JPH0349168B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a contact signal generation circuit. When controlling a plant using a computer, the status of various contacts in the plant (on or off) is converted into digital signals of logic ``0'' and ``1'' and input into the computer. A contact signal generation circuit is used as a circuit for this purpose.

Prior Art Conventionally, there has been a circuit of this type as shown in FIG. In the figure, K _c is the contact that generates the status signal, V _c is the voltage source, R _i is the current limiting resistor, and PC
is a photo coupler, R _p is a pull-up resistor, V _p is a voltage source, 1 is a light emitting diode of the photo coupler, and 2 is a photo transistor.
transistor), 3 is an output terminal.

When the contact K _c is off, the light emitting diode 1 does not emit light, no current flows through the phototransistor 2, the voltage at the output terminal 3 is at a high voltage level, and a logic "1" signal is output.

When contact K _c is on, light emitting diode 1 emits light, current flows through phototransistor 2, and the voltage at output terminal 3 becomes a low voltage level, resulting in logic "0".
Outputs the signal.

By the way, in order to prevent the contact K _c from oxidizing, the voltage of V _c is set relatively high to about 24 V to 48 V to generate a minute discharge when the contact K _c turns on and off. contact
The power consumption W while K _c is in the on state is the voltage source V _c
If the voltage value of is V _c and the current of light emitting diode 1 is I _l , then it is expressed as W = V _c × I _l . When there are many such contacts, power consumption increases and the heat generated accordingly. The disadvantage was that it became larger.

Purpose of the Invention The present invention was made in order to eliminate the above-mentioned drawbacks in conventional circuits, and at the time of transition from OFF to ON, a voltage sufficient to cause a minute discharge of the contact is applied to the contact. It is an object of the present invention to provide a contact signal generating circuit that can reduce power consumption by lowering the voltage of a power supply when the contact is in an on state.

Structure of the Invention In order to achieve the above-mentioned object, in the present invention, when the contact is in the OFF state, the voltage of the capacitor charged to the first voltage value is applied to the contact, and while the contact continues to be in the ON state, the voltage of the capacitor charged to the first voltage value is applied to the contact. A circuit in which current flows from a power supply having a second voltage value lower than the first voltage value to the contacts via a resistor, and in this case, the capacitor charging circuit that charges the capacitor to the first voltage value has a high resistance. is inserted, so that the power flowing from the capacitor charging circuit to the contact is sufficiently small.Embodiments of the present invention will be described below with reference to the drawings.

Embodiment of the invention FIG. 2 is a connection diagram showing an embodiment of the invention.
In Figure 2, the same symbols as in Figure 1 indicate the same or equivalent parts, R _p is a discharge resistance, C _p1 is a capacitor,
V _c is the first power supply, R _C1 is the first resistor, D _C1 is the first diode for blocking reverse current, V _d is the second power supply, R _d1 is the second resistor, D _d1 is the reverse current A second diode for blocking.

In this specification, the series circuit of K _{c ,} R _{p , and} C _p1 is referred to as a capacitor discharge circuit _. It is called the charging circuit of V _d ,
A circuit consisting of R _d1 and D _d1 connected in series and connected in parallel to capacitor C _p1 is called a signal current circuit, and a photocoupler PC is inserted in this signal current circuit for current detection. Further, V _i1 indicates the voltage between the contacts K _c . The voltage of the second power supply V _d is set lower than the voltage of the first power supply V _c .

Fig. 3 is an operation time chart showing the operation of each part in Fig. 2. Fig. 3 a shows the on/off of contact K _c ,
Figure b shows _Vi1 , and figure c shows the output of the output terminal 3.

When contact K _c is off, capacitor C _p1 is charged to V _c . No current flows from the power supply V _c or V _d . Therefore, the output terminal 3 outputs a logic "1" signal. When contact K _c is turned on from off, V _i1 changes from V _c to 0. If V _c in Fig. 2 and V _c in Fig. 1 are set to the same voltage, a weak spark will occur in Fig. 1. If it does, a weak spark will also appear in the case shown in Figure 2. However, if the capacitor C _p1 is quickly discharged and the first resistor R _c1 is set to a high resistance, the current flowing from V _c to the contact K _c becomes minute, but V _d → PC → R _d1 → D The current of _d1 → R _p → K _c is a current value that allows the light emitting diode 1 to emit sufficient light because although V _d is low, R _d1 also has a low resistance value, and a logic "0" signal is output from the output terminal 3. be done.

