JPH0422307Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field] This invention is incorporated into a clamp tester that mainly measures current and voltage in power supply circuits such as power lines, and is used to check the continuity of electrical circuits of equipment and equipment. The present invention relates to continuity check circuits used in

[Technical background] If equipment connected to a power supply circuit malfunctions or stops working, measure the current, voltage, etc. of the power supply circuit using a clamp tester, etc., and check the results. If it is determined that the power supply circuit is normal, the cause of the failure will be investigated for the failed device. However, depending on the type of equipment and the state of installation at the site, it may not be possible to conduct an investigation easily, and the user is not always equipped with various measuring instruments. In such cases, a so-called continuity check is carried out to check for disconnections, poor connections, etc., in electrical circuits located at the installed power supply input section or other locations that can be touched from the outside. This investigation is relatively simple and has become one of the most effective means of discovering the cause of failures. Therefore, general users have desired a continuity check tester that is easy to handle.

[Purpose of the invention] This invention was made in response to the above-mentioned user requests.The purpose was to incorporate a continuity check circuit controlled by a microcomputer into the clamp tester body, and to use this circuit. The object of the present invention is to realize a continuity check circuit for a clamp tester that can be used in common for measuring other electrical quantities such as current and voltage.

[Example] This invention will be described in detail below with reference to an example shown in the accompanying drawings.

FIG. 1 shows a clamp tester to which this invention is applied. Referring to the figure, two test leads 2 and 3 are attached to a main body 1 of the clamp tester so that they can be inserted and removed using banana plugs (not shown) or the like.

Set the function switch 4 to the "continuity check" position, for example, and connect the test leads 2 and 3.
When the conductors 5 and 6 at the tips of the test leads 2 and 3 are applied to a circuit to be checked (not shown), a voltage is applied from the main body 1 to the circuit to be checked via the test leads 2 and 3. When the circuit to be checked is in a conductive state, a constant current is caused to flow, and due to the resistance of the circuit to be checked and this constant current, a relatively low level voltage is generated between the conductor portions 5 and 6 of the test leads 2 and 3. Occur. If the circuit to be checked is disconnected, a relatively high level voltage applied from the main body 1 will appear between the conductor portions 5 and 6. These voltages are detected within the main unit 1, and for high level voltages the indicator 7 will display a ``1'' which promises to mean, for example, a break in the circuit, and for low level voltages the conductor will be disconnected. The ``0'' that was promised to indicate the status is now displayed. Furthermore, a small buzzer or the like may be incorporated to emit a sound when in a conductive state.

In addition, when measuring the current of the power supply circuit, etc., after setting the function switch 4 to a predetermined position, push the knob 8 and switch the clamp cores 9, 1.
0 is opened and the wire to be measured is wrapped around it in the same way as a normal clamp tester, and the value on the display 7 is read.

FIG. 2 shows an embodiment of this continuity check circuit. For example, a resistance/voltage conversion signal is emitted from the signal source 15, and the function switch 4
This resistance/voltage conversion signal is input to the comparator 16 via the conductor portions 5 and 6 of the test leads 2 and 3 in FIG.
This refers to the voltage that appears between

When the function switch 4 is set to the continuity check position, for example, a control signal for forming a reference voltage is sent from the function switch 4 to the microcomputer 17. In the microcomputer 17, a continuity check program is started by this control signal.
A reference voltage signal having a preset digital value is sent to the D/A converter 18. In the D/A converter 18, this digital value reference voltage signal is converted into an analog voltage signal, and the analog voltage signal is sent from the D/A converter 18 to the comparator 16. In the comparator 16, a level comparison is made between this reference voltage signal and the resistance/voltage conversion signal, and if the level of the resistance/voltage conversion signal is higher than the level of the reference voltage signal, the level "1" is output from the microcomparator 17. ” is sent to the display 7. As a result, "1", which means, for example, a disconnection in the circuit under test, is displayed in each digit on the display 7, as described above. Furthermore, if the level of the resistance/voltage conversion signal is lower than the level of the reference voltage signal, the microcomputer 17 outputs a voltage signal of level "0", and each digit of the display 7 indicates that the circuit under test is in a conductive state. For example, "0" is displayed, which means that there is a certain value.

In this case, conventionally there are a low resistance continuity test that is applied to circuits with a relatively small resistance value in the conductive state, and a high resistance continuity test that is applied to circuits that have a relatively large resistance value, but the low resistance continuity test For example, if a circuit element containing some resistance is present in the circuit under test, it is often easy to determine that there is a conduction failure. Furthermore, although there is no erroneous judgment as described above in the high resistance continuity test, a good judgment may be made even if, for example, a part of the circuit is only disconnected or there is a poor contact. In this continuity check circuit, the value of the digital signal applied from the microcomputer 17 to the D/A converter 18 can be set in multiple stages as necessary. Therefore, the level of the reference voltage output from the D/A converter 18 is also variable, and the comparator 16 can check in detail whether the conduction state of the circuit under test is good or not. In this case, the microcomputer 17
reads the full scale value of the ohm range used for resistance measurement, such as 1 ohm, 10 ohm, etc., or their half value, and converts it to the D/A converter 18.
It is also possible to output it to the threshold value of the comparator 16. FIG. 3 shows an example of a flowchart when the operation of this continuity check circuit is controlled by the microcomputer 17 as described above.

Note that when the electrical quantity to be measured is different from the continuity check, such as in current measurement, the signal to be measured is input from the signal source 20. This signal source 20 corresponds to the current or voltage induced in the clamp cores 9 and 10 when viewed from FIG. 1 above. The function switch 4 is set at a predetermined position different from that for the continuity check, for example at a position labeled "current". As a result, the microcomputer 17 starts operating according to the current measurement program. In this case, from the microcomputer 17, for example,
The digital signal at the level corresponding to MSB is
The signal is sent to the A converter 18. This digital signal is converted into an analog value by the D/A converter 18 and applied to the comparator 16 as a reference voltage. The current signal to be measured is converted into a voltage signal via an input circuit (not shown) built into the function switch 4, for example, and then sent to the comparator 16. This signal voltage and the reference voltage are compared, and depending on whether the output of the comparator 16 is 1 or 0, the microcomputer 17 generates a digital signal that decreases in the LSB direction. This signal is converted into a reference voltage in the D/A converter as described above, and compared with the signal under measurement by the comparator 16. In this way, the signals are sequentially compared up to the LSB, and as a result, the signal under test is converted into a digital value and displayed on the display 7. As mentioned above, this continuity check circuit can also be used for other electrical measurements such as current measurements.

[Effect] As explained above, in the clamp tester, this continuity check circuit is connected to the comparator 16.
It is equipped with a microcomputer 17, a D/A converter 18, etc., and receives a voltage signal proportional to the magnitude of the resistance component of the circuit to be checked, such as a power supply circuit, and this voltage signal is set in advance in the comparator 16. After being compared with a reference voltage, it is possible to determine whether the circuit to be checked is conductive or non-conductive based on the level difference between the comparison outputs.
In other words, if the output of the comparator 16 is "0"
If the input signal voltage is at a level lower than the reference voltage, the circuit to be checked is in a conductive state, and if the output of the comparator 16 is, for example, at a "1" level, the input signal voltage is at a higher level than the reference voltage, so it is in a disconnected state. . By displaying the output level "0" or "1" of the comparator 16 on the display 7, the conduction or non-conduction state of the circuit to be checked can be easily determined.

Further, the reference voltage of the comparator 16 is formed by converting the digital value signal voltage emitted from the microcomputer 17 into an analog value by the D/A converter 18, but the level of this reference voltage is not necessary. Since the switching operation of the switching device 4 can be changed in multiple stages, it is possible to almost prevent erroneous determination as to whether the conduction state is good or bad. This continuity check circuit can be used in common for many types of electrical quality measurements by selecting the appropriate program depending on the object to be measured, and can greatly contribute to the miniaturization and multifunctionality of clamp testers. .

[Brief explanation of the drawing]

All attached drawings relate to embodiments of this invention.
Figure 1 is a schematic plan view of a clamp tester to which this invention is applied, Figure 2 is a block diagram of its continuity check circuit, and Figure 3 is a flowchart when the operation of the continuity check circuit is controlled by a microcomputer. be. In the figure, 1 is the clamp tester main body, 4 is a function switch, 7 is a display, 15 is a signal source, 16
is a comparator, 17 is a microcomputer,
18 is a D/A converter.

Claims (1)

[Scope of Claim for Utility Model Registration] A switch for selecting the electrical quantity to be measured in the continuity check circuit of the clamp tester, which is built into the clamp tester body so that it can be used in common with the measurement of other electrical quantities such as current and voltage. a comparator that receives a voltage signal substantially proportional to the resistance of the circuit under test through a device, compares the voltage signal with a reference voltage of a predetermined level, and outputs an L level or H level signal; a D/A converter that forms a reference voltage at a predetermined level and outputs it to the comparator; and a digital signal corresponding to the reference voltage at the predetermined level in connection with the selection operation of the switch to the D/A converter. A clamp tester further comprising: a microcomputer that sends out an identification signal indicating whether the circuit under test is conductive or non-conductive in accordance with the level or H level signal output from the comparator. Continuity check circuit.