A connection of an alarm device, which is integrated into an already 
available alarm unit, with a sensor device without a cable is also 
possible. In all cases, a TV monitoring of a computer with connected 
peripherals is possible when sensor and alarm devices are connected by a 
telephone line or without a cable. 
For actuation or deactuation of the alarm device, an operational device is 
provided. In the simplest case, it is preferably formed as a key-operated 
switch, with a LED, if necessary, for displaying the switch position. Such 
an operational device or element can be used for monitoring a computer 
with connected peripherals. If a plurality of computers with connected 
peripherals, i.e., an entire bureau complex should be monitored, an 
operational device, which is formed as a programmable operational unit for 
actuating or deactuating one or more alarm device, is provided. Thereby, 
targeted separate or a plurality of alarm devices can be addressed, i.e., 
actuated and deactuated. It is also possible to divide a plurality of 
computers which, e.g., are connected with each other, in separate groups, 
with a particular operational unit being associated with each separate 
group. Generally, with an actuated alarm device, when a ground connection 
is interrupted between a computer and a connected peripheral, both an 
acoustic and an optical alarm signal can be generated which, e.g., can 
then be manually turned off. 
In addition to monitoring a connection between a computer and a connected 
peripheral, the computer itself can be monitored against opening of the 
housing, provided the computer has a two-part metal housing with a ground 
line between the two housing parts. This takes place when the ground line 
has an additional sensor device between the two housing parts for 
monitoring a ground connection therebetween, with the alarm device being 
actuated by the additional sensor device for signaling an interrupted 
ground connection. Naturally, to this end, also spring contacts or the 
like, which are released when the housing is opened, can be used. In case, 
the computer includes an interchangeable hard disc, this hard disc can 
also be monitored against an unauthorized withdrawal, by monitoring the 
available ground connection between the computer and the hard disc. This 
is effected by providing in the ground line a looped-in sensor device 
between the computer and the hard disc for monitoring a continuous ground 
connection between the computer and the hard disc. In this case, the alarm 
device is also actuated and by this sensor device for signaling an 
interrupted ground connection. All in all, the last mentioned measures 
permit to monitor the computer against the opening of its housing and 
against withdrawal of the hard disc independently of whether the computer 
is connected or not with peripherals such as monitor, printer and the 
like. It should be understood that other components, such as streamer, 
CD-ROM disc drive or the like can be secured, similar to the hard disc, 
with an inventive monitoring device.

The drawings show a monitoring device for a computer 1 having a changeable 
hard disc 2 and connected with a monitor 3 and a printer 4. The 
peripherals 3 and 4, like the changeable hard disc 2, are connected with 
the computer 1 by a respective ground line 5. Additionally, there is 
provided a respective ground connection 6 serving as a reference 
potential. Each ground line 5 has a looped-in sensor device 7 provided 
between the peripherals 3, 4 and the computer for monitoring a continuous 
ground connection therebetween. The sensor device 7 is provided for 
sensing the deviations of the electrical potential at a respective 
looped-in end of the sensor device 7. There is further provided an alarm 
device 8, which is actuated by the sensor device 7, for signaling an 
interruption of the ground connection. In the exemplary embodiment, the 
sensor device 7 is formed as a plug adaptor pinned on an associated output 
of the computer 1. The sensor device or the plug adapter 7 has, at a 
respective looped-in end, a computer-side input E.sub.1, and an 
apparatus-side input E.sub.2, and serves for sensing of deviations of one 
or both of inputs E.sub.1 and E.sub.2 from the ground potential. 
Additionally, there are provided an operating voltage connection 9 for 
feeding currents to the plug adaptor 7, and an output connection 10 with 
the alarm device 8 for signaling the interruption of the ground 
connection. The alarm device 8 is formed as an alarm card insertable into 
the computer 1 and having an adjustable alarm duration. To provide the 
monitoring device 7 with a network-independent current supply, an 
accumulator (not shown) is provided on the alarm card. The actuation and 
deactuation of the alarm card 8 is effected in the exemplary embodiment 
with an operational element 11 which is formed as a key-operated switch. 
For actuation and deactuation of one or several alarm devices 8, the 
operational element 11 can be formed as a programmable operating unit. 
Such is not shown. 
The computer 1 has a two-part metal housing with a ground line 5 between 
the two housing parts. For monitoring an unauthorized opening of the 
two-part metal housing, this ground line 5 has an additional looped-in 
sensor device 7 provided between the two housing parts for monitoring a 
continuous ground connection between the two housing parts, with the alarm 
card 8 being also actuated by this additional sensor device for signaling 
an interrupted ground connection. This, however, is not shown. 
