JPH0683121B2 - Interface device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an interface device that is inserted in the middle of a transmission line that connects a device provided on site and a control device that controls the device.

[Prior Art] In general, a process control device transmits a control signal from a control device provided in a supervisory control room to a controlled device provided on site through a transmission line to control a necessary process value. Field equipment is controlled in response to this. Then, a signal indicating the controlled state is transmitted from a transmitter provided on site to a monitoring device provided in the monitoring control room through a transmission line different from the transmission line provided for control. In this case, the oscillator has a function of transmitting the controlled state by an analog signal or a digital signal, and its selection is performed via a transmission line connected to the oscillator. However, since the monitoring device does not have the selection function, the interface device is connected to the transmission line and the selection operation is performed from the interface device.

This state is shown in FIG. 3, and the interface device 4 is inserted in the middle of the transmission line 3 connecting the transmitter 1 and the monitoring device 2. The interface device 4 is for ease of maintenance, the fourth and the lower module 4 ₁ connected to the transmission line 3, as shown in FIG, upper module 4 that removably fitted to the lower module 4 ₁ It consists of ₂ and. The function of the transmitter is selected by operating an operation unit (not shown) provided in the upper module.

[Problems to be Solved by the Invention] However, in such a device, if the upper module fails, it will be removed and repaired, but if it is removed, there is no signal processing portion. As a result, the signal from the oscillator 1 is cut off, and there is a problem that the system goes into a down state. For this purpose, it is conceivable to replace the failed upper module with a spare one, but in any case, the system will be down during the removal.

Therefore, although the interface device originally has a secondary function of selecting the signal transmission mode of the oscillator, it is not preferable to bring down the main system even for a short time due to the failure of the interface device.

[Means for Solving the Problem] In order to solve such a problem, the present invention provides a communication between a lower module that cuts off a signal supplied from a transmitter when a conduction prohibition signal is supplied, and a transmitter. An interface device is configured with an upper module that sends a conduction prohibition signal to the lower module when transmitting and receiving a digital signal, and holds the transmitter output signal immediately before sending the conduction prohibition signal and sends it to the monitoring device. is there.

[Operation] Since the continuity prohibition signal is sent to the lower module only when digital communication is performed between the upper module and the transmitter, the continuity prohibition signal is not generated even if the upper module is removed, and continuity is ensured. It remains as it is. When digital communication is performed between the transmitter and the interface device, the transmission line is cut off, but since the transmitter output signal immediately before digital communication is held and supplied to the monitoring device, signal continuity is maintained. Reserved.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
Lower module 4 ₁ in FIG inserted in series to the transmission line 3 _1, 3 _2, switches 4 ₁₁ and the resistor 4 _12, the upper module as a look-off time supplied conduction prohibiting signal always on
It is composed of a connector 4 ₁₃ that mate with a connector 4 _{21 of} 4 ₂ . The oscillator 1 is connected to the monitoring device 2 via the lower module 4 ₁ and the transmission lines 3 ₁ and 3 ₂ , and a DC power supply is supplied via the power supply 2 ₁ and the resistor 2 ₂ of the monitoring device 2. And usually
The oscillator 1 represents a state in which the controlled device (not shown) is in a 100% operating state by a direct current of 20 mA and a state in which it is in a 0% operating state by a direct current of 4 mA.

Figure 2 is a circuit diagram showing a lower module 4 ₁ details,
The switch 4 ₁₁ is composed of a transistor 4 ₁₁ a and a resistor 4 ₁₁ b. In such apparatus thus configured, when the upper module is inserted, "1" level signal is supplied to the base of the transistor 4 ₁₁ a, that transistor is turned on. That is, the conduction prohibition signal is not supplied. When the upper module 4 ₂ is pulled out in this state, the base of the transistor 4 ₁₁ a becomes open. However, since the transistor is the power from the power supply 2 ₁ monitoring device 2 is supplied, still "1" level signal is supplied.
Therefore, even if the upper module is pulled out, it remains in the ON state. That is, the signal being sent from the transmitter 1 withdrawn for repair upper module 4 ₂ is supplied to the monitoring device 2.

