WO1997039600A1

WO1997039600A1 - A method and a system for data communication over a data line

Info

Publication number: WO1997039600A1
Application number: PCT/NO1997/000105
Authority: WO
Inventors: Einar Gotaas
Original assignee: Einar Gotaas
Priority date: 1996-04-18
Filing date: 1997-04-18
Publication date: 1997-10-23
Also published as: NO301678B1; NO961528L; NO961528D0; AU2414697A

Abstract

Data communication over a data line (DL) between a central unit (CU) and a plurality of stations (S) is controlled by means of a special addressing scheme: each respective station (S) is connected to a particular electrical potential (VN), and one data line conductor is imparted a controllable or automatically variable DC voltage level (VA). By comparing the potential (VN) of each respective station and the DC voltage level (VA) of the line, and using special criteria, one particular of the stations (S) is activated to communicate over the data line (DL), while the other stations remain inactive until the DC voltage level (VA) of the data line 'hits' another stations (S).

Description

A METHOD AND A SYSTEM FOR DATA COMMUNICATION OVER A DATA LINE

The present invention describes a method for collecting measurement values from sensors monitoring electrical/physical parameters, e.g. for a battery of series connected electrical single cells.

This may e.g. relate to monitoring voltage, acid level and temperature for each respective cell in lead accumulators in a submarine, or similar emergency power batteries for power plants, telecom or the like. Common to all these applications is that the accumulator cells are located together as a battery of cells in a room which is classified as explosion hazardous.

In a submarine as many as 200 single cells may be connected in series, while in emergency power batteries there are usually 24 cells connected in series. There are various sensor systems based upon the provision of one sensor module for each single cell of the battery. This sensor, or rather this station, is able to measure the cell voltage, temperature, liquid level etc.

All of the sensors, or measuring stations, can be connected to a common data collection line, thus being able to transmit data to a common central unit, using minimum cabling. In order that the central unit may distinguish between the various stations, each respective station must be programmed with an identity number at the time of mounting the station in the battery cell. Consequently, all stations will have a different identity number. The fact that not every station is identical and exchangeable, results in increased system costs. The present invention makes possible the use of identical stations, without already programmed addresses. The central unit will be able to recognize the battery cell in which the station is located.

In accordance with the invention a method and a system is provided for data communication over a data line between a processor controlled central unit and a number of stations, and the scope and the defining features of the invention appear from the appended independent patent claims 1 and 6. Further advan- tageous embodiments of the application appear from the attached dependent patent claims 2-5 and 7-10.

A more detailed description of the invention will now follow, referring to the appended drawing, where fig. 1 shows a simplified circuit diagram with an embodiment of a system in accordance with the invention, connected for monitoring a battery of series connected single cells, and fig. 2 shows a similar diagram as in fig. 1 , for a second embodiment of the system of the invention. CU is a common central unit. It contains a microcontroller μP for general data communication. The communication may pass via line DK possibly to other computers. The microcontroller μP may also transmit and receive signals on a general, digital data line DL. Between the microcontroller μP and the data line DL there is connected a generally two-way line interface TO. This line interface may often be constructed in such a manner that it provides complete or part galvanic separation between the data line and the microcontroller.

An electronic circuit U_A may apply a variable DC voltage V_A to one of the data line conductors. This DC voltage must refer to a fixed potential, often the common earth of the whole system. The conductor to which a DC voltage is applied via U_A, may in principle also be a carrier for rapid digital information.

Many single stations S are connected to the common data line DL. Fig. 1 , which shows an example in which the stations monitor battery cells, shows the particular station which belongs to accumulator cell C_N.

The data signal from the data line into the station is connected to a generally two-way line interface T1. The line interface T1 also has a connection to the control unit KL of the station. T1 may often provide complete or part galvanic separation between the data line and the station.

