-
The present invention regards a programmable system for
stabilising and regulating voltage, in particular for the
improved management of lighting units using fluorescent
bulbs and more generally those of the gas discharge type.
-
It is known that this type of bulb, to be switched on,
requires a predetermined ignition voltage and that, when it
has been switched on, after a period of heating which
depends, amongst other things, upon the environment
temperature, the supply voltage can be substantially
reduced, still being kept above a predetermined minimum,
which is necessary to avoid the light turn off.
-
It is also known that the light flow of this type of
bulb is not directly proportional to the supply voltage and
to the power taken up and that the maximum lighting
efficiency is obtained in a range of supply voltages lower
than the voltage needed to switch it on.
-
In such a range the light flow can be regulated, by
varying the supply voltage, to adapt it to the user's
requirements.
-
Finally, it is known that the application of excessive
voltages does not give a significant increase in the light
flow and substantially reduce the useful life of the bulb.
-
Therefore, management systems have been designed which
take care of supplying such types of bulb with a regulated
voltage, obtained from the mains, modulated to carry out the
switching on and the heating of the bulbs in optimal
conditions, then reduced and kept constant, independently
from variations in the mains voltage, to obtain a
predetermined light flow (also variable in time according to
suitable programs) in conditions of optimal efficiency.
-
An example of this type of system is provided by
document EP0753986.
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Basically, in these systems the regulated supply
voltage of the lighting unit is obtained with an
autotransformer with many taps, selectively connected to the
output one at a time, through switches controlled from a
control and supervision station. Even if the use of solid
state switches has been proposed, for reasons of cost and of
safety the use of electromagnetic relays is generally
preferred.
-
The choice of this type of regulation has numerous
advantages with respect to alternative solutions, like the
use of variable coupling transformers or completely
electronic regulators, but at the same time brings a
plurality of problems to be tackled and solved.
-
First of all, the fine regulation of the output voltage
requires, also by exploiting the known expedient of the
reversing device, a high number of taps and of corresponding
connection relays which it is desirable to reduce to the
minimum.
-
Then the switching of the taps must be able to take
place under load, to avoid the bulbs turn off. Therefore,
by-pass circuits are necessary controlled by further relays
to ensure the load supply during the switching transient of
the taps.
-
Indeed, it is materially impossible to obtain a
switching with electromagnetic relays which is rapid and at
the same time synchronous with the transition to zero of the
alternating current applied to the load.
-
The by-pass circuits must dissipate the minimum power
possible and at the same time ensure a voltage near to and
preferably within the voltages which are switched, without
for this reason requiring the use of a number of by-pass
relays equal to the number of tap switching relays.
-
Finally, to avoid short circuits and at the same time
to ensure the load supply without gaps in voltage/current it
is necessary to verify, with reliable control systems, the
open and closed state of every switching device before
carrying out switching operations which could cause a short
circuit, with catastrophic effects on the apparatus.
-
These problems are solved by the system object of the
present invention as defined in the claims.
-
The characteristics and advantages of the present
invention will become clearer from the following description
of a preferred embodiment, with reference to the attached
drawings wherein:
- figure 1 is a block diagram of the whole of a system
for the optimised management of a lighting unit and of
equipment comprising many systems;
- figure 2 is a power module circuit diagram for the
system of figure 1;
- figure 3 is a circuit diagram of the detector devices
of the state of the electromagnetic switches of the
power module;
- figure 4 is an exemplifying diagram of voltage/lighting
which represents a preferred management method of the
lighting in a tunnel with the equipment of figure 1;
- figure 5 is an electrical diagram of a preferred
embodiment of a photoresistor based brightness sensor
and an auxiliary A/D conversion module for the system
and equipment of figure 1.
With reference to figure 1 the system essentially comprises
a control unit 1, with a microprocessor, a power module 2,
with power section 2A and control section 2B, and a
visualisation and command module 3, with luminous
indicators, display and keyboard.
-
Through a manual or remote control switch 4 and a
magnetothermic protection switch 5 the alternating voltage
of the mains, in the figures nominally 225 V, is applied to
the system.
-
In the control unit 1 an AC/DC power supply feeder 7,
connected to the mains through a transformer 6, supplies the
control unit 1 and the control section 2B (through feed
wires 80) with the required stabilised continuous service
voltages (±5V, +12V). The feeding of the control section is
thus subordinated to the prior feeding of the control unit 1
which can verify the presence of the correct service voltage
value applied to section 2B before controlling its
intervention.
-
The mains voltage, input to the power section 2A, is
regulated so as to obtain in output a predetermined voltage
value which is applied to a load Z, consisting of a bulb
set, with the closing of an electromagnetic switch 18,
controlled by the control unit 1.
-
The control unit 1 and the control section 2B
communicate through a channel 8, with serial or parallel
interface.
-
According to the switching commands received from the
command module 3, of the room temperature detected by a
sensor 9, and possibly of the external lighting conditions
detected by a sensor 10 and transferred to the control unit
through an auxiliary module 130, the control unit 1
instructs the control section 2B so that the voltage to be
applied to the load takes on an appropriate value, for
switching on, heating and maintaining such as to ensure a
predetermined level of lighting, detected by a sensor 11.
-
For safety the different sensors and the possible
auxiliary module are electrically decoupled from the control
unit, both in terms of the power supply and in terms of the
output signal, transmitted to the control unit 1 through
optoelectronic devices 12,13,14.
-
The control section 2B, as a function of the actual
mains voltage, measured through a measuring transformer 15,
and of the desired output voltage value, commands the power
section to regulate the output voltage to the desired value
and it controls it by means of a measuring transformer 16
which ensures the necessary feedback.
-
It also ensures, through a transformer 17, that the
current and therefore the power absorbed does not exceed
predetermined values beyond which it is necessary to
activate the ventilation system and, at worst, to shut down
the system. An inner overheating protector, not illustrated,
can also be foreseen.
-
Although it is "intelligent", section 2B operates as a
slave to the commands of the control unit 1, to which all
the necessary information is transferred.
-
Although it is not illustrated in figure 1, it is clear
that the control unit 1 can be, and in general is, also
equipped with communication interfaces (modem and/or serial
ports) to receive commands or transmit data to a remote
supervision centre.
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It must be noted that in regulation systems fed by a
three-phase network three identical power modules can be
present, controlled by a common control unit 1 through the
channel 8 (in this case a BUS)or channels dedicated to and
possibly provided with many sensors, to independently
monitor the state of three distinct lighting sets.
-
For this, as well as the power module 2, two further
modules 102, 103, identical to module 2 and obviously fed by
the other two phases of the network, respectively, are
represented in figure 1.
-
Other aspects of figure 1 shall be considered further
on.
-
Figure 2 represents the structure of the power module
2A, 2B of figure 1 in greater detail, wherein the main (even
if not exclusive) innovative aspects of the present
invention are actually to be found.
-
The power module comprises an inlet autotransformer 19
with inlet terminals N (neutral) and F (phase) to which the
mains voltage, for example with a nominal value of 225 V, is
applied.
-
The autotransformer is equipped with an output terminal
U to supply a load with a somewhat reduced nominal voltage
equal to about 200 V which defines the average value of the
regulation range in which the output voltage can be varied.
-
It is also equipped with a first group of M taps
referenced in order as 20,21,22 (four in the represented
preferred embodiment) upon which is available a nominal
voltage referred to the neutral feeding potential equal to
0, 15, 30 and 45 V, respectively.
-
The autotransformer is further equipped with a second
group of N taps referenced in order as 24,25,26,27 (four in
the preferred embodiment) upon which is available a nominal
voltage, referred to the neutral potential, equal to
105,165,225,285V, respectively.
-
It should immediately be noted that the voltage between
adjacent taps of the first group is nominally equal to 15V
whereas the voltage between adjacent taps of the second
group, as well as between the tap of the second group
adjacent to the tap of the first group, is equal to M • 15V,
that is 60 nominal volts.
-
In other words and more generally, if the taps of the
first group are electrically spaced out on the winding of
the autotransformer by K turns, the taps of the second group
are electrically spaced out by M • K turns, as are the
electrically adjacent taps 24 and 23 of the first and of the
second group respectively.
-
It is therefore clear that by selectively connecting a
tap of the first group and a tap of the second group, or
else two taps of the first group, to the terminals of a load
of the first group, it is possible to feed the load with a
discreet voltage which can be varied in multiples of 15V,
between a minimum of 15 nominal volts and a maximum of 285
nominal volts.
-
Finally, by connecting the load terminals to the same
tap, and from this point of view it does not matter which,
it is possible to apply a zero voltage to the load.
-
Therefore with only M+N taps it is possible to apply to
the load any of M • (N+1) distinct alternate voltages, of
which one is zero.
-
It is clear that significant advantages with respect to
the known solutions are only provided by M and N >2 and
preferably with M=N.
-
In figure 2 the voltages available at the M+N output
taps are selectively connected to the primary 28 of a
voltage reducing auxiliary transformer 29, conveniently but
not necessarily with a turn ratio close to 1/7, by means of
two groups of electromagnetic switches 30, 31 and through a
DPDT (Double Pole Double Throw) relay 32 with the function
of reversing switch.
