BACKGROUND OF THE INVENTION

The invention is related to the electronic monitoring of fuses, that is, the indication of fuse blowout. Often it is important that a blown-out fuse is noticed quickly by means other than through the visual inspection of fuses, and in automation systems especially the information on a blown-out fuse must be transmitted automatically.

Some handle-type fuse models comprise a component which protrudes when the fuse blows out and it can be arranged to transmit the mechanical contact information. However, this is not possible with most fuses, in which case, the condition of the fuse must be concluded by measuring the voltage after the fuse or current running through the fuse. In order to recognise a blown-out fuse in an arrangement utilising current measurement, it is required that the circuit load is switched on. Alternatively, you can measure the voltage over the fuse, which is in practice 0V with an undamaged fuse. With a blown-out fuse the voltage over the fuse is almost similar to the supply voltage, assuming that the load is switched on.

CN 201274274 Y introduces a fuse monitoring coupling in which a LED controlled by a transistor indicates that the fuse has blown out. Such couplings are suitable only for circuits with very low voltages and, additionally, the sizing of components requires that the voltage is relatively stable.

In some applications it is necessary that the fuse guard indicates the condition of fuses both in the positive and negative poles of the DC voltage supply. An additional requirement may be that the fuse guard can be applied to a very wide range of rated supply voltages or, at least, it must allow even large voltage variations in the supply voltage circuit.

SHORT DESCRIPTION OF THE INVENTION

The purpose of the invention is to achieve an arrangement and method which solves the problems mentioned above. This can be achieved with the mentioned invention, characterised by the independent claims. The preferred embodiments of the invention are defined in the dependent claims.

The invention is based on a coupling in which a standard reference voltage is arranged to be created independent of the fuse blowing out; in which a voltage divider coupling is connected to the output pole of the monitored fuse to create a measurement voltage; which coupling comprises a comparison element to compare these two voltages and to control an indication element to indicate or forward information on the fuse's condition. The reference voltage and the auxiliary voltage needed by the comparison and indication elements can be created, for example, with the help of a zener diode and serial resistance from the supply voltage before the fuse. To achieve a larger rated voltage range without unnecessary power consumption created in the serial resistance, you can affordably use a constant current power source coupling in series with a zener diode. To create a reference and auxiliary voltage, it is also possible to use a separate auxiliary power source, such as a battery, a power source equipped with an AC transformer and rectification, or a DC/DC converter fed from a DC circuit.

The invention can be used to monitor the condition of the DC voltage circuit supply and the fuses connected to the positive and the negative pole.

SHORT DESCRIPTION OF PATTERNS

This chapter describes in more detail the preferred embodiments of the invention, referring to drawings in which

Figure 1 illustrates an arrangement according to an embodiment of the invention, in which the reference and auxiliary voltage circuit has constant current power sources (2a,2b,2c), and the resistance chains operate as the voltage dividers of the measurement voltage;

Figure 2 illustrates an arrangement according to an embodiment of the invention, which comprises a resistance chain in the reference and auxiliary voltage circuit, and the resistance chains operate as the voltage dividers of the measurement voltage; Figure 3 illustrates an arrangement according to an embodiment of the invention, which comprises external auxiliary voltage sources, and the resistance chains operate as the voltage dividers of the measurement voltage;

Figure 4 illustrates an arrangement according to an embodiment of the invention, which comprises external auxiliary voltage sources, and the zener-diode resistance chains operate as the voltage dividers of the measurement voltage;

Figure 5 illustrates an arrangement according to an embodiment of the invention, which comprises external auxiliary voltage sources, and the resistance-zener-diode resistance chains operate as the voltage dividers of the measurement voltage;

Figure 6 illustrates an arrangement according to an embodiment of the invention, which comprises external auxiliary voltage sources, a controller circuit as a comparison element, and the resistance chains operate as the voltage dividers of the measurement voltage;

Figure 7 illustrates, according to an embodiment of the invention, a circuit diagram to create the reference and auxiliary voltage;

Figure 8 illustrates, according to an embodiment of the invention, a circuit diagram to create the constant current power source;

Figure 9 illustrates, according to an embodiment of the invention, a circuit diagram to create the logic element;

DETAILED EXPLANATION OF THE INVENTION

Figure 1 illustrates a block diagram for the condition monitoring arrangement of fuses connected to the positive and negative supply poles of the DC voltage circuit, in which the reference and auxiliary voltage circuit comprises a three-module constant current power source.

