IL136837A

IL136837A - Method for connecting a remotely powered peripheral unit

Info

Publication number: IL136837A
Application number: IL13683798A
Authority: IL
Original assignee: Ericsson Austria Ag
Priority date: 1997-12-23
Filing date: 1998-12-21
Publication date: 2004-12-15
Also published as: SI20296A; IL136837A0; EP1042908A1; AT407321B; WO1999034591A1; ATA218397A; HUP0100695A2; HUP0100695A3; AU1646699A

Description

METHOD FOR CONNECTING A REMOTELY POWERED PERIPHERAL UNIT Ericsson Austria Aktiengesellschaft Procedure for the connection of a remotely powered peripheral device The invention concerns a procedure for the connection of a peripheral device in a message transmission system, remotely powered via a transmission line from a central location, whereby, in the initial stage, the peripheral device will be connected to the transmission line in a state of switched-off remote power input voltage.

Remote power inputs of various local telecommunication devices are widely used in many telephone systems, e.g. in Pair-Gain systems. For this purpose a DC voltage source exists at a central location, e.g. an exchange, which provides the required operating current for the device connected to the peripheral ends of the transmission line. The main task of the transmission line is in the transmission of signals or data in the low voltage range. Therefore, no personal safety provisions are usually provided for such transmission lines. Voltage ranges which constitute a danger to the human body are therefore not applied even in common remote power inputs. The usual supply voltage thus amounts to 48 V or 60 V, with a tolerance of up to 20% to be tolerated. Nevertheless, the developments of the past years show a clear tendency towards increasing device performances, which, within the limits of the supply voltage, cause very high currents resulting in power dissipation.

Thus, some of the network providers have begun to considerably increase supply voltages for remote powered electrical installations such as Pair-Gain systems, HDSL or ADSL systems and others up to, for example, +/- 60 V to +/- 135 V, causing additional significance to the problem of personal safety. Although current limits are provided for, various operations, such as work on pylons, may cause of extremely dangerous situations, when the sense of balance or other reflexes are disturbed for a short time as the result of electric shock.

There have been made several attempts as a solution of this problem, with a view to prevent the danger of personal risk. For this purpose the connecting operations may be performed with switched-off remote power unit. This, however, creates the problem of having to ensure that no dangerous high voltage for remote power input is present in the transmission line during the installation period.

It must therefore be ensured that operational supply input voltage cannot be caused where peripheral devices are not connected or are connected incorrectly.

In this regard, there has been attempted to apply a voltage and then to ascertain, by measuring the current actually flowing in the transmission line, whether the device is indeed connected or the transmission line has open peripheral ends.

The use of transmission or reception of data has also been proposed in the framework of solutions intended to examine, on the basis of an established data flow, whether or not the peripheral device is connected.

The disadvantage of these known procedures is that the remote power input voltage needs to be fully activated, in order to receive usable evidence regarding the correct connection of the remotely powered device. Data transfer functions in most cases only in the course of operational voltage, while the internal resistance of the peripheral device, which is accessible during current measuring, is highly dependent on the applied input voltage, so that no reliable statements can be made at reduced operational voltage.

Another possibility of circumventing these obstacles is to provide a specific resistor in the peripheral device, which can be switched off during operation, and which can be used to determine the state of connection of the peripheral device at a voltage which does not constitute a safety hazard. The disadvantage of this solution is the need for a separate switch in the remotely powered device, which requires to monitor the provision and subsequent switching-off of the measurement resistance. For this purpose, the measurement resistance would need to be designed for a relatively low range of ohm values, in order to distinguish such measurement from the measuring values caused by leakage current in the cables. Cable faults, however, can easily lead to false results.

The object of this invention is therefore to establish a procedure of the kind mentioned at the beginning, by means of which the personal safety during the installation of remote powered devices becomes possible, and which allows a precise definition and distinction of the connection states of a peripheral device.

The object is achieved according to the present invention in that in a second stage, a test voltage, which is lower than the remote power input voltage of the device intended for the operation, is applied to the central location ends of the transmission line, and the connection status of the peripheral ends of the transmission line is established by measuring the current flowing into the transmission line at the central location end, and that, in a third stage, the remote power input voltage is increased to operational input voltage during determination of the correct connection status of the transmission line.