-
The secondary 33 of the transformer 29 is connected in
series between the output terminal U of the autotransformer
and the switch 18 for connecting to the load Z.
-
Therefore, it is clear that to the load Z can be
applied a base voltage (200 nominal volts present at
terminal U) increased or decreased (according to the closing
position of the switch 32) by the voltage induced in the
secondary 33 which varies from 0 to 285/7 V, that is about
40.7 V, in steps of about 2.1 nominal volts.
-
The (nominal) range of variability of the regulated
feed voltage of the load thus extends from about 159V to
about 241V, which is more than sufficient to ensure an
effective and regulated output voltage of between 175 and
215V also in the case of variations in the mains voltage of
up to ± 10% of the nominal voltage.
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The first group 30 of electromagnetic switches, of the
SPDT type, comprises M (M=4) relays 34,35,36,37 with the
common pole connected to the sockets 20,21,22,23
respectively of the first group and the normally open
contact(that is with the relay de-energised) collectively
connected to a pair of contacts of the reversing switch 32.
-
The second group 31 of electromagnetic switches, of the
SPDT type, comprises N+1 (N=4) relays, 38,39,40,41,42 with
the common pole connected to the sockets 27,26,25,24
respectively, of the first group and to the socket 23 of the
second group and with the normally open contact collectively
connected to the other pair of contacts of the switch 32.
-
Obviously only one relay at a time of each of the two
groups must be energised into closing to avoid the short
circuit of a part of the autotransformer and the switching
closed of any one of the relays must take place only when it
is certain that the other relays of the same group,
therefore all of those in the same group, are open.
-
Later on we shall see how this problem is solved in an
innovative manner.
-
Here, to conclude the description of figure 2, it
should be observed that to ensure the supply continuity of
the load and at the same time to avoid short-circuiting, it
is necessary to foresee by-pass devices and circuits.
-
Advantageously, the number of these circuits is less
than the number of relays of each group: for the first group
these consist of a single by-pass circuit, consisting of a
relay 43 with the common pole connected to an intermediate
tap 22 of the first group of tap and the contact which is
normally open connected to the output node of the first
group of relays through a current-limiting resistor 44.
-
For the second group of relays are foreseen, on the
other hand, with rounding off in defect to the nearest
integral number, (N+1)/2 by-pass circuits (thus in the
figures 2 circuits) with the common pole respectively
connected to taps of the second group separated by one tap,
in figure 2 the intermediate tap 26,24, and with the contact
which is normally open connected to the output node of the
second group of relays through a common current-limiting
resistor 47.
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The value of the limiting resistors is suitably chosen
to limit both the circulating current to acceptable values
when a by-pass circuit is closed together with a relay of
the corresponding group, and the voltage drop on the
resistor, when the only by-pass circuit is closed and
crossed by the feed current of the primary winding of the
transformer 29 (which in the example described is a function
of the load current in the ratio 1/7).
-
Therefore, for example, if the maximum current foreseen
in the primary 28 is 4A the resistor 47 can indicatively
have a value of 20Ω and the resistor 44 a value of 10Ω.
-
In addition the by-pass relays 43,45,46, which
collectively constitute a third group 73 of relays, a
further relay 48, which is normally open, is foreseen to
short circuit the primary winding 28 of the transformer when
the inverter switch is activated.
-
The inverter switch is activated when the voltage
applied to the primary 28 is zero, that is when the relays
37 and 42 are closed and consequently the primary is in
short circuit. In this condition the primary 28 and the
secondary 33 reverse their roles: the transformer is fed
with current through the winding 33 which functions as a
primary. Since the winding 28, which functions as a
secondary, is in short circuit, the drop in voltage on the
winding 33 is negligible (due only to resistance and
dispersion reactance).
-
If, however, the winding 28 is open, as happens during
the course of the switching of the relay 32 (unless a
mechanically polarised relay is foreseen which closes before
opening and which is intrinsically slow and not very
reliable) the transformer 29 behaves like an idle
transformer, fed with current, that is as a reactance which
introduces, as a function of the feed current, a high and
unacceptable drop in voltage, at most limited by the
saturation of the magnetic core, which significantly reduces
the voltage applied to the load.
It is, therefore, appropriate that during the course of the
switching of the inversion relay 32 the short circuit of the
winding 28 be ensured.