The main circuit is created between the positive (+) and negative (-) supply poles of the DC voltage circuit, including the load 8 and the fuses (7a, 7b) which protect the circuit. In principle, already one fuse would be sufficient, but due to, for example, possible earth faults, both poles are often equipped with fuses. In practice, only one of the two fuses blows out because of an overload or a short circuit in the circuit. Therefore, a fuse guard has been arranged to monitor both fuses and to indicate if at least one of them has blown out. The fuse guard and the elements inside it are separated with a dotted line in the diagram.

The monitored fuse 7a has been connected to the positive pole of supply, and the monitored fuse 7b to the negative pole. An auxiliary voltage source (1a, 1 b) has been connected between the supply poles (+) and (-) to feed the reference voltage (U _R EFa,U _R EFb) to the inverting input (-) of the comparator (4a ,4b) and the auxiliary voltages required by the comparator (4a,4b), the logic element 5 and the indication element 6. Three constant current power source modules (2a,2b,2c) have been connected between the auxiliary voltage sources (1 a,1 b) connected in series. The number of constant current power source modules depends on their internal connection and how high a nominal voltage the arrangement is desired to cover. The use of constant current power sources allows a wider nominal voltage range and greater variation - for example, 1 10V DC - 500V DC ± 20%.

The supply of the DC voltage circuit is connected to the input poles (7a1 ,7b1 ) of fuses (7a, 7b), and a circuit forming the reference and auxiliary voltage is also connected between the poles. The output poles (7a ₂ ,7b ₂ ) of the fuses are meant to be the connection points of load 8, but at the same time they are also used for connecting the resistance (3b, 3c) of the first end of the voltage divider connection, which is arranged to form the measurement voltage (U1 _a ,U1 b) of the fuse guard. The resistance (3a,3d) of the other end of the voltage divider connection has been connected to the potential connected to the opposite supply voltage pole of the DC circuit.

The voltage divider circuit produces a measurement voltage (U1 _a ,U1 b) to the non-inverting input (+) of the comparator. In practice, the measurement voltage resistances (3a, 3b, 3c, 3d) in the voltage divider circuit are formed from several resistors connected in series within the limits of their power handling capacity and voltage strength. The connection operates as follows: when the fuse (7a,7b) is intact, the measurement voltage (U1 _a ,U1 _b ) is greater than the reference voltage (U _R EFa,U _R EFb), in which case the comparators' outputs correspond to the logic zero status. If either fuse blows out, the output of the comparator monitoring it will rise to logic status "1". The arrangement for monitoring two fuses comprises a simple logic element, formed with an "OR" operation, which indicates the blowing out of at least one of the two fuses and controls the indication element accordingly. Affordably, the indication element comprises a relay and, for example, a red LED indicating a blown-out fuse. In addition, it is possible to connect a green LED to indicate that the DC voltage circuit is live, the fuse guard is working, and the fuse or fuses are intact.

Figure 2 presents a solution in accordance with Figure 1 , except that the standard constant current power source or sources (2a,2b,2c) has been replaced with a voltage divider chain (2d,2e,2f). The connection is significantly simpler, since the constant current power source comprising several components is replaced only with a resistor. This connection is suitable for solutions in which the rated voltage range and its fluctuation range are very limited - for example, 110V ± 5%.

Figure 3 illustrates a solution in accordance with Figure 1 , except that instead of the auxiliary power source coupling connected between the supply poles of the DC voltage circuit has been equipped with a separate auxiliary voltage source (2g,2h). The auxiliary voltage source can be a battery, an AC voltage-powered transformer and a rectifier connected to it, or a DC/DC converter supplied by a DC voltage circuit.

