JPS6234299Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an indicator protection circuit that protects an indicator (meter) of a measuring instrument from excessive input.

The present applicant previously filed an application as U.S. Pat. According to this, the relay that drives the circuit-breaking relay contact can be an inexpensive relay with a single contact because it is electrically self-held by an electric circuit, and an expensive relay with a mechanical self-holding function can be used. There's no need. In addition, since excessive input is indicated by the pointer of the indicating instrument, it is not possible to
It has the advantage of not requiring any LEDs or lamps. The present invention is a further improvement of the above-mentioned protection circuit, and its purpose is to use an indicator to display excessive input and battery voltage, and to reset the protection circuit and check battery voltage using the same switch. An object of the present invention is to provide a protection circuit for an indicating instrument that operates in a manner similar to that described above.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

The drawing shows an embodiment in which the indicating meter protection circuit according to the present invention is applied to a DC ammeter, and this DC ammeter has a positive input terminal 1 and a negative input terminal 2. Between the two,
A series circuit consisting of a normally closed relay contact 3s for circuit breaking, an indicator protection resistor 4, and an indicator (meter) 5 is connected. Reference numeral 6 denotes an indicator protection circuit connected between both terminals of the indicator 5, which includes a battery 7, a relay holding circuit 8, and a battery voltage checker for checking the voltage of the battery 7. A reset/battery voltage check switch 1 selectively connects the circuit 9, the relay holding circuit 8, and the battery voltage check circuit 9 to the battery 7.
0. The relay holding circuit 8 includes a relay coil 3 that drives the relay contact 3s, and an indicator 5.
Operates due to excessive voltage applied between both terminals of
It has an NPN transistor 11 and an NPN transistor 12 that operates in conjunction with this transistor 11 to close a circuit including a relay coil 3 and a battery 7, and in this case, the base of the transistor 11 is connected to an indicator via a resistor _R1 . 5, the emitter is connected to the other terminal of the indicator 5, that is, the input terminal 2, and the collector is connected to the base of the transistor ₁₂ via a resistor R2. The emitter of the transistor 12 is connected to the positive electrode side of the battery 7 via the switch 10, and the collector is connected to the negative electrode side of the battery 7 via the relay coil 3. Further, a series circuit consisting of a resistor _R3 and a diode 13 is connected between the base of the transistor 11 and the collector of the transistor 12. The battery voltage check circuit 9 has a resistor _R4 and a diode 14, each connected to the battery 7 via a switch 10. In this case, the cathode of the diode 14 is connected to the battery 7 through a switch 10.
It is connected to one terminal of the indicator 5 via R ₅ and a resistor R ₁ . The switch 10 has a movable contact 15 connected to the positive electrode side of the battery 7, two fixed contacts, that is, a fixed contact a on the relay holding circuit 8 side connected to the emitter of the transistor 12, a resistor _R4 and a diode 14. A fixed contact b on the battery voltage check circuit 9 side is connected to the anode. In addition, in a circuit tester, the battery 7 is generally used not only as the protection circuit 6 but also as a power source for a circuit that measures resistance, etc., so in order to check the battery voltage of the battery 7 more accurately, For example, it is preferable to set the resistance value of the resistor _R4 to a value approximately equal to the actual load of these circuits, taking into account the voltage drop consumed by the circuits that constitute the resistance meter. Reference numeral 16 is a capacitor connected between the base and emitter of the transistor 12, which prevents the transistor 12 from turning on due to a surge current when the movable contact 15 is switched from the fixed contact B side to the A side. are doing.