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Having described the structure of the power module one
can immediately understand its function, as it is commanded
by the control section 2B which comprises a microprocessor
49 with relative memory, driving circuits of the different
relays and communication port with the control unit 1
(Fig.1).
-
To start up the system the control unit 1 firstly asks
for a predetermined voltage to be supplied in output.
-
The control section 2B, after having measured the
actual mains voltage available, determines, upon the basis
of stored information, which of the relays of the first and
of the second group must be closed and the position which
the switch 32 must be in to obtain the desired voltage in
output. Therefore, it commands their closing with a possible
switching of the relay 32.
-
All of these operations are carried out at no load,
preferably but not necessarily in sequence.
-
Through the closing of a pair of relays, at the output
of the power section a voltage is made available which is
measured and compared to the desired one.
-
If the differential is less than a certain value (also
programmable) it is indicated to the control unit 1 that it
can proceed to the connection of the load with the closing
of the switch 18. Otherwise it is necessary to modify the
output value, in general with just the opening of a relay of
the first group and the subsequent closing of another relay
of the same group.
-
For this adjustment, even if it is carried out at no
load, a rigorous ordering must be respected between the
opening of the first switch and the closing of the second.
In other words the control section 2B must verify, by means
of circuits discussed later on, that the first switch is
actually open before putting the second relay into closed
state.
-
The same condition must be verified also in the case
where it is necessary to open (even simultaneously) both a
switch of the first group and of the second. The closing of
the switches which replace the first in closed state must
take place subsequently. This is necessary to avoid the
short-circuiting of portions of the autotransformer's
windings.
-
More complex is the procedure to be followed to modify
the output voltage under load, that is when the switch 18 is
closed, both to keep the output voltage constant as the
mains voltage varies, as well as to obtain in output a
voltage which can vary according to a predetermined time
profile established by the control unit 1 (ignition ramp,
heating voltage, voltage reduction ramp, maintenance
voltage).
-
In this case, before opening a relay, either of the
first or of the second group, it is necessary to close a by-pass
circuit, to make sure that the by-pass circuit is
closed and, only after having carried out this check, to
open the relay. After having checked that the relay to be
opened is actually open one can proceed to the closing of
the relay which must replace in closed position the one just
opened. Finally, the by-pass circuit can only be opened
after having checked that the relay already moved closed is
actually closed.
-
The same procedure must be repeated, in sequence and
after the first, in the case that to regulate the voltage to
the desired value it is necessary to switch a relay both of
the first and of the second group.
-
The procedure to be followed for the activation of the
reversing switch 32 is entirely analogous.
-
Firstly, it is necessary to move closed the two relays
42,37, if they were not already closed, respecting the
procedure already seen and to check that they are closed.
-
In this condition the voltage set for the primary 28 is
zero. It is necessary to then move closed the short circuit
relay 48 and preferably, even if not necessarily, check the
state thereof.
-
Indeed, since the short circuit relay switches to a
zero voltage between the contacts, there is no risk of
electric arcs which could damage the contacts and cause, by
welding, the jamming of the relay.
-
With the short circuit relay closed it is then possible
to actuate the inverter switch 32 and finally to reopen the
short circuit relay.
-
Also this opening switching takes place with zero
voltage between the contacts and the current is switched
onto the parallel short circuit path formed by the relays
37,42, which are closed, therefore without the development
of an electric arc.
-
In this condition, with the procedures already seen it
is then possible to establish a non -zero voltage in the
primary 28 with the opening of one or other of the switches
37,42 or of both, and the closing of corresponding switches
of the first and/or second group, taking care to activate
the necessary by-pass circuits.
-
It is therefore clear, keeping in mind that the
switching time of an electromagnetic relay is in the order
of 10 ms, that switching procedures where a load is present
require a non-negligible time, no less than 40 ms and than
80 ms when the switching of two relays of the first and of
the second group is necessary.
-
In the absence of a check on the state of the relay,
this time, for safety and to take account of the inevitable
dispersions of the switching times, must necessarily be
increased, separating the different operations in time,
increasing the intervention times of the by-pass circuits
and consequently the amount of energy dissipated and the
duration of the voltage transients, reducing the regulation
speed.
-
It is, therefore, desirable to have control circuits
which allow the execution time of the procedures to be
reduced to the minimum and which rapidly provide information
that the different switching operations commanded have
actually taken place.
-
This is even more important since, whereas the contacts
of the inverter switch and of the short circuit relay open
and close without the development of electrical arcs, the
contacts of the other relays switch under a load, which is
inductive what's more, with a non-zero voltage between the
open contacts and consequently with the development of
electrical arcs which can cause the welding and the jamming
of the contacts which no longer obey the electromagnetic
command of the relay.
