GB2226197A

GB2226197A - Circuit arrangement for monitoring a fuse in medical equipment

Info

Publication number: GB2226197A
Application number: GB8924720A
Authority: GB
Inventors: Jurgen Hoffman; Rudolf Muller
Original assignee: Medizin und Labortechnik Leipzig VEB
Current assignee: Medizin und Labortechnik Leipzig VEB
Priority date: 1988-11-03
Filing date: 1989-11-02
Publication date: 1990-06-20
Also published as: DD276758A1; GB8924720D0

Abstract

A circuit arrangement for signaling a defective fuse in a secondary current circuit with unstabilised d.c. or a.c. voltage supply, includes a fuse 1 connected to a supply conductor A and in parallel with the emitter/base path of a pnp transistor 2. The collector of the transistor 2 is connected to one anode of a two-colour light-emitting diode 5, the second anode being in connection with the fuse. The common cathode of the LED 5 and the transistor base are linked via resistors 7, 8 to a supply conductor B. When the fuse 1 is intact, transistor 2 is blocked and only the second anode of the LED 5 is illuminated by way of on-off switch 6. If the fuse has blown, transistor 2 turns on, both anodes of the LED 5 are actuated, and both colours are displayed. Diodes 3, 4 may be omitted. <IMAGE>

Description

Circuit Arrangement For Monitoring Secondary Circuits in Medical Equipment The invention relates to a circuit arrangement for monitoring secondary circuits in medical equipment, more particularly for indicating defective fuses in secondary circuits with unstabilised d.c. or a.c. voltage supply.

In various items of medical equipment electro mechanical function-specific components are in operation, such as pump motors for intermixing fluid sleep-inducing chemicals into the gas breathed by and supplied to the patient (DE-OS 34 01 923), or devices for heating the moistening fluid and the breathed gases (DE-PS 24 36 406) with unstabilised d.c. or a.c. voltage.

In order to protect the transformer and rectifier of the electro mechanical function-specific component and of the other assembled electronic components in the medical equipment, which may also be operated in parallel therewith, a fail-safe device is necessary on the secondary side, in order to prevent an impermissibly high current resulting from mechanical or electrical problems instigated, for example, by seizing up, interturn short circuits etc. For this safety inserts are used, usually fuses of known type which are connected into the current path of the relevant conductor in the relevant user set-up of the medical equipment.

In order tc monitor electronically the operating condition of fuse sets, an arrangement was known in which loads or parallel cables protected by fuses are fed from an a.c. or d.c. voltage network (DE-OS 35 15 773). In this specification a high-impedance parallel path or a Zener diode having a protective rectifier diode is associated with each fuse set, and this is fed via a bridge rectifier and a cold conductor ((PTC resistor)) with a parallel resistance, in which irrespective of the level of the mains voltage when there is a fault, i.e. when a fuse set burns out, the Zener diode delivers a constant d.c. voltage to a parallel connected optical coupler, which switches through and with the aid of an additional d.c. voltage source actuates an electronic alarm and control device connected to ((following on from)) said optical coupler.

This circuit arrangement for checking on the condition of electrical fuses was achieved at great cost, but is unfortunately too costly for monitoring secondary current circuits in medical equipment.

Much simpler is a circuit arrangement for indicating a damaged fuse by means of a light-emitting diode, which is connected (DE-AS 25 51 447) to a transistor and possibly to a resistor in series between the two connections of the current supply. After the fuse and parallel to the load lies a resistive ((IR)) voltage divider, the division point of which is connected to the base of the transistor. The crux of this arrangement lies in the fact that an intact fuse insert is indicated by the illumination of the light-emitting diode, so long as the transistor controlling the light-emitting diode receives base current via the base voltage divider which is formed from two resistors. When the fuse insert has burned through this base current is dispensed with, the transistor then blocks and the light-emitting diode goes out.

Such a check on the condition of electrical fuses is a disadvantage however, since in normal operation an additional current load is required for the lightemitting diode. Moreover, when using a two-colour lightemitting diode normal operation is shown by simultaneous lighting of, for example, a light-emitting diode signalling the applied operating voltage and of the light- emitting diode indicating the condition of the fuse in a colour blend, so that there is an unsatisfactory indication.

The object of the invention is to avoid the disadvantages of known checking circuits for fuses and, using existing optical indicators in medical equipment with the minimum of additional expenditure on components, to signal any interruptions of fuses in secondary current circuits faultlessly, in optical terms, and without delay.

The invention seeks to develop a circuit arrangement for monitoring secondary current circuits in medical equipment, which gives an immediate optical indication when these current circuits fail due to fuses which have burned through so as to avoid the resultant error functions. Moreover, it should be improved so that when a two-colour light-emitting diode is used there is a blended colour indication only when there is a defect in the current circuit or when there is a defective fuse, however when the medical equipment is operating normally, i.e. when there is no fault in the fuse insert, the d.c. or a.c. voltage present is indicated by a primary colour as is logical.

According to the invention, there is provided a circuit arrangement for monitoring secondary circuits in medical equipment, more particularly for indicating a defective fuse in a secondary current circuit having unstabilised d.c. or a.c. voltage supply, characterised in that the fuse is located in parallel with respect to the emitter/base-path of a pnp transistor the collector of the transistor is connected to one anode of a twocolour light-emitting diode, the other anode of which is in connection with the fuse and the common cathode of the two-colour light-emitting diode is applied via a first resistor, and the transistor base via a second resistor, to the potential of the connector B.