The central unit microcontroller μP and the station control unit KL may communicate via T1 , DL and TO. This may in principle occur by means of many different, previously known techniques. Measurement values to be forwarded, as well as power supply etc., are received by the control unit KL via data bus T inside the measuring station. In principle these signals can be provided in many possible ways.

When a plurality of stations have been connected to the common data line DL, the central unit microcontroller must find out with which station communication takes place. In the present invention this is solved in a new manner.

Station S in the drawing is connected to, and measures, battery cell C_N. This cell is part of the complete battery which is formed by cells C₀ to C_N+4 in the drawing. The voltage of the terminal with the lower potential is V_N. The other terminal has potential V_N+1. These voltages are connected via the two series resistors RS to two of the inputs of a window comparator KA. The input voltages to the comparator are U_N and U_N+1.

The DC potential from data line DK is connected via a series resistor RB to the third input of the window comparator. The voltage input to the comparator is

U_L.

The comparator KA delivers a signal M to the station control unit KL when U_L is within a predetermined voltage range/voltage window. This range must have its maximum value lower than U_N+1 and its minimum value higher than U_N. It should be noted that every station has a voltage window which is defined similarly relative to its connection points to the cell. However, every cell (C_N etc.) of the series connection is on a different potential.

The selective addressing takes place at the time when the stations are connected to series connected cells. At that point of time, every station will activate its control unit SL for different values of V_A on the common data line DL.

V_A is in this case controlled from the central unit, and hence a controlled addressing is achieved.

Thus, in the case shown, the particular station S which is depicted, is attached to a certain accumulator cell having a certain potential on one pole. A next station (or measuring probe) S will be attached to the next accumulator cell in the row, and consequently will be assigned to the (higher) potential of the next cell, etc. The fact that a certain station (or measuring probe) is assigned to a certain potential, is utilized in the addressing system disclosed here:

The DC generator UA attached to the central unit has its negative side connected to safety earth in the drawing. Similarly, the negative pole of the first accumulator is connected to safety earth (in principle, only a common potential is necessary). The variable DC voltage V_A from the generator U_A is connected to one of the conductors of the data line DL, and thus determines the line potential. By increasing the voltage V_A (from generator U_A) from 0 volts and up to the total voltage of the complete accumulator series, every measuring station (which is attached to a respective cell) will receive an activating signal (and a disconnec¬ ting signal). Each respective measuring station will be activated only when the DC potential of the data line DL corresponds to the potential to which the measuring station is connected.

Thus, it can be determined which measuring probe S is activated, by regulating the DC voltage V_A supplied by the generator U_A which in its turn is controlled by central unit CU.

Fig. 2 shows an alternative manner of controlling the addressing. The DC voltage generator U_Ab has no control from the central unit microcontroller. It comprises a free-running oscillator, which oscillator varies the voltage V_Ab from 0 volts and up to the total battery voltage (V_N+5 according to the drawing). The electrical supply to the generator may e.g. be taken from the battery. This entails that a total galvanic separation can be achieved between the data line and the central unit.

In principle it is of course not necessary that the invention is centered on measuring accumulator cells, however an assigned, measurable and specific potential for every measuring station S will be necessary for the use of this addressing scheme.

Hence, a "voltage window" is selected corresponding to the potential to which the station is connected. The station control unit will then initiate data trans- mission when the DC voltage of the data line is in a certain range attached to the station potential, e.g. as shown, between the negative and positive potential of the two connection points of the station, via the two resistors RS. It should be noted here that the resistance of resistor RB can be made very large, e.g. 10 Mohm, so that the small DC current running from the data line to the measuring station will not represent a safety risk, assuming that an accumulator cell area is a typical explosion hazardous area. In many applications there is no need of a to-way communication between the central unit and the stations. It is sufficient that the stations re-transmit data continuously when the comparator activates the station control unit KL. V_Ab (fig. 2) is controlled independently of the central unit microcontroller. By raising V_Ab relatively slowly from 0 volt to the maximum voltage of the series connection, every station will connect and disconnect successively, one by one. By selecting the predetermined range for activating the comparator to be smaller than V_N+rV_N, there will, when V_A rises continuously from 0 to a maximum value, be time slots in which no station is connected. The central unit may observe this, and in a simple manner assign the received data blocks to each respective station.

