JPS6362036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a system for centrally monitoring detectors (sensors) that are distributed and arranged to monitor the status of various devices or devices. Generally, in this type of system, it is desirable that the length of the transmission line, the number of sensors, etc. have little influence on the signal.

Figure 1 is a schematic configuration diagram showing an outline of a general centralized monitoring system, Figure 2 is a configuration diagram showing a specific example of a sensor, Figures 3 and 4 are configuration diagrams showing a 3-wire centralized monitoring system, and Figure 2 is a configuration diagram showing a specific example of a sensor. FIG. 3 shows a case where there is one sensor, and FIG. 4 shows a case where there are a plurality of sensors.

That is, as an example of a conventional centralized monitoring system _, a centralized monitoring system for disaster prevention such as gas leakage or fire is known, and as shown in _FIG . An individual transmission system is used that connects to the central monitoring board 1 via line L. Incidentally, such a disaster prevention system is usually equipped with a backup power source 3 consisting exclusively of a storage battery so that monitoring can be performed even in the event of a power outage. In addition, the output signal of the sensor in this type of system is, for example, a voltage signal of 0-6-12 volts (0V...
...for power outages, 6V for normal conditions, and 12V for abnormal conditions), and 3-wire or 4-wire systems are used to connect the signal to the central monitoring board, including the power supply line. For this reason, if a three-wire type is used, for example, the sensor will be constructed as shown in FIG.

In the figure, 21 is a power supply unit, 22 is a detection unit,
TS ₁ and TS ₂ are power supply terminals, C is a smoothing capacitor,
T is a detection terminal, R and R ₁ are resistors, TR ₁ is a transistor, ZD ₁ is a Zener diode, and TG is a signal terminal. That is, the output terminal T of the detection unit 22 is always at a low level, so the transistor TR ₁ is off, and the signal terminal TG has a voltage drop of a Zener diode (for example, 6V) from the power supply voltage (for example, 12V). ) minus the specified voltage (6V)
It is output based on the voltage of the common line l (the negative side of the power supply line and the negative side of the signal line are shared). On the other hand, when an abnormality is detected in the detection section 22, the detection terminal T becomes high level and the transistor _TR1 becomes conductive, so that the power supply voltage is directly sent from the terminal G as an output. Note that in the case of a power outage, the power supply voltage becomes zero and the output of the signal terminal TG also becomes zero, so that the power outage can be detected.

A system in which one of the sensors configured in this manner is connected to a remote central monitoring board is shown in FIG. In the figure, 11 is a comparator, 12 is a comparison reference voltage, 13 is a power supply, and _Rz is an impedance adjustment resistor.

Since the current consumption i ₀ of the sensor flows through the common line l, if the line resistance of the common line l is R _l , ΔV=
A voltage drop of R _l i ₀ will occur. Therefore, the received voltage at the central monitoring board 1 is the sensor output voltage V ₀ plus the drop ΔV (V ₀
+ΔV). This voltage drop ΔV not only varies depending on the line length and line diameter, but also varies depending on the connected sensors, for example, when a large number of sensors 2 ₁ to 2 _o are connected to a common power line as shown in Fig. 4. (ΔV=R _l i ₀ ×n), it becomes difficult to set the reference voltage of the comparator 11 in the centralized monitoring panel 1, and there is a risk of malfunction.

FIG. 5 is a block diagram showing another conventional example of a sensor, and FIG. 6 is a block diagram showing a centralized monitoring system using the sensor.

As is clear from FIG. 5, in this embodiment, the signal output from the detection section 22 is insulated using an isolated DC-DC converter 23, and is constructed using a four-wire system. Therefore, as shown in Fig. 6, the current consumption i of the sensor does not affect the signal voltage, and the signal current flowing through the signal line
Since i ₁ can be kept small enough that the voltage drop due to the line resistance is not a problem, the transmitted signal can be maintained at a stable level. However, this method has the disadvantage of increasing costs because it requires the addition of expensive equipment such as an isolated DC-DC converter.

The present invention has been made to eliminate such drawbacks, and an object of the present invention is to provide a centralized monitoring system that can transmit stable signals at low cost without using the above-mentioned expensive equipment.

The feature is that in a system that centrally monitors various sensors using the sensor power supply method, by connecting a diode from the power supply negative terminal of each sensor to the signal negative terminal so that the polarity is reversed,
The point is that the influence of the sensor current consumption on the signal voltage is removed.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 7 is a block diagram showing an embodiment of the sensor, and FIG. 8 is a block diagram showing a centralized monitoring system using the sensor.

