Pressure monitoring device

A pressure monitoring device is disclosed which is adapted to couple a source of fluid with a tripping device. The tripping device includes a tripping switch movable between a first position in which a tripping signal is generated and a second position in which a tripping signal is not generated, and biasing means for biasing the tripping switch into the first position. The pressure monitoring device comprises pressure transmission means which is operable in a first mode and in a second mode, and coupling means having a first position and a second position. The pressure transmission means when operating in the first mode is responsive to the pressure of the fluid being monitored and when operating in the second mode is independent of the pressure of the fluid. The coupling means is operatively associated with the pressure transmission means and the tripping device for coupling the pressure transmission means to the tripping device. The coupling means transmits a pressure signal proportional to the pressure of the fluid to the tripping switch when the coupling means is in the first position and the pressure transmission means is operating in the first mode whereby the tripping device generates a tripping signal when the pressure of the fluid passes a predetermined limit. Further, the coupling means forces the tripping switch into the second position independent of the pressure of the fluid when the coupling means is in the second position.

BACKGROUND OF THE INVENTION 
The present invention relates to a pressure monitoring device and more 
particularly to a pressure monitoring device which is adapted to couple a 
source of fluid with a tripping device in such a manner that a tripping 
signal is generated when the pressure of the fluid being monitored passes 
a certain predetermined limit. 
It is often desirable to couple pressure monitoring devices to fluid 
systems employing pressurized fluids in order to monitor the fluid 
pressure and generate a signal if the pressure passes predetermined 
limits, i.e., goes above a high pressure limit or below a low pressure 
limit. The signal generated when the pressure passes the predetermined 
limit may for example be an alarm signal to actuate an alarming device 
such as a light or buzzer, or the signal may be used to actuate a device 
to adjust the pressure of the fluid or even shut down the system. In such 
systems employing pressure monitoring devices, it may also be desirable to 
prevent generation of the tripping signal when the monitoring device is 
by-passed and/or disconnected from the fluid system, in order not to 
generate a "false" tripping signal. 
For example, pressure monitoring devices are useful in dialysis systems to 
monitor the pressure of the blood being dialized and to generate a 
tripping signal in the event that the blood pressure falls below a certain 
limit. Further, it may be desirable in such systems that the tripping 
signal not be generated when the blood lines are disconnected from the 
dialysis system and/or patient. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a pressure 
monitoring device adapted to couple a source of fluid with a tripping 
device in which the tripping device includes a tripping switch movable 
between the first position in which a tripping signal is generated and a 
second position in which a tripping signal is not generated, and biasing 
means biasing the tripping switch into the first position. The pressure 
monitoring device comprises pressure transmission means operable in a 
first mode and in a second mode, and coupling means having a first 
position and a second position. The pressure transmission means when 
operating in the first mode is responsive to the pressure of the fluid 
being monitored and when operating in the second mode is independent of 
the pressure of the fluid. The coupling means is operatively associated 
with the pressure transmission means and the tripping device for coupling 
the pressure transmission means to the tripping device. The coupling means 
transmits a pressure signal proportional to the pressure of the fluid to 
the tripping switch when the coupling means is in the first position and 
the pressure transmission means is operating in the first mode whereby the 
tripping device generates a tripping signal when the pressure of the fluid 
being monitored passes a predetermined limit. Further, the coupling means 
forces the tripping switch into the second position independent of the 
pressure of the fluid when the coupling means is in the second position. 
In a preferred embodiment of the present invention, the coupling means 
comprises a spring device having two different operating positions. In one 
of the operating positions, the pressure signal is directly transmitted to 
the tripping device independent of any biasing force of the spring device, 
and in the other operating position, the spring device provides the sole 
pressure on the tripping switch independent of the pressure of the fluid. 
In a still further preferred embodiment, the spring device comprises a 
plate spring, the ends of which are held a distance apart less than the 
length of the plate spring so that the plate spring is bowed in each of 
the two operating positions. 
These and other features of the present invention will now be described 
with reference to the enclosed drawings in which a preferred embodiment of 
the invention is shown.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, there is shown in FIG. 1 a pressure 
monitoring device in accordance with the present invention which is 
arranged so that it monitors the pressure in a line 1. Line 1 may for 
example be a blood line in a dialysis system where it is desirable to 
monitor the blood pressure and to generate a tripping signal if the blood 
pressure falls below a certain limit. Such a dialysis system may for 
example be of the type shown in U.S. Patent Application Ser. Nos. 841,898 
and 841,899 both filed on Oct. 13, 1977. To facilitate the monitoring, the 
line 1 is provided with a flexible monitoring pad 2. To this monitoring 
pad 2 is connected a further line 3 which is intended for the calibration 
of the pressure monitoring device in order to aid in adjustment of the 
predetermined pressure limit at which a tripping signal will be generated. 
This line 3 may therefore be connected or connectable to a conventional 
pressure gauge which indicates the actual pressure in the line 1. 
When the pressure monitoring device is to be utilized for the detecting or 
monitoring of the pressure in the line 1, the line 1 with the pad 2 and 
the connecting line 3 are introduced into a housing 4 which contains an 
internal sensing element 5. In the embodiment shown this sensing element 
has the form of a wheel which is manually adjustable in relation to a 
transmission shaft 6. This adjustability is achieved in any suitable 
manner, not shown on the drawing, e.g. in that the wheel is threaded on or 
in the transmission shaft 6. The shaft 6 passes through a bushing 7 which 
is permanently fixed to the housing 4. 