In this manner, the installation can be conducted in a voltage-free state and any risk to installation personnel at high voltage may be ruled out. The input capacities existing in the peripheral devices, which differ significantly from the performance capacities, may be used in this case to detect the correct connection status by measuring the charge volume, which flows in the transmission line after applying the test voltage. The advantage is that a relatively low voltage, which is safe for humans, is applied, and possible leakage currents can be taken into account. This enables danger-free working conditions during the installation of the peripheral device. If the charge volume measured after the application of the test voltage lies within predefined limit values, which are in accordance with the size of the input capacity value of the peripheral device, the device can be considered as being appropriately connected, and the remote power input voltage can be increased to the value required for the operation. If this is not the case, then the remote power input voltage is switched off and the capacity is given ample time to discharge. After some time, another measuring cycle, involving renewed application of the hazard-free test voltage, may be performed.

Only after a positive measuring result has been achieved, the voltage in the central location will be increased to full remote power input voltage. Thus, the required operational input voltage will exist only after the correct connection of the peripheral device and thus will not endanger the installation personnel.

When a too low charge quantity is measured, it can be assumed that the device is not connected or that the transmission line is faulty. A charge volume that is too high results from a device with a faulty input component, or from erroneously parallel-switched local components, or a transmission line which is short-circuited or has an excessive leakage current.

A further embodiment of the invention may consist in that the test for voltage is connected as a voltage jump to the central location ends of the transmission line. This allows a precisely defined switch from OFF status to TEST status.

According to another embodiment of the present invention, it consists in that the test voltage is repeatedly applied and the charge volume flowing in the transmission lines is continuously determined, until the correct connection status of the transmission line is established.

Thus, a permanent monitoring of the connection status of the transmission line is performed, which only terminates after the peripheral device has been connected. The time increments between the individual measuring procedures are preferably being selected periodically. However, if required, a switch to manual steering of the time increments may be provided, in order to achieve, if desired, a more precise influence on the measurement, should the installation situation require this. The testing personnel can thus turn the measuring procedure on and off at will.

According to a further variation of the invention, the charge flowing into the transmission line can be measured by integration of the current flowing into the peripheral device during the application of the test voltage.

In this manner, the charge volume flowing into the transmission line can be measured indirectly via the current, whereby the measurement of negatively influenced interference signals, which may occur during direct charge measurements on the transmission lines, do not affect the measuring results.

Furthermore, the invention relates to a circuit arrangement for the performance of the procedure according to the present invention, which allows precise and reliable determination of the connection status of a peripheral device.

The object is achieved according to the present invention in that there are provided a unit for generating a voltage jump and a unit for determining the charge volume fed in the transmission line.

According to a further development of the invention, the unit for determining the charge quantity consists of a unit for generating a voltage being proportional to the current flowing into the peripheral device and an integrator unit linked to this unit.

A simple embodiment according to the present invention consists in that the unit for generating a voltage being proportional to the current consists of an ohmic resistor.

Furthermore, for the purpose of automatic detection of the connection status of a peripheral device, it consists in that at the output of the integrator unit, one input of a comparator unit is connected, the other input of the comperator unit, being connected to a reference voltage source, by which the threshold value for change in the comparator output may be adjusted.

In this context, the integrator will preferably be composed of an inverting operational amplifier with an integrating capacitor in a counter-coupling branch.

In order to prevent false integration results due to leakage currents in faulty installation of the transmission lines, according to an additional embodiment of the present invention, a resistor be switched parallel to the integrated capacitor may be provided.

In a further development of the present invention, the integrator may consist of an RC element, residing in an especially simple switch embodiment of the integrator circuit.