-
From this point of view, more than desirable, it is
mandatory to foresee control systems which provide the
direct information of the contact switching having taken
place, not mediated by the behaviour of auxiliary contacts,
the behaviour of which does not necessarily reflect that of
the contacts which must be monitored.
-
In this manner it is possible to avoid that a relay
failure has catastrophic effects, timely blocking the
further development of the switching procedures upon the
first detection of the failure, carrying out attempts at
repeating the command and, after a suitable number of
attempts, for example three, having checked that the defect
is permanent, definitively blocking the operation and
indicating the failure.
-
Figure 3 shows a preferred embodiment of the circuits
for checking the open/closed state of the switch contacts.
-
Firstly, let us consider the second group 31 of
electromagnetic switches, comprising switches
38,39,40,41,42, with the common pole connected to the
autotransformer tap at which there is the nominal voltage of
285,225,165,105 and 45V respectively.
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The contacts which are normally closed or inactive of
the two switches 38,39 are connected to the inputs of a
detector circuit 50 which provides in output a logic signal
1 asserted (for example a voltage of about 5V) when both of
the switches are in rest position and a logic signal 0 when
even only one of the switches 38,39 is switched with the
common pole closing on the active pole.
-
The structure of the detector circuit is very simple
and comprises a rectifying bridge 51 connected to the
inactive poles, which are normally closed, of relays 38,39,
through a resistor 52 of a suitable value. The bridge feeds,
in voltage rectified and filtered by a capacitor 72, through
a second resistor 53, the light emitting diode of an
optoelectronic coupler 54 whose phototransistor, connected
between a suitable voltage (+5V) and ground, with a suitable
resistance 55 in series with the emitter, imposes at the
output, connected to the node between emitter and resistor
55, a logic signal 1 when the detector circuit is fed (that
is, the switches 38,39 are both switched to open the active
pole and to close the inactive pole) and a logic signal 0
when even only one of the switches is switched to close onto
the active pole and therefore the detector circuit is not
powered.
-
The value of the resistor 53 and of the capacitor 72 is
chosen so that the time constant RC of the circuit has a
predetermined value, in the order of 5ms.
-
The value of the resistor 52, in relation to that of
the resistor 53 is chosen according to the feed voltage (in
our case 60 nominal volts being the effective value) so that
the light emitting diode is energised with a suitable
current, for example 10mA.
-
Identical to that described is the structure of the
detector circuit 56, with two inputs respectively connected
to the inactive pole of the switches 40,41. The detector 56
recognises the open state (level 1 as output) of both of the
switches or the closed state (level 0 as output) of even
only one of the switches.
-
Substantially identical is also the structure of the
detector circuit 57, with the only difference in the (lower)
value of the resistor 52 within the circuit, to take account
of the fact that the circuit has inputs connected
respectively to the inactive pole of the switch 42 and to
the tap with a nominal voltage of 30V so as to be fed (when
the switch 42 is open) with a voltage of 15V.
-
This circuit reveals the open or closed state of the
only switch 42.
-
The outputs of the detector circuits 50,56,57 are
connected to the inputs of a NAND gate 58 which outputs a
logic signal 0 when all of the switches of the first group
31 are open and a logic signal 1 when one of the group
switches is closed.
Since only one of the group switches can and must be closed
at once (otherwise a short circuit forms) the information in
output from the gate 58 and applied in input to the
microprocessor 49 (Fig.2) is adequate to check the
open/closed state of the switches and to verify if a switch
(activated one at a time) has correctly responded to the
closing and opening commands.
-
Incidentally, it is suitable to note that to achieve
maximum safety, the commands to close the switches of the
same group are obtained by decoding a binary code, so as to
rule out any possibility of commanding more than one switch
of the same group to close simultaneously, due to an error
or to a failure developed upstream of the decoder.
-
The information received from the microprocessor is not
just adequate but is also rapid.
-
Indeed, when a switch is closed, the feeding of the
detector circuit, which corresponds to the input signal,
switches as soon as the inactive contact opens and before
the closing onto the active pole takes place. The time
constant of the detector circuit replaces the flight and
bounce time of the mobile armature and ensures that the
closing signal is received when the switching is definitely
taking place and is about to be completed, without
significant delays. In the same way, when the switch is
opened, the detector circuit is supplied with current as
soon as the common pole closes on the inactive contact and
the switching has definitely taken place.
-
Therefore, it is not at all necessary to take account
of the response time of the relay and of the possible
dispersions thereof.