In Fig. 7, ZD ₂ to _{ZD 4} are Zener diodes, TR ₂ is a transistor, R ₂ to _{R 4} are resistors, and D
is a diode, and the others are the same as those described so far.

Here, the output terminal T of the detection unit 22 is normally at a high level, and this causes the transistor TR ₂ to be connected via the Zener diode ZD ₂ and the resistors R ₂ and R ₃ .
A base current flows through, and this becomes conductive. Therefore, since the Zener diode ZD ₄ is shorted,
The output voltage from terminal TG ₁ is a Zener diode
This becomes a predetermined voltage determined by ZD ₃ , and this is sent to the central monitoring board. On the other hand, in the event of an abnormality, the detection terminal T becomes low level, so the transistor TR ₂ is turned off, and thereby the signal output voltage from the terminal TG ₁ becomes a predetermined voltage determined by the Zener diodes ZD ₃ and DZ ₄ . .

Next, a system using such a sensor will be described with reference to FIG.

Now, let R _l be the resistance of the line, and let R l be the current consumption of the sensor.
If i ₀ and the current flowing to the negative side of the signal line is i ₂ , the negative side terminal of the sensor's power supply becomes higher than the ground potential of the monitoring board 1 by ΔV=R _l i ₀ , and similarly the negative side of the signal line of the sensor The terminal also becomes higher than the ground potential of the monitoring board by ΔV'=R _l i ₂ . However, as can be seen from FIG. 7, the current i ₂ can be limited to the Zener current flowing through the transistor TR ₂ , the Zener diode ZD ₃ and the resistor R ₄ , so the above ΔV′ can be ignored with respect to the signal voltage. (signal voltage
V ₀ ≫ΔV′). Therefore, the negative side terminal of the power supply has a high potential (ΔV>ΔV') compared to the negative side terminal of the signal, but
Since the circulation of the current is cut off by the diode D specially provided according to the present invention,
Current consumption _i0 of the sensor does not affect the signal voltage. In other words, the received voltage on the central monitoring board side in this case is V ₀ + R _i i ₂ − _{R l} i ₁ (V ₀ : sensor signal voltage, i ₁ : current flowing to the positive side of the signal line), but V ₀ >> Since R _l i ₂ and R _l i ₁ can be set, the influence of sensor current consumption on the signal voltage can be eliminated. Note that if the current consumption of the sensor is small or if the line is short (line resistance R _l is small), the sensor can be of a three-wire type as shown in FIG. 2.

As described above, according to the present invention, it is possible to transmit voltage signals with high precision using a simple configuration that only requires adding a diode that cuts the current flowing from the negative side terminal of the power supply to the negative side of the signal line. can.

Note that the present invention can be applied not only to the above-mentioned centralized monitoring system, but also to general systems in which power is supplied from sensors, while signals from each sensor are transmitted by voltage level.

[Brief explanation of drawings]

Fig. 1 is a schematic block diagram showing the outline of a general centralized monitoring system, Fig. 2 is a block diagram showing a conventional sensor example, Figs. 3 and 4 are block diagrams showing a 3-wire centralized monitoring system, FIG. 5 is a block diagram showing another conventional example of a sensor, FIG. 6 is a block diagram showing a centralized monitoring system using the sensor, FIG. 7 is a block diagram showing an embodiment of the sensor according to the present invention, and FIG. FIG. 1 is a configuration diagram showing a centralized monitoring system using the sensor. Code explanation, 1... Central monitoring board, 2, 2 ₁ ~ 2 _o ...
...sensor, 3...standby power supply, 11...comparator, 12...comparison voltage, 13...power supply, 21...
Power supply section, 22...Detection section, 23...Insulated DC-
DC converter, L, l...transmission line, TS ₁ , TS ₂ ,
T, TG ₁ , TG ₂ ... terminal, C ... smoothing capacitor, R, R _z , R _l , R ₁ to R ₄ ... resistance, TR ₁ , TR ₂
...transistor, ZD ₁ to _{ZD 4} ... Zener diode, D... diode.

Claims (1)

[Claims] 1 Power is supplied from a central monitoring device to multiple sensors that monitor the status of various devices or equipment via a common power line, and signals from each sensor are sent in the form of voltage signals via individual signal lines. In a signal transmission system for transmitting to a central monitoring device, a diode is provided between the negative side terminal of the power line and the negative side of the signal line in each sensor, and the diode prevents the sensor current consumption from going around to the signal line. A signal transmission system characterized by: