JP3129005B2 - Signal converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in industrial process signal processing, etc., and measures the resistance value of a resistance sensor such as a resistance temperature detector, and measures the resistance value as a physical quantity (temperature, etc.) to be measured.
And a signal converter that converts the signal into a normalized signal (1 to 5 V or the like) corresponding to and outputs the signal. In the drawings, the same reference numerals indicate the same or corresponding parts.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing an example of the configuration of a conventional signal converter having a resistance input. FIG. 3 is an explanatory diagram of a signal calculation procedure realized by software in the CPU 1 of FIG. First, in the circuit of Figure 2, reference voltage E _R and the resistor R, R ', a bridge circuit comprised of resistor sensor R _MSR, the resistance value of the resistance sensor R _MSR is converted into a voltage. That is, the switch SW1 (SW1-1, SW1-2, S
W1-3) is adapted to be controlled by the CPU 1, was charged in this SW1-3,1-2,1-1 sequential time division, two voltage signals obtained by the bridge circuit, i.e. the terminal I _- , I _O (I _{O, A / D} described later)
, And a voltage (I _{+, A / D} described later) between the connection point of the terminal I− and the resistors R and R ′ is measured via the A / D conversion circuit 2.

[0003] A / D conversion circuit 2 A _MP1 constituting the amplifies the voltage signal is switched by the switch SW1 in the operational amplifier, also of the next stage which constitute the A / D converter circuit 2 A / D
Give to the converter. This A / D converter is an example of an integral type, and a switch SW2 (SW
2-1, SW2-2, signal switch and the resistor R ₁ of SW2-3), a capacitor C and an operational amplifier A _MP2 · A _MP3.

The switch SW2 is first controlled by the CPU1.
Switch SW2-1 is connected, through a resistor R _2, and discharges the charges accumulated in the integrating capacitor C. Next, CP
Only SW2-2 is connected by U1, and amplifier A _MP1
Is applied the output voltage to the resistor R _1, a current the resistor R ₁ is stored in the capacitor C by the amplifier A _MP2. The connection of the switches SW2-2 by performing a predetermined time, the input signal of the integration amplifier, i.e. voltage corresponding to the input or output voltage of the amplifier A _MP1 is charged in the capacitor C. Then by turning on only the switch SW2-3 by CPU 1, the reference voltage -E _r, stored electric charge in the capacitor C is discharged at a constant gradient. Operational amplifier A
_MP3 is a comparator that compares the voltage of the capacitor C with 0V.
The CPU 1 monitors the output of the comparator A _MP3 , measures the time until the voltage of the capacitor C becomes 0 after the switch SW2-3 is turned on, and takes the value of the input signal as time data (digital signal). Put in. The above operation is performed by the switch SW1
Control in combination with
A / D-converts two voltage signals.

Next, FIG. 3 shows a signal realized by software.
This is the procedure for calculating the number. I_{O, A / D}・ I _{+, A / D}Described in Figure 2
This is the result of A / D conversion of the two voltage signals.
First, A / D conversion values of two reference input values prepared in advance and
Compared and scaled. This scale conversion is
The A / D conversion value can be used in conjunction with the next-
This is done to convert to a logical amount.

[0006]

However, in the above measurement by the bridge circuit, if the resistance value of the wiring connecting the resistance sensor _RMSR and the signal converter becomes large, the influence cannot be ignored. In addition, in order to form a bridge circuit accurately, the two resistors R must be balanced, which greatly imposes restrictions on manufacturing.

Therefore, an object of the present invention is to provide a signal converter which can solve such a problem.