The present invention will now be described in detail, by means of following drawings without being limited by them: Fig. 1 shows a block diagram of a remotely powered message transfer system with a central location, a transmission line and a peripheral device; Fig. 2 shows a partial presentation of the input component of a peripheral device; Figs. 3 and 4 each show a block diagram of a form of an embodiment of the circuit layout according to the invention, for the performance of the procedure according to the present invention; Fig. 5 shows a schematic circuit diagram of an embodiment of the circuit arrangement according to the present invention; Figs. 6, 7, and 8 show the temporal process of the remote power input voltage appearing on the peripheral device, the current induced thereby, and the output voltage of the integrator-unit and the comparator-unit of the circuit layout according to Fig. 5 with regard to a correctly connected peripheral device; Figs. 9, 10, and 11 show the temporal process of the remote power input voltage, the induced current, and the output voltage of the integrator unit and the comparator unit shown in circuit layout according to Fig. 5, where excessive leakage current exists on the transmission lines; Figs. 12, 13, and 14 show the temporal process of the remote power input voltage, the induced current, and the output voltage of the integrator unit and the comparator unit shown in the circuit arrangement according to Fig. 5, where the peripheral device input capacity is less than sufficient; Figs. 15, 16, and 17 show the temporal process of the remote power input voltage, the induced current, and the output voltage of the integrator unit and the comparator unit shown in the circuit arrangement according to Fig. 5, where the peripheral device input capacitance is excessive; Fig. 18 shows a schematic circuit diagram of another embodiment of the circuit arrangement according to the present invention; and Figs. 19, 20, and 21 show the temporal process of the remote power input voltage, the induced current, and the output voltage of the integrator-unit and the comparator-unit shown in the circuit arrangement according to Fig. 18 with regard to a correctly connected peripheral device.

Fig. 1 shows a message transfer system according to the current state of the art, in which a peripheral device, e.g. a local 2, is connected via a transmission line 1 to a central location, e.g. an exchange 7. Analog voice signals and/or digital data are transmitted to or received from local 2 via an exchange unit 3. In order to ensure independent power supply to the local, irrespective of the current on-site conditions, it is remotely powered by a remote power input installation 20, whereby in many cases the operating input voltage can lie below a safety-related critical value of, for example, 60 VDC. In such a case, there is no immediate danger from the effect of this voltage on the installation personnel during the connection procedure of such a peripheral device, since it is assumed that a physically healthy person can overcome such voltages without risk. Therefore, there is no problem in maintaining fully the remote power input voltage, even when peripheral device 2 is not yet connected. The responsible technician can thus connect the local to transmission line 1 without exposing himself to any further danger.

Because peripheral devices of this kind are required to carry out an increasing number of functions in modern message transfer systems, the input performance of these devices has been constantly increased in the past years. However, if the remote power input voltage is to remain below the danger limit of 60 V, an increased input current has to be chosen subsequently which creates then an increased current has to be chosen which creates an increased voltage drop at the line resistances of the transmission line and thus result in increased power dissipation. In order to prevent this, many net operators have begun to provide higher remote power input voltages, in some cases of up to ±135 VDC with ground connection or 270 VDC without ground connection. This means, however, that the risk to the installation personnel can no longer be ruled out, especially because direct current bears a higher degree of risk than alternating current of comparable intensity.

In order to avoid unwanted electric shocks, a procedure is suggested for the connection of a device, which is remotely powered from a central location via a transmission line, to an information transfer system, whereby, in an initial stage, the peripheral device 2 is connected to transmission line 1 , while the remote power input voltage is switched off. In a second stage in the process according to the present invention, a test voltage, which is lower than the remote power input voltage of the peripheral device 2 intended for the operation, is applied to the central location end of the transmission line 1 , and the connection status of the peripheral ends of the transmission line 1 is established by measuring the current flowing into the transmission line at the central location end. In a subsequent third stage, the remote power input voltage is increased to operational input voltage during the determination of the correct connection status of the transmission line 1.

In principle, no remote power input voltage remains on the transmission line 1 before connecting the peripheral device. This leaves the peripheral ends without voltage, and the connection work can be completed without endangering the installation personnel. Once the correct connection status has been established, i.e. the connection work has been completed correctly, the remote power input voltage is increased to operational value.

By measuring the charge, it is possible to determine the input capacitance of the peripheral device 2, which differs significantly from the line capacity and other parasitic capacities. For this purpose, in Fig. 2 the input component of a local 2, which usually consists of a DC-DC-transducer 5, and which, besides capacitors 4 and 6, has a bridge rectifier in order to allow a polarity-independent connection. The capacities of capacitors 4 and 6 are significantly higher than the line capacities of the transmission line 1 ; and accordingly, on the basis of the charge measurement, they enable reliable differentiation whether the related device 2 is correctly connected or whether it is not. However, the charge measurement can also be conducted by voltages that are not hazardous for humans.

