JP3073806B2 - Digital Multimeters - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital multimeter, and more particularly, to a digital multimeter having an erroneous operation prevention function.

[0002]

2. Description of the Related Art Generally, a digital multimeter is provided with a function changeover switch composed of a rotary switch or the like. By switching the switch, a digital multimeter can perform AC and DC current and voltage measurement as well as resistance measurement and frequency measurement. The measured value is displayed on a digital display (liquid crystal display panel).

In an actual operation, one of a pair of test leads is inserted into one of a current input terminal and a voltage input terminal, and the other test lead is connected to a common terminal. Therefore, care must be taken when connecting the test leads to the current input terminals.

[0004]

For this reason, in the prior art, when the function switch is set to a range other than the current measurement range, when the test lead is inserted into the current input terminal, it is erroneously operated by a buzzer or the like. I'll let you know.

However, since the buzzer sounds only under the above-mentioned specific conditions, it is not enough to alert the user, and there is a problem in reliability.

On the other hand, even when the function is in the current measurement range and the test lead is correctly inserted into the current input terminal, an inadvertent application of a voltage to the test lead may cause an operation error. There is also. As described above, errors are likely to occur as a whole when measuring current.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and its structural features include an input section including a current input terminal and a voltage input terminal, a function changeover switch and a plurality of operation switches. An operation setting unit including a setting switch, an A / D converter for converting an analog signal input from the input unit into a digital signal, a digital display, an erroneous operation alarm unit, A digital multimeter including a central processing means (CPU) for performing predetermined processing specified by the operation setting section on the digital signal and displaying the digital signal on the digital display, and operating the erroneous operation alarm means at the time of erroneous operation; And a test lead detecting means for detecting that a test lead is connected to the current input terminal.
The PU receives the test lead detection signal from the test lead detection unit, activates the operation alarm unit, determines whether the operation setting switch is operated, operates the switch, and switches the function switch. Only when the switch is switched to the current measurement range, the erroneous operation warning means is stopped.

[0008]

According to the above arrangement, when the test lead is connected to the current input terminal, the operation alarm means, for example, a buzzer is sounded unconditionally. To stop this, first, either a specific operation setting switch or the same operation setting switch must be pressed. The buzzer stops only when the function changeover switch points to the current measurement range. If it is set to a range other than the current measurement range, the fuzzer will continue to sound.

Therefore, when starting the current measurement, the user is first warned by a buzzer, and then is required to press the operation setting switch, so that a double check is required.

[0010]

FIG. 1 shows an operation surface of a digital multimeter according to this embodiment. According to the operation surface, a rotary function changeover switch 1 is provided on the operation surface.
0, various operation setting switches 11, a liquid crystal display panel 12, and an input unit 13 are provided.

In this case, the operation setting switch 11
Shift switch 11a, frequency setting switch 11b, range setting switch 11c, hold switch 11d, buzzer switch 11e, comparator function switch 11
f, recorder function switch 1 for storing maximum and minimum values
1g and a relative function switch 11h for displaying a relative value between the input signal and an arbitrary reference value are provided.

In FIG. 1, the display of all functions is displayed on a liquid crystal display panel 12, and an input section 13 has four terminals, that is, current input terminals 13a, mA-A when measuring A (ampere). μA (milli, microamp)
A current input terminal 13b for measurement, a common terminal 13c, and a voltage input terminal 13d for measuring V.OMEGA..diode are arranged.

FIG. 2 shows a schematic block diagram of this digital multimeter including a current input circuit of one input terminal 13a as an example. It should be understood that the other current input terminal 13b and its current input circuit are similarly configured.

According to this, the current input terminal 13a is provided with a pair of contact pieces C1 and C2 which divide a conductive cylinder into two along its axial direction and are electrically insulated from each other in a normal state. I have. These contact pieces C1 and C2 are
When a plug of a test lead (not shown) is inserted between them, they are electrically connected to each other via the plug.

In this case, one contact piece C1 is connected to the power supply + V in the meter via two resistors R1 and R2 connected in series.
It is connected to the. Also, between the resistors R1 and R2,
A test lead detection circuit 15 composed of, for example, a logic IC using these as voltage dividing resistors is connected.

The other contact piece C 2 is connected to an A / D converter 17 via a fuse 16 and an input resistor 18. The input resistor 18 is connected in parallel to the A / D converter 17 and serves as a shunt, and a protection circuit for forcibly blowing the fuse 16 when an overvoltage is applied to the current input terminal 13a. Act as

An analog input signal is converted into a digital signal by an A / D converter 17 and is processed by a central processing unit (CPU) 1.
9 The CPU 19 processes the digital signal according to the conditions set by the function changeover switch 10 and the various operation setting switches 11 and displays the digital signal on the liquid crystal display panel 12. Further, at the time of an erroneous operation, the buzzer 20 as an erroneous operation warning means is operated. In addition, CPU
Reference numeral 19 denotes a ROM 19a in which a program for operating each function is written, and a RAM which stores measurement data and the like.
19b.

Next, the erroneous operation prevention function will be described with reference to the flowchart of FIG.

The test lead plug is connected to the current input terminal 13
a, the test lead detection circuit 1
The detection end of No. 5 is held at “Hi” by the power supply + V.

The test lead plug is connected to the current input terminal 13
When inserted into a, the contact pieces C1 and C2 conduct. As a result, the detection end of the test lead detection circuit 15 becomes “L”.
The detection circuit 15 supplies a test read detection signal to the CPU 19 from the detection circuit 15.

Upon receiving the test lead detection signal, the CPU 19 sounds the buzzer 20 regardless of the setting of the function changeover switch 10.

Here, in order to stop the buzzer 20, first,
The user must press the operation setting switch 11. In this embodiment, any one of the switches 11a to 11h may be pressed. If this operation is neglected, the buzzer 20 will continue to sound.

When the operation setting switch 11 is pressed, the CPU 19 determines whether the function changeover switch 10 is set to the current measurement range as the next step.

If the current measuring range is set, the buzzer 20 is stopped and the measuring state is entered. When the current measurement range is not set, the function changeover switch 1
The buzzer 20 will sound until 0 is switched to the same range.

In the above embodiment, the buzzer 20 has been described as an erroneous operation warning means. However, an error display such as "Err" may be displayed on the liquid crystal display panel 12, or the liquid crystal display and the buzzer sound may be displayed. You may use together.

As another example, when the function changeover switch is set to a position other than the current measurement range even though the plug of the test lead is connected to the current input terminal, "Err" is displayed on the liquid crystal display panel. Such an error display can be performed.

[0027]

As described above, according to the present invention, when the test lead is connected to the current input terminal, an alarm is first issued regardless of the setting of the function setting switch, and the user is notified of something. Operation, and then determine whether the function is properly selected. As a result, the user is first warned by a buzzer when starting current measurement, and then presses the operation setting switch Is required, a double check must be performed, and the reliability of preventing erroneous operations is further improved.

[Brief description of the drawings]

FIG. 1 is a front view showing an operation surface of a digital multimeter according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram of the embodiment.

FIG. 3 is a flowchart for explaining an erroneous operation prevention function of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Function switch 11 Operation setting switch 12 Liquid crystal display panel 13 Input part 13a, 13b Current input terminal 15 Test lead detection circuit 17 A / D converter 18 Input resistance 19 CPU 20 Buzzer

Claims (1)

(57) [Claims] An input unit including a current input terminal and a voltage input terminal; an operation setting unit including a function changeover switch and a plurality of operation setting switches; and an analog signal input from the input unit is converted into a digital signal. A /
A D converter, a digital display, an erroneous operation warning unit, and a predetermined process designated by the operation setting unit on the digital signal from the A / D converter and displaying the digital signal on the digital display; A digital multimeter including a central processing means (CPU) for operating the erroneous operation alarm means at the time of erroneous operation, comprising: a test lead detecting means for detecting that a test lead is connected to the current input terminal; Receives the test lead detection signal from the test lead detection means, activates the operation alarm means, judges whether the operation setting switch has been operated, operates the switch, and operates the function changeover switch. Only when the current is switched to the current measurement range, the erroneous operation alarm is stopped. Le multimeter.