JPH07212202A - Multi-point signal input device - Google Patents

Abstract

PURPOSE:To make possible high-accuracy measurement by parallelly connecting two semiconductor switches to the system of a terminal, to which the low voltage side of a two-terminal input is connected, at least to reduce an error voltage caused by ON resistance CONSTITUTION:When measuring a DC voltage input VDC of two terminals connected to a measuring channel CH2, semiconductor switches SW1I, SW1A and SW1B are turned off, switches SWb1 and SWb2 are also turned off, semiconductor switches SW2A, SW2B and SW2B2 are turned on and a switch SW5 is turned on as well. Thus, the voltage of the DC voltage input VDC is fetched into an arithmetic part AU, and prescribed arithmetic processing is performed. In this case, the semiconductor switches SW2B1 and SW2B2 are parallelly connected to an input terminal L(B) on the low voltage side. Therefore, the ON resistance is almost reduced by half, and the error voltage caused by the ON resistance can be reduced. In this case, the number of semiconductor switches to be parallelly connected is not limited at two but it can be over three as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-point signal input device, and more particularly to improvement of a device using a semiconductor switch as an input changeover switch element.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an example of an input block of a multipoint measuring apparatus such as a recorder. In the figure, IN1 to INn are input terminals corresponding to a plurality of measurement channels and are connected to the multiplexer MPX. The multiplexer MPX has these input terminals IN1 to I
Any analog signal input to Nn is selectively input to the attenuator ATT. The output signal of the attenuator ATT is applied to the A / D converter ADC via the preamplifier PA, converted into a digital signal, and applied to a signal processing unit (not shown).

In recent years, as such a multiplexer MPX, a semiconductor having a high breakdown voltage (for example, about 1500 V) is provided because it has higher reliability than a relay having mechanical contacts, and can be miniaturized to increase the packaging density. A switch is used. FIG. 6 is a circuit diagram showing an example of such a semiconductor switch. In the figure, reference numeral 1 denotes a light emitting diode which is selectively driven, and the output light thereof is detected by a light receiving element 2 formed of a plurality of photodiodes connected in series. Switching elements 3 and 4 are composed of FETs, and are connected so as to be simultaneously turned on and off by the detection output of the light receiving element 2. That is, the anode of the light receiving element 2 connected in series is connected to the gates of the respective switching elements 3 and 4, and the cathode of the light receiving element 2 connected in series is the connection point of the source S of the switching element 3 and the source S of the switching element 4. It is connected to the.

In the configuration of FIG. 6, assuming that an analog signal is input to the drain D of the switching element 3, the light emitting diode 1 is selectively driven to be turned on, so that the switching elements 3 and 4 are simultaneously turned on. As a result, an analog signal is output to the drain D of the switching element 4. FIG. 7 is a circuit diagram showing an example of the multiplexer MPX, and the semiconductor switch AS of FIG. 6 is shown as a simple switch. In FIG. 7, 1CH-
Since three signal lines are provided for each measurement channel of 30CH, three semiconductor switches A are provided for each measurement channel.
S is provided. And 1CH-10CH, 11CH
.About.20CH and 21CH to 30CH are divided into groups G1 to G3, respectively, and the output signal lines L1 to L3 of the groups G1 to G3 are directly connected to a common signal line L0.

In the configuration of FIG. 7, assuming that the measurement channel CH1 to which the analog signal of the voltage Va is input is selected and the other measurement channels are turned off, the voltage Va is shared by the common signal line L0 and It is also applied to the output side of a total of 29 sets of switches of each measurement channel turned off via the output signal lines L1 to L3 to charge the capacitance between the input and output of the semiconductor switch and to connect between the drain and the drain of FIG. The capacitance of is also charged. Then, the electric charge charged in each switch of each measurement channel is discharged when the measurement channel is switched and no voltage is applied.

For example, when the measurement channel CH2 is subsequently selected, the error voltage V given to the measurement channel CH2 by the discharge current is as follows. The ON resistance of the switch of the measurement channel CH2 is R, the discharge current of each measurement channel is i, and the discharge current is If the number of measurement channels affected by is N, then V = R × i × N.