Fig. 3 and 4 each show the configurations on the side of the central location, which are appropriate for the implementation of the procedure according to the present invention. For this purpose, are provided in Fig. 3 a unit 10 for generating a voltage jump and a unit 1 1 for determining the charge volume which is input into the transmission line are provided in Fig. 3.

The voltage jump unit 10 generates a steep as possible a voltage jump on the transmission line 1 , in order to enable an evaluation of the temporal behavior of the capacities being present at the peripheral end of the transmission line 1. Thus, the test voltage is applied as a voltage jump at the central location ends of the transmission line 1. This voltage jump is, in the form in which it appears at the peripheral device, shown, for example, in Fig. 6. The rounded form of this voltage jump is a result of the loading process of the input capacitors of local 2, which takes place at this time. As can be observed in Fig. 6, the size of the voltage is in a range which is not dangerous to humans.

The unit 1 1 for the measurement of charges in Fig. 3 is switched directly into the current path, which, however, creates difficulties for practical implementation, since it is difficult to measure charges in this direct form, and the measurement is also very susceptible to interference.

An advantageous variant of this procedure is shown in Fig. 4, which provides a unit 13 for generating a voltage being proportional to the current flowing to the peripheral device 2 in the current path, and which may consist, for example of a preferably low-range ohmic resistor. This unit 13 is connected at its outputs to an integrator-unit 14 through its outputs. The integrator-unit 14 integrates the voltage applied to it, and thus generates an output quantity being proportional to the charge volume flowing into the transmission line 1.

From the charge volume thus determined, it is possible to derive the capacities existing at the peripheral ends of the transmission line 1 , and consequently a statement can be made with regard to whether or not the peripheral device 2 has been correctly connected.

In practice, one may operate in that the test voltage is repeatedly applied and the charge volume flowing in the transmission lines is continuously determined, until the correct connection status of the transmission line is established. Thus, the status of the ends of the transmission line is constantly monitored and the testing personnel receive immediately notification in case of a positive measuring result.

For a better detection of the correct connection status, one input of a comparator-unit 15 is connected to the output of the integrator-unit 14, which comparitor-unit 15 is connected at the other input to a reference voltage source Uref, by which the threshold value for the change of the comparator output can be adjusted.

With the aid of the comparator unit, it can at least be determined whether the charge volume flowing in the transmission line 1 exceeds a predefined threshold value, which can be defined in such a manner that the input capacities of the peripheral device 2, which are small in relation to the input capacities of the peripheral device 2, can be distinguished from the first. It is thus possible to establish whether there is present an open line end, i.e. a non-connected peripheral device, or a connected line end.

This differentiation may be made with the embodiment according to Fig. 4, as long as no large leakage currents appear on the transmission line 1 due to low insulation resistance or similar effects. Such leakage currents cause a permanent emission of charges, which will be integrated into the integrator unit 14 just like the charge of a capacitor. This negative effect on the procedure according to the present invention may be avoided by use of a circuit embodiment as shown in Fig. 5. For better understanding of the function, Fig. 5 also contains substitute circuit diagrams. The transmission line 1 , for example, is approximately represented by a line resistor R8, a line capacitor C5 and a line inductance LI , while the peripheral device 2, for example, a local composed of Pair-Gain systems or HDSL units, is represented by an input resistor R9 and an input capacitor C4, whereby any leakage currents resulting from the transmission line 1 are taken into consideration in resistor R9. The unit for generating a voltage 13, which is proportional to the current, is formed by a low-resistance ohmic resistor Rl , which is connected at one end to the two- wire transmission line 1, and at the other end to a connection of the unit 10 for generating a voltage jump. The other end of the unit 10 is connected to the other wire of the transmission line 1.

Figs. 6 to 17 show the temporal processes of four different, real connection conditions, which are for improved clarity given below: State I (Figs. 6 to 8): The peripheral device 2 is connected correctly; State II (Figs. 9 to 1 1): The transmission line creates excessive line leakage currents; State III (Figs. 12 to 14): The input capacities of the peripheral device 2 is too low, or the device is not connected; and State IV (Figs. 15 to 17): The input capacities of the peripheral device 2 are too high.

