JPH0226191B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mechanism for changing the measurement range of a digital multimeter.

The purpose of the present invention is to
Makes a sound, eliminates microwave mistakes, and at the same time
The purpose is to increase the durability of the DMM by preventing its misuse.

This will be explained below with reference to the drawings. Figure 1 shows the conventional
In the external view of the DMM, 1 is the DMM main body, 2 is the power switch, and 3 is AC-DC (hereinafter abbreviated as AC-DC).
The changeover switch, 4, is a function and measurement range changeover switch. In Figure 1, the voltage is 2V to 1000V.
4 ranges of resistance, 4 ranges of resistance from 2KΩ to 2MΩ, and 4 ranges of current from 2mA to 2A.
8 is the range selection position. 5 and 6 are input terminal portions, and 7 is a display portion. FIG. 1 shows a case with a liquid crystal display unit. Figure 2 9 shows another specific example of a conventional measurement range switch, where L-H (LOW-High) corresponds to the voltage function in Figure 1.
2V-20V, H corresponds to 200V-1000V. 8' is the anchor position, and there are three positions: VOLTS-OHMS-AMP. FIG. 3 shows still another specific example of the conventional product, which is a DMM having an auto-ranging circuit. 10 is an auto range and range hold switch.

When using the above conventional DMM, please follow the steps 3.
Applying AC voltage in the DC range by mistakenly thinking that the AC-DC switch is set to AC, or applying 200V
If you mistakenly think that you have switched to the range (or H range) and apply 100V while staying in the 2V range (or L range), or in the case of the auto range DMM shown in Figure 3, it is easier to measure by holding the range. When measuring with a range, the user may hold the range lower than the input signal level and apply the input without realizing it, making it very easy to misuse the DMM.

The present invention eliminates this drawback, and an embodiment thereof is shown in FIG. Reference numeral 11 in FIG. 4 is a buzzer, and the buzzer sounds for a short time immediately after switching the AC-DC changeover switch 2, the L-H changeover switch 9, and the function switch 4. If the buzzer does not sound, it means that the switch is stuck in the middle or the range is not being changed. FIG. 5 shows another embodiment of the present invention, where 12 and 13 are push switches or touch switches, and 12 is a touch switch.
AC-DC switching, 13 is range switching, and each time you press it, the decimal point moves one place in conjunction with the range. At the same time, a buzzer will sound briefly to notify you that the range has been changed.

When attempting to notify range changes with a buzzer sound, the buzzer sounds only when the range change switch is operated reliably and the range is reliably changed.
It must be configured to drive the buzzer.
If this is not done, a buzzer will sound even when a chattering input is made due to an erroneous operation of the switch, causing the user to misunderstand the switch and even encouraging erroneous use.

FIG. 6 shows an embodiment of a buzzer drive circuit that detects that the measurement range used in the present invention has been reliably changed and drives a buzzer for a predetermined time.
The timing chart is shown in the figure. In FIG. 6, 14 is an input part for a range switching signal, 15 is a clock signal input part of several Hz to several hundred Hz for determining the operation timing of the flip-flop, and 16 is a clock signal input part of several KHz for determining the driving frequency of the buzzer. 17 is an inverter, 18 is a first flip-flop, 19 is a second flip-flop, 20
is an exclusive OR gate (EX-OR gate), 21
is a NAND gate, and 11 is a buzzer. As shown in FIG. 7, the range switching signal b changes from high to low or from low to high in response to changing the range. Now, assuming that the state changes from high to low at timing 22, the output c and Q output d of the first flip-flop 18 are as follows.
At the falling edge of the clock signal a after this 22 timing, the signals change from high to low and from low to high, respectively. Also, the second flip-flop 19
The M output e changes from low to high at the rising edge of the clock signal a in accordance with the change in the output of the first flip-flop 18. As a result EX−
The output f of the OR gate 20 is the clock signal a.
is high from the falling edge to the rising edge of
Supplied from the NAND gate 21 to the buzzer 11,
Emit a buzzer sound. Similarly, when the range switching signal b changes from high to low at timing 23, a buzzer sound is generated from the falling edge to the rising edge of the clock signal a.

When the change in the range switching signal b is shorter than the pulse width of the clock signal a, as in the case of a chattering input, the first flip-flop 18
Since the output does not change, the drive pulse h is not supplied to the buzzer 11. Therefore, it is possible to prevent the buzzer from sounding erroneously due to erroneous operation of the range selector switch.

As described above, the present invention includes a buzzer drive circuit that reliably detects that the measurement range has been changed and drives a buzzer for a predetermined period of time, thereby ensuring that the user is aware of the change in the measurement range. It has a great effect in that it can reliably prevent the misuse of the DMM, such as preventing the user from misperceiving it, as it can also prevent malfunctions caused by erroneous operation. be.

[Brief explanation of drawings]

Figures 1, 2, and 3 are external views of conventional DMMs, and Figures 4 and 5 are examples of the DMM of the present invention.
FIG. 6 shows an embodiment of the circuit used in the DMM of the present invention, and FIG. 7 shows its timing chart. 14... Range switching signal input section, 15, 16...
...Clock signal input section, 17...Inverter, 1
8...first flip-flop, 19...second flip-flop, 20...EX-OR gate,
21...NAND gate.

Claims (1)

[Claims] 1. In a digital multimeter having means for changing the measurement range, detecting that the measurement range has been changed by inputting a range switching signal to a first flip-flop that operates based on a clock signal of a predetermined period; A buzzer circuit that inputs the detection output signal of the first flip-flop to a second flip-flop that operates based on the clock signal and outputs a buzzer sound for a predetermined time determined by the output signals of the first and second flip-flops. A digital multimeter characterized by having.