JPH0733170Y2 - Digital multimeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a digital multimeter capable of performing at least voltage measurement and frequency measurement.

[Prior Art] It is known that a digital multimeter capable of measuring AC voltage is provided with a frequency counter (frequency measurement) function. It is also known to share an attenuator (input level adjusting circuit) of an input circuit for voltage measurement with frequency measurement.

In the frequency measurement, adjusting the input level with an attenuator enables measurement in which the adverse effects of noise are reduced. For example, when applying a measurement signal to a frequency measurement circuit having a sensitivity of 10 mV, accurate measurement becomes difficult unless the noise component is sufficiently smaller than 10 mV. Therefore, when the input signal is 1 V and the noise component is 50 mV, for example, if the measurement signal is 100 mV and the noise component is 5 mV through the 1/10 attenuator, accurate measurement becomes possible.

[Problems to be solved by the invention] By the way, it is convenient if the display of the range of the attenuator can be confirmed in the frequency measurement.

As one of the methods for displaying or confirming the range of the attenuator, a method of providing one range switch for each range and confirming the range of the attenuator from the on / off state of the switch can be considered. However, in this case, one range switch must be provided for each range. Further, in this case, it is difficult to confirm unless the on / off state of the switch is clearly distinguished.
As another method, it is conceivable to provide a display dedicated to the attenuator in addition to the display of the measurement data, but this leads to an increase in the number of parts, an increase in panel size, and an increase in cost.

Therefore, an object of the present invention is to provide a digital multimeter that can easily know the state of the input level adjusting circuit during frequency measurement.

[Means for Solving the Problems] The present invention for achieving the above object includes an input terminal for selectively inputting a measured voltage and a measured frequency signal, and a voltage dividing resistor coupled to the input terminal. An input level adjusting circuit composed of a combination of a plurality of voltage dividing setting switches for obtaining a plurality of voltage dividing ratios connected to the voltage dividing resistor, a voltage measurement of a signal obtained through the input level adjusting circuit, and the A voltage and frequency measuring circuit for measuring the frequency of the signal,
A measurement mode selection switch for giving a signal indicating whether to operate the voltage and frequency measurement circuit in the voltage measurement mode or the frequency measurement mode, and for displaying a measurement result obtained from the voltage and frequency measurement circuit In a digital multimeter including a display, a switch state detection circuit for detecting the on / off state of the voltage division ratio setting switch, a signal indicating the switch state obtained from the switch state detection circuit, and the measurement mode selection switch. In response to the signal indicating the frequency measurement mode obtained in response to the operation of, the state of level adjustment in the input level adjustment circuit for a fixed time within a fixed time from the time when the frequency measurement mode is selected. Displayed on the display and obtained from the voltage and frequency measurement circuit after the elapse of the fixed time. Those related to the digital multimeter, characterized in that a and control circuitry for displaying the frequency measurement results in the location and the same place of displaying the status of the level adjustment in the display.

[Operation] The display in the above invention is used both for displaying the measurement result and for displaying the level adjustment state (attenuator range) in the input level adjustment circuit. That is, the display device displays a plurality of types in a time division manner. The control circuit determines the input level adjustment state based on the output of the switch state detection circuit, forms a signal for displaying this, and sends it to the display.

[Embodiment] Next, a digital multimeter according to an embodiment of the present invention will be described with reference to FIGS.

As shown functionally in FIG. 1, the digital multimeter with a counter has a pair of input terminals 1a and 1b, an input level adjusting circuit (attenuator) 2, an AC voltage measuring circuit 3, a frequency measuring circuit 4, and switch detection. It has a circuit 5, a control circuit 6, and a display 7.

An AC voltage to be measured or a frequency signal to be measured is input to the input terminals 1a and 1b.

The input level adjusting circuit 2 includes a voltage dividing circuit 2a and a switch circuit 2b.
And is configured to divide (attenuate) an input signal and output the divided signal. FIG. 2 shows an example of this, in which the voltage dividing resistors R1 and R2 connected between the input terminals 1a and 1b,
R3, R4 and the frequency characteristic correction capacitors C1, C2, C3, C4 constitute the voltage dividing circuit 2a, and the switches S1 to S4 selectively extracting the non-voltage dividing output and the voltage dividing output constitute the switch circuit 2b. ing. In this input level adjusting circuit 2, the attenuation ratio is zero when the switch S1 is on, 1/10 when the switch S2 is on, 1/100 when the switch S3 is on, and the switch S4 is on. Sometimes 1/1000
Is.

AC voltage measuring circuit 3 connected to the input level adjusting circuit 2
Is configured to have a digital counter to measure the voltage under test. The voltage measurement is performed in response to the operation of the AC voltage measurement mode selection switch 12b shown in FIG.

Frequency measuring circuit 4 connected to input level adjusting circuit 2
Is configured to measure the measured frequency with a digital counter. This frequency measuring circuit 4 is the third
Frequency measurement is executed in response to the operation of the frequency measurement mode selection switch 12b in the figure. Although the AC voltage measuring circuit 3 and the frequency measuring circuit 4 are shown independently in FIG. 1, they may be configured to share many parts.

The switch detection circuit 5 is configured to detect the on / off state of the switches S1 to S4. The switch detection circuit 5 may detect the on / off state of the switches S1 to S4 by a switch that interlocks with the switches S1 to S4, or a signal for controlling the on / off states of the switches S1 to S4 as a switch state detection signal. You may use it.

