JPS6017253B2 - Isolated digital signal input circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process input/output circuit used for process calculation control, etc., and particularly relates to an isolated digital signal input signal circuit for detecting contact and voltage ON/OFF state signals. be.

In computer control of processes, etc., it is necessary to handle digital signals such as the on/off status of contacts and voltages in addition to analog signals.

Since these signals are often transmitted from a different potential from the computer side or transmitted over long distances, it is desirable that the circuits handling these signals be insulated circuits.

Conventionally, practical circuits used for this purpose include a method that utilizes transformer-coupled r modulation, a method that detects changes in conductance by opening and closing one of multiple windings, and a method that uses light emitting technology that has been put into practical use recently. A typical example is an optical coupling circuit system consisting of a diode and a light-receiving diode.

However, the transformer-coupled peak modulation method generally has a complicated circuit, and is not necessarily suitable for this type of purpose, which requires a low cost and a large number of circuits.

Furthermore, the conductance modulation method using winding opening/closing has difficulty in operating over long distance wiring because the opening/closing impedance includes the wiring impedance from the source to the input circuit. Furthermore, in addition to being relatively expensive, the optical coupling circuit method described above requires a large drive current, and especially when the wiring impedance is large, the power consumption of the voltage oscillation source or the voltage bias source during contact input becomes large. It wasn't economical.

The present invention was invented in view of the above points, and its main purpose is to provide an isolated digital signal input circuit that has a simple circuit configuration, is small in size, and is inexpensive.

One object of the present invention is to provide a high-speed, high-precision isolated digital signal input circuit that can be wired over long distances.

One object of the present invention is to provide an isolated digital signal input circuit that requires low power consumption for circuit operation.

The main features of the present invention include a transformer having a primary winding and a secondary winding, a series circuit of a one-way switch and a capacitor connected to the secondary winding, and an impedance element connected to the primary winding. A configuration is adopted in which pulses are applied so that a pulse voltage of sufficient magnitude is generated to activate the one-way switch on the secondary side, and a digital signal source is connected in parallel to the capacitor on the secondary side. The contact input or voltage input state is stored in the secondary capacitor in advance, and when the pulse voltage is induced, the amplitude of the primary winding voltage is limited to the voltage value of the secondary capacitor. It is configured to equivalently read the status signal on the secondary side.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a circuit diagram of a basic embodiment of the present invention for detecting voltage on/off state signals, and 1 is a primary winding 1.
This is a transformer having primary and secondary windings 12.

A pulse generation source 2 is connected to the primary winding 11 via a current limiting resistor 15.
0 is connected thereto, and an output signal terminal 30 from which the terminal voltage of the primary winding 11 is taken out is further connected via a diode 16.

A diode 13 and a small-capacity storage capacitor 14 are connected in series to the secondary winding 12, and terminals 41-42 of a pair of wiring conductors are connected to both ends of the capacitor 4, and the other end 43 of the wiring conductor is connected to the secondary winding 12. A signal source switch 50 and a voltage source 60 are connected to the switch 44 .

70 and 80 indicate the equivalent resistance and stray capacitance of the wiring conductor, respectively. If the contact 51 of the switch 50 is on the contact 52 side as shown in the figure (voltage on state), the terminal voltage of the capacitor 14 is the wiring conductor. If the capacitor 14 is charged to the value of the voltage source 60 through the wire resistance 70 and the contact 51 of the switch 50 is closed to the contact 53 side (voltage off state), the voltage of the capacitor 14 is discharged and becomes zero. The capacitor 14 always stores the voltage on/off signal state.

In such a configuration, the circuit shown in FIG. 1 operates as follows.

From the pulse generation source 20 to the diode 1 on the secondary side of the transformer 1
3 is applied to the primary winding 11 through the resistor 15, this voltage is simultaneously induced in the secondary winding 12, and the voltage at the terminals of the secondary winding 12 increases to the voltage across the capacitor 14. When the voltage becomes slightly larger than the terminal voltage (more precisely, when the voltage becomes larger than the forward voltage drop of the diode 13), the diode 13 becomes conductive, and the turns ratio of the primary winding 11 and the secondary winding 12 becomes 1. : If 1, primary winding 1 of transformer 1
The terminal voltage of the capacitor 14 is limited to the terminal voltage of the capacitor 14, and if this voltage is taken out from the output terminal 30 through the diode 16, a pulse voltage equal to the terminal voltage of the capacitor 14 is detected.

Note that the voltage drop due to diode 13 is
6. As explained earlier, the terminal voltage of the capacitor always corresponds to the status signal of the signal source, and after all, the on/off status of the signal source voltage is detected from the output terminal 30 as a circuit-isolated signal. will be done.

