JP3106459B2 - Electricity generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric quantity generator capable of generating electric quantities such as voltage, current, and equivalent resistance at arbitrary values.

[0002]

2. Description of the Related Art The values of voltage and current are measured by a digital voltmeter or the like, and the output of a resistance thermometer or the output of a thermocouple is measured by a thermometer. A generator that generates voltage and current is used. On the other hand, the resistance values of resistors and resistance temperature detectors are measured with a digital multimeter or various thermometers, recorders, and transducers that use resistance temperature sensors as sensors. , Or a standard resistor of a known value, or a solid-state standard resistor such as a decade switching resistor. However, calibration with solid resistors is possible for certain points (values),
Calibration at any point requires a large standard resistor, such as a contact-switching decade dial resistor.

In recent years, a resistance generator for generating a virtual resistance equivalently using electronic means has been used in place of the above-mentioned solid standard resistor for calibrating the resistance meter. . For the measurement of the resistance, a constant current source for generating a current I for resistance measurement is usually provided inside the measuring instrument, and the measured current I flows through the resistance R to be measured, and a voltage drop V ( = I * R) to obtain the measured resistance R
Is obtained. Therefore, in order to electronically generate a virtual resistance, the measured current I is known and the desired resistance value R
It is sufficient to generate a terminal voltage V corresponding to
Thereby, a virtual equivalent resistance Req (= V / I) can be generated between the terminals. If the ohmmeter is calibrated using such an equivalent resistance Req, calibration at an arbitrary point becomes possible, and there is a feature that the calibration can be performed with much higher precision than when using a solid-state resistor.

By the way, a standard voltage and current for calibrating a measuring instrument for measuring voltage and current, and an equivalent resistance obtained by the above-mentioned electronic means in place of a solid resistor for calibrating an ohmmeter are used. Can be generated by one calibrator, which is extremely convenient for calibration.

[0005]

SUMMARY OF THE INVENTION The present invention provides a standard voltage / current generator for calibrating a measuring instrument for measuring a voltage, a current, a resistance temperature detector or a thermocouple output, and a method for calibrating an ohmmeter. It is an object of the present invention to realize a device that can generate the above-mentioned various amounts of electricity by using a device for generating the equivalent resistance of the same by integrating the main constituent elements into one and integrating them. . Hereinafter, the present invention will be described with reference to the drawings.

[0006]

In order to achieve the above object, the present invention provides a D / A comprising a time-division multiplication potentiometer for multiplying a pulse width corresponding to a set value by an input voltage.
From the converter and the D / A converter, the voltage, current or
Take the voltage when it is assumed that there is a resistor between the terminals.
Voltage or current between the output terminal
Sometimes, it is assumed that a resistor exists between the reference voltage source for applying an output to the D / A converter as an input voltage and the output terminal.
When a voltage generator when the virtual, and a current-voltage conversion circuit applied its output converts a current that flows from the output terminal to the voltage as an input voltage to the D / A converter.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an embodiment of an electric quantity generator according to the present invention. In the figure, 1
0 is a reference power supply for generating a reference voltage Vs, 20 is a voltage /
The output terminal of the reference power supply 10 is connected to the contact 21 by a changeover switch having a current generating contact 21 and an equivalent resistance generating contact 22. Reference numeral 30 denotes a known digital-to-analog converter (D / A converter) composed of a time-division multiplication potentiometer having a filter on the output side inside. As shown in FIG. 2, this D / A converter has a pulse width t1 having a constant period to and a variable pulse width t1, that is, a variable duty ratio, as shown in FIG. , A signal corresponding to the product of the input voltage corresponding to the peak value is generated, the signal is smoothed by an internal filter, and the average value is taken out from the D / A converter. In the embodiment, the pulse width of the set value D is controlled by a microprocessor (not shown), but may be set manually.

Reference numeral 40 is an output circuit, and reference numerals 51 and 52 are output terminals for extracting the generated voltage, current and resistance. The output circuit 40 comprises an operational amplifier 41, a gain switching circuit 42 for switching the gain when a voltage and a resistance are generated, and a switching contact 43 for switching the generation of a voltage, a resistance and a current. The gain switching circuit 42 includes resistors 42a and 42b; Switching contact 42c,
42d. The resistors 42a and 42b are connected to the amplifier 4
The switching contact 42c is connected to the resistor 42a, and the switching contact 42d is connected to the connection point between the resistors 42a and 42b. The other side of the switching contacts 42c and 42d is connected to the + input terminal of the amplifier 41 together with the other side of the switching contact 43. The output circuit 40 having such a configuration is connected between the output terminal of the D / A converter 30 and the output terminal 51.

Reference numeral 60 denotes an output switching circuit, which has switching contacts 61 to 63 for switching the generation of voltage, current, and equivalent resistance, respectively.
And a resistor 64 connected to the switching contact 62. The switching contact 63 is connected in series to a line connecting the output terminal 52 and the input terminal of the current / voltage conversion circuit 70, the switching contact 61 is directly connected between the output terminal 52 and the common COM, and the switching contact 62 is connected to a resistor 64. Is connected between the output terminal 52 and the common COM. The connection point between the switching contact 62 and the resistor 64 is connected to the switching contact 4 in the output circuit 40.
3 is connected to the other side.

Reference numeral 70 denotes a current / voltage conversion circuit. This conversion circuit comprises an operational amplifier 71 and a resistor 72 connected to its feedback circuit.
The output terminal is connected to an equivalent resistance generating terminal 22 of the changeover switch 20. Next, the operation of the device of the present invention having such a configuration will be described for voltage generation, current generation, and generation of virtual resistance.

(A) Voltage generation In this case, the changeover switch 20 is connected to the contact 21. The switching contact 42c or 42d is turned on, and 43 is turned off. or,
The contact 61 is turned on, and the contacts 62 and 63 are turned off. By turning on and off the switches and the contacts in this manner, the output voltage Vs of the reference power supply 10 is applied to the D / A converter 30 via the contacts 21 of the switch 20. In the D / A converter 30, as the set value D in FIG.
As shown in the figure, a pulse width signal having a variable duty ratio (t1 / to) is given, and the pulse width signal is multiplied by the input reference voltage Vs. The result of the multiplication is averaged by an internal filter, and an output V2 represented by the following equation (1) is taken out from the D / A converter 30.

V2 = (t1 / to) · Vs (1) The voltage V2 is applied to the amplifier 41 constituting the output circuit 40. The output of the amplifier 41 is fed back to the amplifier 41 directly or by dividing the voltage depending on the connection state of the switching contact 42c or 42d of the gain switching circuit 42. as a result,
The amplifier 41 outputs a stable voltage according to the gain, and this output is taken out from the terminals 51 and 52 as an output voltage Vo. The output voltage Vo is represented by the following equation (2).

Vo = Vs · k1 · k2 (2) Here, k1 = V2 / Vs = t1 / to k2 = gain of output circuit 40 The output voltage Vo expressed by the equation (2) is a D / A converter. By changing k1 with the set value D of 30, the value can be changed arbitrarily. Therefore, the output terminals 51, 52
By connecting a voltmeter or the like to be calibrated, the voltmeter can be calibrated in the same manner as the calibration using a conventional standard voltage / current generator.

(B) Current generation. In this case, the changeover switch 20 is connected to the contact 21 as in the case of the voltage generation. The switching contacts 42c and 42d are turned off and 43 is turned on. Further, the contacts 61 and 63 are turned off and the contact 62 is turned on. An ammeter to be calibrated is connected between the terminals 51 and 52.

In this way, the changeover switch and the contact are turned on.
By turning off, the reference power supply 10
The output voltage Vs is output by the D / A converter 30 as a voltage V2 represented by the equation (1) that is varied according to the set value D. This voltage V2 is supplied to the output terminal 5 via the output circuit 40.
1 and 52 are supplied to the ammeter to be calibrated. Assuming that the current passed through the ammeter is Io, this Io flows through the resistor 64 from the terminal 52 through the contact 62. Current Io
The voltage generated in the resistor 64 (the resistance value of which is Rs) is fed back to the amplifier 41 in the output circuit 40 and controlled. This current Io is represented by the following equation (3).

Io = Vs · k1 / Rs (3) The output current Io expressed by the equation (3) is obtained by changing k1 with the set value D of the D / A converter 30 in the same manner as the voltage generation. Can be changed arbitrarily. Therefore, the ammeter to be calibrated connected to the output terminals 51 and 52 can be calibrated in the same manner as calibrated using the conventional standard voltage / current generator.