Figure 4 illustrates a solution in accordance with Figure 3, except that the sub-resistance 3d of the first voltage divider circuit of measurement voltage has been replaced with a zener diode 3e, and the main resistance 3a of the second voltage divider circuit of the measurement voltage has been replaced with a zener diode 3f. In this case, when the monitored fuse is intact, the zener diode (3e,3f) defines the measurement voltage supplied to the comparator.

Figure 5 illustrates the solution in accordance with Figure 3, except that a zener diode (3g,3h) has been connected in series with the resistance (3c,3d) of the voltage divider circuit of measurement voltage, and a zener voltage runs through the diode when the monitored fuse is intact. Depending on the supply voltage, the resistances of the voltage divider circuit define the circuit's current, which is adjusted high enough to make the zener diode work but low enough not to exceed the power handling capacity of the zener diode or cause unnecessary power consumption in serial resistances.

Figure 6 illustrates a connection which deviates from the previous figures in that the comparators are replaced by a controller circuit 4c including an analogue-digital converter. The figure presents a separate auxiliary voltage source 2h which feeds the supply voltage required by both the controller circuit 4c and the pull-up resistor 3p. In practice, the auxiliary voltage source can supply voltage through the zener power source 1 c which stabilises the auxiliary voltage required by the controller circuit and creates a possibly different auxiliary voltage U3 for the the pull-up resistor 3p in the measurement voltage circuit used for monitoring the fuse 7b. The ground, i.e. 0V of the auxiliary voltage is connected to the potential of the DC voltage supply circuit's negative pole.

Reference voltage UREFC is created with the voltage divider circuit (3j,3k) and supplied to the first input of the controller circuit's 4c A/D converter. A voltage divider chain (3m,3n) forming the measurement voltage has been connected to the output pole 7a2 of the first monitored fuse 7a. The measurement voltage U1 _c is supplied from the intermediate output of the chain to the second input of the controller circuit's 4c A/D converter. The resistance 3r is connected to the output pole 7b ₂ of the second monitored fuse 7b. The other end of the resistance is connected to a connection point to which the other end of the pull-up resistor 3p, and the parallel sub-resistances, i.e. the resistance 3q and the resistances (3s,3t), connected in parallel to it and in series with each other, forming a voltage distribution with the resistance 3r and the resistor 3p, are connected to. From the intermediate point of the voltage distribution formed by the series-connected resistances (3s,3t) , the measurement voltage U1 _d is supplied to the third input of the A D converter of the controller. The controller circuit 4 c controls the indication element 6 to indicate that one or two fuses have blown out. The controller circuit may also be equipped with a data transfer feature, such as an Ethernet interface, in which case the information on fuse condition can be transmitted through the data transfer network.

However, the controller circuit in Figure 6 can be replaced with two linear comparators (4a, 4b) so that the reference voltage UREF _C is connected to the inverting (-) input of the first comparator (4a) and the non-inverting (+) input of the second comparator (4b), and the intermediate output for resistances (3m, 3n) of the voltage divider circuit connected to the output (7a2) of the first fuse (7a) is connected to the non-inverting (+) input of the first comparator (4a), and the intermediate output between the resistances (3s,3t) of the voltage divider connection connected to the output (7b2) of the second fuse (7b) is connected to the inverting input of the second comparator (4b). The comparator outputs are connected to the logic element (5). The comparators (4a,4b) can be integrated to a single housing whose operating voltage, i.e. connection's auxiliary voltage, as well as the reference voltage U _RE F _C , can also be supplied from the main circuit - for example, through the constant current power source and be regulated with a zener diode.

Figure 7 illustrates a circuit diagram for the series-connected auxiliary voltage sources (1a, 1 b) in a fuse guard monitoring two fuses in accordance with Figures 1 and 2. The circuit is supplied from the positive and negative poles of the DC voltage supply through fuse resistor R102.