-
Totally identical to the structure of the detector
circuit 57 is the structure of the detector circuits 59,60
with inputs connected to the inactive poles of the relays
37,36 and 35,34 respectively and outputs connected to the
inputs of a NAND gate 61.
-
The NAND gate 61, like the gate 58, has in output a
logic signal 0 when all of the relays of the group 30 are
de-energised, thus open, and a logic signal 1 when one of
the relays responds correctly to an energise command,
closing itself.
-
Totally similar to the previous ones is the structure
of the detector circuits 62, 63 which respectively monitor
the state of the by-pass relays 45,46 and the state of the
by-pass relay 43.
-
In particular circuit 63 is identical to circuit 57
already described, receiving in input a voltage of 15V, and
circuit 62, receiving in input a voltage of 120V, differs
from circuit 50 only for the fact that it has a higher value
of the internal resistance 52.
-
The outputs of circuits 62,63, arranged in logic NAND
from gate 64, provide a logic signal 0 when all of the by-pass
circuits are open and a logic signal 1 when one of the
by-pass circuits is closed.
-
Although it is not indispensable, it is also possible
to foresee a circuit 65 to detect the open or closed state
of the short circuit switch 48.
-
The structure of the detector circuit 65, a diagram of
which is shown in the figures, is similar to that of circuit
50 and differs from the latter only because the former
foresees, as well as the inversion of the output signal
(obtained with the grounding of the phototransistor emitter
and the connection of the output to the collector), a Zener
diode 66 in parallel with the capacitor 52. The Zener diode
limits the current injected into the light emitting diode.
-
Indeed, in this case the voltage applied in input,
according to the different working conditions of the
regulation system, can vary from 0 to 165V (a voltage of
165V is applied to one input and a variable voltage from 0
to 285V is applied to the other).
-
It should immediately be noted that the response of
circuit 65 is ambiguous: the outlet signal depends not just
upon the open or closed state of switch 48 but also on the
input voltage which can be 0 or so low (15÷45V) as not to
lead to the energising of the optoelectronic device.
-
The ambiguity can be solved remembering that the short
circuit relay can and must be moved closed only when
switches 42 and 37 are both closed and the voltage of 45V
referring to the neutral is applied to both of the poles of
the inverter switch 32.
-
In this condition the circuit receives in input a
voltage of 120V, which is more than adequate.
-
This condition can be taken account of directly by the
microprocessor 49 (which knows when switches 42 and 37 are
closed because it is the microprocessor itself which
commands its closing) and in this case the output of circuit
64 can be connected to an input gate of the microprocessor.
-
Yet more advantageously, as represented in figure 3, it
is possible to connect the output of circuit 65 to an input
of NAND gate 64, with the intermediary of a NAND gate 67
with a masking function.
-
Two signals CL42 and CL37 (available in output from the
microprocessor 49) which close the two switches 42 and 47
are applied to two inputs of NAND gate 67.
-
The state 1 present at the output of circuit 65 is
transferred (with inversion) to the input of NAND 64, only
if CL42 and CL37 are at 1. Otherwise NAND gate 67 applies
the logic signal 1 in input to gate 64 and masks the
ambiguous states of the detector circuit 65.
-
It must also be noted that the closing of the short
circuit relay does not take place at the same time as the
intervention of the by-pass relays, for which reason the
information in output from the NAND gate 64 can be
interpreted without any ambiguity and referring to the
particular relay which is activated from time to time.
-
In conclusion, with the described detector circuits it
is possible to recognise the switching of all of the
switches of the power section, detecting it directly on the
contacts, in a reliable and rapid manner, without delays to
ensure a safety margin for dispersions in behaviour.
-
Only the behaviour of the reversing switch 32 cannot be
monitored with detector circuits of the type described
because at the intervention step all of the contacts have
the same potential.
-
This does not constitute a problem because the lack of
switching does not carry the risk of catastrophic failures
and ends up with the impossibility of obtaining the desired
variation of the output voltage.
-
It is therefore possible to detect the non-operation of
the switch, straight afterwards, by simply verifying if the
variation in voltage which comes about from an immediately
subsequent procedure of switching the group relays is in the
desired direction or else the opposite direction.
-
In the previous description the optimised management
system was essentially considered as a voltage regulation
system.
-
From this point of view the system described, thanks to
the fineness of regulation which is allowed (furthermore
capable of being incremented even only slightly increasing
the number of taps of the autotransformer and the
corresponding number of relays) and thanks to the speed of
response, can be conveniently used as a voltage stabiliser
for the feeding of whatever type of load, as well as a
programmable voltage regulator for feeding whatever type of
load, the voltage of which must be regulated and possibly
modified for whatever reason (for example for "margining"
operations in a laboratory or to regulate the speed of
motors fed in alternating current, replacing TRIAC
partialising devices which do not allow the mains voltage to
be increased and in particular have the serious drawback of
introducing high width harmonics in the developed waveform.
