JPH0454460Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Purpose of the Invention] (Field of Industrial Application) The present invention relates to a high impedance input switching circuit, and is particularly used as an input circuit of a measuring instrument.

(Prior Art) It is desirable that the input circuit of a measuring instrument has as high impedance as possible in order to suppress the influence of current flowing during measurement. On the other hand, the measurement range is usually 1/10,
The steps are 1/10 of 1/100...
To achieve this, a circuit as shown in FIG. 4 is used.

This uses a relay terminal assembly 20 having seven contacts, and by changing the shorting position with a two-core shorting socket, three ranges of 1, 1/10, and 1/100 are realized. That is, two input terminals 2
The high side of No. 1 is connected to the No. 2 pin of the relay terminal assembly 20, and the grounded low side forms the low side of the output terminal 24. R ₂ = between the No. 3 pin of the relay terminal assembly 20 and the low side input/output terminal.
Three resistors, 9MΩ, R ₃ = 900KΩ, and R ₄ = 100KΩ, are connected in series, and the connection points of R ₂ and R ₃ are connected to pin 4, respectively. Further, pin 1, pin 5, and pin 7 are connected to the input side of an operational amplifier 23, and the output side of this operational amplifier 23 constitutes the high side of the overall output terminals. Note that a protective resistor is connected between pin 1 and the input side of the operational amplifier 23.
A 100KΩ resistor _R1 is inserted.

This switching circuit is used as follows.

First, when obtaining an attenuation factor of 1, as shown by the broken line 22 in FIG. 4, pins 1 and 2 and pins 3 and 4 of the relay terminal assembly 20 are short-circuited using short-circuit sockets, respectively. In addition, 3
The short circuit between pin No. 4 and pin No. 4 has no relation to the circuit. As a result, a signal is input to the operational amplifier 23 via the 100KΩ series resistor _R1 . At this time, the series resistors R ₂ to _{R 4} forming the attenuator are separated from the input circuit, so the input impedance becomes 100 MΩ or more.

Next, in order to obtain a range with an attenuation of 1/10, pins 2 to 3 and 4 of the relay terminal assembly 20
Short-circuit between pin No. 5 and pin No. 5, respectively. As a result, between the input terminal 21 and the operational amplifier 23, a series resistance R ₂ =9MΩ and a parallel resistance R ₃ +R ₄ =900KΩ+
This means that 100KΩ=1MΩ is inserted, and as a result of voltage division by these, a signal is input to the operational amplifier 23 at an attenuation rate of R ₃ +R ₄ /R ₂ +R ₃ +R ₄ =2/10.

The input impedance at this time is 10MΩ.

Next, to obtain a range with an attenuation of 1/100, short-circuit between pins 2 and 3 and pins 6 and 7 of the relay terminals. As a result, a series resistance R ₂ +R ₃ =9.9MΩ and a parallel resistance R ₄ =0.1MΩ are inserted between the input terminal 21 and the operational amplifier 23, and as a result of voltage division by these, the operational amplifier 23 A signal is input at an attenuation rate of R ₄ /R ₂ +R ₃ +R ₄ =1/100. The input impedance at this time is 10MΩ.

Such a circuit can be easily implemented using a rotary switch or a pushbutton switch.

(Problem to be solved by the invention) However, when using a relay terminal assembly and shorting socket as a simple switching means, two shorting sockets are required, and when changing the range, these two shorting sockets are used. Since it has to be moved, there is a problem in that the operability is not good and switching errors are likely to occur.

The present invention was devised to solve these problems, and an object of the present invention is to provide a high impedance switching circuit with a reduced number of parts and improved operability.

[Structure of the idea]

(Means for Solving the Problems) A high impedance input switching circuit according to the present invention includes a pair of input terminals, a relay terminal assembly in which a plurality of terminals are arranged at a predetermined pitch, and a length corresponding to the predetermined pitch. a single shorting member that shorts any adjacent terminals in the relay terminal assembly; and a signal processing unit that inputs a signal to a first terminal of the relay terminal assembly connected to one side of the input terminal. a high resistance value resistor connected between one side input terminal of the unit, and one end thereof connected to a second terminal adjacent to the first terminal;
When the other end is connected to one side input terminal of the signal processing section, and the first and second terminals are short-circuited by the shorting member, the combined resistance value with the high resistance value resistor is the same as that of the signal processing section. and an input adjustment resistor forming an input resistance value, the relay terminal assembly
1 connected to one side input terminal of the signal processing section
or a terminal group including a plurality of third terminals and voltage dividing resistors located adjacent to the terminals and each having a different resistance value connected to the other side of the input terminal; The resistor is configured to provide a desired attenuation rate by the high resistance value resistor and the voltage dividing resistor by sequentially switching and short-circuiting one of the terminals of the group and the third terminal adjacent thereto using the short-circuiting member. This is characterized in that a resistance value of is selected.