On the other hand, every time the timing pulse voltage of the lower module 4 ₁ at the point A (not shown) is supplied, and is held in the sample-and-hold circuit 4 ₂₂ of the upper module 4 _2. Here, when changing the format of the signal upper module 4 ₂ is outputted from the transmitter 1 from an analog form to a digital form, CP
U4 ₂₃ turns on switches 4 ₂₄ and 4 ₂₅ , switches 4 ₁₁ , 4
Control ₃₂ off. That because it is given hereafter performs digital communication, it sends a conductive inhibit signal to the switch 4 _11. Therefore, the DC signal output from the oscillator 1 is cut off, but the value immediately before the transmission line is cut off, which was held by the sample hold circuit 4 ₂₂ , is passed through the operational amplifier 4 ₂₆ , the switch 4 ₂₅ , and the transistor 4 ₂₇ . And transmitted to the monitoring device 2. Therefore, the value immediately before the transmission line is cut off can be continuously received. Such a state immediately before the transmission line blocking Leave supplied to the monitoring device 2, the upper module 4 ₂ communicates with the transmitter 1 via the transceiver 4 _28, digital form the output signal of the transmitter 1 from an analog form Make a selection to change to. At this time, the transmitter 1 has an upper module.
Power is supplied through the power source 4 _{29 of} 4 ₂ and the resistor 4 ₃₀ .

When the signal output format of the oscillator 1 is changed to a digital signal in this way, the oscillator output signal is supplied to the CPU 4 ₂₅ via the bidirectional transceiver 4 ₂₈ , and the CPU 4 ₂₅ sends the signal to D / The signal is converted into an analog signal via the A converter 4 ₃₁ and is sent out, and the switch 4 ₂₅ is turned off and the switch 4 ₃₂ is turned on. The signal converted into an analog signal by the D / A converter 4 ₃₁ by this is the switch 4 ₃₂ and the transistor 4 _27.
Is supplied to the monitoring device 2 via the.

Therefore, the monitoring device 2 can monitor the oscillator 1 regardless of whether the signal format is the analog format or the digital format. Note that the signal supplied to the monitoring device is the value immediately before the transmission line is cut off during the transition period from when the transmission line is cut off until the oscillator output signal format switches from an analog signal to a digital signal. The change in value is gradual. Therefore, it is sufficient to supply the hold value of the sample hold circuit until the digital signal is transmitted from the transmitter, and in this way the continuity of the signal can be secured.

[Effects of the Invention] As described above, according to the present invention, the conduction prohibition signal is sent to the lower module only when the upper module performs digital communication with the transmitter. The continuity prohibition signal is not supplied to. Therefore, the transmission line is not interrupted even if the upper module is removed for repair or the like. Further, when performing digital communication, the value immediately before the transmission line is cut off is held, and the held process value is supplied to the monitoring device until a new value is obtained, so that the continuity of the signal can be secured. Have.

[Brief description of drawings]

1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing details of the upper module in FIG. 1, and FIG.
FIG. 4 is a diagram showing a conventional system, and FIG. 4 is a diagram showing a fitted state of an upper module and a lower module. 1 ... Oscillator, 2 ... Monitoring device, 3 ... Transmission line, 4 ...
… Interface, 4 ₁₁ , 4 ₂₄ , 4 ₂₅ , 4 ₃₂ …… Switch, 4
₁₁ a …… transistor, 4 ₁₁ b, 4 ₁₂ , 4 ₃₀ …… resistor.

Claims (1)

[Claims] 1. A system in which a status signal generated from a transmitter is supplied to a monitoring device via a transmission line, the interface device being connected in the middle of the transmission line to control the operating state of the transmitter. Is composed of a lower module that is inserted in series with the transmission line and an upper module that is detachably attached to the lower module.The lower module is a signal that is supplied from a transmitter when a conduction prohibition signal is supplied. The upper module has a circuit interrupting means, and the upper module sends a continuity prohibition signal to the lower module when transmitting and receiving a digital signal to and from the oscillator, and a continuity prohibition signal. The interface having a signal holding means for holding the output signal of the oscillator immediately before the operation and outputting it to the monitoring device. Chair apparatus.