[0007]

However, since the ON resistance R of the semiconductor switch is relatively large, the error voltage V also becomes large, and in the case of FIG. 7, N = 28, which is accompanied by the analog input signal of each measurement channel. Will adversely affect the measurement results of. The present invention solves such a conventional problem, and a first object thereof is to provide a multipoint signal input device capable of performing highly accurate measurement by reducing the influence of the ON resistance of a semiconductor switch. It is to be realized.

Another object of the present invention is to realize a multi-point signal input device which can be used for two-terminal input and three-terminal input without increasing the number of semiconductor switches used for each measurement channel and can perform highly accurate measurement. It is in.

[0009]

A multi-point signal input device of the present invention has a plurality of measurement channel input terminal groups each having three terminals selected via a semiconductor switch, and a two-terminal input. In a multi-point signal input device capable of mixed connection with three-terminal input, at least two semiconductor switches are connected in parallel to a system of terminals to which the low-voltage side of the two-terminal input is connected.

[0010]

Since at least two semiconductor switches are connected in parallel to the terminal system to which the low-voltage side of the two-terminal input is connected, the combined value of the ON resistance of the semiconductor switches connected in parallel to this terminal system is If the ON resistances of the above are equal, it becomes 1 / a plurality of one ON resistance.

As a result, the error voltage caused by the ON resistance of the semiconductor switch can be reduced, and highly accurate measurement can be performed.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. Figure 1
At the input terminals A, B, b of the measurement channel CH1
Is connected to a temperature measuring resistor RTD having three terminals, and a DC voltage input VDC having two terminals is connected to input terminals H (A) and L (B) of the measurement channel CH2. The input terminal A of the measurement channel CH1 is connected to the current source I via the semiconductor switch SW _1I, and is also connected to the input terminal A / + of the arithmetic unit AU via the semiconductor switch SW _1A .
The input terminal B of the measurement channel CH1 is a semiconductor switch S
It is connected to the input terminal B / − of the arithmetic unit AU via W _1B and to the common potential point via the switch SW _B. The input terminal b of the measurement channel CH1 is connected to the input terminal b of the arithmetic unit AU via the switch SW _b1, and is also connected to the common potential point via the switch SW _b2 . Input terminal H of the measurement channel CH2 (A) is an input terminal A of the arithmetic unit AU through the semiconductor switch SW _2A
It is connected to / +. The input terminal L (B) of the measurement channel CH2 is connected to the input terminal B / − of the arithmetic unit AU via the parallel circuit of the semiconductor switches SW _2B1 and SW _2B2 , and is also connected to the common potential point via the switch SW _B. Has been done. The input terminal b of the measurement channel CH2 is connected to the input terminal B / − of the arithmetic unit AU via the switch SW _b1, and is also connected to the common potential point via the switch SW _b2 .

In such a structure, when measuring the resistance temperature detector RTD connected to the measurement channel CH1, the semiconductor switches SW _1I , SW _1A and SW _1B are turned on and the switches SW _b1 and SW _b2 are also turned on. , Semiconductor switches SW _2A , SW _2B1 , SW _{2 B2} are turned off and switch S
Also turn off W _B. As a result, the output current of the current source I flows through the resistance temperature detector RTD. Then, each of the voltage V _A of the three-terminal of RTD RTD in this state, V _B, V _b
By taking in the calculation unit AU and performing a predetermined calculation represented by, for example, 2V _B −V _A , the resistance value of the resistance temperature detector RTD can be obtained without being affected by the lead wire resistance or the ON resistance of the semiconductor switch. It can be obtained with high accuracy.

On the other hand, when measuring the DC voltage input VDC connected to the measurement channel CH2, the semiconductor switches SW _1I , SW _1A and SW _1B are turned off and the switches SW _b1 and SW _b2 are also turned off. S
W _2A, SW _2B1, the SW _2B2 is turned on also turn on the switch SW _B. As a result, the voltage of the DC voltage input VDC is taken into the arithmetic unit AU and the predetermined arithmetic processing is performed.
Here, since the semiconductor switches SW _2B1 and SW _2B2 are connected in parallel, the ON resistance becomes almost half, and the error voltage due to the ON resistance can be reduced. The number of semiconductor switches connected in parallel is not limited to two and may be three or more.

By the way, in the circuit configuration of FIG. 1, three semiconductor switches are used for each channel in order to reduce the cost of parts, so that the measurement channel CH1 is used.
There is a problem in that there is no degree of freedom for changing the input signal, because the three-terminal resistance temperature detector input is fixed and the measurement channel CH2 is fixed to the two-terminal DC voltage input or thermocouple input, respectively.

FIG. 2 shows an embodiment for ensuring the degree of freedom for changing the input signal. In the embodiment of FIG. 2, four semiconductor switches are provided for each measurement channel,
The input terminal B of the measurement channel CH1 is also connected to the input terminal B /-of the arithmetic unit AU through the parallel circuit of the two semiconductor switches _SW1B1 and _SW1B2 , and the input terminal H (A) of the measurement channel CH2 is also a semiconductor. The current source I is connected via the switch SW2I.

With this configuration, 2-terminal input or 3-input is provided for each of the measurement channels CH1 and CH2.
Terminal inputs can be connected, and for two-terminal inputs, highly accurate measurement can be performed with less influence of error voltage due to ON resistance of the semiconductor switch. Also in FIG. 2, the number of semiconductor switches connected in parallel is not limited to two and may be three or more.

However, according to the configuration of FIG.
The cost of parts increases as the number of switches increases. Figure 3
3 is a circuit diagram of an embodiment in which the problem of FIG. 2 is also solved.
The same reference numerals are given to the same portions as. Difference between FIG. 3 and FIG.
The point is that the semiconductor switch SW_1I, SW _2IAnd of the current source I
Between the current source I and the common potential point are selectively switched and connected.
Exchange switch SW_AConnected to each measurement channel
One semiconductor switch SW on the terminal B of the channel_1B, SW_2B
Is connected, and the two-terminal input has the opposite polarity to the terminal A,
The connection between B and the input terminal of the arithmetic unit AU is A
That is, /-, B / +, and b. That is,
In Figure 2, connect the positive side of DC voltage input VDC to terminal A
Since the negative side is connected to terminal B, terminal A is high
It becomes the terminal H on the pressure side and the terminal B becomes the terminal L on the low voltage side.
However, in FIG. 1, the positive side of the DC voltage input VDC is set to the terminal B.
Since it is connected and the negative side is connected to terminal A, terminal B
Becomes terminal H on the high voltage side and terminal A becomes terminal L on the low voltage side.
It

In such a configuration, when measuring the resistance temperature detector RTD connected to the measurement channel CH1, the changeover switch SW _{A is changed over} to the current source I side,
The semiconductor switches SW _1I , SW _1A , and SW _1B are turned on, and the switches SW _b1 and SW _b2 are also turned on.
_2A , SW _2B1 , and SW _2B2 are turned off, and the switch SW _B is also turned off. As a result, the output current of the current source I flows through the resistance temperature detector RTD. And the resistance temperature detector R in this state
Each of the voltage V _A of the three terminals TD, V _B, takes in V _b to the arithmetic unit AU, e.g. 2V _B by performing a predetermined calculation expressed by -V _A, lead resistance and the semiconductor switch on The resistance value of the resistance temperature detector RTD can be obtained with high accuracy without being affected by the resistance.

On the other hand, in measuring the DC voltage input VDC connected to the measurement channel CH2, the changeover switch SW _{A is changed over} to the common potential point side and the semiconductor switches SW _1I , SW _1A and SW _1B are turned off. Switch S
W _b1 and SW _b2 are also turned off, and semiconductor switches SW _2A and SW
_2B1 and SW _2B2 are turned on and the switch SW _B is also turned on. As a result, the voltage of the DC voltage input VDC is
It is taken into U and a predetermined arithmetic processing is performed. here,
Since the semiconductor switches SW _2I and SW _2A are connected in parallel, the on-resistance is almost halved, and the error voltage due to the on-resistance can be reduced.

That is, by configuring as shown in FIG. 3, the number of semiconductor switches used in each measurement channel can be reduced from 4 to 3 as compared with FIG. 7, and can be shared for 2 terminal input and 3 terminal input. Highly accurate measurement with less error voltage due to switch on-resistance can be performed. As the number of measurement channels increases, it becomes advantageous in terms of mounting space for parts and cost.