(Function) This input switching circuit uses a single short-circuit member (short-circuit socket) to sequentially switch the short-circuit state between the terminals on the relay terminal assembly, thereby making it possible to change the attenuation factor while maintaining high impedance. can. That is, for an attenuation factor of 1, a very high impedance is obtained because the input terminals are separated by short-circuiting the first and second terminals, and for other attenuation factors, By sequentially switching and shorting the third terminal on the relay terminal assembly and the adjacent terminal, a voltage dividing circuit is formed by the voltage dividing resistor and the high resistance value resistor, and the input impedance at this time is high. Since the resistance value is dominated by resistance, high impedance can be maintained.

(Embodiments) Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings.

1 to 3 are circuit diagrams showing embodiments of the present invention, in which FIG. 1 is a 3-range, a 2-range
The figure shows the case of 2 ranges, and FIG. 3 shows the case of 4 ranges.

First, according to FIG. 1, the 2nd pin of the relay terminal assembly 10 is always connected to the high side of the pair of input terminals 11. This 2nd pin is connected to a resistor _R2 of 9 MΩ.
The relay terminal assembly 10 has five connection pins arranged at equal pitches on a support plate, with a resistor _R1 connected between the first pin and the input terminal of the operational amplifier 13 to adjust the input resistance, the fourth pin directly connected to the input terminal of the operational amplifier 23, and the third and fifth pins connected to the low side (ground side) of the input/output terminals and resistors _R3 = 1 MΩ and _R4 =
The connection is made via 90.9KΩ. Note that pin 2 corresponds to the first terminal in the claims of the utility model, pin 1 corresponds to the second terminal, and pin 4 corresponds to the third terminal.

To explain the operation of such a configuration, first, when the attenuation factor is 1, the first and second pins of the relay terminal assembly are short-circuited by the short-circuiting socket 12, which is a short-circuiting member. As a result, the input resistance as a protection resistance for the operational amplifier 13 becomes a composite resistance of two resistances R ₁ and R ₂ connected in parallel. This combined resistance value can be determined by selecting the value of the resistor _R1 in accordance with the characteristics of the operational amplifier 13.
For example, the value is in the range of 100KΩ to 1MΩ. The reason why a high resistance and a resistance connected in parallel are used for an attenuation factor of 1 is as follows. When the attenuation rate is other than 1, a high resistance is required because voltage division is performed, whereas for an attenuation rate of 1, only this high resistance performs current limitation. but,
This is because a high resistance is easily induced, and when an input filter is configured, the time constant becomes too large, so it is necessary to reduce the resistance value.

The input impedance in this case is determined by the characteristics of the operational amplifier, and is, for example, 100 MΩ or more.

Next, to obtain an attenuation rate of 1/10, connect the 3rd and 4th pins of the relay terminal assembly 10 to the short-circuit socket 12.
Short circuit using. As a result, a series resistance _R2 of 9MΩ is connected between the input terminal 11 and the operational amplifier 13.
A voltage dividing resistor R ₃ of 1 MΩ is connected, and a signal is input to the operational amplifier 13 at an attenuation rate of R ₃ /R ₂ +R ₃ =1/10 due to the voltage dividing effect. The input impedance in this case is
_R2 + _R3 =10MΩ.

Next, in order to obtain an attenuation factor of 1/100, the shorting socket 12 is inserted so as to short-circuit the 4th pin and the 5th pin of the relay terminal assembly 10. This results in
9MΩ between input terminal 11 and operational amplifier 13
This means that the series resistor R ₂ and the voltage dividing resistor R ₄ of 90.9KΩ are connected, and due to the voltage dividing effect of these, the signal is transmitted to the operational amplifier 13 at an attenuation rate of R ₄ /R ₂ +R ₄ ≒ 1/100. is input. In addition, the input impedance in this case is R ₂ + R ₄ =
It is 9.0909MΩ.

FIG. 2 explains another embodiment of the present invention, and is a circuit diagram showing a two-range input switching circuit that obtains attenuation factors of 1 and 1/10. In this case, the configuration and operation are the same as in the case of FIG. 1, except that the No. 5 pin of the relay terminal and the resistor _R5 for the 1/100 range are removed from the configuration of FIG. 1, so a detailed explanation will be omitted.