From the above there is the substantial advantage for the invention as compared to known circuits for condition checking electrical, namely that a fuse failure caused by impermissibly high current may be recognised immediately and consequently the mechanical or electrical error may be overcome, and the functioning of the equipment may be re-established, relatively quickly.

In accordance with the invention the second anode of the two-colour light-emitting diode may be in connection with one connection contact of an on/off switch, its other connection contact being linked to the fuse. By this means, operation of the two-colour light-emitting diode, is implemented, in which switching on and off may occur either by hand or dependent upon the d.c. or a.c.

voltage supply.

Thus the invention has a circuit arrangement for monitoring secondary current circuits in medical equipment, which when the fuse is intact does not allow the passage of base current into the transistor and prevents the first diode of the two-colour lightemitting diode from lighting up. AS the second diode is added on connected up so the Normal current flow is indicated by the second diode, with a primary colour, which is switched on.

However, if the fuse has burned through the transistor receives base current which modulates it and causes the first diode to light up. Together with the otherwise already switched-on second diode the two-colour lightemitting diode signals the defective condition of the fuse with a blended colour indication.

Further details of the invention are apparent from the following description of two embodiments.

The invention will be explained in greater detail below by way of the drawings in two embodiments. In these Fig. 1 shows an electrical circuit diagram of a circuit for optical display of the condition of a fuse and Fig. 2 shows a modified circuit diagram of a circuit circuit according to Fig. 1 in a preferred design.

In the embodiment shown in Fig. 1 the fuse 1 which is to be monitored lies parallel to the emitter/base path of a pnp transistor 2 and to two oppositely connected diodes 3,4. The collector of the transistor 2 is linked to one anode of a two colour light emitting diode 5, the other anode being connected to one connection of an on/6ff switch 6, which in turn is in connection with the fuse 1 through its other connection. The common cathode of the two colour light emitting diode 5 is connected via a resistor 7, and the two diodes 3,4 linked on the cathode side are connected via a resistor 8, to the potential of the connection B.

The embodiment shown in Fig. 2 differs slightly from that according to Fig. 1. With the exception of the two diodes 3,4 the circuit layout was retained, so that renewed description should be superfluous.

The fuse 1, the transistor 2, the two-colour lightemitting diode 5, the on/off switch 6 and the two resistors 7,8 are connected just as those in the circuit diagram according to Fig. 1. The circuit in the preferred embodiment according to Fig. 2 also monitors the failure of the fuse 1 reliably, when it is interrupted for example by a high secondary current brought about by a short circuit. Since it is not in every case that a failure of a fuse 1 incurs a total failure of the equipment it is advisable to signal the fuse failure immediately and optically.

Normally, i.e. when the fuse 1 has not burned through, in accordance with Fig. 1 any positive voltage half-wave at the connection A, via the diode 3, reaches the cathode of the diode 4, which is switched to tte blocking state so that during this phase base current is not able to flow in the transistor 2. On the other hand, with a negative voltage half-wave at the connection A the first diode of the two colour light emitting diode 5 which is polarised in a blocking state prevents illumination.If the fuse 1 has burned through then the transistor 2 receives a base current via the resistor 8 and the diode 4, said current resulting in through switching of the transistor 2, so that, together with the second diode of the two colour light emitting diode 5, which is switched on by the on/off switch 6 and signals the switched on condition of the equipment, a blended colour is displayed.

In the simplified circuit simplified according to Fig.

2, which no longer contains the diodes 3,4 in the circuit according to Fig. 1, the resistor 8 lies parallel to the secondary load (not shown). Since the resistor 8 is highly resistive and only takes on the supply of the base current for the transistor 2 when the fuse 1 has burned through, in practice there is no increase in the current loading of the circuit as compared to that according to Fig. 1.

LIST OF REFERENCE SYMBOLS USED 1 fuse 2 pnp transistor 3 diode 4 diode 5 two-colour light-emitting diode 6 switch, on/off 7 resistor 8 resistor

Claims

Patent Claims 1. A circuit arrangement for monitoring secondary circuits in medical equipment, more particularly for indicating a defective fuse in a secondary current circuit having unstabilised d.c. or a.c. voltage supply, characterised in that the fuse (1) is located in parallel with respect to the emitter/base path of a pnp transistor (2), the collector of the transistor (2) is connected to one anode of a two-colour light-emitting diode (5), the other anode of which is in connection with the fuse (1), and the common cathode of the twocolour light-emitting diode (5) is applied via a resistor (7) and the transistor base via a second resistor (8), to the potential of the connection B.
2. A circuit arangement according to claim 1, wheein the emitter/base path also includes two oppositely connected diodes (3,4), the junction point of which is connected to said second resistor.
3. A circuit arrangement according ta claim 1, or 2, characterised in that the second anode of the twocolour light-emitting diode (5) is in connection with one contact of an on/off switch (6), the other contact of which is linked to the fuse (1).
4. A circuit arrangement substantially as herein described with reference to the accompanying drawings.