JPH0349167B2 - - 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, Kc is the contact that generates the status signal, Vc is the voltage source, Ri is the current limiting resistor, and PC
is a photo coupler, Ro is a pull-up resistor, Vo 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 Kc 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 the contact Kc is on, the light emitting diode 1 emits light, current flows through the phototransistor 2, and the voltage at the output terminal 3 becomes a low voltage level, resulting in logic "0".
Outputs the signal.

By the way, in order to prevent oxidation of the contact Kc, the voltage of Vc is set relatively high to about 24 V to 48 V, and a minute discharge is generated when the contact Kc turns on and off. contact
The power consumption W while Kc is on is the voltage source Vc
The voltage value of is Vc, and the current of light emitting diode 1 is Il
Then, it is expressed as W=Vc×Il, and when a large number of such contacts exist, there is a drawback that power consumption increases and heat generation increases accordingly.

Purpose of the Invention The present invention has been made to eliminate the above-mentioned drawbacks in conventional circuits, and at the time of transition between on and off, a voltage that can cause a minute discharge of the contact is applied to the contact, and the contact is turned on and off. It is an object of the present invention to provide a contact signal generation circuit that can reduce power consumption by lowering the voltage of the power supply when in the state.

Structure of the Invention In order to achieve the above 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 in the on state, the voltage of the capacitor charged to the first voltage value is applied to the contact. is a circuit in which a current flows from a power supply having a second voltage value lower than the first voltage value to the contacts via a resistor, and a capacitor charging circuit that charges the capacitor to the first voltage value has a high resistance. Because the capacitor charging circuit is inserted into the contact, the current flowing from this capacitor charging circuit to the contact is sufficiently small, and during the transition period when the contact changes from the on state to the off state, there is a back electromotive force induced in the coil inserted in series with the contact. The above first contact point is
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 Fig. 2, the same symbols as in Fig. 1 indicate the same or equivalent parts, Rp is the discharge resistance, L is the coil, Cp ₁ is the capacitor, Vc is the first power supply, Rc ₁ is the first resistor, and Dc ₁ is the The first diode for reverse current blocking, Vd is the second power supply, Rd ₁ is the second resistor, Dd ₁ is the second diode for reverse current blocking, Ds is the third
diode.

In this specification, the series circuit of Kc, L, Rp, and Cp ₁ is called a capacitor discharge circuit, and the circuit consisting of the series connection of Vc, Rc ₁ , and Dc ₁ and connected in parallel to the capacitor Cp ₁ is called a capacitor discharge circuit. This circuit is called the charging circuit, and the circuit consisting of Vd, Rd ₁ , and Dd ₁ connected in series and connected in parallel to the capacitor Cp ₁ is called the signal current circuit, and a photocoupler PC is inserted into this signal current circuit for current detection. has been done. Furthermore, Vi ₁ indicates the voltage between the contacts Kc. The voltage of the second power supply Vd is set lower than the voltage of the first power supply Vc.

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 Kc,
The figure b shows Vi ₁ , and the figure c shows the output of the output terminal 3.

When contact Kc is off, capacitor Cp ₁ is charged to Vc. No current flows from the power supply Vc or Vd. Therefore, the output terminal 3 outputs a logic "1" signal. When contact Kc is turned on from off, Vi ₁ changes from Vc to 0, and Vc in Figure 2
If the voltage and Vc in Figure 1 are set to the same voltage, the first
If a weak spark is produced in the case shown in the figure, a weak spark is also produced in the case shown in Fig. 2. But capacitor Cp ₁
If it is discharged quickly and the first resistor Rc ₁ is set to high resistance, the current flowing from Vc to contact Kc will be small, but Vd→PC→Rd ₁ →Dd ₁ →Rp→L
→The current of Kc is a current value that allows the light emitting diode 1 to emit sufficient light because Vd is low but Rd ₁ also has a low resistance value, and the output terminal 3 outputs a logic "0".
signal is output.

For example, Vc = 48V, Vd = 12V, the current of light emitting diode 1 is 0.01A (Ri = 4.8KΩ, Rd ₁ = 1.2KΩ),
If Rc ₁ = 48KΩ, in the case of Figure 1, the power consumption for one contact is 48 × 0.01 = 0.48W, but in the case of Figure 2, the power consumption for one contact is 12 × 0.01 + 48 ×0.001=0.168W, which is reduced to about 1/3.

Next, when the contact Kc changes from on to off, the current flowing through the coil L decreases rapidly, so the coil L
A back electromotive force is generated across the terminal, the voltage Vi ₁ rises rapidly, and this increased voltage is applied to the contact Kc. If the coil L were not present, the moment the contact Kc turned from on to off, the voltage Vi ₁ would suddenly rise to a point equal to Vd, and then increase to Vc according to a large time constant of Cp ₁ Rc ₁ . Since they rise to approximately the same point, no minute sparks are generated at the contact point Kc.

Also, excessive voltage is generated in coil L, and contact Kc
If a strong spark discharge occurs, there is a risk of damaging the contact Kc, so the peak value of Vi ₁ when the contact Kc changes from on to off is clamped to Vc by a diode Ds. However, even without clamping with the diode Ds, when the value of the coil L is appropriately selected, the peak value of Vi ₁ can be adjusted so as not to greatly exceed Vc. The dotted line in the circuit of the diode Ds means that the same purpose can be achieved without connecting the diode Ds. In other words, when the contact Kc is opened, a voltage is generated between the contacts due to a transient phenomenon, but the waveform of that voltage is determined by the current flowing through the contact, the inductance value of the coil L, the resistance value of the discharge resistor Rp, and the capacitor Cp. It is well known that the inductance value of _the coil L is determined by the capacitance value of be.

In the circuit shown in Figure 2, a photocoupler PC is inserted in series between Vd and Rd ₁ as a current detection circuit that detects the current of the signal current circuit configured by connecting Vd, Rd ₁ , and Dd ₁ in series. Any other circuit may be used as the current detection circuit for detecting the current flowing in the series circuit of Vd, Rd ₁ and Dd ₁ .

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 that is used to charge the capacitor is connected to the contacts through a high resistance, and during the transition period when the contacts change from on to off, a voltage is generated in the coil inserted in series with the contacts. Since a voltage is applied to the contact, a high voltage is applied to the contact during the on/off transition state of the contact, and a contact signal generating circuit can be obtained that consumes less power when the contact is on.

[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. Kc...Contact, Rp...Discharge resistance, L...Coil, Cp ₁ ...Capacitor, Vc...First power supply,
Vd...Second power supply, Rc ₁ ...First resistor, Rd ₁ ...
...Second resistance, Dc ₁ ...First diode, Dd ₁
...Second diode, 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 coil, a discharge resistor, and a capacitor are connected in series, a first power source, a first resistor, and a first diode for blocking reverse current are connected in series, and this series connection is connected to the capacitor described above. A capacitor charging circuit configured by connecting in parallel with the first power source, 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. A signal current circuit configured by connecting the above capacitor in parallel, and logic "0" depending on the presence or absence of current in this signal current circuit.
A current detection circuit generates a binary signal of "1", and when the state of the contact changes from OFF to ON, the capacitor is quickly discharged, and after the capacitor is discharged, the current flowing to the contact is connected to the second resistor. The resistance value of the first resistor is set to be sufficiently large as determined by the series circuit of the discharge resistor and the second power supply, and when the state of the contact changes from on to off, the and means for selecting an inductance value of the coil so that a peak value of the voltage generated between the contacts is approximately the same as the voltage of the first power source.