This invention relates to an improved clogged-filter signalling indicator.
In the prior art, differential clogging indicators with visual and
electrical or only electrical signalling of the clogged condition of a filter with
which they are associated are known. These indicators are generally used in oil-pressure
circuits in which failure to replace the filtering element could cause damage to
the machine on which it is installed. As known, a clogging indicator generally includes
a membrane or other movable member subject to the pressure of the fluid passing
through the filter and that, upon reaching a predetermined state of clogging of
the filter, opens or closes an electrical contact connected to an appropriate signalling
and/or control circuit. Said circuit generally stops operation of the machine to
Unfortunately, it has been noted that the filter is not always replaced
promptly upon signalling by the indicator of clogging but it might happen that when
the indicator signals clogging someone decides to place a jumper in parallel with
the signalling contacts of the indicator or disconnect the wire or connector so
as to eliminate the clog signal and be able to continue using the machine.
Although signalling of clogging is usually done with a certain advance
just to avoid damage, continuing for a long time with the use of the machine after
signalling of clogging could cause serious damage to the machine.
Especially, once the jumper is removed or the wire or connector is
reconnected, it is no longer possible to prove that there has been tampering and
in case of a machine under guarantee the damage falls onto the guiltless firm that
produced the machine.
The general purpose of this invention is to remedy the above mentioned
shortcomings by making available a clog sensor that would allow eliminating the
possibility of easy tampering therewith.
In view of this purpose it was sought to provide in accordance with
this invention a clogged-filter indicator in a fluidic installation equipped with
an electrical connector to which leads an electrical circuit contained in the indicator
and clogged-condition sensing means commanding said circuit to changeover from a
first condition to a second condition upon sensing of a clogged condition and characterized
in that in the circuit there is an electrically controllable member for further
control of the circuit between the two conditions.
To clarify the explanation of the innovative principles of this invention
and its advantages compared with the prior art there is described below with the
aid of the annexed drawings a possible embodiment thereof by way of non-limiting
example applying said principles. In the drawings:
- FIG 1 shows a partially cross-sectioned diagrammatic view of a clogging indicator
realized in accordance with the principles of this invention, and
- FIG 2 shows an electrical diagram of the indicator of FIG 1.
With reference to the figures, FIG 1 shows a clogging indicator designated
as a whole by reference number 10 for use with a filter in a fluidic installation
(not shown). The indicator includes a union 11 for connection with the hydraulic
system and an external electrical connector 12 to which leads an electrical circuit
contained in the indicator. The indicator could be fitted on a purposeful base 20
for connection with the control device 19 of the machine whose filter is to be monitored.
Means 13 inside the device 10 and for sensing of the clogged condition
command the electrical circuit to changeover from a first condition to a second
condition upon sensing of a clogged condition. In particular, the clog sensing means
include a member sensitive to the set pressure to cause the electrical signalling
contact 14 in the indicator to go off when the fluid pressure to the union 11 reaches
a figure that has been preset as a symptom of excessive clogging of the associated
The pressure sensor device could be realized in various ways as known
and readily imaginable to those skilled in the art. For example, an elastic membrane
15 could be provided subject on one side to the fluid pressure and an adjustable
load spring 16. Movement of the membrane or of the internal movable device causes
release of the switch 14 which is realized for example as a 'Reed' contact or a
magnetically operated microswitch.
The contact 14 is advantageously of the normally closed type and opens
upon sensing of the predetermined clogged condition.
Again advantageously the condition of the electric circuit could be
merely of closed circuit between two terminals 17, 18 of the connector 12 when there
is no clogging and of open circuit between the same two terminals when the clogged
condition is sensed.
In accordance with this invention, in the electric circuit of the
indicator there is a member 21 electrically controllable from the outside to command
the circuit between the two predetermined conditions subsequently. Control of this
member takes place through a third terminal 22 located on the connector 12. Advantageously,
the member 21 is fitted into a spacer arranged between the body of the indicator
containing the clog sensors and the electrical connector.
In the preferred embodiment of which the circuit is shown in greater
detail in FIG 2 the controllable member is a relay 21 with control coil connected
between one of the two terminals 17, 18 and the third control terminal 22. The relay
has a normally closed contact 23 connected in series with the signalling contact
14. In this manner, by applying an appropriate voltage from the outside to the control
terminal 22 as regards the terminal 18, the relay causes opening of the circuit
between the terminals 17 and 18 while simulating signalling of the clogged condition.
With the indicator described, the machine-control circuit (not shown
because readily imaginable to those skilled in the art) could thus easily verify
whether the indicator has been tampered with. Indeed, the tampering could be done
for example by creation of a short circuit on the connector signalling terminals
or by removal of the clogging indicator and its replacement with a jumper on the
terminals of the connector 20.
With such tampering, there would be false indication of lack of clogging
of the filters with resulting risk of damaging the associated hydraulic circuit.
The appropriately instructed control circuit could however command changeover of
the indicator to the clogged condition by means of the terminal 22. If the clogged
condition continues to not be signalled it means that there has been malfunction
of or tampering with the indicator and this could be promptly sensed before occurrence
of a failure of the hydraulic circuit following an undetected clogging of the filter
associated with the indicator.
It is now clear that the preset purposes have been achieved by making
available an indicator capable of control of tampering and verification of the indicator
Naturally the above description of an embodiment applying the innovative
principles of this invention is given by way of non-limiting example of said principles
within the scope of the exclusive right claimed here. For example, the conditions
of the circuit that signal clogged and not-clogged could be more complicated than
the mere opening or closing of the circuit as readily imaginable to those skilled
in the art. The circuit could also be not only electromechanical but electronic.
For example, the relay could be replaced entirely or partially with an appropriate
As known in the field, the clogged-condition sensor means could also
be different from those described here. The sensor could detect loss of charge upstream
or downstream of the filter.
Even the manner of use of the indicator could be different. For example,
the control circuit 19 of a machine in which the indicator in accordance with this
invention is installed could carry out either a cyclic control at predetermined
intervals through the control terminal 22 or a control after a predetermined time
from a clog signal and return to the non-clogged condition. Indeed, return to the
non-clogged condition could be due to actual replacement or cleaning of the filter
or to tampering in an attempt to make the machine operative immediately without
first proceeding to cleaning or replacement of the filter.