JPH063465B2 - Signal processor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of use) The present invention amplifies a plurality of analog measurement voltages selectively taken into an amplifier via a multiplexer and adds the amplified analog measurement voltage to an integrating A / D converter, The present invention relates to a signal processing device configured to convert into a digital signal.

(Prior Art) FIG. 2 is a configuration diagram showing a main part of an example of such a conventional signal processing device, and shows an example of a recorder. In FIG. 2, H and L are input terminals for a thermocouple, a DC voltage, etc., the H terminal is connected to the amplifier 1 via the resistor R ₁ and the switch SW ₁ , and the L terminal is connected to the common potential point. There is. A temperature sensor 2 outputs a temperature signal for compensating the cold junction temperature of the thermocouple, and its output terminal is connected to the amplifier 1 via the switch SW ₂ . An example of such a temperature sensor 2 is a Vbe of a transistor.
The one using the temperature change of is used. Rt is a resistance temperature detector having three terminals A, B, and b, a constant current source 3 for applying a reference current is connected to the terminal A, and a terminal b has a resistance R ₂
Is connected to the common potential point via. Reference numeral 4 is a signal conversion circuit for converting a resistance value (Ω) into a temperature value (° C.) based on the potential difference between the terminals A and B of the resistance temperature detector Rt, which is connected to the amplifier 1 via the output terminal switch SW _3. SW ₄ connected is a switch for connecting the common potential point to the amplifier 1. These switches SW _{1 to} SW ₄ form a multiplexer that switches the input of the amplifier 1. The output of the amplifier 1 is applied to, for example, an A / D converter 6 of integral type via a resistor R ₃ and an adder 5, and is converted into a digital signal. Reference numeral 7 is a reference voltage source that outputs a positive reference voltage, and 8 is a reference voltage source that outputs a negative reference voltage. The output voltage of the reference voltage source 7 is applied to the A / D converter 6 as a reference for setting the discharge current of the integrator of the A / D converter 6, and the reference voltage source 8 is used as a reference for the output voltage of the reference voltage source 8. Has been added to. The output voltage of the reference voltage source 8 is applied to the A / D converter 6 via the resistor R ₄ and the adder 5, and the A / D converter 6 corresponds to positive and negative voltages centered at a voltage of zero. It is used as a reference for setting the offset current for the purpose. A / D converter 6
The digital signal converted by (1) is added to the arithmetic circuit 10 composed of a microprocessor, a digital circuit, etc. via a signal insulating circuit 9 such as a photocoupler. Arithmetic circuit 10
Is, for example, the A / D converter 6 with SW ₄ turned on.
Performs necessary arithmetic processing such as automatic zero point compensation by software for the measurement result based on the digital signal output of, the conversion of the thermocouple output voltage to the temperature signal, and the linearization of the measurement signal. The result calculated in this way is added to a recording unit (not shown) and recorded.

(Problems to be solved by the invention) However, according to such a conventional configuration, since the span of the A / D converter 6 is set according to the output voltages of the reference voltage sources 7 and 8, these reference voltages are set. The peripheral circuit including the voltage sources 7 and 8 must maintain high accuracy and high stability for a long period of time, the circuit configuration becomes complicated, and expensive circuit parts must be used, resulting in high cost. There are drawbacks.

The present invention focuses on such a point, and an object thereof is to provide a signal processing device capable of highly accurate measurement with a relatively simple circuit configuration.

(Means for Solving the Problems) In the present invention which achieves such an object, an A / D of an integral type is obtained by amplifying a plurality of analog measurement voltages V _i selectively taken into an amplifier via a multiplexer. In the signal processing device configured to convert to a digital signal in addition to the converter, the voltage V of the common potential point is set for each measurement cycle in which each measurement of the plurality of analog measurement voltages V _i is one measurement cycle.
A known reference voltage V _F corresponding to the full span of the _Z and A / D converters is selectively applied to the amplifier via a multiplexer, and the gain of the amplifier is set to a first gain G1 to set V
By measuring _Z and V _F , the measurement result V _Z (G1), V _F
(G1) is obtained and the second gain G2 is set to measure V _i and V _Z to obtain measurement results V _i (G2) and V _Z.
Z (G2) is obtained, and these measurement results and known reference voltage V
Based on _F, and performs the calculation represented by _{V i = [{V i (} G2) -V Z (G2)} / {V F (G1) -V Z (G1)}] V F .