The auxiliary voltage source comprises a zener diode (V101 ,V08), and a voltage equal to the rated voltage runs through it. To remove high- frequency interference, an interference suppression capacitor (C101 .C02) has been connected parallel to it. The ferrite-core interference suppression coils (L101.L01 ) and (L102.L02), and the filtering capacitor (C102.C03) are connected to the poles of the interference suppression capacitor.

Changes in the connection's zener current also cause changes to the voltage over it. For this, the capacitor (C102.C03) has been oversized in comparison to the load caused by the load, in which case the supply voltage stays as stable as possible despite the changes in the supply current. Using the coupling formed by the zener-based auxiliary voltage source and the constant current power sources, it is preferred to realise the regulation of a low DC voltage in the connection of both supply poles (upper and lower part) in a high-voltage DC network.

Between the auxiliary voltage sources there are either constant current power sources (2a,2b,2c) or correspondingly resistances (2d,2e,2f) connected in series.

Figure 8 illustrates the circuit diagram of the constant current power source. It comprises, together with the zener-based voltage regulation in accordance with Figure 7, a voltage-insulation solution which is based on protective impedance created by the constant current power source (2a,2b,2c). Individual protective impedance has been realised with the constant current power source, which keeps the impedance constant in relation to the voltage over it. A chained connection using several constant current power sources creates the voltage distribution, which safely divides a high supply voltage to smaller proportions. Voltage division is based on the serial connection of constant current power sources with the same impedance value. This creates a basis for voltage insulation and the creation of operating voltage.

The basic functionality of protective impedance is based on a constant current power source, which has the following main components: FET transistor V102, FET transistor's overvoltage protector zener diode V106, filtering capacitor C103, current measurement resistor R107, and the rest of the auxiliary components, which create the control circuit of the connection.

In the connection illustrated in Figure 8, the FET transistor V102 is a FET based on the enhancement-type. FET's channel will open when the grid-emitter voltage reaches the positive opening voltage, which in this connection is about 2-4 V DC. The constant current is created by adjusting the grid-emitter voltage. The highest allowed collector-emitter voltage of FET in this connection is 240V DC, which limits the voltage range over one constant current power source. Voltage over a FET is also limited by the limits of safe operating voltage and operating current ranges defined for the component.

Connected in parallel with the FET transistor, a 220 V DC zener diode protects FET and other components from overvoltage. The zener diode also operates as a spender of short circuit current and power in an overvoltage situation, and, for safety, it also operates as an alternative current route if FET has been damaged so that it does not conduct current at all. If there is a FET short circuit, a single constant current power source does not create a voltage distribution in the connection at all, which leads to situation that the fuse resistor R102 will blow out. In a connection with several constant current power sources the fuse resistor will blow out when the supply voltage exceeds the sum of the threshold voltages of protective zener diodes V101 and V107.

The filtering capacitor C103 connected in parallel with the constant current power source operates as the stabilizer for the connection itself, as well as for the voltage distribution created by the constant current power sources. The capacitor also conducts high-frequency voltage and current transients through it, which helps to keep the voltage distribution more stable also during the momentary disturbance situations of the supply circuit.

The resistor R107 operates as the basic component of the constant current power source's control circuit, and the control circuit uses the voltage through the resistor to limit the base voltage of FET. The same voltage is also connected over the base emitter of transistor V103, and the voltage reference over V104. Transistor V103 is connected to the conducting state when the voltage of the resistor R107 exceeds the base and voltage reference voltages. When transistor V103 is conductive, it controls the grid-emitter voltage of FET's V102 towards the voltage level, in which case FET limits its collector-emitter current. Based on this, the current of the constant current power source will be kept below a certain maximum value.

Noteworthy in the connection is the change of FET's V102 grid- emitter voltage in relation to the current running through the resistor R107. The current running through the resistor R107 helps to decrease the FET's grid- emitter voltage, when potential in FET's emitter increases in relation to the earth ground of the constant current power source. In other words, FET's grid- emitter voltage will decrease even if the transistor will not change the current running through itself.

