JPS61196626A - Signal input circuit - Google Patents

Abstract

PURPOSE:To keep always a contact at the satisfactory condition and to prevent the deterioration of the input signal by destructing electrically the membrane of the contact in the signal input circuit having the detecting part of the large impedance and having at least one contact at the input signal system path. CONSTITUTION:A capacity element 19, when an electric current flows from a direct current electric power source 16 into contacts 14a and 14b, forms a by-pass path to make the electric current value into the constant size or above. At a timing circuit 22, switch elements 18 and 21 are made into the off condition, an input part 12 is made into a receiving condition, and then, the signal of a detecting part 11 is inputted through the contacts 14a and 14b to the input part 12. After the measurement, the receiving function of the input part 12 is prohibited, the switch element 18 is turned on, and then, a pulse-shaped voltage is impressed between input signal system lines from a direct current electric current 16, the electric current flows through the contact 14a, the capacity element 19 and the contact 14b and the membrane is destructed by the Joule heat which occurs at the contacts 14a and 14b. Next, when the switch element 21 is turned on, the charge accumulated at the capacity element is smoothly discharged through the switch element 21 and a resistance 20.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides at least one input signal path between a detection section and an input section that detects all signals transmitted from the detection section via a transmission line. The present invention relates to a signal input circuit in which two contacts are connected in series, and a film formed on the surface of the contacts is destroyed to prevent an increase in contact resistance.

[Conventional technology]

For example, in process control measurements, the signal path of the signal input circuit that detects all signals at each measurement point in the process and transmits them to the input section of the signal processing section through all transmission lines, includes various signals including the detection side. Electrical contacts 1 For example, contacts such as detection relays, mechanical contacts, switching switches, connectors of printed circuit boards, etc. are used as circuit components.

[Problem that the invention seeks to solve]

However, these contacts tend to have various films such as oxide films and corrosive gases formed on their surfaces, and this film increases the p-contact resistance, causing deterioration of input signals and reduced reliability. . As a result, it loses its function as a contact point,
Problems such as shortened lifespan were common. This was particularly noticeable as the input signal became lower in level.

In order to prevent the formation of this contact film, conventional contact materials such as gold, which do not easily form a film, or contacts with a smooth or hermetic seal structure have been used. The materials are expensive and the cost is high. In addition, the latter type of contact often has a complicated structure, resulting in high manufacturing costs.

Therefore, in order to solve this problem, the applicant of the present application has separately proposed a complete signal input circuit as shown in FIG. This can be used as a detection input to turn on a relay contact,
This shows the case of digital input due to OFF, and current limiting resistor 6 and switch T? A film removal circuit is constituted by a nine current power supply 5 connected via the 9-channel power source 5, and a timing circuit 8 that controls the switch 7 and the relay contact 1 to turn on and off at regular intervals. Both relays 71i and 71i are turned on, and a current from the DC power source 5j flows through the relay contact 1, completely destroying the contact film. In addition, 2 and 3 in Fig. 3 are voltage dividing resistors connected between the driving power source E+ and the relay contact 1, and 4
is amplified at the input section for receiving the low level and flat level signal sounds generated at the voltage dividing point P of the voltage dividing resistors 2 and 3 in accordance with the ON/OFF state of the relay contact 1.

In the signal input circuit of the above configuration, by passing a pulsed current from the full DC power source 5 to the relay contact 1 at regular intervals, the film generated on the surface of the relay contact 1 can be electrically destroyed, so the contact resistance can prevent an increase in At this time, it is not limited to the relay contact 1, but the same applies even if the input signal path between the detection unit serving as the signal source and the amplifier 4 includes a connector such as a printed circuit board or a contact such as a changeover switch. Can destroy contact film.

However, in a signal input circuit configured in this way, it is fine if the impedance of the detection section is small, but if it becomes large, for example on the order of several tens of ohms, = 3 = The impedance of the detection section causes the current to be lower than the DC power source. It became difficult to flow the liquid to all contacts, making it unsuitable for practical use.

The present invention has been made in view of the above circumstances, and is aimed at reducing the amount of film that forms on the surface of a contact inserted into the input signal path between the detection section and the input section when the impedance of the detection section is large. It provides a complete signal input enclosure that can electrically destroy the signal and prevent an increase in contact resistance.

[Means for solving problems]

The signal input circuit according to the present invention has a power supply section connected to the switch element with all valves in order to allow the entire current to flow into at least one contact connected in series to the input signal path between the detection section and the input section. , a capacitive element connected in parallel between both ends of the detecting section, a means for completely discharging the charge accumulated in the capacitive element, and a means for completely discharging the receiving function of the input section and turning on and off the switching element. A timing circuit is provided for control, and the timing circuit disables the receiving function of the input section and turns on the switch element, so that current flows from the power supply section into the contact and destroys the contact film. This is what I did.

[For production]

In the present invention, by connecting a capacitive element in parallel with the detection part, this capacitive element creates a bypass path, so that when a pulsed current flows from the power supply part to all contacts, the current value is increased to a certain level or more. Can be done.

