Device, method, and control module for monitoring a two-wire line

Abstract

The invention relates to a device (1) and a corresponding method for monitoring a two-wire line (2), in particular a two-wire line (2) of a fire protection system. The device (1) comprises a passive terminating component (10) for terminating the two-wire line (2), wherein the passive terminating component has a chargeable energy storage (12), a constant current source (20) for providing a measuring current (I1) to the passive terminating component, a voltage detection unit (30) for detecting a voltage curve (V1) at output terminals (4, 6) of the two-wire line (2), a control unit (40) for controlling the constant current source (12) and for evaluating the detected voltage curve, the control unit (40) being configured to separately determine a series resistance (RL) and a parallel resistance (PS) of the two-wire line (2).

Claims

1. A device for monitoring a two-wire line of a fire protection system, comprising: a passive terminating component for terminating the two-wire line, wherein the passive terminating component has a chargeable energy storage, a constant current source for providing a measuring current to the passive terminating component, a voltage detection unit for detecting a voltage curve at output terminals of the two-wire line, and a control unit for controlling the constant current source and for evaluating the detected voltage curve, the control unit being configured to determine a series resistance and a parallel resistance of the two-wire line, the control unit being configured to evaluate the detected voltage curve in response to a change in the provided measuring current and to charge the chargeable energy storage during a predetermined first period by controlling the constant current source and to evaluate a self-discharging of the chargeable energy storage during a subsequent second period after a switching off of the constant current source.

2. The device according to claim 1, wherein the chargeable energy storage of the passive terminating component comprises a capacitor arranged between the two wires of the two-wire line.

3. The device according to claim 2, wherein the capacitor has a capacitance above 0.1 μF.

4. The device according to claim 3, wherein the capacitor comprises a capacitance in a range from 1 μF to 10 μF.

5. The device according to claim 1, wherein the control unit is configured to determine the series resistance and the parallel resistance of the two-wire line from the detected voltage curve over time during the first period and second period.

6. The device according to claim 5, wherein the control unit is configured to determine the parallel resistance and the series resistance of the two-wire line on the basis of two approximations, based on one another, of the detected voltage curve during the first period and second period.

7. The device according to claim 6, wherein the control unit is configured to use discrete values of the detected voltage curve to approximate constants of two linear equations of the voltage in the first order of a time-dependent variable during the first period and second period.

8. The device according to claim 7, wherein the use of the discrete values of the detected voltage curve comprises the least squares method.

9. The device according to claim 1, wherein the two-wire line comprises multiple two-wire lines and the control unit is designed to monitor the multiple two-wire lines.

10. A method for monitoring a two-wire line of a fire protection system, the method comprising: providing a measuring current to a passive terminating component for terminating the two-wire line, wherein the passive terminating component comprises a chargeable energy storage, detecting a voltage curve at output terminals of the two-wire line, and evaluating the detected voltage curve in order to determine a series resistance and a parallel resistance of the two-wire line, wherein the measuring current is provided in a first period for charging the chargeable energy storage and is not provided in a subsequent second period, and wherein the detected voltage curve at the output terminals is detected and evaluated during the first period and the second period.

11. The method according to claim 10, wherein the parallel resistance and the series resistance of the two-wire line are determined on the basis of two approximations, based on one another, of the detected voltage curve during the first period and second period.

12. The method according to claim 9, wherein discrete values of the detected voltage curve are used to determine the parallel resistance and the series resistance from approximated constants of two linear equations of the voltage in the first order of a time-dependent variable during the first period and second period.

13. A control module of a fire alarm and/or extinguishing control center for monitoring the two-wire line of the fire protection system, wherein the control module is configured to carry out the method according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and designs are described below with reference to the accompanying drawings. The figures show:

(2) FIG. 1: schematically and exemplarily shows an example of a device according to the invention for monitoring a two-wire line and

(3) FIG. 2: schematically and exemplarily shows voltage curves at different resistances.

MODE(S) FOR CARRYING OUT THE INVENTION

(4) FIG. 1 schematically and exemplarily shows a first example of a device 1 according to the invention for monitoring a two-wire line 2. The two-wire line 2 is connected at two output terminals 4, 6, for example, to a center 100 of a fire protection system, such as a fire alarm and/or extinguishing control center. It is important to ensure that resistances occurring via the cable are within the permissible range, such that, for example, sufficient voltage drops or is present in a triggering event.