In this configuration, almost no current is constantly flowing through the wiring, so the effects of the impedance and stray capacitance of the wiring, which had the greatest influence in circuits conventionally used for this type of purpose, are almost eliminated, making it impractical for practical use. No restrictions on upper wiring length.

In addition, the excitation of the transformer 1 is not done with the terminal voltage of the capacitor, but with an excessive voltage from a separately provided pulse generation source. Due to this action, the sag and vibration of the operating waveform are significantly reduced, making detection faster and more accurate.

Specifically, the driving pulse for the pulse generation source 20 can have an amplitude of 5 V and a pulse width of about 0.1 seconds.

In this case, the size of the transformer 1 can be extremely small because the voltage-time product (V.S) is only 0.5 x 10-6 volts/sec, and the storage capacitor 14 can also be small. Small and inexpensive.

Furthermore, since the secondary side of the transformer 1 directly constitutes a filter circuit, it is essentially resistant to noise. FIG. 2 shows a circuit diagram of an embodiment of the present invention in which on/off state signals of contacts are used as a digital signal source, and the same reference numerals as in FIG. 1 indicate corresponding parts.

The wiring resistance and stray capacitance are omitted here.

Switch 5 serving as a signal source and terminal 43 of a pair of wiring conductors
-44, 41-42 are connected to both ends of the capacitor 14 correspondingly. Here, since a voltage source is not included on the signal source side, a series circuit of a high resistance 90 and a voltage source 60 is connected to both ends of the capacitor 14.

With this configuration, when the switch 50 is in the off state as shown in the figure, a charging current flows from the voltage source 60 to the capacitor 14 via the resistor 90, and the terminal voltage of the capacitor 14 is determined by the magnitude of the voltage source 60. It is charged to a certain value.

Also, when the switch 50 is on, the capacitor 4
becomes short-circuited and discharged, and the terminal voltage becomes zero.

In this way, when the switch 50 is turned on, the capacitor 14 is
A state signal (voltage level) corresponding to the off state is always stored.

The operation of this circuit is similar to that shown in Fig. 1, and the pulse generation source 2
By exciting the primary winding 11 of the transformer 1 from zero through the resistor 15 and obtaining the terminal voltage of the capacitor 14 from the output terminal 30, the on/off state signal of the switch 50 can be detected.

FIG. 3 shows an embodiment in which the circuit of FIG. 2 is applied to multi-channel contact state input, and the subscripts a to d indicate the division of each channel. Here, a circuit system is shown that can detect contact state signals of four channels a to d, which are transmitted from different potentials (not shown). In FIG. 3, the transformers that transmit signals are indicated by la to ld, and the secondary side diodes 13a to 13d, capacitors 14a to 14d, and wiring terminals are 41a to 41d, 42a to 42d, 43a to 43d,
44a to 44d, contact input signal sources 50a to 50d, primary side drive current limiting resistors 15a to 15d, diodes 16a to 16d, signal detection terminals 30a to 30d, and signal detection circuit 35. . In addition, here, each point has an independent insulated bias power source 100 using a high frequency power source at each point so that each input contact can operate at an independent potential, and each point is connected to each other via high bias resistances 90a to 90d. Connected in parallel to the channel storage capacitor.

The bias power source 100 and bias resistor 90 correspond to the voltage source 60 and high resistance 90 in FIG. 2, respectively.

In this configuration, the storage capacitors 14a to 14d of each channel have voltages at both high and low levels corresponding to the on/off state of the signal source contacts (in the figure, 50d is on and low level, and the others are off and high level). is memorized. In this state, when a pulse is emitted from the pulse generation source 20' to excite the primary side of each transformer, a low level voltage is generated at the signal detection terminals 30a to 30d at 30b corresponding to the contact state of the signal source. Since high-level voltages are generated in the others, the signal detection circuit 35 can instantly detect these voltages.

In the specific example shown in FIG. 3, the driving pulse of the pulse generation source 20 is a high-speed pulse of 5V and 0.1 fs, the current limiting resistor 16 is 2KQ, the voltage source 100 is 5V, and the memory capacitor 14 is 0.01 French F, resistor 90 was 10KO, wiring resistance 70 was 0 arc, and input threshold voltage of detection circuit 35 (voltage for correcting voltage drop at low level due to wiring resistance) was 2V. It worked stable enough.