The individual diagrams each show: Figs. 6, 9, 12, 15 show the temporal process of voltage VI at resistor R9; Figs. 7, 10, 13, 16 show the temporal process of current 1 through resistor R8; and Figs. 8, 1 1, 14, 17 show the temporal process of voltage V2 at the output of an integrator Ul, and the temporal process of voltage V3 at the output of a comparator U5.

The temporal process of the voltage VI and the temporal process of the current 1 are determined mainly by the value of the input capacity C4. In Fig. 7, the current 1 , upon applying the voltage jump, first jumps to its maximum value, because the capacitor C4, which at first is uncharged, acts like a short circuit. However, with increasing charge volume, the current decreases, and after a period of approximately 100 milliseconds it reaches the zero value. The time-dependent current propagation could just as well be used for measuring the input capacity of the peripheral device. However, in this kind of measurement the line resistance of the transmission line and the current limitation of the voltage jump unit 10 are strongly incorporated in the range of values of the current propagation, thus resulting in a range of relatively large tolerance, within which a correct connection status may exist, as a result of this it becomes difficult to precisely determine this connection status.

The current propagation is transformed through the unit 13 into a voltage that is proportional to it and that is applied to the input of the integrator-unit 14. This integrator-unit includes, according to the embodiment of Fig. 5, an inverting operational amplifier Ul , which is provided with an integrating capacitor C3 in the counter-coupling branch.

In order to remove the influence caused by leakage currents in the transmission line, a resistor 4 is switched parallel to the integrator capacitor, preventing the appearance of leakage currents, after the charging process of input capacitor C4, as a result of faulty insulation - as may be the case with old lines - and the subsequent creation of an increased charge, which may then be interpreted as additional capacity on the input of the peripheral device. The resistor R4 is dimensioned so as to cause a discharge of the integrator capacitor C3 after the charging process of the input capacitor C4 has been completed, and thus reduces the output voltage of the integrator Ul after having reached a maximum value.

By the characteristic propagation of the voltage V2 appearing under this condition, as shown in Fig. 8, the correct connection status of the peripheral device 2 can be detected by the comparator-unit 15 being switched thereafter. For this purpose a reference voltage Uref is provided at the reference input of an operational amplifier U5, which forms the comparator unit, and thus a threshold voltage is defined, which is determined in Fig. 8, for example, as 2.5 V. At time tl , the output voltage of the integrator Ul exceeds the defined voltage threshold, and thus causes a tilting of the output status of the comparator-unit 15. The integrated charge increases further; at time t2, it reaches a maximum value, at which time the input capacitor C4 is present in a charged state. The relatively moderate decline propagation, after exceeding the maximum starting voltage value, is determined by the parallel resistor R4, the value of which lies at least ten time beneath the worst possible insulation resistance of the transmission line. By the discharge of the integrator capacitor C3, the starting voltage V2 of the integrator-unit 14 falls beneath the threshold of 2.5 V and thus again causes a tilting of the output status of the comparator unit 15. The time span between tl and t3 ,may thus be processed by appropriate logics. Within a certain tolerance, the appearance of this time span can be interpreted as the correct connection of the peripheral device 2.

As an alternative, the state of the comparator output can be queried at approximately three points in time. For example, the following conditions may be determined. At time t = 0, the starting status must be at low potential; at time t = 100 milliseconds, it must be at high potential; and at time t = 400 milliseconds, it must again be at low potential, if a correct connection status is to exist.

Where a status II according to Figs. 9, 10, and 1 1 exists, the query condition is fulfilled for t = 0 and for t = 100 milliseconds, but is not fulfilled for t = 400 milliseconds. This is caused by too low an insulation resistance of the transmission line, causing R9 to strongly decrease. The leakage currents so induced give rise on a constant flow of charge to the transmission line 1. In such a case, the connection status of the peripheral device cannot be determined unequivocally. For that purpose, the insulation of the transmission line would have to be renewed, or other causes for this constant current flow would have to be removed. In any case, there does not exceed any appropriate operational status, which would be suited for an increase of the remote power input voltage.