(5) A terminating component 10 with a reverse polarity protection designed as diode 52 and a load represented as resistor 54 is typically provided at a termination 8 of the two-wire line. In this way, a short circuit via the two-wire line is prevented and, at the same time, the possibility of monitoring with a current flowing through the terminating component 10 is provided. In particular, due to the reverse polarity protection no monitoring current ever passes through the terminating component 10.

(6) The two-wire line, to which in particular multiple participants such as detectors, alarm transmitters, etc. are connected, can be modelled as a combination of series resistance R.sub.L and parallel resistance R.sub.S. One aim of the present invention is the ability to determine or monitor the series resistance R.sub.L and the parallel resistance R.sub.S separately. For this purpose, the invention proposes a particularly simple passive terminating component 10 which is connected to the termination 8 of the two-wire line 2. Compared to the conventional terminating component 50, which only determines the total line resistance, this makes the separate determination of R.sub.L and R.sub.S possible.

(7) The terminating component 10 according to the invention has a chargeable energy storage 12, which in the example shown is designed as a capacitor with a capacitance C. Furthermore, the passive terminating component 10 does not show any temperature dependence of the determination, such that the capacitance C can be determined automatically and, thus, no configuration/calibration of the terminating component 10 is necessary.

(8) In accordance with the invention, a control unit 40 now determines the parallel resistance R.sub.S and the series resistance R.sub.L together with the capacitance C on the basis of a voltage curve U(t), the function of which is described with reference to FIG. 2.

(9) A constant current source 20 is arranged between the output terminals 4, 6 to provide a constant but preferably adjustable measuring current I1 via the chargeable energy storage 12 of the passive terminating component 10.

(10) Furthermore, a voltage detection unit 30 is provided for detecting a voltage curve U(t) between the output terminals 4, 6. The control unit 40 is configured to control the constant current source 20 and to evaluate the voltage curve U(t) detected by the voltage detection unit 30. Here the control unit 40 enables the convenient determination of the series resistance R.sub.L and the parallel resistance R.sub.S of the two-wire line 2, as explained below.

(11) In summary, the control unit 40 is intended to be able to make a reliable statement as to whether the existing line resistances R.sub.L, R.sub.S enable sufficient voltage to be applied to the load in a triggering event.

(12) The control unit 40 is either designed as a separate module, for example, within the fire alarm and/or extinguishing control center 100, or may be designed as an integral part of the fire alarm and/or extinguishing control center 100. In a preferred case, all the components of the device 1 for monitoring a two-wire line which are provided on the side of the center are designed in the form of a monitoring module, which is shown in FIG. 1 with dashed lines. In this case, for example, a further control unit 45 of the fire alarm and/or extinguishing control center 100 will handle the supplementary functions for fire monitoring and/or extinguishing control.

(13) The voltage curve U(t) at the module terminals 4, 6 is measured continuously. Here, the chargeable energy storage 12 is first charged with the current I1 via the constant current source 20 for a certain period T1. Subsequently, the constant current source 20 is switched off and the self-discharging of the capacitance C via the parallel resistor R.sub.S is observed over a period T2. Finally, the chargeable energy storage 12 is completely discharged during a subsequent period T3 via a discharge resistor of a discharge unit 60.

(14) FIG. 2 schematically shows a diagram 300 in which the detected voltage over time U(t) is represented. In particular, the subdivision into the periods T1, T2 and T3 has been made and four different voltage curves 310, 312, 320, 322 for respectively two different values of the series resistance R.sub.L and respectively two different values of the parallel resistance R.sub.S have been recorded. During the second period T2, these four voltage curves 310, 312, 320, 322 coincide onto two voltage curves 314, 324, since the time behavior of the self-discharging is independent of the series resistance R.sub.L.

(15) The moments in which the constant current source 20 is switched on and switched off are particularly interesting and important for the calculation. The line resistance can be determined directly from the jumps 330, 340 in the voltage curve U1. The time behavior of the self-discharging is characterized only by a time constant which depends on the capacitance C and the parallel resistance R.sub.S.

(16) The following differential equation of voltage U applies to the charging process during period T1:

(17) $\begin{array}{cc}U={\mathrm{IR}}_L+R_S\left(I-C\frac{\partial U}{\partial t}\right)& \left(1\right)\end{array}$

(18) It is assumed that the capacitor is completely discharged at the beginning of each measurement, i.e. prior to period T1. With U(t=0)=0 a solution of the equation (1) is given by

(19) $\begin{array}{cc}U\left(t\right)=I\left[R_L+R_S\left(1-e^{-\frac{t-T_s}{R_{S}C}}\right)\right]U\left(0-\right)=0U\left(0+\right)={\mathrm{IR}}_L& \left(2\right)\end{array}$

(20) During self-discharging, i.e. during period T2, no voltage drops across the series resistance R.sub.L. Thus, the standard equation of the discharging of the capacitor can be used

(21) $\begin{array}{cc}U\left(t\right)=U\left(T_L+\right)e^{-\frac{t-T_L}{R_{S}C}}U\left(T_L+\right)=U_C\left(T_L-\right)& \left(3\right)\end{array}$

(22) The forced discharging during the third period T3 is not considered. The discharging time need only be selected long enough to ensure that the chargeable energy storage 12 is completely discharged at the beginning of the next measurement.

(23) The 3-part measuring sequence explained above and sketched in FIG. 2 is preferably repeated periodically to determine the resistance values. Discrete voltage values are available for each measurement, which can be divided into charging and self-discharging processes. One advantage of the solution according to the invention is the short time required for the detection of a fault, which is in the range of a few milliseconds.

(24) In the following, for further processing, the voltage curve U(t) is divided into the measured value curves U1, U2 and U3 which correspond to the periods T1, T2 and T3. Thus, in particular the measured value vectors U1 and U2 are available from the voltage detection unit 30, which are acquired during the periods T1 and T2. The aim of the following calculations is to determine from U1 and U2 as accurately as possible the parameters R.sub.L and P.sub.S as well as, incidentally, C.

(25) For this purpose, equations (2) and (3), in which these parameters occur, are considered. It is noticeable that equation (3) contains two unknown values: The time constant τ=R.sub.S*C and the start value U(T.sub.L+). The control unit 40 preferably first determines these constants before determining the remaining unknown values in a separate subsequent step using equation (2).

(26) As already mentioned, the aim is to make statements about the parameters on the basis of the recorded measurement series of the voltage curves U1 and U2. Equations (2) and (3) define the progression of the voltage values over time, where the parameters that best reproduce the curve are determined by means of an estimation or approximation. In this example, the least square method is used for this purpose to project N observed measured values onto a function with the smallest possible averaged error, in this case onto a linear first-order equation of time t:
y(t)=α+βt

(27) With the least square method, an associated measurement error ϵ.sub.i, which describes a deviation from the ideal measurement curve, is added to the measured values y.sub.i recorded at the respective corresponding times t.sub.i:
y.sub.i=α+βt.sub.i+ϵ.sub.i

(28) $Q\left(\alpha ,\beta \right)=y_i=\alpha +\beta t_i+e_i$$Q\left(\alpha ,\beta \right)=\underset{i=1}{\overset{N}{.Math.}}{e}_i=\underset{t=1}{\overset{N}{.Math.}}{\left(y_i-\alpha -\beta t_i\right)}^2\stackrel{t}{=}\min$$\hat{\alpha }=\stackrel{\_}{y}-\tilde{\beta }\stackrel{\_}{t}$$\hat{\beta }=\frac{\underset{i=1}{\overset{N}{.Math.}}\left(t_i-\stackrel{\_}{t}\right)\left(y_i-\stackrel{\_}{y}\right)}{\underset{i=1}{\overset{N}{.Math.}}{\left(t_i-\stackrel{\_}{t}\right)}^2}=\frac{\mathrm{cov}\left(t,y\right)}{\mathrm{var}\left(t\right)}$

(29) The least square method first adds the squares of the individual measurement errors ϵ.sub.i to obtain a sum Q, which depends on the two parameters α and β. The subsequent minimization of this sum leads to the best estimates {circumflex over (α)}, {circumflex over (β)} for the parameters α and β.