In this way, the present invention has a one-way switch and a capacitor on the secondary side of the transformer, stores a digital status signal in the capacitor at all times, and connects the primary winding of the transformer to the one-way switch. The digital status signal is detected from the primary winding by exciting the appropriate polarity and limiting the terminal voltage of the primary winding to the terminal voltage of the capacitor, so the following [1]
Effects 1 to 2 can be expected. '1} It is easy to obtain high withstand voltage with a simple insulation circuit.

(Small size and withstand voltage of 500 to 1000 V) (2) Is the read time short? High speed operation.

(About 10 seconds) {3} The circuit part is small and can be constructed at low cost.

'4} Long distance wiring is possible. (Several items to 10 ships possible)
[5} High noise resistance. (Moat contact with Acloy is also possible) '6} The power required for circuit operation is small. (several meters
Note that the present invention may be implemented in the following modifications and applications.

(1) By appropriately changing the primary and secondary winding ratio of the transformer, increasing the number of primary windings to 4, for example, and increasing the number of secondary windings, the voltage of the pulse generation source can be increased. It is also possible to reduce the offset voltage on the low level side of the output signal terminal voltage.

■ A voltage source is provided in series with the storage capacitor, but in this case a discharge resistor is provided in parallel with the capacitor.

{3} A diode installed on the secondary side of a transformer is used as a one-way switch that is off during normal operation and turned on during pulse excitation.Instead of a diode, a transistor or thyristor can be used as a one-way switch. Can be used.

(4) Use a constant current pulse source as the pulse generation source. In this case, a current limiting resistor is not required. '5} In the case of multi-channel input, perform pulse drive in time division to reduce operating power.

The present invention has been explained above with reference to voltage-driven pulse transformers, but there are two driving methods for driving ordinary transformers: voltage drive and current drive. It can also be operated as

FIG. 4 shows the successor of the current drive transformer, and FIG. 5 shows its operating waveforms.

In FIG. 4, when a drive pulse of -Es is applied to the drive terminal 21, an exciting current flows from the ground terminal to the drive terminal 21 through the winding 11 and the resistor 15, and the pulse transformer Via the winding 11 electromagnetic energy is stored. This electromagnetic energy generates a flagback voltage in the primary winding 11 and the secondary winding 12 such that the mark becomes positive when the driving of the terminal 21 is completed, and this voltage is passed through the diode 13 to the capacitor 14. The input voltage is limited to the value of the input voltage i, which is the terminal fin pressure of
The river generates a positive pulse voltage equal to the input voltage Ei.
FIG. 5 shows these voltage waveforms, where {a} is the voltage applied to the drive terminal 21, 'b'' is the winding voltage, [
d is the voltage at the output terminal 30. Such current drive has the following advantages over voltage drive. [11
Since it is a current drive, it is only necessary to flow a sufficient excitation current, and even a large input voltage (Ei) can be read out with a small drive voltage (1 Es) (wide operating range).

■ Since the excitation period and readout period are different,
At the time of reading, the reading becomes highly accurate without being affected by the drop in winding resistance due to the excitation current on the excitation side.

[Brief explanation of the drawing]

FIGS. 1 to 4 are circuit diagrams of an embodiment of the present invention, and FIG.
This figure is a waveform diagram for explaining the operation of FIG. 4. DESCRIPTION OF SYMBOLS 1... Transformer, 13... Diode, 14... Capacitor, 15... Current limiting resistor, 20... Pulse source, 30... Output terminal, 50... Switch, 60...
... Voltage source, 70... Wiring resistance, 80... Stray capacitance, 90...
High resistance. Younger brother's figure 2 figure 3 figure 4 younger brother's figure

Claims (1)

[Claims] 1. A digital signal source, a capacitor that constantly stores the state of the signal source in the form of voltage, a transformer having a primary winding and a secondary winding, and a secondary winding of the transformer. a one-way switch connected between the line and the capacitor, and a pulse generation source connected to the primary winding of the transformer, the voltage being induced in the secondary winding at the time the state of the signal source is retrieved. A pulse voltage is applied to the primary winding so that the voltage at which the switch is turned on is a certain value sufficient to temporarily turn on the switch, and a pulse-like signal corresponding to the state of the signal source is transmitted from both ends of the primary winding. An isolated digital signal input circuit characterized in that it can be taken out. 2. The device according to claim 1, which uses a voltage on/off state signal as a digital signal source, wherein the voltage on/off state signal is directly applied to both ends of a capacitor. Isolated digital input circuit. 3 In a device that uses the on/off state signal of a contact as a digital signal source, a configuration in which both ends of the contact are connected correspondingly to both ends of a capacitor, and a series circuit of a high resistance and a voltage source is connected to both ends of the capacitor. An isolated digital signal input circuit according to claim 1, characterized in that: