JPH04274768A - Digital insulation resistance tester - Google Patents

Abstract

PURPOSE:To increase the resolution of digital display by having an arithmetic control unit which contains a driving unit driving a digital display unit on the basis of an integrated value in each of a plurality of conversion periods of an A/D converter and by providing a decimal point display element one digit higher for the display element of the uppermost digit of the display unit. CONSTITUTION:An output voltage of a DC-DC converter is divided by resistors 8 and 9 and fed back to an oscillator 5 and it is subjected to a pulse width control by a transistor 4 so that it will be a desired output voltage. A voltage at one end of a resistor Rx to be measured is divided by resistors 11 and 12 and given to an A/D converter 13. A current Ix flowing through the resistor Rx is converted into a voltage V by an I/V converter 14 and further into a positive potential by an inversion amplifier 15 and given to the A/D converter 13. As for the A/D converter 13, that of 4000 counts is used, for instance, and thereby display of which the resolution is increased by one digit can be attained. The A/D converter 13 outputs count data being proportional to a measured value of the resistance of the resistor Rx to be measured and a microprocessor 16 conducts an arithmetic processing for driving a display unit 17.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital insulation resistance meter.

0002

2. Description of the Related Art One type of insulation resistance meter is a digital insulation resistance meter that is configured to convert a resistance measurement value into a digital signal and display it digitally on a digital display. Further, in such a digital insulation resistance meter, a reference resistance value is set by an external setting operation, the magnitude of the resistance measurement value is compared, and the result is notified by a buzzer.

0003

[Problems to be Solved by the Invention] However, with the conventional configuration provided with only a digital display, it is less intuitive than an analog display type in which the pointer swings according to the magnitude of the resistance measurement value. It is not possible to grasp the magnitude of the resistance measurement value. Another problem with the digital display type is that it has an auto range and the displayed digits change automatically, so you have to wait until the displayed value has settled down before you can know the resistance measurement value, resulting in poor responsiveness. There is.

Furthermore, in the conventional digital display section, only decimal point display elements are provided up to the display element of the most significant digit. As a result, for example, the resistance measurement value in the first effective measurement range of 0.02MΩ to 10MΩ of 100V/20MΩ is “0.02MΩ” using the digital display unit displaying “1999”.
If you try to display "MΩ", the display will be "0.020", and if the display of the least significant digit changes by ±1, it will change by 5%, which will not meet the accuracy specified by JIS C 1302. Setting the display unit to ``kΩ'' will improve resolution, but it will require conversion with the specified value of ``MΩ'' and cannot be read directly.

Furthermore, since a thumb rotary switch or the like must be provided as means for setting a reference value for comparing resistance measurement values, there is a problem that the structure becomes complicated and it is difficult to achieve miniaturization.

The present invention solves the problems of the conventional digital insulation resistance meter, and its purpose is to provide an intuitive display similar to the analog display type in which the pointer swings according to the magnitude of the resistance measurement value. It is possible to grasp the magnitude of the resistance measurement value intuitively, improve the resolution of the digital display of the resistance measurement value,
The object of the present invention is to realize a digital insulation resistance meter that allows easy setting of a reference value for comparative measurement of measured resistance values.

[0007]

[Means for Solving the Problems] The present invention provides an A/D converter that converts a resistance measurement value into a digital signal, and a digital display that digitally displays the resistance measurement value based on the output data of the A/D converter. a bar graph display section that logarithmically displays a resistance measurement value based on the output data of the A/D converter; and a bar graph display section that drives the bar graph display section for each conversion cycle of the A/D converter; The present invention is characterized by comprising an arithmetic control section including a drive section that drives the digital display section based on the integrated value of the A/D converter for each of a plurality of predetermined conversion cycles. Further, the present invention is characterized in that the display element of the most significant digit of the digital display section is provided with a decimal point display element one digit higher. moreover,
The present invention is characterized in that the arithmetic control section is provided with a resistance value comparison section that takes in an arbitrary resistance measurement value as a reference value and compares the magnitude of subsequent resistance measurement values.