(30) As mentioned above, equation (3) is first used for the self-discharging process during period T2, since it is only influenced by two of the three parameters. For the sake of simplicity, the time at which the constant current source 20 is switched off is shifted to the zero time point:

(31) $\begin{array}{cc}U\left(t\right)=U\left(T_L+\right)e^{-\frac{t}{R_{S}C}}\tau =R_{S}CU\left(t\right)=U\left(T_L+\right)e^{-\frac{t}{\tau }}& \left(3a\right)\end{array}$

(32) This equation is not linear but exponentially dependent on time t. As a consequence, the equation is exponential and thus non-linear and must be logarithmized on both sides to convert it into a linear first-order equation of time t.

(33) Here the usual calculation laws for the natural logarithm are applied:

(34) $\begin{array}{cc}\log \left(x*y\right)=\log \left(x\right)+\log \left(y\right)\log \left(e^x\right)=x\log \left(U\left(t\right)\right)=\log \text{(}U\left(T_L+\right)-\frac{t}{\tau }& \\ \log \left(U\left(t\right)\right)={\alpha }_2+{\beta }_{2}t& \left(4\right)\\ {\alpha }_2=\log \left(U\left(T_L+\right)\right)& \left(5\right)\\ {\beta }_2=-\frac{1}{\tau }& \left(6\right)\end{array}$

(35) In equation (4) the now linear form can be seen in relation to t. This means that first all detected voltages U2 are logarithmized. The least square approach can then be applied to these values in a simple way, cf. equation (4).

(36) The parameters α.sub.2 and β.sub.2 follow from the application of the least square approach to all measured values during self-discharging of U2. Subsequently, the time constant τ can be determined using equation (6):

(37) $\tau =-\frac{1}{{\beta }_2}$

(38) The desired parameters R.sub.S, R.sub.L and C thus remain unknown. However, they can now be determined by considering the charging process.

(39) Equation (2) already described the voltage curve of the charging process. Shifted to the zero time point and using the time constant τ it can be written as

(40) $\begin{array}{cc}U\left(t\right)=I\left[R_L+R_S\left(1-e^{-\frac{t}{\tau }}\right)\right]& \left(7\right)\end{array}$

(41) In contrast to the discharging curve, this exponential curve has an additional offset. Thus, it cannot be calculated directly using the least square approach.

(42) However, the time constant τ has already been determined. Equation (7) can thus be converted into a linear form, cf. equation (8):

(43) $\begin{array}{cc}U\left(t\right)=I\left(R_L+R_S\right)-{\mathrm{IR}}_S{e}^{-\frac{t}{\tau }}& \\ U\left(t\right)={\alpha }_1+{\beta }_1{e}^{-\frac{t}{\tau }}& \left(8\right)\\ {\alpha }_1=I\left(R_L+R_S\right)& \left(9\right)\\ {\beta }_1=-{\mathrm{IR}}_S& \left(10\right)\end{array}$

(44) To do this, using the known time constant τ, the corresponding exponential function must be calculated for each time value.

(45) Upon applying the least square approach to all measured values U1, i.e. from period T1, the parameters α.sub.1 and β.sub.1 are obtained. With the equations (10, 9, 3a) the desired parameters R.sub.S, R.sub.L and C finally can be calculated directly:

(46) 0$R_S=-\frac{{\beta }_1}{I}{R}_L=\frac{{\alpha }_1}{I}-R_S$$C=\frac{\tau }{R_S}$

(47) This means that after each charging/self-discharging curve, the required values can be precisely specified by carrying out only two least square estimates.

(48) The time durations T1, T2 and T3, for example, may be in the range of fractions of milliseconds, particularly 0.1-1 ms, and particularly preferred 0.5 ms, or a few milliseconds. Thus, given the short measuring time, an appropriately high rate of measurement repetition is possible.

LIST OF UTILIZED REFERENCE NUMBERS

(49) 1 Device for monitoring a two-wire line 2 Two-wire line 4, 6 Output terminal of the two-wire line 8 Termination of the two-wire line 10 Terminating component 12 Chargeable energy storage 20 Constant current source 30 Voltage detection unit 40 Control unit 45 Control unit 50 Load with reverse polarity protection 52 Diode 54 Resistor 60 Discharge unit 100 Fire alarm and/or extinguishing control center R.sub.L Series resistance R.sub.S Parallel resistance C Capacity I1 Measuring current U(t) Voltage curve T1 First period T2 Second period T3 Third period 300 Diagram 310, 312, 314, 320, 322, 324, 326 Voltage curve 330 Voltage jump 340 Voltage jump