Claims

1. A method for data communication over a data line (DL), between a processor-controlled central unit (CU) and a plurality of stations (S) having a logic control unit (KL), each station (S) being connected to a different potential (V_N), e.g. potentiala attached to single cells (C_N) in a series-connected battery, characterized in that the DC potential of the data line (DL) is regulated separately by means of a DC voltage generator (U_A, U_Ab) connected between one ofthe data line conductors and a common reference point, e.g. ground, that a comparator (KA) attached to the logic control unit (KL) of each respective station (S) determines the difference between the data line (DL) DC potential and the attached particular potential (V_N) of the station, and that the station (S) is activated for measurement and communication when this difference is within a predetermined range of values.

2. The method of claim 1 , characterized in that the DC voltage output of the DC voltage generator (U_A) is controlled directly from the central unit (CU), possibly in such a manner that the DC output voltage is swept across a predetermined voltage range, possibly at a variable speed.

3. The method of claim 1 , characterized in that the maximum DC voltage of the DC voltage generator (U_Ab) is determined by a maximum DC potential (V_N+5) among the connected potentials, and that the DC voltage generator (U_Ab) autonomously and possibly at a variable speed sweeps its DC output voltage from a reference value, e.g. ground potential, to the maximum DC voltage which e.g. may be the maximum voltage in a battery of series connected single cells.

4. The method of claim 1 , 2 or 3, characterized in that every station (S) transmits data to the data line (DL) continuously and repetitively as long as the difference between the data line DC potential and the attached and measured potential (V_N) of the station is within the predetermined range of values.

5. The method of claim 4, depending on claim 3, characterized in that the central unit (CU) identifies which stations (S) are transmitting data, based upon the number of time slots without data communi¬ cation having appeared while the DC output voltage of the DC voltage generator (U_Ab) is increased from the reference value toward the maximum DC voltage.

6. A system for data communication over a data line (DL), between a processor-controlled central unit (CU) and a plurality of stations (S) having a logic control unit (KL), each respective station (S) being connected to a different potential (V_N), e.g. potentials attached to single cells (C_N) in a series connected battery, characterized in that a DC voltage generator (U_A, U_Ab) is connected between one of the data line conductors and a reference point, e.g. ground, for separate regulating ofthe DC potential of the data line, in every station (S) a comparator (KA) is attached to the logic control unit (KL) to receive the data line DC potential and the connected potential (V_N) of the station in order to determine the difference therebetween, and that the station (S) is adapted to be activated for measurement and communication when the difference is in a predetermined range of values.

7. The system ofclaim 6, characterized in that the DC voltage generator (U_A) has an input for receiving a control signal from the central unit (CU), so that the central unit (CU) controls the DC potential of the data line (DL) and the time progress thereof,

8. The system of claim 6, characterized in that the DC voltage generator (U_Ab) is adapted for autonomous, sweeping operation where the DC output voltage thereof is^ increased from a reference value, e.g. ground potential, and up to a maximum DC potential (V_N+5) among the connected potentials, said maximum DC potential being e.g. the maximum voltage of a battery of series connected single cells.

9. The system of claim 6, 7 or 8, characterized in that each station (S) is adapted to transmit data on the data line (DL) continuously and repetitively as long as the difference between the data line DC potential and the measured potential (V_N) attached to the station is within the predetermined range of values.

10. The system of claim 9, depending on claim 8, characterized in that the central unit processor (μP) is adapted to detect time slots without data communication on the data line (DL), and to identify which stations (S) are transmitting data, based upon the number of such time slots which have appeared while the DC output voltage of the DC voltage generator (U_Ab) is increased from the reference value toward the maximum potential (V_N+5).