The resistor R105 operates in the connection as the auxiliary current route for the transistor's base-emitter current in the start-up situation of the control circuit. The purpose of the voltage reference V104 is to stabilise the functionality of the connection in relation to temperature changes. At largest, the voltage variation of transistor V103's base emitter may be 0.4-0.8 V DC, in which case precise control in relation to the resistor R107 is not possible. This situation is improved with voltage reference, in which case the voltage variation the resistor R107 is between 3,4 and 3,8V DC, and the proportional effect of temperature to the limiting voltage will decrease.

Resistors R103, R104 and R106 are operating when forming the control voltage for FET's grid-emitter voltage, when voltage is connected over the constant current power source.

When voltage increases, the voltage distribution created by resistors also increase the base-emitter voltage of FET to the extent when the current running through FET and resistor R107 starts to control the control circuit limiting the current. The division of resistors is placed so that FET's grid- emitter voltage will increase, using the smallest possible supply voltage value, to the threshold voltage, which makes it possible to achieve the desired current value already during the start-up.

The zener diode V105 operates as the limiter of FET's base- emitter voltage in a situation in which the control circuit cannot limit it. This situation is possible when a voltage high enough to connect the protective zener diode V106 to a conductive state is connected over the constant current power source. In the conductive situation, the protective zener diode operates as a non-limiting element in the connection, in which case no limiting voltage will be created over resistor R107. However, resistors R103, R104 and R106 aim to raise FET's grid-emitter voltage in accordance with the resistor division. However, the resistor division will cause too high a voltage to FET's grid- emitter section, so it must be limited with the zener diode V105.

The connection based on protective impedance chain consumes little power if the power feed requirement of voltage sources is not extensive. The constant current chain supports well the variation of supply voltage because it adjusts its protective impedance automatically according to the voltage over it. In a similar transformer connection a wide-range voltage variation may be a problem. When realised with transformer and/or chopper technology, the connection requires secondary coils with a high isolation capability in the low and high ends of the voltage supply. Figure 9 illustrates the structure of the logic part. When more than one fuse is monitored with separate comparators, the logic element 5 is needed to create a logical "OR" operation between their outputs. This can be easily achieved with an NAND logic circuit equipped with the Schmitt trigger inputs. The output D01 of the first comparator and the output D02 of the second comparator are connected to the inputs (1 ,2) of the block D01 -A in the logic circuit D01. To be prepared for short-term error pulses, an RC filter has been arranged, with resistor R41 and capacitor C1 1 , between the parallel- connected inputs (12,13) of the output channel (3) in the NAND block D01 -A and the following block D01 -D. A dual opposite-parallel diode (V26) has been connected to the output (11 ) of the block D01 -D. The resistors (R42, R43), connected together from the other end, are connected to the poles of the dual diode, and a pull-up capacitor (C12) has been connected to this connection point, and this point has been connected to the inputs (9,10) of the following NAND block D01 -C. This connection creates a delay which starts from the moment the voltage is switched on. During this delay, the high-capacity filter capacitor, arranged to feed the indication unit (6) relay, has time to get charged before the fuse guard is ready to operate. During the abovementioned delay, the output (8) of the NAND block D01 -C remains in the logical "0" state, in which case the signal level of the pole D03 controlling the relay of the indication element 6 and the red LED signal light keeps low, and the signal level of the pole D04 controlled by the output (6) of the last NAND block D01 -B keeps high in the logical state "1 " and lights up the green LED signal light of the indication element.

The figure does not illustrate the function of indication unit 6, but the relay and the LED signal lights can be controlled with a simple transistor connection.

A certain embodiment comprises an arrangement to monitor the condition of the DC voltage circuit fuse (7a,7b), which arrangement comprises means to create a reference voltage (UREFSI _I UREF^UREFC), to create the measurement voltage (Uia,Uib,Ui _c ,Uici) of the voltage divider circuit (3a,...,3h,3m,...,3t) connected between the fuse output pole (7a2,7b2) and the adjacent supply pole (-,+), and a comparison element to compare the mentioned voltages and to control an indication element, such as a relay or signal light.