For example, V _c = 48V, V _d = 12V, the current of photodiode 1 is 0.01A (R _i = 4.8KΩ, R _d1 = 1.2KΩ),
If R _c1 = 48KΩ, in the case of Figure 1, the power consumption for one contact is 48 x 0.01 = 0.48W, but in the case of Figure 2, the power consumption for one contact is 12 x 0.01 + 48 ×0.001=0.168W, which is reduced to about 1/3.

Next, when the contact K _c changes from on to off, the capacitor C _p1 becomes V _d → light emitting diode 1 → R _d1 → D _d1 →
C _p1 is charged in the circuit and the time constant determined by C _p1 R _d1 is small, so the voltage of C _p1 (i.e. contact K _c
V _i1 ) in the off state quickly reaches a voltage approximately equal to V _d , after which V _c →R _c1 →D _c1 →C _p1
However, since the time constant determined by C _p1 R _c1 is set large, the voltage V _i1 gradually increases from V _d to V _c and has the rising waveform shown in Figure 3c. Become. Therefore, when V _i1 reaches a voltage close to V _c , the distance between the contact points K _c is sufficiently large and no spark discharge occurs.

However, if contact K _c is kept in the off state,
V _i1 is almost equal to V _c , and in the process of changing from OFF to ON state, the distance between the contact points gradually decreases while V _i1 is maintained at V _c , so a weak spark discharge occurs. Prevents oxidation of contact K _c .

Also, when contact K _c changes from off to on and the voltage of capacitor C _p1 falls below V _d , V _d → PC → R _d1 →
Current flows through D _d1 and light emitting diode 1 emits light,
When the contact K _c changes from on to off and the voltage V _i1 exceeds V _d , the current of V _d → PC → R _d1 → D _d1 does not flow and the light emitting diode 1 stops emitting light, so the output of the output terminal 3 is The result will be as shown in Figure 3c.

In the circuit shown in Figure 2, a photocoupler PC is inserted in series between V _d and R _d1 as a current detection circuit that detects the current of the signal current circuit configured by connecting V _d , R _d1 , and D _d1 in series. However, any other circuit may be used as the current detection circuit for detecting the current flowing in the series circuit of V _d , R _d1 , and D _d1 .

Effects of the Present Invention As described above, according to the present invention, a capacitor is charged to a high voltage and this charging voltage is applied to a contact, and while the contact is in an on state, a current from a low voltage power source flows through the contact. The high-voltage power supply used to charge the capacitor is connected to the contacts through a high resistance, so in the transient state where the contacts turn from OFF to ON, a minute spark discharge is generated at the contacts, causing the contact to close. It is possible to obtain a contact signal generation circuit that can prevent oxidation and consumes less power when the contacts are in the on state.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing a conventional circuit, FIG. 2 is a connection diagram showing an embodiment of the present invention, and FIG. 3 is an operation time chart showing the operation of each part in FIG. K _c ... Contact, R _p ... Discharge resistance, C _p1 ... Capacitor, V _c ... First power supply, V _d ... Second power supply,
R _c1 ...first resistance, R _d1 ...second resistance, D _c1 ...
...First diode, D _d1 ...Second diode, C _c ...Coupled differential circuit, PC...Photocoupler (current detection circuit). Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A capacitor discharge circuit in which a contact, a discharge resistor, and a capacitor are connected in series, a first power supply, a first resistor, and a first diode for blocking reverse flow are connected in series, and this series connection is connected to the capacitor. A capacitor charging circuit configured by connecting in parallel, a second power source having a lower voltage than the first power source, a second resistor, and a second diode for blocking reverse current are connected in series, and this series connection is established. A signal current circuit configured by connecting in parallel to the above capacitor, and a logic "0" or "1" depending on the presence or absence of current in this signal current circuit.
a current detection circuit that generates a value signal, the capacitor is immediately discharged when the state of the contact changes from off to on, and after the capacitor is discharged, the current flowing through the contact is connected to the second resistor and the discharge. A contact signal generation circuit in which the resistance value of the first resistor is sufficiently large as determined by a series circuit with the resistor and the second power supply.