(Example) Hereinafter, it demonstrates in detail using drawing.

FIG. 1 is a structural explanatory view showing a main part of an embodiment of the present invention, and the same parts as those in FIG. 2 are designated by the same reference numerals. In FIG. 1, a terminal A of the resistance temperature detector Rt is connected to a terminal 11 to which a voltage −V is applied via a resistance R ₅ and to an amplifier 1 via a resistance R ₆ and a switch SW ₅ , B is connected to the amplifier 1 via the resistor R ₇ and the switch SW ₆ , the terminal b is connected to the common potential point via the resistor R _s, and is also connected to the amplifier 1 via the resistor R ₈ and the switch SW _7. ing. Here, as the resistance R _s , a resistor having a known resistance value and a high stability with a small change in the resistance value due to the measured physical quantity is used. Also,
The amplifier 1 has an A / D converter 6 via a switch SW _8.
A reference voltage source 12 for generating a reference voltage V _F corresponding to the full-span input is connected. A voltage + V is applied to the A / D converter 6 instead of the conventional reference voltage source 7 at a terminal 13
In addition to the conventional reference voltage source 8, the adder 5 is connected to a terminal 14 to which a voltage -V is applied via a changeover switch SW ₉ and resistors R ₉ and R ₁₀ . Here, the switch SW ₁ ~SW ₈ constitutes a multiplexer.

The operation of the apparatus thus configured will be described.

First, in measuring the DC voltage and the thermocouple output voltage V _i , the switches SW ₄ and SW ₈ are sequentially and selectively turned on with the gain of the amplifier 1 set to the first gain G1 (for example, 1). The voltage V _{Z at the} common potential point and the output voltage V _F of the reference voltage source 12 are measured, and the amplifier 1
Is set to the second gain G2 required for measuring the DC voltage and the thermocouple output voltage V _i , the switch S
W ₁ and SW ₄ are sequentially and selectively turned on to measure the DC voltage or the output voltage V _{i of the} thermocouple and the voltage V _Z at the common potential point for compensating the offset of the amplifier 1, and the respective measurement results V _Z (G1), V _F (G1), V _i (G
2), V _Z (G2) is stored in the arithmetic circuit 10. And
In the arithmetic circuit 10, these measurement results V _Z (G1),
Based on V _F (G1), V _i (G2), V _F (G2) and the output voltage value V _F of the known reference voltage source 12, the calculation shown in the equation (1) is performed.

V _i = [{V _i (G2) −V _Z (G2)} / {V _F (G1) −V _Z (G1)}] V _F (1) With this configuration, except the reference voltage source 12 The characteristics of each of the circuits are not required to change only during the period of measuring the voltages at these four locations, and the circuit configuration can be relatively simple, and inexpensive circuit components can be used, resulting in cost reduction. It can be reduced.

When measuring the output voltage V _J of the temperature sensor 2 for compensating for the cold junction temperature of the thermocouple, the gain of the amplifier 1 is set to 1 and V _Z (G1) and V _F (G1) are used as described above.
Is measured and the gain of the amplifier 1 is set to the temperature sensor 2
The common potential point for compensating the output voltage V _J of the temperature sensor 2 and the offset of the amplifier 1 by sequentially turning on the switches SW ₂ and SW ₄ in a state where the gain G necessary for measuring the output voltage of is set. a voltage _{V Z} and measurements, each of these measurements _{V Z (G1), V F} (G1), V J (G
2), V _Z (G2) is stored in the arithmetic circuit 10. And
The arithmetic circuit 10 uses the measurement results V _Z (G1), V _F (G
1), V _J (G2), V _F (G2) and a known output voltage value V _F of the reference voltage source 12 are calculated as shown in the equation (2).

_{V J = [{V J (} G2) -V Z (G2)} / {V F (G1) -V Z (G1)}] V F (2) further calculating circuit 10, which is calculated this way Voltage V
Convert _J into a temperature signal (° C).

Next, the temperature measurement by the resistance temperature detector R _t will be described. The RTD R _t, applying a constant voltage -V from the terminal 11. In this state, sequentially selectively turn on the switch _{SW 5, SW 6, SW 7} , SW 4 while keeping the gain of the amplifier 1 constant, the terminal A of the RTD _{R t,} B, voltage b V _A , V _B , V _b and the voltage V _Z at the common potential point are measured, and the respective measurement results V _A , V _B , V _b , V _Z are calculated.
Store in 10. Then, in the arithmetic circuit 10, these measurement results V _A , V _B , V _b , V _Z and the known resistance value R
Based on _s , the calculation shown in the equation (3) is performed.

_{R t = [{V A +} V b -2V B} / {V b -V Z}] R s (3) and further, the arithmetic circuit 10, the thus calculated resistance value _{R t} (Omega) Convert to temperature signal (℃).

With this configuration, the conventional resistance temperature detector R _t
A constant current source for applying a reference current to the RTD R _t was required temperature measuring device using and RTD R _t
A signal conversion circuit for converting a resistance value (Ω) into a temperature value (° C) based on the potential difference between the terminals A and B is unnecessary, the circuit configuration is relatively simple, and high accuracy and The number of circuit components that require stability is small, and the cost can be reduced.

Incidentally, in the configuration of FIG. 1, the measurement voltage V _A at the time of resistance measurement operation _RTD, V B, _{V b,} the output of the amplifier 1 in relation to V _Z is only in the range from zero to positive Become.
This means that when the A / D converter 6 is configured to be able to convert an analog input signal in the range of both positive and negative polarities in full span into a digital signal, it is converted with 1/2 resolution. I will end up. Therefore, in the apparatus of FIG. 1, the resistor R ₉ or R ₁₀ is selectively connected to the adder 5 by the change-over switch SW ₉ to change the offset amount applied to the A / D converter 6. That is, for example, when the resistor R ₉ is connected, the A / D converter 6 can convert an analog input signal in the range of both positive and negative polarities centered on zero in full span into a digital signal. _{When 10} is connected, the A / D converter 6 can convert an analog input signal in the range of zero to positive polarity into a digital signal in full span,
The resolution can be increased.

In the above embodiment, an example in which a temperature measuring resistor whose temperature is a measurement physical quantity is used as the conversion resistor is shown, but a gauge resistor or the like whose resistance value changes according to pressure or strain may be used. A plurality of measurement systems including these conversion resistors may be provided and switched by a multiplexer.

Further, in the above embodiment, the example in which the signal processing device is incorporated in the recorder has been described, but it may be incorporated in a data logger or the like.

(Effects of the Invention) As described above, according to the present invention, it is possible to realize a signal processing device that can perform highly accurate measurement with a relatively simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing a main part of a recorder using an embodiment of the present invention, and FIG. 2 is a structural structural view showing a main part of an example of a recorder using a conventional signal processing device. . 1 ... Amplifier, 2 ... Temperature sensor, 5 ... Adder, 6 ... A / D
Converter, 9 ... signal insulation circuit, 10 ... computing circuit, 12 ... reference voltage source, R t _... RTD, R s _... reference resistor.

Claims (1)

[Claims] 1. A signal configured to amplify a plurality of analog measurement voltages V _i selectively taken into an amplifier via a multiplexer, add the analog measurement voltage V _i to an integrating A / D converter, and convert the analog measurement voltage into a digital signal. In the processing device, the voltage V _Z at the common potential point and the known reference voltage V _F corresponding to the full span of the A / D converter are measured for each measurement cycle with each measurement of the plurality of analog measurement voltages V _i being one measurement cycle. Is added to the amplifier via a multiplexer, the gain of the amplifier is set to the first gain G1, and V _Z and V _F are measured to obtain the measurement results V _Z (G1) and V _F (G1). with V _i is set to the second gain _G2, determined by measuring the V _Z results V _{i (G2),} obtains the V Z _(G2), based on these measurements and the known reference voltage V _{F, V i = [{V i (} G2) _{V Z (G2)} / {} V F (G1) -V Z (G1)}] signal processing device and performing an arithmetic operation represented by _{V F.}