FIG. 3 is a circuit diagram showing still another embodiment of the present invention, which has four attenuation rates of 1, 1/10, 1/100, and 1/1000.
An input switching circuit having a range is shown.

According to the figure, in addition to the configuration shown in Figure 1, the voltage dividing resistor for forming an attenuation factor of 1/1000 is 9.009KΩ.
A resistor _R5 is connected between pin 7 of the relay terminal assembly 10 and the low side of the input terminal 11, and pin 7 and pin 6, which is shorted when the 1/1000 range is selected, are connected to the input terminal of the operational amplifier 13. It is connected.

The operation in the range of attenuation factor 1 to 1/100 in this configuration is the same as in the case of FIG.
By short-circuiting pins 6 and 7, a 9MΩ series resistor R ₂ and a 0.009KΩ voltage dividing resistor R ₅ are connected between the input terminal 11 and the input of the operational amplifier 13.
are connected, and due to these voltage division effects, a signal is input to the operational amplifier 13 at an attenuation rate of R ₅ /R ₂ +R ₅ ≈1/1000. In this case the input impedance is R ₂ +
R ₅ =9.009MΩ. Note that in this example, 4
Pin No. 6 and pin No. 6 correspond to the third terminal.

As you can see from the above explanation, the series resistance R ₂ controls the input impedance value, so
It is necessary to select a sufficiently high resistance value.

Furthermore, since a two-core shorting socket is used, a resistor can be connected to each of the two terminals adjacent to the terminal drawn out from the input terminal of the operational amplifier to form a voltage dividing circuit. Taking this fact into consideration, the required number of terminals N in the case of n range is determined.

First of all, if n is an even number, two contacts are required for the attenuation degree to be 1, a terminal for connecting a parallel resistor that is one less than the number of ranges, and a lead wire for connecting this parallel resistor to the operational amplifier. Since n/2 terminals are required to be connected, N=2+(n-1)+n/2=3n+2/2...(1).

Next, if n is an odd number, the attenuation degree is 1
Since we need 2 contacts for parallel resistance, (n-1) contacts for parallel resistance, and n-1/2 contacts for lead wire, N=2+(n-1)+n-1/2=3n+1/2... …(2) becomes.

Also, the resistance R _o (n≧
The value of 3) is obtained from _Ro /R ₂ + _Ro = 1/D, as follows: Ro ₌ R ₂ /D-1 (3).

As described above, a high impedance input switching circuit having a desired attenuation rate and number of ranges can be obtained.

[Effect of idea]

As explained above in detail based on the examples,
According to the present invention, when the attenuation degree is 1, the resistance between the input terminals is disconnected to obtain a very high impedance, and at the attenuation degree other than 1, the desired attenuation rate is achieved by a voltage dividing resistor formed by a series resistor having a high resistance value and a short circuit. This makes it possible to easily switch ranges using only one shorting socket, reducing the number of parts, saving space, and reducing switching errors.

[Brief explanation of the drawing]

1 to 3 are circuit diagrams showing embodiments of the high impedance input switching circuit according to the present invention,
FIG. 4 is a circuit diagram showing an example of a conventional input switching circuit. 10, 20... Relay terminal, 11, 21... Input terminal, 13, 23... Operational amplifier, 14, 24...
...Output terminal.

Claims (1)

[Claims for Utility Model Registration] A relay terminal assembly including a pair of input terminals, a plurality of terminals arranged at a predetermined pitch, and an arbitrary adjacent terminal in the relay terminal assembly having a length corresponding to the predetermined pitch. a single short-circuit member that short-circuits the input terminal; and a single short-circuit member connected between the first terminal of the relay terminal assembly connected to one side of the input terminal and one input terminal of the signal processing unit to which the signal is input. a high-resistance resistor, one end of which is connected to a second terminal adjacent to the first terminal, the other end of which is connected to one input terminal of the signal processing section, and the first and second terminals are connected to each other; an input adjustment resistor whose combined resistance value with the high resistance value resistor constitutes an input resistance value of the signal processing section when the terminal is short-circuited by the shorting member; one or more third terminals connected to one side input terminal
and a terminal group in which a voltage dividing resistor located adjacent to this terminal and having a different resistance value is connected between the terminal and the other side of the input terminal,
By sequentially switching and short-circuiting one of the terminals of this terminal group and the third terminal adjacent thereto with the short-circuiting member, a desired attenuation rate is provided by the high-resistance resistor and the voltage-dividing resistor; A high impedance input switching circuit in which a resistance value of the resistor is selected.