The housing 4 together with a bracket 8 is attached to a fixed machine 
element 9 which may consist for example of the wall of a control unit. At 
its extreme end the transmission shaft 6 carries a movable bracket 10. 
This bracket is U-shaped and carries between the ends of its side pieces a 
plate spring 11. This plate spring in turn carries a pressure transmission 
element 12 which is adapted so that it acts upon a movable spring-loaded 
actuating element 13 of a tripping device, such as for example, a 
conventional microswitch 14. 
As shown, the ends of the plate spring 11 are fixed to the side pieces of 
U-shaped bracket 10 so that the ends of the plate spring 11 are separated 
or spaced a distance less then the total length of the plate spring 11. 
Thus, as is apparent, the plate spring 11 is movable between two 
positions--a first position in which it is bowed or flexed upwardly toward 
transmission shaft 6 (as shown in FIG. 1) and a second position in which 
it is bowed or flexed downwardly toward the spring loaded actuating 
element 13 of microswitch 14 (as shown in FIG. 2). 
The microswitch 14 may be of any suitable type, and therefore its inner 
mechanical construction is not shown in detail. It is important only that 
its actuating element 13 should be pressed in against the action of a 
spring force. However, FIG. 1 does show a diagramatic representation of 
how microswitch 14 can be used to activate an alarm lamp or light 16. As 
shown, microswitch 14 obtains its energy from a source 17 and will 
generate a signal when the spring-loaded actuating element 13 is raised or 
moved upwards an amount which is sufficient to complete the circuit via 
line 15, alarm lamp 16 and source 17. Naturally, the signal generated by 
microswitch 14 can also be used for purposes other than for lighting an 
alarm lamp 16. For example, the signal, besides or in addition to 
activating the alarm 16, may also activate means for adjusting the 
pressure in line 1, e.g. by starting a pump, or opening or closing a valve 
in line 1. 
The microswitch 14 is fixed to the bracket 8 with the help of a fixed stud 
18 and nuts 19 and 20. Thus, in the position shown, a pressure signal 
proportional to the pressure of the fluid is transmitted from the pad 2 
via the sensing element 5, the pressure transmission shaft 6, the plate 
spring 11, and the pressure transmission element 12 to the movable 
actuating element 13 of the microswitch 14. It is to be noted that when 
the spring 11 is in the position shown in FIG. 1, i.e., flexed toward the 
pressure transmission shaft 6, the spring pressure of the plate spring 11 
does not affect the loading of the actuating element 13. 
It is to be noted that by manually adjusting the position of the sensing 
element 5 relative to the shaft 6, the pressure limit at which the 
microswitch 14 trips can be readily varied. For example, if the wheel 5 is 
raised, relative to shaft 6, the distance between the top of the wheel 5 
and the bottom of the pressure transmission element 12 is increased. Thus, 
wheel 5 will have to move upwards a greater distance within the housing 4 
before the spring loaded actuating element 13 will complete the circuit 
15, 16, 17. This in turn means that a lower fluid pressure is required to 
trip microswitch 14. Similarly, lowering of the wheel 5 relative to the 
shaft 6 will increase the value of the pressure at which the microswitch 
14 is tripped. Further, it is apparent that use of a pressure gauge 
connected to line 3 which provides a visual indication of the pressure in 
line 1 may be useful in setting this predetermined limit at which 
microswitch 14 will trip. 
If the pressure monitoring device is to be by-passed, such as for example, 
when the blood line is to be disconnected from the dialysis system and/or 
the patient, the tube 1, its pad 2 and its connecting line 3 may be 
removed from the housing 4. This is shown in FIG. 2. Subsequently, the 
wheel or sensing element 5 is gripped and moved out manually to the 
position shown in FIG. 2 and the plate spring 11 flipped or snapped over 
to its other position as shown in FIG. 2. That is, the plate spring 11 is 
moved to its second position in which it is bowed toward the spring-loaded 
actuating element 13. 
In this position, the bracket 10 affixed to transmission shaft 6 is pressed 
against the fixed bushing 7 and the pressure transmission element 12 is 
pressed against the actuating element 13 to maintain the actuating element 
13 in its fully recessed or retracted position to prevent any signal from 
being emitted from the circuit 15, 16, 17. As can be appreciated, this is 
achieved by making the pressure exerted by the plate spring 11 sufficient 
to overcome the internal spring force of the microswitch 14. Thus, when in 
the position shown in FIG. 2, the microswitch 14 is only influenced by the 
pressure exerted by plate spring 11, and not by the pressure of the fluid. 
This is desirable in order to prevent generation of any "false" tripping 
signals when the pressure monitoring device is being by-passed. That is, 
when the fluid line 1 and pad 2 have been removed from the housing 4, the 
position of the plate spring 11 as shown in FIG. 2 will prevent a 
misunderstanding regarding an alarm condition since no tripping signal can 
be generated. 
Further, it should be appreciated that, when the tubes are introduced into 
the housing 4, the system may be automatically returned to the position 
shown in FIG. 1 and activated so that the circuit 15, 16, 17 is closed if 
the pressure in the line 1 drops below a predetermined value which can be 
set by means of the wheel 5. 
Naturally, the invention is not limited exclusively to the embodiment 
described above, but can be varied within the scope of the following 
claims. It will be obvious for example to those versed in the art, that 
the plate spring shown can be substituted by other spring devices which 
are moved between two different operating positions. Such a system may be 
constructed for example with the help of a lever mechanism and optional 
springs. It will probably be found, however, that the simple plate spring 
shown represents the most convenient arrangement.