JPH0137052B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for converting analog voltages at multiple points into digital quantities, and in particular, a device for converting analog voltages at multiple points into digital quantities, and in particular, a device for converting analog voltages at multiple points into digital quantities, and in particular, a device for converting analog voltages at multiple points into digital quantities. are taken in individually in a time-division manner via isolation means, amplified by a preamplifier, and then converted into an analog
The present invention relates to a method for detecting a disconnection in an analog input signal of a device for digital conversion.

[Conventional technology]

In an analog-to-digital converter that converts analog input voltages at multiple points into digital quantities, measurement errors may occur due to disconnection of analog input lines or the like. Therefore, it is desired as an effective method to automatically detect disconnection of the analog input line.

A method shown in FIG. 7 is known as an example of this type of wire breakage detection method. In Fig. 7, the input voltages Es ₁ to Esn from the analog signal source 2 are applied to the filter capacitors via signal lines and resistors R _f1 to R _fo .
Charged to C _f1 ~ C _fo . The data import unit 3 is
Sampling switch SW ₁₁ for each point in time division
Operate SWn ₁ and SWn ₂ to transform the isolation transformer Rs ₁ to
Import data via TRsn.

From the disconnection detection signal generator 1, an isolation transformer is connected.
A disconnection detection signal is applied to the signal line via TR ₁₁ to TR ₁ n, and the current controlled by the resistors R ₁₁ to _{R 1} n flows into the filter capacitors C _f1 to C _fo , causing a disconnection. The detection voltage v ₀ is charged.

If the signal line is not disconnected, disconnection detection voltage v ₀
is discharged through analog signal source 2 and resistors R _f1 to R _fo .

When the signal line is disconnected, the disconnection detection voltage v ₀ remains in the filter capacitors C _f1 to C _fo . The disconnection detection voltage v ₀ is set to a value exceeding the reading range, and disconnection is detected by overscaling the reading range when reading data. In this prior art wire breakage detection method, since a wire breakage detection voltage is applied to each point, it is necessary to insulate each wire breakage detection signal generating section 1. Therefore, there is a problem that the circuit configuration becomes complicated.

Examples of improvements to the problems of the prior art include the "disconnection detection circuit" (prior art 1) described in Japanese Patent Application Laid-Open No. 58-766 (prior art 1) and the "disconnection detection method" described in Japanese Patent Publication No. 56-6510. There is (Prior Art 2). Prior art 1 realizes a circuit that applies a disconnection detection voltage by connecting a battery and a high resistance in series between signal lines. Conventional technology 2 first reads data, and then applies a pulsed current from the secondary side of an isolation transformer for data capture.
This applied pulsed current becomes a charging current for the filter capacitor. The data is read in again and a disconnection is detected based on the voltage.

[Problem that the invention seeks to solve]

Although the above-mentioned prior art 1 simplifies the circuit configuration, it requires periodic replacement over the life of the battery, which is inconvenient in actual use. Furthermore, in conventional technique 2, after applying a pulsed current, the charge is discharged through the signal line, and then data is taken in again. If this is implemented using hardware, the internal circuit will be complicated, and if this is implemented using software, the number of steps will increase.

[Means for solving problems]

In order to solve the conventional problems, the present invention applies a common conductive jacket to the signal input line and applies a disconnection detection signal to the conductive jacket. It is characterized in that a disconnection detection signal induced into the signal input line by capacitive coupling is polarized by a diode attached to each signal input line to obtain a disconnection detection voltage.

[Effect]

The present invention uses the conductive jacket of the signal input line as a means to generate a voltage in the input signal filter capacitor to scale over the reading range for disconnection detection. A wire breakage detection voltage is generated, and a straight wire breakage can be reliably determined from read data with a simple circuit configuration and a minimum number of steps. This will be explained in detail with reference to the drawings below.

〔Example〕

FIG. 1 shows an embodiment of the present invention. The same reference numerals as in FIG. 7 indicate the same parts. The method of capturing analog data is the same as the conventional technique explained with reference to FIG.

Each signal input line has a resistor R _f1 for input filter.
~ _Rfo , capacitors _Cf1 ~ _Cfo , and rectifying diodes _D21 ~ _D2n are installed. A part of the signal input line is covered with a conductive jacket 4,
A disconnection detection signal is applied to the conductive jacket 4 via an insulation transformer _TR2 .

FIG. 2 is an equivalent representation of the disconnection detection circuit shown in FIG. 1 for a set of signal input lines. In Figure 2, 5 is a disconnection detection signal generation circuit including an isolation transformer TR ₂ , C ₁ and C ₂ are capacitances of capacitance between the conductive jacket and the signal input line, and C ₃ and C ₄ are the circuits passing through the filter circuit. This is the coupling capacitance when looking at the disconnection detection signal generation circuit from the subsequent signal input line.

Now, the value of the filter capacitor C _f is C _f >>C ₁ ,
If C ₂ , C ₃ , and C ₄ are set and the frequency of the disconnection detection signal is sufficiently high, C _f can be approximated as a short circuit.

FIG. 3 is an approximate circuit of FIG. 2 in consideration of the above-mentioned state. The resistance in Figure 3 is the resistance of the diode.
It becomes a parallel circuit of R _D and filter resistor R _f . Furthermore, the presence or absence of disconnection in a signal source located sufficiently far away can be ignored in terms of high frequency.