-
However, it is clear, as has been highlighted, that the
described system can also operate as a brightness regulator,
keeping in mind that the light emission is to a great extent
dependent upon the feed voltage of the bulbs and the
brightness of an environment also depends upon the possible
variable light contribution coming from the outside.
Therefore, a direct relationship between feed voltage and
brightness of the room does not exist.
-
For this purpose it is sufficient to foresee a
brightness sensor 11 (Fig.1) and to slave the operation of
the system to the signal emitted by the sensor, conveniently
converted into digital form and compared with a desired
brightness value.
-
The brightness sensor can also carry out a twilight
function and the system can be programmed, obviously with
suitable hysterisis, to switch on a light bulb when the
brightness falls below a certain level, to keep the lighting
at a desired level, in case variable according to time
bands, and to switch off the light bulb if the brightness
goes above another predetermined level.
-
A specific application of this type consists of the
regulation of lighting in tunnels.
-
It is known that current lighting units for tunnels can
consist of a line which is always switched on, known as
"permanent" lighting, of a second low consumption line which
is always switched on even in the case of a power cut since
it is fed from UPS (Uninterrupted Power Supply), known as
tracing, and of a certain number of intensifying circuits
(generally from 1 to 3, according to the length of the
tunnel) which switch on or off in relation to the brightness
outside, to reduce glaring effects when leaving the tunnel
and to allow the gradual adaptation to the lighting inside
upon entering.
-
This solution offers only four brightness values and
cannot adapt to all the intermediate conditions.
-
The system which has been described, appropriately
replicated to constitute a piece of equipment, also
effectively solves this problem and allows the brightness to
be regulated gradually, with a high resolution, by
controlling the selective intervention of the intensifying
circuits according to the brightness outside.
-
To better understand this aspect it is suitable to
refer to figure 1.
-
In figure 1, as well as the base system which has been
described, hereafter known as unit A, two other units B and
C, identical to the previous one, are present.
-
For simple reasons of constructive modularity and of
programming, units B and C are each equipped, like unit A,
with a central unit, such as 1, with at least one power
module, such as 2, and with a keyboard, such as 3, so as to
be able to be programmed individually in a coordinated
manner.
-
However, it is obvious that a single keyboard, with a
bus connection, represented by the dashed line 104 can be
used to program the operation of the three units.
-
The element common to the three units which completes
the equipment consists of an auxiliary module 130 and of a
brightness sensor 10 which, through the auxiliary module
130, sends a binary code, representing the level of
brightness outside, to the three units on respective optoinsulated
serial ports.
-
It should be noted that, in place of the bus 104 and of
a keyboard dedicated to each unit A, B and C the auxiliary
module 130 could allow the exchange of information between
the different units A, B, C and the programming thereof with
a single keyboard.
-
Unit A can be programmed to manage the permanent line,
unit B to manage the intensifying line or lines and unit C
to manage the tracing line, all according to the brightness
outside, measured with a single sensor 10.
-
Figure 4 represents in a voltage V/external brightness
level L qualitative diagram, a preferred form of regulation
of the voltage for the different lighting lines.
-
For external brightness values less than L1 units A and
C supply to the permanent line (P) and to the tracing line
(T) a feed voltage which increases with the external
brightness. The voltage can be different for the two lines
but, for clearness of representation it is represented as
equal.
-
When the external brightness is greater than L1 unit B
activates the feed of a first intensifying line RNF1,
whereas the feed of the permanent line and of the tracing
remain unchanged, as represented in the figures. If so
desired, for very long tunnels or for particular
requirements the feed voltage of the permanent and tracing
lines could also be reduced and subsequently incremented.
-
It is clear that initially the voltage necessary for
switching on and heating is applied to the intensifying
line, said voltage then being reduced to a suitable value.
-
As the brightness outside increases, the feed voltage
of the intensifying line is increased from L1 and L2.
-
When the external brightness is greater than L2, with
the same criterion, the second intensifying line RNF2 is
activated and the feed voltage of the other intensifying
line is reduced.
-
Finally, if the external brightness is greater than L3,
the third intensifying line RNF3, if present, is activated
with the same criteria.
-
The same criteria is followed, with a suitable
hysterisis, to reduce and remove the feed to the
intensifying lines, in the case of reduction of external
brightness.