The control circuit 6 has a range selection switch 11 shown in FIG.
The switch circuit 2b is controlled to be turned on / off in response to the operations of a and 11b, and the range is displayed on the display 7 only for a certain period of time when the frequency measurement mode selection switch 12d is operated and when the range switching operation is performed. Have a function to do. Further, the voltage measurement value obtained from the AC voltage measurement circuit 3 and the frequency measurement value obtained from the frequency measurement circuit 4 are sent to the display 7.

On the panel 10 of the digital multimeter, as shown in FIG. 3, input terminals 1a, 1b, display 7, range selection down switch 11a, range selection up switch 11b, DC voltage measurement mode selection switch 12a, AC voltage measurement. A mode selection switch 12b, a resistance measurement mode selection switch 12c, and a frequency measurement mode selection switch 12d are provided.

The display 7 comprises a numeral display 7a and a unit display 7b for V, mV, kHz, Hz and the like. The numerical display 7a is commonly used for voltage, frequency and the like.

Frequency measurement is performed according to the flow chart of FIG. When the circuit under test is connected to the input terminals 1a and 1b and the power is turned on and then the frequency measurement mode switch 12d is turned on, the control circuit 6 follows the block 21 of FIG. The voltage dividing ratio (attenuation ratio) in the adjusting circuit 2 is recognized and displayed on the display unit 7. That is, as shown in FIG. 4, 10 is displayed on the numeral display 7a and V is displayed on the unit display 7b. This shows that the 10V range, that is, the attenuation ratio is 1/10. The control circuit 6 displays the range for a certain period of time, and thereafter displays the frequency measurement shown in block 22 and the measured value display shown in block 23 in FIG. As shown in Fig. 3, the measured value display shows 0.12346 on the numerical display 7a and the unit display 7b.
It is achieved by displaying in kHz.

Next, in block 24 of FIG. 5, it is judged whether or not there is a key input (switch operation), and if there is a key input, in block 25 the range key (range selection switches 11a, 11b)
Is determined. Range selection switch 11a, 1
When 1b is operated, the range is changed by selecting the switches S1 to S4 shown in FIG. 2 as shown in block 26. When changing the range, the range display is executed again for a fixed time. On the other hand, if the mode switching is determined in block 27, the frequency measurement mode ends. It should be noted that the range display is about 0.5 seconds, but since it is a simple display such as 1, 10, 100, etc., it can be sufficiently recognized within a short time.

When the AC voltage measuring mode selection switch 12b is operated, the AC voltage measuring circuit 3 is operated, the measured voltage value is displayed on the numerical display 7a, and V or mV is displayed on the unit display 7b.

The range is switched by operating the range selection down switch 11a or the range selection up switch 11b. That is, the two switches 11a and 11b do not correspond to the switches S1 to S4 shown in FIG.
It is configured to operate S4. Therefore, the panel occupying area of the operation unit for selecting the range is small.

[Advantage of Device] As described above, according to the present invention, the level adjustment state of the input level adjustment circuit and the frequency measurement result in the frequency measurement mode are time-divisionally displayed at the same location on the same display. Therefore, a dedicated display for displaying the level adjustment status is not required, and the cost and size of the digital multimeter can be reduced. Further, since the level adjustment state is displayed only for a certain period of time, power consumption is reduced as compared with continuous display.

[Brief description of drawings]

FIG. 1 is a block diagram showing the principle of a digital multimeter according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing in detail the input level adjusting circuit of FIG. 1, and FIG. 3 is a digital diagram of the embodiment. FIG. 4 is a front view showing the configuration of the front panel of the multimeter in a frequency measured value display state, FIG. 4 is a front view showing the panel of FIG. 3 in a 10 V range display state, and FIG. 5 is a flow chart of frequency measurement. 1 ... Input terminal, 2 ... Input level adjusting circuit, 2a ... Voltage dividing circuit, 2b ... Switch circuit, 3 ... AC voltage measuring circuit, 4 ... Frequency measuring circuit, 5 ... Switch detecting circuit,
6 ... control circuit, 7 ... indicator.

Claims (1)

[Scope of utility model registration request] 1. An input terminal for selectively inputting a voltage to be measured and a frequency signal to be measured, a voltage dividing resistor coupled to the input terminal, and a plurality of stages of voltage dividing connected to the voltage dividing resistor. An input level adjusting circuit comprising a combination of a plurality of voltage division ratio setting switches, a voltage and frequency measuring circuit for measuring the voltage of the signal obtained through the input level adjusting circuit and the frequency of the signal, A measurement mode selection switch for giving a signal indicating whether to operate the voltage and frequency measurement circuit in the voltage measurement mode or the frequency measurement mode, and for displaying the measurement result obtained from the voltage and frequency measurement circuit. In a digital multimeter including a display, a switch state detection circuit for detecting an on / off state of the voltage division ratio setting switch, and the switch state In response to the signal indicating the switch state obtained from the output circuit and the signal indicating the frequency measurement mode obtained in response to the operation of the measurement mode selection switch, the frequency measurement mode is constant from the time when the mode is selected. The state of level adjustment in the input level adjustment circuit is displayed on the display for a fixed time within the time, and the frequency measurement result obtained from the voltage and frequency measurement circuit after the fixed time has elapsed is displayed on the display. A digital multimeter, which is provided with a control circuit for displaying the level adjustment status at the same place as the display position.