[0008]

[Operation] The A/D converter converts the resistance measurement value into a digital signal at relatively high speed, and the bar graph display section displays the value as a bar graph at each conversion cycle of the A/D converter. digitally displays the integrated value for each predetermined plurality of conversion cycles. As a result, the bar graph display section displays the magnitude of the resistance measurement value in the same way as a conventional needle type, allowing you to intuitively grasp the magnitude of the resistance measurement value, and the digital display section can be used as needed. The magnitude of the resistance measurement value is digitally displayed with high precision while also driving the decimal point display element one digit higher than the upper digit.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention. A DC power source 1 is connected to one end of the primary winding 3 of a transformer 2,
The other end of the next winding 3 is connected to a common potential point via a transistor 4. Oscillator 5 is connected to the base of transistor 4.
is connected. A voltage doubler rectifier circuit 7 is connected to the secondary winding 6 of the transformer 2 . A part of the output of the voltage doubler rectifier circuit 7 is applied to the oscillator 5 via a voltage divider circuit consisting of a series circuit of resistors 8 and 9, and a part is applied to the oscillator 5 via a protective resistor 10 to one end of the resistor to be measured RX. terminal T1 (EARTH
). A part of the output of the protective resistor 10 is connected to the resistor 11.
, and 12 in series to the VX terminal of the double integral type A/D converter 13. A terminal T2 (LINE) to which the other end of the resistance to be measured RX is connected is connected to the Vref terminal of the A/D converter 13 via a series circuit of an I/V converter 14 and an inverting amplifier 15. A/D converter 13 is connected to microprocessor 16 via a bus. This microprocessor 16 includes a display section 17 made of an LCD, a switch 18 that sets a comparator mode for comparing resistance measurement values, a buzzer 19 that is driven according to the comparison result, and an isolator 20 that exchanges signals with the outside. etc. are connected. In addition,
The microprocessor 16 has a built-in LCD driver.

FIG. 2 is an external view of such a device. 2
1 is a function changeover switch, which generates a voltage of 10
Switches between 00V/500V/250V, AC voltage measurement, power off, and continuity check. 22 is M
This switch 22 is a Ω (insulation resistance) measurement switch.
By turning on, the DC voltage set by the function changeover switch 21 is generated and the insulation resistance is measured. Note that this switch 22 is configured so that it can be fixed in a position perpendicular to a plane by pulling up and rotating the end portion, and by setting it in this state, continuous measurement can be performed. 23 is a data hold switch. By turning on this switch 23, the displayed value on the display section 17 is fixed, and by turning it on again, the fixed state of the displayed value is released. 24 is the display section 17
This is a switch that turns on and off the internal lighting. Note that the internal lighting is configured to be automatically turned off after a certain period of time (for example, 10 minutes) has elapsed after the lighting operation. The comparator mode switch 18 is set so that the switch 21 is set to M.
It is valid only when the Ω measurement mode is set and the switch 22 is turned on. Every time this switch 18 is turned on, the comparator mode changes from 0.1 MΩ to 0.
．． It cycles through each mode: 2MΩ→0.4MΩ→XMΩ→release. It is configured such that the comparator mode can be exited by continuing the on state for a certain period of time (for example, 1 second) in the middle of each mode. Arbitrary reference resistance value XM
Ω stores the displayed value at the time of switching from 0.4 MΩ to XMΩ, and this value is cleared when the power is turned off. In the comparator mode, when the measured resistance value is smaller than the set value, "LOW" is displayed on the display section 17 and the buzzer 19 sounds. 25 is a high voltage display alarm, which uses a light emitting diode, for example. While this light emitting diode 25 is lit, it indicates that a voltage is being output between the measurement terminals T1 and T2.

In such a configuration, a voltage dividing circuit consisting of a series circuit of a transformer 2, a transistor 4, an oscillator 5, a voltage doubler rectifier 7, and resistors 8 and 9 is a DC-DC converter that boosts and rectifies the output voltage of the DC power supply 1. It constitutes a DC converter. The output voltage of this DC-DC converter is resistor 8,
The voltage is divided by the series circuit 9 and fed back to the oscillator 5, and the pulse width is controlled by the transistor 4 so that the desired output voltage is obtained. The voltage at one end of the resistor to be measured RX is the resistor 11, 12
A/D converter 13 of double integral type is divided by a series circuit of
It is added as VX to . Current I flowing through the resistance to be measured RX
X is converted to a voltage V by the I/V converter 14, then converted to a positive potential by the inverting amplifier 15, and then sent to the A/D converter 13 as Vr.
Added as ef. As the A/D converter 13, for example, a 4000 count converter is used. Here, the resistance to be measured RX is determined by RX=VX/IX=(VX/Vref)C0NST. The A/D converter 13 outputs count data proportional to the resistance measurement value of the resistor RX to be measured to the microprocessor 16. The microprocessor 16 is connected to the display unit 1
Arithmetic processing for driving the display unit 17 is performed according to the configuration of No. 7.

FIG. 3 is a diagram showing an example of the display section 17. The digital display has a 4-digit segment display pattern D.
1 to D4 and four decimal point display patterns DP1 to DP4 for the digit one digit above each digit are used. In this case, if an A/D converter 13 with a 4000 count output is used, then the
It is possible to display up to "000" and increase the resolution by one digit without changing the unit. For example, when the measured resistance value is 0.02MΩ, the conventional display value is "0.020", but with the present invention, it is ".0200", which is 0.5%
resolution can be obtained. Further, this digital display section is configured to display "OL" when the measurement result exceeds the displayable value.

A function pattern FP is provided on the right side of the segment display pattern D1 for selectively lighting up and displaying an alarm state, a unit, etc. according to the measurement mode. On the left side of the decimal point display pattern DP4, a comparator mode display pattern CP is provided that selectively lights up and displays the magnitude of the reference resistance value in the comparison mode. Here, 0.1 MΩ, 0.2 MΩ, and 0.4 MΩ indicate fixed data, and XMΩ indicates an arbitrary resistance value.

[0014] As a bar graph display section, 0 to 2000
42 display patterns BG that can logarithmically display the A range of MΩ and the B range of 0 to 200 MΩ over 3 digits.
1 to BG42 are arranged in a row. A short-circuit display pattern SP is provided on the right side of the display pattern BG1, and an infinity display pattern IP that displays infinity is provided on the left side of the display pattern BG42. The short circuit display pattern SP is lit when the resistance measurement value is less than approximately 0.1 (.01) MΩ, and the infinity display pattern IP is lit when the resistance measurement value exceeds approximately 4000 (400) MΩ.

A high voltage display pattern HP that is lit and displayed in conjunction with the light emitting diode 25 is provided between the digital display section and the bar graph display section. A logarithmic scale display pattern LP is provided at the upper part of the bar graph display section along the arrangement direction of the display patterns BG1 to BG42. In the numerical display of this logarithmic scale display pattern LP, the digits are switched in conjunction with the switching of the range. At the top of the logarithmic scale display pattern LP, there is a "L" that lights up when the displayed value of the resistance measurement value is smaller than the reference resistance setting value of the comparator.
OW” display pattern P1, “SLEEP” display pattern P2 that foretells the low power consumption mode and flashes when the low power consumption mode is entered, and “DATA・H” display pattern P3 that lights up when the display value is held. , “R・H” display pattern P4 that lights up when the range is on hold, “E” that lights up when an external trigger is applied
XT・T" display pattern P5 and a display pattern P6 that lights up to prompt battery replacement are provided in a row.

FIG. 4 is an explanatory diagram of the allocation of the bar graph display section to each range. The microprocessor 16 has 42 display patterns BG1 forming a bar graph display section.
Weighting data of bar graph display positions assigned to each of BG42 is stored as table data.

FIG. 5 is an explanatory diagram of the operation sequence of the A/D converter 13. While exchanging data with the microprocessor 16, the A/D converter 13 switches between "auto zero" → "A/D mode communication" → "high-speed A/D (10 times integration)" → "high-precision A/D"D" loop operation is executed. Auto zero performs zero calibration. In A/D mode communication, conversion range data and the like are communicated. The high-speed A/D outputs display data for bar graph display. This high speed A/
At stage D, when the count data exceeds 400 and becomes an overload, the process passes and returns to auto-zero, generates conversion range data that increases the conversion range by one digit, and transmits it to the microprocessor 16 in the subsequent A/D mode communication. Then, generation of conversion range data and A/D conversion are repeatedly executed until the conversion data is determined, and the determined conversion data is outputted together with the conversion range data as display data for displaying a bar graph. As the final data of the high-speed A/D, nine sample data are successively output. On the other hand, high precision A/
At D, display data for digital display, which is obtained by integrating the conversion data determined by the high-speed A/D for 10 times, is output. These display sample rates are, for example, approximately 2 times per second (approximately 440 ms) for digital display, and approximately 20 times per second (approximately 40 ms) for bar graph display.

By the way, since the bar graph display section is composed of 42 display patterns BG1 to BG42 as described above, the high speed A/D outputs the upper 40 counts from the 400 count data. If this is expressed in hexadecimal, it becomes 0 to 28h. The microprocessor 16 is A
Display data for bar graph display is created by adding 30 h each time the display range increases by one digit as digit information for identifying the display range to the maximum 28 h of converted data added from the /D converter 13. For example, if the conversion data added from the A/D converter 13 is 05h, in the case of the A range in FIG. 4, the display data in the 4MΩ range will be 05h, and the bar graph display will display 0.5MΩ. , 40MΩ
The display data in the range becomes 35h and the bar graph display section shows 5MΩ, and the display data in the range of 400MΩ becomes 65h and the bargraph display section shows 50MΩ.
is displayed, and the display data in the range of 4000MΩ is 9
At 5h, the bar graph display section will display 500MΩ. Data for bar graph display like this is
It is created for comparison with the table data of the 42 display patterns BG1 to BG42 of the bar graph display section described above stored in the microprocessor 16.

FIG. 6 is a flowchart illustrating the flow of bar graph display processing in the A range of FIG. The microprocessor 16 takes in the two-digit hexadecimal conversion data of the high-speed A/D described above together with the conversion range data, and determines from the conversion range data whether the conversion data is included in the 4MΩ range (step 1). 4M
If the conversion data is included in the Ω range, the process jumps to step 7 for reading table data. If the converted data is not included in the 4MΩ range, 30h digit information is added to the converted data (step 2). Next, it is determined from the conversion range data whether the conversion data is included in the 40MΩ range (step 3). If the conversion data is included in the 40MΩ range, jump to step 7. If the converted data is not included in the 40 MΩ range, 30h digit information is further added to the converted data (step 4). Next, it is determined from the conversion range data whether the conversion data is included in the 400MΩ range (
Step 5). If the conversion data is included in the 400MΩ range, jump to step 7; if the conversion data is not included in the 400MΩ range, add digit information of 30h to the conversion data (step 6), then proceed to step 7. do. After reading the table data in step 7, predetermined digit information is added to the comparison value corresponding to the bar data in FIG. The bar graph display data consisting of the converted data is compared (step 8). Then, it is determined whether or not the comparison result is negative (step 9). If the comparison result is negative, the display element is turned on (step 10), and if the comparison result is not negative, the display element is turned off (step 11). Such comparison processing is executed for all display elements BG1 to BG42 for each display data (step 12).

[0020] With this configuration, the display elements of the bar graph display section are illuminated starting from the infinity position on the left side and moving toward the zero position on the right side, similar to the conventional pointer indication. An analog display can be obtained. In addition,
The lighting display form of the bar graph can also be displayed in reverse.

[0021]

[Effects of the Invention] As explained above, according to the present invention,
The size of the resistance measurement value can be grasped intuitively, similar to the analog display type in which the pointer swings according to the size of the resistance measurement value.
It is possible to realize a digital insulation resistance meter in which the resolution of digital display of resistance measurement values can be increased and a reference value for comparison measurement of resistance measurement values can be easily set.

[Brief explanation of the drawing]

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

FIG. 2 is an external view of the device in FIG. 1;

FIG. 3 is an explanatory diagram of a pattern of the display section in FIG. 2;

4 is an explanatory diagram of the allocation of the bar graph display section of FIG. 3 to each range; FIG.

5 is an explanatory diagram of the operation sequence of the A/D converter 13 in FIG. 1. FIG.

FIG. 6 is a flowchart illustrating the flow of operation of bar graph display processing in the A range of FIG. 4;

[Explanation of symbols]

13 Double integral A/D converter 16 Microprocessor (arithmetic control unit) 17
Display section

Claims (3)

[Claims] 1. An A/D converter that converts a resistance measurement value into a digital signal, and a digital display section that digitally displays the resistance measurement value based on output data of the A/D converter.
a bar graph display section that displays a resistance measurement value logarithmically based on output data of the A/D converter; and a digital display section that drives the bar graph display section for each conversion period of the A/D converter; A digital insulation resistance meter comprising: an arithmetic control section including a drive section that drives the A/D converter based on integrated values of the A/D converter for each of a plurality of predetermined conversion cycles. 2. The digital insulation resistance meter according to claim 1, wherein the display element of the most significant digit of the digital display section is provided with a decimal point display element one digit higher. 3. The digital insulation according to claim 1, wherein the arithmetic control section is provided with a resistance value comparison section that takes in an arbitrary resistance measurement value as a reference value and compares the magnitude of subsequent resistance measurement values. Resistance meter.