[0008]

In order to solve the above-mentioned problems, a signal converter according to the present invention comprises an A / D converter (A / D converter).
And D such as converter 2), the A / D converter (having the A / D conversion output data read writing CPU the (1, etc.) and with the via) control such as a switch SW2, resistor sensor (R _MSR such as A) a signal converter for measuring the resistance value and obtaining the temperature and the like, wherein one terminal of each of first and second wirings is connected to one terminal of the resistance sensor;
The first wiring and the resistance equal to the one terminal of the third wiring with (wiring resistance r or the like) connected to the other terminal of the resistance sensor, a predetermined DC voltage (DC voltage source E _R, etc.) The first and the third through a predetermined series resistance (R, etc.)
In the signal converter applied between the other terminals (terminals I _O , I _−, etc.) of the first wiring, the voltage (V _O) between the other terminals of the first and third wirings is controlled by the CPU. Etc., hereinafter referred to as a first measurement voltage).
Means for switching and inputting to the conversion means (switches SW1-1, SW1-1)
SW1-3, etc.) and a voltage between the other terminals of the second and third wirings (such as V ₊ , hereinafter referred to as a second measured voltage) controlled by the CPU.
Means for switching and inputting to the conversion means (switches SW1-2, SW1-2)
SW1-3, etc.), and the CPU is configured to convert the output data of the first and second measured voltages by the A / D converter and a predetermined operation parameter (3 ) To calculate and output the resistance value of only the resistance sensor.

According to a second aspect of the present invention, in the signal converter according to the first aspect, the operation parameters are such that the resistance values of the first and third wirings can be ignored. The first or second measurement voltage (V _{O, F} , V _{O, B,} etc.) when the sensor is replaced by two resistors (R _{MSR, F} , R _{MSR, B,} etc.) having known different values, respectively.
Is determined using the A / D conversion output data.

[0010]

A current is supplied from the reference voltage source E _R to the resistance sensor _RMSR including the wiring via a predetermined series resistance R, and the resistance sensor _RMSR and two wirings (wiring resistance 2r) connected to both ends thereof are connected. the voltage drop V _O of the resistive sensor R _MSR
And A / D conversion data of a voltage drop V ₊ for one wire (wiring resistance r) connected to one end thereof, and in a prior adjustment, the wiring resistance is removed, and a known resistance replacing the resistance sensor is replaced. The CPU then causes the CPU to calculate and output an accurate resistance value that does not include the wiring resistance of the resistance sensor, from the calculation parameters obtained and held from the measured data of the voltage drop.

[0011]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. Compared with the conventional circuit example shown in FIG.
One voltage source E _R , one resistor R, and a resistance sensor R
Consists of _MSR . The circuit configuration other than the above is shown in FIG.
Is equivalent to the circuit example of FIG. Resistive sensor R _MSR is three with each internal resistance r (2 present on the upper side of the sensor in this example, one on the lower end side) terminal I _O of the signal converter via the wire, I _+, I _- It is connected to the. In the present invention, the switch SW1 (SW1-1, SW1-2, SW1-
By the switching of 3), the terminal I _- voltage at the terminal I _O for V _O and also terminals I _- for terminals I ₊ voltage V ₊
Is applied to the A / D conversion circuit 2 and measured. The input voltages V _O and V ₊ are expressed by the following equations (1) and (2).

[Equation 1] V _O = (2r + R _MSR ) × E _R / (R + 2r + R _MSR ) (1) V ₊ = (r + R _MSR ) × E _R / (R + 2r + R _MSR ) ... (2) Here, r is a resistance of one wire connecting the resistance sensor _RMSR and the signal converter as described above. Then (1)
Eliminating r by equation (2) yields equation (3).

[Equation 2] R _MSR = [V ₊ -(V _O -V ₊ )] × R / (E _R -V _O ) (3) Equation (3) is a voltage source E _R If the value of the resistance R can be determined quantitatively in advance, it is possible to determine R _MSR . Therefore, in order to obtain the values of E _R and R, at the wiring resistance r = 0, R _MSR is replaced with two known fixed values R _{MSR, F} and R _{MSR, B} and each input voltage V
Obtain _{O, F} and V _{O, B.} Then, the following equation is obtained from the equation (3).