To explain the operation, the indicator protection circuit 6 is normally used with the movable contact 15 of the switch 10 in contact with the fixed contact a. The voltage drop of the indicator 5 at full scale is normally 50 mV to 100 mV, whereas the transistor 11 has a base-emitter potential.
Silicon transistors that operate at around 600mV are used. Therefore, when an excessive input that exceeds the operating voltage of the transistor 11 is applied to the indicator 5, the transistor 11 is turned on and the transistor 12 is turned on through its emitter-collector.
Since the base current flows, the transistor 12 is also turned on. As a result, battery 7, transistor 1
The circuit including the emitter collector of No. 2 and the relay coil 3 is closed, and the relay coil 3 is excited by the current from the battery 7, so that the relay contact 3s
is opened and the indicator 5 is protected from excessive input. In this case, since the collector potential of the transistor 12 is higher than the base potential of the transistor 11, the collector potential of the transistor 12 is connected to the transistor 11 via the resistor _R3 and the diode 13.
A current is supplied between the base and emitter of the transistor 11 and the transistor 12 to keep the on state and supply a holding current to the relay coil 3. This causes the relay coil 3 to connect to the relay contact 3.
Self-retain s. On the other hand, when the transistor 11 is in the on state, its base potential is almost constant without being affected by voltage fluctuations of the battery 7. Therefore, by selecting the resistance value of the resistor _R1 , the voltage from the collector of the transistor 12 to the resistor _R3 can be changed. With the current supplied through the diode 13, the pointer of the indicator 5 can be stopped near the full scale of the scale plate, thereby causing the pointer of the indicator 5 to indicate an excessive input. Note that the presence of the diodes 13 and 14 prevents excessive input from flowing into the collector side of the transistor 12 and the resistor _R4 side.

To reset the relay holding circuit 8, the movable contact 15 of the switch 10 is switched from the fixed contact a side to the b side. As a result, the relay holding circuit 8 is disconnected from the current 7, so the relay coil 3 is deenergized and the relay contact 3s is closed. On the other hand, a battery voltage check circuit 9 is connected to the battery 7. That is, a resistor R ₄ close to the actual load is connected to the battery 7, and a voltmeter circuit is formed that reaches the indicator 5 via the diode 14, resistors R ₅ and R ₁ , and the pointer of the indicator 5 The voltage of the battery 7 will be displayed. In this case, the resistor _R5 is a resistor for configuring the voltmeter, and its resistance value is the indicator meter 5.
The battery voltage is set to be displayed using the voltage scale.

As explained above, according to the present invention, the circuit breaker relay is electrically self-maintained by the relay holding circuit that operates in response to excessive input applied to the indicating instrument, so it is different from the conventional mechanical self-holding relay. An inexpensive single-contact relay can be used instead. Furthermore, since the indicator is used to display excessive input and battery voltage, it is possible to omit indicators such as LEDs and lamps for displaying these. Furthermore, by using a single switch to reset the relay holding circuit and check the battery voltage, it becomes easier to operate and the configuration of the meter can be further simplified.

[Brief explanation of the drawing]

The drawing is a circuit diagram showing an indicator protection circuit according to the present invention. In the figure, reference numbers 1 and 2 are input terminals, 3s is a relay contact, 3 is a relay coil, 5 is an indicator, 6 is an indicator protection circuit, 7 is a battery, 8 is a relay holding circuit, and 9 is a battery voltage check circuit. , 10 is a changeover switch, 11 and 12 are transistors, 13 and 14 are diodes, and R ₁ to _{R 5} are resistors.

Claims (1)

[Claims for Utility Model Registration] An indicator protection circuit having a relay contact 3s that cuts off a circuit including the indicator 5 in response to an excessive input applied to the indicator 5, comprising: a battery 7; The relay coil 3 of the relay contact 3s operates when the voltage across the indicator 5 is excessive.
A resistance value approximately equal to the load consumed by a relay holding circuit 8 that supplies a self-holding current to the input device 5 and a current for indicating excessive input to the indicator 5, and a resistance measuring circuit etc. whose power source is the battery 7. a first resistor R ₄ and said indicator 5 set to
a battery voltage check circuit 9 having a second resistor R ₅ that operates as a voltmeter to display the remaining voltage of the battery 7; An indicator protection circuit characterized by comprising a changeover switch 10 for connection.