In the circuit shown in Fig. 3, the high frequency power supply has v ₀ shown in Fig. 4.
When a signal is input, the voltage generated across the resistor becomes v _R in Figure 4. The rise of the waveform of this voltage v _R is determined by the voltage division of C ₁ and C ₃ //C ₄ ,
The curved part is τ = {Series value of C ₂ and (C ₃ + C ₄ )}×
(R _f //R _D ). In the actual circuit shown in FIG. 1, the rising waveform has a certain slope due to the internal resistance of the transformer that is the signal source.

If the equivalent circuit of FIG. 2 is redrawn centering around the current flowing through diode D, it becomes as shown in FIG. 5. SL in FIG. 5 indicates the presence or absence of a disconnection in a signal source located sufficiently far away, and indicates a simulated disconnection switch. Here, the voltage generated across the resistor R _f is v _R as shown in Figure 4.
It is. This v _R causes current to flow through the diode D and the filter capacitor C _f . A current that does not pass through the diode D also flows through the filter capacitor C _f , but it is canceled out when v _D is positive and negative, so it is not a problem here. Note that 6 is an equivalent current source.

In FIG. 5, when the simulated disconnection switch Sl is open, that is, when the line is disconnected, the following occurs.

v When _R is a positive peak, the filter capacitor
Charging current flows through C _f through diode D, and v _c
increases with a certain time constant. This time constant is v _R
It is determined by (forward resistance R _D of diode D)×C _f . Next, even if v _R changes to the negative side, the diode D is in the opposite direction, so the filter capacitor
No current flows through C _f , and the accumulated charge remains in the filter capacitor C _f without being discharged. When the next mountain comes, it will be charged again. In this way, a voltage is gradually accumulated in the filter capacitor C _f as shown in FIG. 6a. After a sufficient period of time has elapsed, a voltage remains in the filter capacitor C _f as shown in FIG. 6b. This value is approximately equal to the peak value of v _R. This becomes the disconnection detection voltage.

In Fig. 5, when the simulated disconnection switch Sl is closed, that is, when the line is not disconnected, the DC voltage charged in the filter capacitor C _f is equivalent)
Since the wire is discharged through the resistor R _f , almost no disconnection detection voltage is generated.

Set the disconnection detection voltage to a value higher than the reading range, and read the analog data using the method described above. Normally, the voltage of the signal source is read, and in the event of a disconnection, the disconnection detection voltage is read, so a disconnection can be detected by data overscaling.

〔Effect of the invention〕

As described above, according to the present invention, the conductive jacket of the signal input line is used as a method for generating a voltage in the input signal filter capacitor to overscale the reading range in order to detect a disconnection. , it is possible to generate disconnection detection voltages at once for a plurality of input points. Therefore, there is no need to insulate the circuit for applying the disconnection detection voltage at each point, which simplifies the circuit configuration.

Further, by constantly applying a disconnection detection signal, a disconnection can be determined directly from the read data, so a disconnection can be reliably detected with a minimum number of steps.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an equivalent circuit of the embodiment of Fig. 1, and Fig. 3 is a block diagram showing an embodiment of the present invention.
An approximation circuit of the equivalent circuit in the figure, Figure 4 is the waveform of each part of the approximate circuit in Figure 3, Figure 5 is the equivalent circuit of Figure 2 rewritten with emphasis on the filter circuit section, Figure 6 is a +
b is a voltage waveform of each part of the circuit shown in FIG. 5, and FIG. 7 is a block diagram of a conventional disconnection detection method. DESCRIPTION OF SYMBOLS 1...Disconnection detection signal generation part, 2...Analog signal source, 3...Data acquisition part, 4...Conductive jacket, 5...Disconnection detection signal generation circuit, 6...Equivalent power flow, SW ₁₁ ~ SWn ₁ , SW ₁₂ ~ SWn ₂ ...Sampling switch, TRs ₁ ~ TRsn, TR ₁₁ ~ TR ₁ n...
Isolation transformer, C _f1 ~ C _fo ... Capacitor, R _f1 ~
R _fo , R ₁₁ ~ _{R 1} n...Resistance, D ₁₁ ~ _{D 1} n, D ₂₁ ~ _{D 2} n,
D ₃ , D...diode, TR ₂ ... isolation transformer,
C _f ...Capacitor for filter, R _f ...Resistance for filter, C ₁ ~ C ₄ ... Capacitive coupling capacitance, R _D ... Diode resistance, Sl... Simulated disconnection switch, Es ₁ ~
Esn...Input voltage.

Claims (1)

[Claims] 1. The analog voltages at multiple points charged in the filter capacitors are individually taken in by time division via insulating means through each of the plurality of signal input lines,
In an analog-to-digital conversion device that performs analog-to-digital conversion after amplification by a preamplifier, each of the plurality of signal input lines includes a resistor for an input filter on one line and a capacitor between both lines on the output side of the resistor, and A rectifying diode is provided in parallel with the capacitor on the input side of the resistor, a common conductive jacket is applied to the plurality of signal input lines, and each signal is connected to each input point of the signal input line by a common high-frequency power source. The input line and the conductive jacket are collectively electrostatically coupled, a disconnection detection signal is applied to the conductive jacket, and the disconnection detection signal induced to the signal input line by the capacitive coupling is transferred to each signal. The rectifier diode attached to each input line performs rectification, charges the filter capacitor, and detects a disconnection when the output of the preamplifier exceeds a certain voltage during charging. Analog input signal disconnection detection method.