[Equation 3] R _{MSR, F} = [V _{O, F} × R / (E _R −V _{O, F} )... (4-1) R _{MSR, B} = [V _{O, B × R / (E} R -V O, B) ........................... (4-2) where the subscript F and B R _MSR and V _O is the full-scale range and the base scale range Represents

From the two equations (4-1) and (4-2),
When the values of the voltage source E _R and the resistance R are obtained, the following expression is obtained. [Equation 4] R = K × R _{MSR, F} (5) E _R = (1 + K) × V _{O, F} (6) where K = (V _{O, F} − V _{O, B} ) / [(R _{MSR, F} × V _{O, B} / R _{MSR, B} ) −V _{O, F} ] (7) Therefore, (5) to (7) are introduced into the equation (3). Thus, the following equation (8) is obtained.

[Equation 5] R_MSR= [V₊− (V_O-V₊)] × R_{MSR, F} / [V_{O, F}+ (V_{O, F}-V_O) / K] (8) In this way, the wiring resistance is determined as described above in the pre-adjustment stage.
The resistance value of the resistance sensor is fixed at r = 0._{MSR, F}And R
_{MSR, B}To the input voltage V to the signal converter at this time.
_{O, F}And V_{O, B}And calculate K (Equation (7)),
This R_{MSR, F}, V _{O, F}, K in the memory of the CPU 1.
At the time of actual temperature measurement
Input voltage V_OAnd V₊Executes equation (8) for CPU1 from
Sensor resistance accurately without the influence of wiring resistance.
Resistance value R_MSRCan be measured.

[0017]

According to the present invention, a current is supplied to the resistance sensor from a predetermined voltage source through a predetermined series resistor, and
The voltage V _O including the wiring resistance of the current sensor and the voltage V ₊ including the wiring resistance of one of the resistance sensors are also used. Since the resistance value that does not include the wiring resistance is calculated and output, there is obtained an advantage that accurate measurement can be performed and a low-cost signal converter can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration as one embodiment of the present invention.

FIG. 2 is a conventional circuit diagram corresponding to FIG.

FIG. 3 is an explanatory diagram of a calculation procedure in FIG. 2;

[Explanation of symbols]

1 CPU 2 A / D conversion circuit 3 Operation parameter R _MSR resistance sensor R Fixed resistance R ₁ Fixed resistance R ₂ Fixed resistance C Capacitor SW1 (SW1-1 to SW1-3) Switch SW2 (SW2-1 to SW2-3) Switch A _MP1 operational amplifier A _MP2 operational amplifier A _MP3 operational amplifier E _R DC voltage source

Claims (2)

(57) [Claims] An A / D converter and a CP for controlling the A / D converter and reading the A / D conversion output data.
U and a signal converter for measuring the resistance value of the resistance sensor and obtaining its temperature and the like, wherein one terminal of each of the first and second wirings is connected to one terminal of the resistance sensor. One end of a third wiring having a resistance value equal to that of the first wiring is connected to the other terminal of the resistance sensor, and a predetermined DC voltage is applied to the first and third terminals via a predetermined series resistance. A signal converter applied between the other terminals of the first wiring and a voltage between the other terminals of the first and third wirings (hereinafter referred to as a first measured voltage)
Means for switching and inputting to the A / D conversion means, and a voltage between the other terminals of the second and third wirings (hereinafter referred to as a second measured voltage) which is also controlled by the CPU. Means for switching and inputting to the conversion means, wherein the CPU outputs the A / A of the first and second measured voltages.
A signal converter for calculating and outputting a resistance value of only the resistance sensor using conversion output data by a D conversion unit and a predetermined calculation parameter held based on a measurement performed in advance. 2. The signal converter according to claim 1, wherein the operation parameters are such that the resistance values of the first and third wirings can be ignored, and the resistance sensor has a known different value. The first when each of the resistors
Alternatively, the signal converter is determined using the A / D conversion output data of the second measurement voltage.