JPS6355260B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a terminal activation method in a two-wire remote monitoring system, and in particular, when an abnormality or state change occurs in the terminal, an interrupt signal is transmitted from the terminal side to the center side, In a terminal startup method in which the center side scans the terminal device where an interrupt has occurred and monitors what state has changed, the interrupt can be executed while data is being transmitted, without the need to provide a dedicated transmission line for interrupts between each terminal device and the center. This makes it possible to judge signals.

The so-called two-wire data transmission method, in which a terminal device and a center are connected via two transmission lines and data from the terminal device is read at the center, is already well known. Since its purpose was primarily automatic meter reading, data transmission was performed by unilaterally selecting and driving terminals from the center.

On the other hand, the two-wire data transmission method described above can be used in a so-called remote monitoring and control method in which the status of terminals located far away is monitored at a central location. There are two methods.The cyclic method is a method in which the terminal is constantly scanned and monitored from the center, and the random method is a method in which an interrupt signal is transmitted from the terminal to the center when the terminal changes in status. This method scans the terminal where the interrupt occurred and monitors what has changed. In the case of the cyclic method, as the number of terminals increases, it takes a long time to monitor all the terminals. For example, if the scan time for one terminal is ta, then if the number of terminals is N, the monitoring time is T. becomes T=Nta. On the other hand, in the case of the random method (terminal startup method), it is only necessary to scan terminals whose status has changed, so T = ta + α
(α = interrupt judgment time), so the monitoring time is shortened, and the center side only needs to see the interrupt, and it is always in a standby state and can do other work, and the center side only needs to see the interrupt. The center can be used for multiple purposes because it can be dealt with when it occurs. However, when the conventional 2-wire data transmission method is used for a random remote monitoring method, it is not possible to activate the center from the terminal side with the conventional 2-wire data transmission method. Therefore, the number of transmission lines and the amount of construction work increase, resulting in higher costs.

The present invention has been made in view of the above-mentioned circumstances, and one embodiment thereof will be described below with reference to the drawings.

FIG. 1 is an electric circuit diagram for explaining an example of a terminal to which the present invention is applied, and FIG. 2 is an electric circuit diagram for explaining an example of a center. The multiple terminals 10 and the center 20 are connected via two transmission lines _L1 and _L2 , respectively. Each terminal 10 includes, for example, a counter 11 and a data conversion circuit 1, as shown in FIG.
transmission lines L ₁ and L ₂ from the center 20.
The clock pulses (see Figure 3a) transmitted through the photocoupler PC ₁ are sent to the counter 11.
The count position of the counter 11 is weighted in the data conversion circuit 12, and the input (state) data (d ₁
Based on _the result of the determination, transistor Tr ₁ is controlled on/off to change the load of the clock pulse, and this change in load is converted into a change in current or voltage on the center side. Such a two-wire data transmission system is known. In the two-wire data transmission system as described above, the present invention provides a means for connecting the transmission line from the terminal side to the center side when an abnormality or state change occurs in the terminal.
transmitting an interrupt signal through L ₁ and L ₂ ;
The center side scans the terminal where an interrupt occurred and monitors what has changed, and the input (state) data of the terminal is
Normally, it is at a low level, and when an abnormality or state change occurs, it becomes a high level. For example, if it is assumed that among the input (state) data d ₁ to d _o of the terminal 10 (A), the data “d ₂ ” has changed (see FIG. 3b), the OR circuit 13 output becomes high level, and photocoupler PC ₁
When is off, that is, when terminal 10(A) is not selected or when the clock pulse is at low level,
Transistor Tr ₂ is made conductive and an interrupt signal is output. This interrupt signal is the terminal power supply E
→ Transistor Tr ₂ → Resistor R ₃ → Diode D ₁ → Transmission line L ₁ → Center side photocoupler PC ₂ → Transistor Tr ₆ (ON when the clock pulse is low level) → Earth → Transmission line L ₂ → Terminal power supply E
flows through the loop of the center side photocoupler.
By turning on the phototransistor of PC ₂ , the interrupt line INT ₁ is set to high level, and the center 20 is notified that an interrupt has occurred in the terminal 10 (A) (see Figure 3 d). The center 20 is the second
As shown in the figure, it has a constant current circuit 21, a terminal select circuit 22, and a data input circuit 23, and when the interrupt line _INT1 becomes high level as described above, the terminal 10(A) It determines that there has been a change and turns on transistor Tr ₃ .
Select terminal 10(A). A clock pulse is supplied to the terminal 10 (A) selected in this way from the center side through the constant current circuit 21 and the transistor Tr ₃ (see Fig. 3a), and the transistor of the photocoupler PC ₁ is synchronized with the clock pulse. The counter 11 counts up the data by turning it on and off, and inputs it to the data conversion circuit 12. The data conversion circuit 12 selects input data for each count value and performs parallel-to-serial conversion, and its output is supplied to the base of the transistor Tr ₁ in synchronization with the high level of the clock pulse. When the state-changed input data "d ₂ " is selected, the transistor Tr ₁ is turned on. When the transistor Tr ₁ is turned on, the resistors R ₁ and R ₂ are connected in parallel, and if R ₁ ≫ R ₂ , then when the transistor Tr ₁ is off (input data is low level), the resistors R 1 and R ₂ are connected in parallel. When transistor Tr ₁ is on (input data is high level), it becomes resistor R ₂ .
Therefore, now set the value of resistor R ₁ below the constant current, and resistor R ₂
If the value of is selected to be greater than the constant current, the potential of the transmission line _L1 will be high level when the input data is low level, and the constant current value _xR2 when the input data is high level.
Therefore, by comparing this level with the reference value at the center side, it is possible to determine at the center side that the input data "d ₂ " of the terminal 10(A) has changed. Incidentally, abnormalities or state changes can be determined in the same manner for other terminals. For example, when an abnormality occurs in the terminal 10 (B) (see Figure 3c), the interrupt line
Generate an interrupt signal to INT ₂ (Figure 3 e)
reference).

As is clear from the above description, according to the present invention, in a two-wire remote monitoring system, an interrupt signal can be transmitted from the terminal side to the center side without providing a dedicated interrupt line between each terminal and the center. As a result, each terminal can be effectively monitored without increasing the amount of work or cost.Also, since the center only needs to process an interrupt when it occurs, the center can be used for multiple purposes. For example, it can be used for centralized monitoring systems such as disaster prevention, crime prevention, and gas leak alarms, and furthermore, it has effects such as being able to determine interrupt signals while transmitting data.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit diagram for explaining an example of a terminal to which the present invention is applied, Fig. 2 is an electric circuit diagram of the center, and Fig. 3 is a time diagram for explaining the operation of the present invention. It's a chat. 10 (10(A), 10(B)...Terminal, 11
... Counter, 12... Data conversion circuit, 13... OR circuit, 20... Center, 21... Constant current circuit, 2
2...Terminal selection circuit, 23...Data input circuit,
_L1 , _L2 ...Transmission line, _PC1 to _PC4 ...Photocoupler.

Claims (1)

[Claims] 1 In a two-wire remote monitoring system in which a center and a terminal are connected by two transmission lines and the center supplies clock pulses to the terminal to monitor the status of the terminal, the terminal a data conversion circuit for monitoring a terminal state using a clock pulse; means for obtaining an AND of a logical sum output signal of a plurality of status data and a low level signal of a clock pulse from the center; means for outputting the terminal power source to the two transmission lines; or means for detecting voltage.