JPH04295997A - Transmission equipment with overcurrent protective function - Google Patents

Abstract

PURPOSE:To prevent the operation of a transmission line from being disabled and a faulty part from not being detected when the short-circuit fault occurs in a transmission line driver in a system where plural transmitters which convert an input signal to a transmission signal and send it to the transmission line by the transmission line driver are installed. CONSTITUTION:A fuse 11 with alarm contact is inserted to a connection line between the transmission line driver 2 and the transmission line 02, and the transmitter OIA is separated from the transmission line 02 when the short-circuit of the driver occurs, which enables the transmission line 02 to be operated, and which enables erroneous output outputted from the transmitter to the outside of the transmission line 02 to be cut off by the alarm contact of the fuse.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a transmission device having at least the function of inputting a measurement signal (analog signal or digital signal) from a measuring instrument, etc., converting this signal into a digital transmission signal, and outputting the signal to a transmission line. In particular, the present invention relates to a transmission device equipped with an overcurrent protection function in the event of an accident. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

0002

2. Description of the Related Art FIG. 2 shows a general circuit configuration of a transmission line for driving a two-wire transmission line. In the figure, 01 is a plurality of transmitters, 02 is a two-wire transmission line commonly connected to this transmitter 01, and 3 is an analog or digital input signal from a device (for example, a measuring instrument) not shown on the left. The input/output interface 1 is a circuit that converts this input signal into a digital transmission signal, and is generally a C
PU is used. 2 is a drive circuit that drives the transmission line 02 and sends this transmission signal to the transmission line 02. However, the transmitter 01 may also have the function of taking in a transmission signal from the transmission line 02, decoding it, and sending it as an analog or digital output signal to a device (for example, a relay) not shown on the left side. In this case, the transmission line drive circuit 2 is replaced by a transmission transceiver, the transmission signal generation circuit (CPU) 1 becomes a transmission signal generation/decoding circuit, and the input/output interface circuit 3, as its name suggests, is an interface for bidirectional signals. It becomes a circuit.

By the way, the following cases can be considered as failure modes of the transmitter 01.

0004

[Table 1]

[0005] The above case NO. In the case of 1, the transmission line 02 is normal, but since normal transmission data is not transmitted, the system determines that the transmitter 01 is malfunctioning in some way. But NO. 2 and NO. In case No. 3, since the transmission line 02 itself is prevented from operating normally by the transmitter 01, it is impossible for the transmission system to determine which transmitter 01 is malfunctioning. (This is noticeable when the transmission line drive circuit 2 fails in short circuit mode.) Therefore, case NO.
．． 2 and 3, various methods have been proposed for disconnecting the transmission line live circuit 2 from the transmission line 02.

[0006]

[Problem to be Solved by the Invention] When the transmission line drive circuit 2 in FIG. 2 is destroyed in the short circuit mode, the current consumption of the transmitter 01 becomes extremely large, which causes the power supply voltage inside the transmitter 01 to drop. Sometimes it happens. Especially the aforementioned NO. In case 2, even though the CPU 1 is originally normal, it malfunctions due to this voltage drop. A malfunction of the CPU 1 affects the input/output, especially the output, of the transmitter 01, causing a malfunction of the system. Therefore, an object of the present invention is to provide a transmission device with an overcurrent protection function in order to prevent such secondary malfunctions.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the transmission device according to claim 1 has a function of converting at least an input signal into a digital transmission signal and sending it to a transmission line (transmission line 02, etc.). In a transmission device (such as transmitter 01A), an overcurrent protection means is provided in series with a connection line that connects the transmission device and the transmission line to detect an overcurrent in the connection line and open the connection line. 'prepared';

0
In the transmission device according to claim 2, in the transmission device according to claim 1, “the overcurrent protection means is a fuse”, and

[0009] In the transmission device according to claim 3, in the transmission device according to claim 2, ``the fuse is a fuse (such as 11) with an alarm contact.''

0010

[Operation] A fuse 11 with an alarm contact is inserted into the connection line between the transmission line drive circuit 2 and the transmission line 02, and when the transmission line drive circuit 2 is short-circuited, the drive circuit 2 is disconnected from the transmission line 02, and the alarm contact is inserted. The signal causes the output of the signal from the input/output interface to the outside of the transmitter to be stopped or rendered harmless.

[0011]

Embodiment FIG. 1 is a block diagram of a transmitter as an embodiment of the present invention, and corresponds to FIG. 2. This new transmitter 01
In A, a fuse 11 with an alarm contact is inserted into the connection line between the transmission line drive circuit 2 and the transmission line 02, and the contact signal when the fuse 11 blows is input to the new input/output interface 3A. has been done. In FIG. 1, a fuse 11 with an alarm contact detects an overcurrent when the transmission line drive circuit 2 fails in short-circuit mode, and connects the transmission line drive circuit 2 to the transmission line 02.
It serves to separate it from The alarm contact of the fuse 11 is directly transmitted to the input/output interface 3A without passing through the transmission signal generation circuit 1 as a CPU section, and automatically stops the output to the external device on the left side of FIG. (such as switching relays to ensure that the motor rotates in a safe direction).

0012

According to the present invention, in the transmitter 01A having at least the function of converting an input signal into a digital transmission signal and sending it to the transmission line 02, the transmitter 01
Since a fuse 11 with an alarm contact is provided in series with the connection line connecting A and the transmission line 02 as an overcurrent protection means that detects an overcurrent in the connection line and opens the connection line, the transmission drive Not only can the transmission drive circuit 2 be automatically disconnected from the transmission line 02 when the circuit 2 fails, but also it is possible to prevent malfunctions of external components other than the transmission line, such as the CPU 1, when the power supply voltage drops.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing a configuration as an embodiment of the present invention.

[Figure 2] Conventional block circuit diagram corresponding to Figure 1

[Explanation of symbols]

01A Transmitter 02 Transmission line 1 Transmission signal generation circuit (CPU) 2 Transmission line drive circuit 3A Input/output interface 11 Fuse with alarm contact

Claims (3)

[Claims] Claim 1: A transmission device having at least a function of converting an input signal into a digital transmission signal and sending it out to a transmission line, wherein a connection line is connected in series to a connection line connecting the transmission device and the transmission line. A transmission device with an overcurrent protection function, comprising an overcurrent protection means that detects an overcurrent and opens the connection line. 2. A transmission device with an overcurrent protection function according to claim 1, wherein the overcurrent protection means is a fuse. 3. A transmission device with an overcurrent protection function according to claim 2, wherein the fuse is a fuse with an alarm contact.