JPH0560798A - Digital multimeter - Google Patents

Abstract

PURPOSE:To prevent erroneous operation positively when a current input terminal is used. CONSTITUTION:In a digital multimeter, a test-lead detecting means 15 for detecting the connection of a test lead to a current input terminal is provided. When the test lead is connected to the current input terminal 13a, an operation alarming means, e.g. a buzzer 20, is sounded regardless of the setting state of a function. To stop the buzzer, at first, an operation setting switch 11 must be depressed. In this case, one of the above described switches 11a-11h must be depressed. It is set that the buzzer is stopped only when a function switch 10 indicates a current measuring range. When the switch is set outside the current measuring range, the buzzer continues to sound. When the user starts the measurement of a current, at first, attention is called with the buzzer, and the depression of the operation setting switch 11 is requested. Thus, the user is obliged to perform double checks, and the reliability in preventing erroneous operation is enhanced.

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 preventing function.

[0002]

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

In actual operation, one of the pair of test leads is inserted into either the current input terminal or the voltage input terminal, and the other test lead is connected to the common terminal. Therefore, be careful when connecting the test leads to the current input terminals.

[0004]

Therefore, conventionally, when the test lead is inserted into the current input terminal when the function changeover switch is set to a position other than the current measurement range, it is possible that a malfunction occurs due to a buzzer or the like. I try to let you know.

However, since the buzzer sounds only under the above-mentioned specific conditions, it is insufficient to call the user's attention, and there is a problem in its reliability.

On the other hand, even when the function is in the current measurement range and the test lead is inserted in the current input terminal in the correct state, a working error of accidentally applying a voltage to the test lead may occur. There is also. Thus, as a whole, errors are likely to occur during current measurement.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and its structural feature is that an input section including a current input terminal and a voltage input terminal, a function changeover switch, and a plurality of operations are provided. From the operation setting section including a setting switch, an A / D converter for converting an analog signal input from the input section into a digital signal, a digital display, an erroneous operation warning means, and the A / D converter. A digital multimeter including a central processing means (CPU) for performing a predetermined process designated by the operation setting section on a digital signal to display the digital signal on the digital display, and for activating the erroneous operation warning means at the time of an erroneous operation. In the above C, there is provided 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 means, operates the operation warning means, then determines whether the operation setting switch is operated, operates the switch, and switches the function. The erroneous operation warning means is stopped only when the switch is switched to the current measurement range.

[0008]

According to the above construction, when the test lead is connected to the current input terminal, the operation alarm means, for example, the buzzer is sounded unconditionally. In order to stop this, first, either the specific operation setting switch or the same operation setting switch must be pressed. Then, the buzzer stops only when the function changeover switch indicates the current measurement range. If it is set to anything other than the current measurement range, the fuzzer will continue to ring.

Therefore, as the user is required to be alerted by the buzzer and then to press the operation setting switch before starting the current measurement, he is forced to make a double check.

[0010]

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

In this case, as 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 that stores the maximum and minimum values
1 g and a relative function switch 11 h for displaying the relative value of the input signal and an arbitrary reference value are prepared.

In FIG. 1, displays of all functions are displayed on the liquid crystal display panel 12, and the input section 13 has four terminals, that is, current input terminals 13a, mA-for measuring A (ampere). μA (millimeter, microampere)
A current input terminal 13b for measuring, a common terminal 13c, and a voltage input terminal 13d for measuring V · Ω / diode are arranged.

FIG. 2 shows a schematic block diagram of this digital multimeter including a current input circuit for one current 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 are electrically conductive cylinders divided into two along the axial direction and which are electrically insulated from each other in the normal state. There is. The 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 through the plug.

In this case, the one contact piece C1 is connected to the in-meter power source + V via two resistors R1 and R2 connected in series.
It is connected to the. Further, between the resistors R1 and R2,
A test lead detection circuit 15 including, for example, a logic IC that uses them as voltage dividing resistors is connected.

The other contact piece C2 is connected to the A / D converter 17 via the fuse 16 and the input resistor 18. The input resistor 18 is connected in parallel with the A / D converter 17, and serves as a shunt resistor and a protection circuit for forcibly blowing the fuse 16 when an overvoltage is applied to the current input terminal 13a. Acts as.

The analog input signal is converted into a digital signal by the A / D converter 17, and the central processing means (CPU) 1
Sent to 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 it on the liquid crystal display plate 12. Further, at the time of 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 for storing measurement data and the like.
19b and.

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

The plug of the test lead is the current input terminal 13
If it is not plugged into a, the test lead detection circuit 1
The detection end of No. 5 is held at “Hi” by the power supply + V.

The plug of the test lead is the current input terminal 13
When it is inserted into a, the contact pieces C1 and C2 become conductive. As a result, the detection end of the test lead detection circuit 15 becomes “L
Then, the detection circuit 15 gives a test lead detection signal to the CPU 19.

When the CPU 19 receives the test lead detection signal, the buzzer 20 sounds 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, it suffices to press any one of the switches 11a to 11h. If this operation is neglected, the buzzer 20 will continue to ring.

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

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

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

As another example, although the plug of the test lead is connected to the current input terminal, when the function changeover switch is set to a position other than the current measurement range, "Err" is displayed on the liquid crystal display panel. It is also possible to display such an error.

[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 informed of something. By performing the operation of, and then determining whether the function is properly selected, the user is first alerted by the buzzer when entering the current measurement, and then presses the operation setting switch. Since it is required, a double check is forced to be performed, and the reliability of erroneous operation prevention is further enhanced.

[Brief description of 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 same embodiment.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. An input section including a current input terminal and a voltage input terminal, an operation setting section including a function changeover switch and a plurality of operation setting switches, and an analog signal input from the input section is converted into a digital signal. A /
The digital signal from the D converter, the digital display, the erroneous operation warning means, and the A / D converter is subjected to the predetermined processing designated by the operation setting section and displayed on the digital display. A digital multimeter having a central processing means (CPU) for operating the erroneous operation warning means at the time of erroneous operation, having a test lead detecting means for detecting connection of a test lead to the current input terminal, and the CPU. Receives the test lead detection signal from the test lead detection means, activates the operation warning means, then determines whether the operation setting switch is operated, the switch is operated, and the function changeover switch is operated. The erroneous operation warning means is stopped only when is switched to the current measurement range. Le multimeter.