The comparison element (4a,4b) can be a linear comparator or a controller circuit equipped with an analogue-digital converter. In an embodiment, the arrangement comprises a voltage divider connection (1a,1b,2a,2b,2c) for forming the reference voltage and the auxiliary voltage for the circuit. The connection comprises at least one constant current power source connection (2a,2b,2c). The arrangement can comprise the reference voltage of an external auxiliary voltage source (2g, 2h) and a circuit to create the auxiliary voltage. The arrangement can comprise means to monitor the fuse connected to the positive and negative poles of the DC voltage circuit, and a logic device to connect the outputs of comparison elements with a logical "OR" operation.

The embodiments are related to the arrangement to monitor the condition of the DC voltage circuit, which arrangement comprises the first and second supply poles to create the operating voltage of the DC circuit, the first fuse (7a) connected to the first supply pole, which first fuse has the supply pole (7a1 ) and output pole (7a2), a fuse (7b) connected to the second supply pole, which second fuse has the input pole (7b1 ) and the output pole (7b2). In the embodiment, one or several reference voltages (L)REFa,UREFb,U EFC) are formed, the first measurement voltage (Uia,Ui _, Uic _, U _1C i) is formed between the output pole (7a2) of the first fuse and the supply pole (7b1 ) of the second fuse, and the second measurement voltage (Uia,Uib,Ui _c ,Ui _d ) is formed between the output pole and the second connection point of the second fuse, which second connection point is either the supply pole of the first fuse or the supply pole of the second fuse. The embodiments compare one or several reference voltages and measurement voltages to estimate the condition of the first or second fuse, and indicate the comparison result.

If more than one reference voltage is created, in a preferred embodiment the reference voltages are equal.

In an embodiment, the mentioned or several reference voltages and/or the auxiliary voltage of the DC circuit can be created from the operating voltage between the first and the second supply pole, that is, the circuit is connected between the input poles of fuses. In another embodiment, one or several external power sources are used to create one or several reference voltages and/or the auxiliary voltage of the DC circuit.

According to the embodiments, the comparison of one or more reference voltages and the measurement voltage can be realised in different ways. In an embodiment, the measurement circuit uses only one comparison unit, which receives one reference voltage and compares it to both measurement voltages.

In another embodiment, two comparison devices, such as comparators, are used for comparison. Separate reference voltages or the same reference voltage can be conducted for them.

In an embodiment, the arrangement comprises a constant current power source connection to create the reference voltage and/or the auxiliary voltage, and to limit the increase of power losses at the higher end of the operating voltage range. In another embodiment, the arrangement comprises a resistive connection to create the reference voltage and/or the auxiliary voltage.

In an embodiment the constant current power source connection or resistive connection is connected to the first and the second supply poles of the DC voltage circuit. The constant current power source connection or the resistive connection is connected in series with one or several auxiliary voltage sources. The connection can be made, for example, so that the serial connection of one or more constant current power sources has been connected in series with the auxiliary voltage sources, so that the auxiliary voltage sources are located in both ends of the constant current power sources.

In an embodiment, the first and/or the second measurement voltage is created with the voltage divider circuit comprising one or several resistors.

In an embodiment, the comparison is performed using the first linear comparator (4a) to monitor the condition of the first fuse, and using the second linear comparator (4b) to monitor the condition of the second fuse. A logic circuit can be connected to the first and the second linear comparators, which logic circuit has been arranged to indicate a damaged fuse if the output of one or several linear comparators indicates a damaged fuse. The indication means to indicate a damaged fuse have been arranged to operate jointly with the logic circuit or controller circuit so that the fault is indicated if one or both fuses are damaged.

The embodiments also comprise a method to monitor the condition of two fuses.

The embodiments described above are not meant to limit the invention but only to clarify the basic idea of the invention. Within the limits of technical functionality, the features presented in different figures can be connected also otherwise than presented in the figures. It is clear that details may vary within the limits of patent requirements.