As a result, even if the impedance of the detection part is large, the contact film can be easily destroyed using the Joule heat generated in the contact.

〔Example〕

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

FIG. 1 shows a basic circuit configuration diagram of a signal input circuit according to an embodiment of the present invention. In the same figure, 11 is a detection unit having an impedance of, for example, 2 to 3Ω, and 12
is an input section 14a, 14b consisting of an amplifier, etc., which receives the signal transmitted from the detection section 11 through all the transmission lines 13;
is the transmission line 13vI between the detection section 11 and the input section 12
- The contacts 9 of a connector section of a printed circuit board or the like connected to the input signal path including the terminals 9 constitute a normal signal input circuit, and the signals of the detecting section 11 are transmitted to the contacts 14a and 14.
input to the input section 12 via the transmission line 13 included in b',
The output is sent to a signal processing section (not shown).

Further, 15 is a series circuit in which a DC power supply 16, a current limiting resistor 1T, and a switching element 18 are connected in series.
One end of this series circuit 15 is connected between one input terminal of the input section 12 and the contact 14a, and the other end is connected between the other input terminal of the input section 12 and the contact 14b. A predetermined amount of current flows from the power supply 16 into the contacts 14a and 14b through the switch element 18. Reference numeral 19 denotes a capacitive element connected in parallel between both ends of the detection unit 11, and this capacitive element 19 is made to have a current value greater than a certain value when the entire current flows from the DC power source 16 into the contacts 14a and 14b. There will be a bypass line for this purpose. Further, 20 is a resistor for quickly discharging all the charges accumulated in the capacitive element 19, and 21 is a switching element connected in parallel between both ends of the series circuit 15. This switching element 21 also has a capacitance. It is for discharging the charge of the element 19. Further, 22 is a timing circuit for inhibiting the reception function of the input section 12 at regular intervals and controlling the on/off of the valley switch elements 18 and 21, and the timing waveform thereof is shown in FIG. 2(a). - Shown in (c).

Therefore, when measuring the analog signal sound detected by the detection section 11, the timing circuit 2
2, when the switch elements 18 and 21t are turned off and the input section 12 is set to the reception state, the signal from the detection section 11 is input to the input section 12 via the input signal path including the resistors 14a and 14b'e. Normal measurement? Let's do it. After the measurement of , the reception function of the input section 12 is prohibited at the timing shown in FIG. 2(a), and the switch element 1B
? When turned on at the timing shown in Figure 2(b), the DC t
fi16! A pulsed voltage is applied to contacts 14a and 14.
The current flows through one contact 14a, the capacitive element 19, and the other contact 14bk. Therefore, those contacts 14a and 14b
The Joule heat generated can destroy the film. Next, the charge accumulated in the second capacitive element 19 of the switch element 21 is transferred to the second capacitive element 19.
and resistor 20' (H). Therefore, this operation is repeated synchronously.
Even if the impedance is as large as about 2 to 3 ohms, the contacts i4a and 14b in the @ input circuit can be maintained in a good condition free from a scaly film, and an increase in contact resistance can be prevented.

The above explanation has been about analog input in a process-based measurement system, but the present invention is designed to prevent damage to the contact film that occurs when the impedance of the detection section is large and the low-level signal flows through the contact. It goes without saying that the present invention can be applied to all of the signal input circuits that are equipped.

〔Effect of the invention〕

As explained above, the present invention provides detection capability with large impedance, and in a signal input circuit having at least one contact in the input signal path, by electrically destroying the film of the contact, Since the contacts can always be kept in good condition without increasing contact resistance, it is possible to completely prevent input signal deterioration and improve reliability. The effect of being measured is increasing.

[Brief explanation of drawings]

FIG. 1 is a basic circuit configuration diagram according to an embodiment of the present invention,
Figures 2 (a) to (c) explain the operation of the above implementation force 1-
FIG. 3 is a circuit configuration diagram showing an example of a signal input (output) path separately proposed by the same applicant. 11...detection section, 12...input section, 13...
・Transmission line, 14a, 14b Fist...Contact point, 15・ψ
...Series circuit, 16--Fist DC power supply, 17Φ-- Current limiting resistor, 18...Switch element, 19...
-Capacitive element, 20...Resistor, 21...Switch element, 22...Timing circuit.

Claims (1)

[Claims] In a signal input circuit in which at least one contact is connected in series to an input signal path between a detection section and an input section that receives a signal transmitted from the detection section via a transmission line, a power supply unit connected via a switch element to allow current to flow; a capacitor element connected in parallel between both ends of the detection unit; means for discharging the charge accumulated in the capacitor element; and the input unit. a timing circuit for inhibiting a reception function of the input section and controlling on/off of the switch element; the timing circuit inhibits the reception function of the input section and turns on the switch element; A signal input circuit characterized in that a current flows into the contact to destroy the contact film.