The status III, shown in Figs. 12, 13, and 14, at time t = 100 milliseconds, does not show that the threshold value of 2.5 V has been exceeded. It may accordingly be deduced that the peripheral device either has a very low input capacity, or that is not connected at all, or is connected incorrectly. By a precise knowledge of the input capacity in such a case one may unequivocally determine that an increase of the remote power input voltage up to the operational value should not be caused, as, otherwise, risk to the installation personnel could not be ruled out. In this manner, open connections of the transmission line cannot cause any damage, and incorrectly connected devices can be saved from destruction.

Status IV, which can be seen in the temporal processes of Figs. 15 to 17, concerns a too high capacity of capacitor C4, which, upon determination at time t = 400 milliseconds results in a comparator output voltage that is still in the high status range and that drops to the lower status only after 500 milliseconds. This is caused by the complete oversteering of the integrator unit 14, as a result of the excessive capacity of the capacitor C4 during the time from t = 50 milliseconds to t = 250 milliseconds.

The reason for the excessive capacity of the capacitor C4 can be that, for example, two or more peripheral devices 2 have been connected in parallel. Start up should therefore be avoided, since the power supply cannot be guaranteed for both devices, or because the two devices would induce an overly high input current in the transmission line and thus an too high degree of dissipated power. It is, however, also possible that the input component of local 2 is faulty, or a transmission line afflicted with a too high degree of leakage currents exists.

Fig. 18 shows an embodiment of circuit arrangement according to the present invention in which the integrator consists of an RC-element. Said RC element consists of the resistor R20 and the capacitor CIO. The current I through the resistor R8, which is induced in case of correct connection status of the peripheral device, is shown in Fig. 19, and the voltage process V2 after integration through the RC element is shown in Fig. 20. Furthermore, the comparator output voltage V3 shows the correct connection status.

PATENT

Claims

CLAIMS 1 . A procedure for the connection of a peripheral device in a message transmission system remotely powered via a transmission line from a central location, whereby, in an initial stage, the peripheral device is connected to the transmission line when the remote power input voltage is switched off, characterized in that in a second stage, a test voltage, which is lower than the remote power input voltage of the device intended for the operation, is applied to the central location ends of the transmission line, and the connection status of the peripheral ends of the transmission line is established by measuring the current flowing into the transmission line at the central location end, and that, in a third stage, the remote power input voltage is increased to operational input voltage during determination of the correct connection status of the transmission line. 2. A procedure according to Claim 1, characterized in that the test voltage is applied to the central location ends of the transmission line as a voltage jump. 3. A procedure according to Claim 1 or 2, characterized in that the test voltage is repeatedly applied and the charge volume flowing in the transmission line is continuously determined, until the correct connection status of the transmission line is established. 4. A procedure according to Claim 2 or 3, characterized in that the charge flowing into the transmission line is measured by integration of the current flowing into the peripheral device in the course of the application of the test voltage. 5. A circuit arrangement for a new transmission system comprising a central location and a peripheral device in which the peripheral device is connected with the central location with a transmission line, whereby the peripheral device is remotedly fed from the central location by a remote feeding device characterized in that the central location comprises in addition a unit for the generation of a voltage jump and a unit for determining the charge volume given into the transmission. 6. A circuit arrangement according to Claim 5, characterized in that the unit for determining the charge volume consists of a unit for generating a voltage being proportional to the current flowing into the peripheral device and of an integrator-unit linked to this unit. 7. A circuit arrangement according to Claim 6, characterized in that the unit for generating a voltage being proportional to the current consists of an ohmic resistor. 8. A circuit arrangement according to Claim 6 or 7, characterized in that one input of a comparator unit is connected to the output of the integrator-unit, while the other input of the comparator unit is connected to a reference voltage source (Uref), by which the threshold value for the change of the comparator output is adjusted. 9. A circuit arrangement according to Claim 6, 7, or 8, characterized in that the integrator consists of an inverting operational amplifier (Ul) with an integrating capacitor (C3) in the counter coupling branch. 10. A circuit arrangement according to Claim 9, characterized in that a resistor (R4) is switched parallel to integrator capacitor (C3).

1. A circuit arrangement according to any of Claims 6, 7, or 8, characterized in that the integrator consists of an RC element (R20, CIO). for the Applicant Dr. Yitzhak Hess & Parters