Additionally or alternatively, a knife switch can be provided on the 
housing part or the alarm card 8 which would detect the opening of the 
metal housing and/or the disablement of the entire computer 1. This is, 
however, also not shown. The same applies to the additional sensor device 
7, which is looped-in in the ground line 5 between the hard card 2 and the 
computer 1, for monitoring a continuous ground connection therebetween. At 
that, the alarm card is actuated and by this additional sensor device 7 
for signalling an interruption of the ground connection. 
Functioning of the sensor device 7, which is formed as an idle current loop 
monitor shown in FIG. 2, will be described below. The sensor device 7 or 
the idle current loop monitor includes, next to the computer side input E1 
and the apparatus side input E.sub.2, an additional ground connection 6 
which serves as a reference potential, an operational voltage connection 9 
for supplying the sensor device 7 with current, and an output connection 
10 to the alarm card 8, which is not shown in FIG. 2, for signaling an 
interrupted ground connection between the input E.sub.1, and the computer 
1 and/or the input E.sub.2 and the monitor 3 or the printer 4. If both 
inputs E.sub.1, and E.sub.2 are under the ground potential, i.e, a 
continuous ground connection between the computer 1 and the monitor 3 or 
the printer 4 exist, then both semiconductors T.sub.1 and T.sub.2 are 
blocked. The output connection 10 is connected with the operational 
voltage connection 9 by a resistance R.sub.5 and has a positive potential, 
and no alarm is produced by the alarm card 8. When a continuous ground 
connection is interrupted, i.e., one of the inputs E.sub.1, and E.sub.2 or 
both inputs E.sub.1, and E.sub.2 are not held at the ground potential any 
more, then either one of the semiconductors T.sub.1, and T.sub.2 or both 
semiconductors T.sub.1, and T.sub.2 are actuated. Then, positive potential 
is applied to a respective base of the semiconductor T.sub.1 and T.sub.2 
over the resistor R.sub.5 and R.sub.2 or over resistor R.sub.4 and the 
combination with base protective resistor R.sub.1 and R.sub.3. The output 
connection 6 is supplied with the ground potential in a similar manner. 
The alarm card recognizes the change of the potential from the operational 
voltage potential to the ground potential and generates a corresponding 
alarm. A similar effect takes place when the operational voltage 
connection is interrupted. Then, also in this case, a ground potential is 
applied to the output connection 10, and the alarm card is actuated. 
FIG. 3 shows another type of a sensor device 7 formed as a signal shape 
monitor of a square wave signal which is fed to an additional input 12 of 
the sensor device 7 and which is negated at a continuous ground 
connection. The functioning will be explained below. 
The core element of the signal shape monitor are three controlled switches 
A, B and C which are commercially available as an integrated switching 
circuit. When both inputs E.sub.1, and E.sub.2 are under the ground 
potential, i.e., a continuous ground connection exists between the 
computer 1 and the monitor 3 and the printer 4, the control inputs of the 
switches A and B are likewise under the ground potential, and both 
switches A and B, as shown are open. The square wave signal, which is fed 
over the additional signal input 12.sub.1 controls then, over the resistor 
R.sub.3, the control input of the switch C, which opens and closes, and 
transmits a negated square wave signal over the output connection 10 to 
the alarm card 8. In this case, no alarm is produced. As soon as one of 
the inputs E.sub.1 and E.sub.2 are not at the ground potential anymore, 
i.e., a continuous ground connection between the computer, and the monitor 
3 or the printer 4 does not exist, the switch A and/or B is closed because 
its control input receives a positive potential from the operational 
voltage connection over the resistance R.sub.1, R.sub.2. As soon as one or 
both switches A and B are closed, the switch C also becomes closed and 
does not open or close in accordance with the square wave signal 
alteration. Consequently, the output connection 10 receives a ground 
potential, and the alarm card 8 produces an alarm. 
The opposite phase position of the square wave signal, which is fed via the 
input side to the additional signal input 12 opposite to the output side 
square wave signal, which is transmitted via the output connection 10 to 
the alarm card 8 at the continuous ground connection, prevents faking of a 
continuous ground connection by manipulating the output connection 10. 
The negated square wave signal can be negated again by further manipulation 
so that it can be verified whether the input side square wave signal 
correspond to the (twice negated) output signal.