FIG. 4 is a circuit diagram showing another embodiment of the present invention, showing an example in which the input terminal group is isolated by a semiconductor switch. In FIG. 4, measurement channel CH1
The input terminals A, B, and b of the temperature measuring resistor RTD having three terminals are connected to the input terminals H (A),
Two-terminal DC voltage input VDC is connected to L (b). The input terminal A of the measurement channel CH1 is connected to the current source I via the semiconductor switch SW _1I and the switch SW _I, and is also connected to the input terminal A / + of the arithmetic unit AU via the semiconductor switch SW _1A . Input terminal B of the measurement channel CH1 is connected to the input terminal B of the arithmetic unit AU through the semiconductor switch SW _1B. Input terminal b of the measuring channel CH1 input terminal b / arithmetic unit AU through the semiconductor switch SW _1b1 - is connected to, and is connected to the common potential point via a semiconductor switch SW _1b2 and the switch SW _b. Measurement channel CH2
Is connected to the current source I via the semiconductor switch SW _2I and the switch SW _I, and the input terminal A / of the arithmetic unit AU is connected via the semiconductor switch SW _2A.
Connected to +. Input terminal B of the measurement channel CH2 is connected to the input terminal B of the arithmetic unit AU through the semiconductor switch SW _2B. The input terminal b of the measurement channel CH2 is connected to the input terminal b / − of the arithmetic unit AU via the semiconductor switch SW _2b1 and the semiconductor switch S
It is connected to the common potential point via W _2b2 and the switch SW _b .

In such a configuration, the measurement channel
For measuring the RTD RTD connected to CH1
Is a semiconductor switch SW_1I, SW_1A, SW_1B, SW
_1b1, SW_1b2Turn on the semiconductor switch SW_2I, SW
_2A, SW_2B, SW_2b1, SW _2b2Switch off and switch S
W_bAlso turn off. As a result, the output current of the current source I is
It flows through the RTD RTD. And temperature measurement in this state
The voltage V of each of the three terminals of the resistor RTD_A, V_B, V_b
Is taken into the arithmetic unit AU and, for example, 2V_B-V_ARepresented by
The lead wire resistance and semiconductor
Resistance temperature detector without being affected by the on resistance of the switch
The resistance value of the RTD can be obtained with high accuracy.

On the other hand, in measuring the DC voltage input VDC connected to the measurement channel CH2, the semiconductor switches SW _1I , SW _1A , SW _1B , SW _1b1 and SW are used.
_1b2 is turned off and semiconductor switches SW _2I , SW _2A , SW
_2B , SW _2b1 and SW _2b2 are turned on and the switch SW _b is also turned on. As a result, the voltage of the DC voltage input VDC is taken into the arithmetic unit AU and the predetermined arithmetic processing is performed. Here, the semiconductor switches SW _2b1 and SW _2b2 are the switch SW
_Since they are connected in parallel via _b , the ON resistance is almost halved as in FIG. 1, and the error voltage due to the ON resistance can be reduced.

[0025]

As described above, according to the present invention,
It is possible to realize a multi-point signal input device that can be used for two-terminal input and three-terminal input without increasing the number of semiconductor switches used for each channel and can perform highly accurate measurement.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the present invention.

FIG. 5 is a circuit diagram showing an example of a conventional multiplexer.

FIG. 6 is a circuit diagram showing an example of a semiconductor switch.

FIG. 7 is a block diagram showing an example of an input block of a multipoint measuring device.

[Explanation of symbols]

1 light emitting diode 2 light receiving elements (photodiodes) 3,4 switching element _{(FET) AS, SW 1I,} SW 1A, SW 1B, SW 1b1, SW 1b2, S
W _2I , SW _2A , SW _{2B ,} SW _2b1 , SW _2b2 Semiconductor switch (analog switch) SW _A selector switch SW _B , SW _b , SW _b1 , SW _b2 switch RTD Resistance thermometer VDC DC voltage input I Current source AU calculation Department

Claims (1)

[Claims] 1. A multi-point signal input device having an input terminal set of a plurality of measurement channels, each set including three terminals selected via a semiconductor switch, and capable of mixed connection of a two-terminal input and a three-terminal input. 2. A multipoint signal input device according to claim 2, wherein at least two semiconductor switches are connected in parallel to a system of terminals to which the low-voltage side of the two-terminal input is connected.