-
Basically, at the entrance and at the exit of the
tunnel a lighting LTOT which can be varied gradually,
without substantial discontinuities, with the level of
brightness outside L, is obtained.
-
To achieve a precise regulation of brightness,
according to one aspect of the present invention and unlike
prior art systems which use photovoltaic cells and expensive
equipment, the system object of the present invention uses
a photoresistor, which is more cost-effective, more reliable
and, being appropriately driven, allows greater precision of
measurement and of regulation in all possible ranges of
brightness.
-
Figure 5 schematically represents the brightness
measuring apparatus adopted.
-
A photoresistor 10, remote from the regulation system,
is connected to the auxiliary module 130 with a screened
cable 78 which protects it to a large extent from
disturbances and atmospheric discharges.
-
The photoresistor 10, in parallel with a resistor 70
and in series with a resistor 71 which functions as a
voltage divider, is fed by a continuous regulated and
constant voltage of -5V.
-
The node which is common to the photoresistor and to
the resistor 71 is connected to the inverting input of an
operational amplifier 74, with suitable feedback provided by
a trimming resistor 75, to ensure a predetermined gain.
-
Two diodes 72,73 connected between the inverting input
and voltages of +5V and -5V respectively, ensure the
protection of the amplifier against overvoltages taken on
through the input cable 78.
-
Not-shown capacitors, in a known way, filter the
transient noise and cutting the frequency response of the
amplifier.
-
The output of the amplifier 74 is connected to an
analogic input port of an integrated circuit for the
acquisition and A/D conversion of signals which circuit
outputs, on three serial ports, and sends to units A,B,C a
binary code representing the input signal, in turn
representing the resistance of the photoresistor 10 and,
fundamentally, the measured level of brightness outside.
-
Through serial input ports, not illustrated, the
circuit can be programmed, to assign and characterise the
ports with which it is equipped as analogue or digital input
ports.
-
Other aspects of the integrated circuit are not
essential.
-
The auxiliary module 130 is fed by an AC/DC power
supply 79, connected to the output of the transformer 6
(Fig.1) and buffered by a battery 77 which ensures the
powering of the module even when there is a main shut down.
The power supply 79 supplies the necessary continuous feed
voltages to the module.
-
In this way all of the functions necessary for
acquiring the brightness value, which is indispensable for
the control of the lighting of tunnels and more generally of
units dependent upon conditions of brightness outside are
gathered in an auxiliary module and do not burden the cost
of the base system which in many cases must only operate as
a programmable voltage stabiliser or regulator.
-
In relation to the use of the described system for the
optimised management of a lighting unit of the gas discharge
type it is interesting to note a special function, capable
of being achieved with the system, consisting of testing the
unit to identify bulbs which are defective and/or nearly run
out.
-
It is known that when a gas discharge bulb has nearly
reached the end of its useful life, it finds it difficult to
keep its switched on state and is particularly sensitive to
rapid reductions in the feed voltage up to a minimum
necessary value, to remain switched on.
-
The described system, indeed, allows these rapid
variations in voltage to be obtained through a command made
manually from keyboard 3 (fig.1).
-
Indeed, it is possible to command a switching on and
warming up sequence, and with this having been carried out a
rapid reduction in the maintenance voltage can be commanded,
in quick succession switching the relays of the second group
(31, Fig. 2) so as to impose relatively wide variations in
voltage, in the described example in the order of 8.4V
without passing through the selective activation of the
relays of the first group.
-
This operation can be carried out in a very brief space
of time, in the order of 100 ms, and it can be followed, in
an equivalent time, by the restoration of the normal
switching on conditions.
-
As a result of this rapid voltage variation, which
substantially consists of a margining operation during the
course of the exercise, the bulbs which are defective and/or
nearly run out remain switched off.
-
This allows the programmed replacement, following the
testing operation or even at an appropriate subsequent time,
of all of the bulbs which are defective and/or have nearly
run out.
-
In this way the number of necessary maintenance
operations is reduced, to the great advantage of the
operative state of the equipment in the cases in which it is
intended to operate in continuous duty.
-
The previous description refers to a preferred
embodiment of a system for the optimised management of
lighting units and it is clear that many variants, in
addition to those already indicated, can be made.
-
For example, the different switching relays can all be
individually equipped with a switch detecting circuit, as is
the case for relays 57 and 63 of figure 3, with outputs of
the detector circuits arranged by groups in logic NAND or
else connected directly to corresponding ports of the
microprocessor, or even connected to a reduced number of
ports and at the extreme to only one, through a multiplexer.