(C) Resistance generation. In this case, the changeover switch 20 is connected to the terminal 22. The switching contact 42c or 42d is turned on, and 43 is turned off. or,
The contacts 61 and 62 are turned off, and the contact 63 is turned on. A resistance meter for calibration is connected to the output terminals 51 and 52.
Note that the voltage generated between the output terminals 51 and 52 is V.

The resistance meter to be calibrated has a current source for measurement therein. IS indicates the current source. Connect the resistance meter to be calibrated to the output terminals 51 and 5 as described above.
2, the current Im obtained by the internal current source IS flows from the output terminal 52 into the device. The current Im flowing into the device is supplied to the current / voltage conversion circuit 70 via the switching contact 63. The current / voltage conversion circuit 70 is an operational amplifier 71 having a resistor 72 in a feedback circuit.
As is well known, the current Im is supplied to the feedback resistor 72.
(The resistance value is represented by r), the voltage is converted into a voltage Vm (= Im · r) corresponding to the current. Converted voltage V
m is applied as an input to the D / A converter 30 via the contact 22 of the changeover switch 20.

In the D / A converter 30, the input voltage V
m is multiplied by a pulse width signal corresponding to the set value D having a variable duty ratio as described above. The result of the multiplication is averaged by an internal filter, and is applied to the output circuit 40. Here, the conversion coefficient of the D / A converter 30 (V2 /
Vm) is k1, and the gain (Vo / V
2) is set to k2. Since the potential of the output terminal 52 is equivalently zero potential, the voltage V between the output terminals 51 and 52 is V = V
It becomes o. Therefore, V is as follows: V = Vo = Vm · k1 · k2 (4) Since Vm is Im · r, V in equation (4) is V = Im · r · k1 · k2 (5) Therefore, if the resistance when the device side is viewed from the output terminals 51 and 52 is Req, Req = V / Im = r · k1 · k2 (6) In the equation (5), k1 corresponds to the set value D of the D / A converter 30. Therefore, k1
, A desired equivalent resistance Req can be generated between the output terminals 51 and 52. This allows
The resistance meter connected to the output terminals 51 and 52 can be calibrated.

In the embodiment described above, D / A
Although the case where the filter is provided inside the converter 30 has been described, the filter may be provided outside the D / A converter 30.

In the present invention, a time-division multiplication type potentiometer is used as the D / A converter 30 in the case of a resistance generating function because the voltage Vm input to the D / A converter is used.
Varies according to the measurement current Im and is not constant. k1 =
When digitally controlling V2 / Vm, a ladder-type D / A converter is generally considered, but the time-division method based on pulse width control is more excellent even if the voltage input thereto changes. This is because linearity is obtained.

[0022]

As described above, according to the present invention, a standard voltage and a current for calibrating a measuring instrument for measuring a voltage, a current, a temperature measuring resistor or a thermocouple output, and the like, and an ohmmeter are used. The main components constituting the device for generating an equivalent resistance for calibration are shared and integrated, thereby realizing a small and inexpensive device for generating the above-mentioned various amounts of electricity.

Therefore, the electric quantity generator according to the present invention is very suitable for use as a calibration device for calibrating a measuring instrument and a resistance meter.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the device of the present invention.

FIG. 2 is a diagram for explaining the operation of the device of FIG. 1;

[Explanation of symbols]

 Reference Signs List 10 Reference power supply 20 Changeover switch 30 D / A converter 40 Output circuit 51, 52 Output terminal 60 Output switching circuit 70 Current / voltage conversion circuit

Claims (1)

(57) [Claims] 1. A D / D converter comprising a time-division multiplication potentiometer for multiplying a pulse width corresponding to a set value by an input voltage.
A voltage between the A converter and this D / A converter
Output terminal that extracts the voltage when it is assumed that a resistance exists
When a voltage or current is generated, the D / A
A reference voltage source to apply the output as the input voltage to the converter, between the output terminals, conductive when the virtual and the resistor are present
An electric quantity generating device comprising a current / voltage conversion circuit which converts a current flowing from the output terminal into a voltage when a pressure is generated, and outputs the voltage as an input voltage to the D / A converter.