JPH0635183Y2 - Digital Multimeters - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention is a means for converting an AC signal into a DC signal by a DC converter, supplying the DC signal to an AD converter, and switching between a high speed mode and a low speed mode. Relates to a digital multimeter.

"Prior Art" Fig. 2 shows a general configuration of a digital multimeter. The signal under test from the input terminal 11 is supplied to the absolute value circuit 13 through the range switching amplifier 12, and the output of the absolute value circuit 13 is RMSD.
The DC signal is supplied to the C converter 14, and the DC signal is supplied to the AD converter 15 and converted into a digital signal, and the digital signal is supplied to the arithmetic unit 17 via the control unit 16 for arithmetic processing. After being applied, the information is displayed on the display unit 18. The control unit 16 controls the range switching amplifier 12 according to the output of the AD converter 15.
To set an appropriate range according to the input signal level.

The RMSDC converter 14 has been conventionally constructed as shown in FIG. That is, the output of the absolute value circuit 13 is the multiplier 19
Is supplied to. The multiplier 19 is a commercially available semiconductor integrated circuit NJM4
200 is used. The output of the multiplier 19 is supplied to the low pass wave filter 22 having the operational amplifier 21, and the output of the low pass wave filter 22 is supplied to the AD converter 15. That is, the output of the absolute value circuit 13 is converted into a DC signal whose magnitude is the effective value of the signal under measurement by the RMSDC converter 14 including a multiplier 19 and a low-pass wave device 22 having an operational amplifier 21. RMSDC converter 14
The output voltage of is supplied to the AD converter 15. The capacitor 24 is inserted into the feedback loop of the operational amplifier 21 via the switch 23.

In the low speed mode in which the input signal frequency is low, the switch 23 is turned on, the capacitor 24 is inserted, and the cutoff frequency is lowered. When the range is exceeded in the low speed mode, the mode is switched to the high speed mode to enable high speed auto range, and when the optimum range is detected, the mode is switched to the low speed mode. That is, when the switch 23 is turned on in the low speed mode and a range over is detected, the switch 23
Is turned off and the optimum range is selected in the high speed mode, and then the switch 23 is turned on to set the low speed mode.

When the switch 23 is turned on again, it is necessary to discharge or charge the capacitor 24 depending on whether the capacitor 24 has a charge or not, and the response deteriorates accordingly.
In other words, it took time to reach a steady state when the switch 23 was turned on again.

[Means for Solving the Problem] According to the present invention, a capacitor inserted in the feedback loop of the operational amplifier of the low pass wave filter in the low speed mode is connected to the output side of the operational amplifier and the ground during operation in the high speed mode. A switch connected between them is provided.

[Embodiment] FIG. 1 shows an essential part of the present invention, and parts corresponding to those in FIG. 3 are designated by the same reference numerals. In this invention, the input side of the operational amplifier 21 of the capacitor 24 is grounded through the switch 25. The switch 25 is turned on and off, contrary to the switch 23. That is, when the switch 23 is on, the switch 25 is off.

Therefore, during the operation in the high speed mode, the switch 23 is turned off, the switch 25 is turned on, the capacitor 24 is connected between the output side of the operational amplifier 21 and the ground, and the output Vo of the operational amplifier 21 is equal to that of the capacitor 24. Both ends are charged. Operational amplifier
Due to the low output impedance of 21, this capacitor 24
The charging of Vo to is fast.

When the switch 23 is switched from the off state to the low speed mode, the switch 23 is turned on and the switch 25 is turned off,
If there is no offset voltage on the input side of the operational amplifier 21, its inverting input terminal and non-inverting input terminal have the same potential,
Since the capacitor 24 is connected to the virtual ground point when the switches 23 and 25 are switched, the charge of the capacitor 24 does not move,
A fast response is realized.

Instead of the switches 23 and 25, one end of the capacitor 24 may be a changeover switch that connects the inverting input terminal to the ground.

[Advantage of Device] As described above, according to this device, during the operation in the high speed mode, the capacitor 24 is connected between the output side of the operational amplifier 21 and the ground, and the capacitor 24 is charged by the output of the operational amplifier 21. Therefore, even if the mode is switched to the low speed mode, the capacitor 24
High-speed response is realized without the movement of electric charges.

[Brief description of drawings]

FIG. 1 is a connection diagram showing a main part of the present invention, FIG. 2 is a block diagram showing a general configuration of a digital multimeter, and FIG. 3 is a connection diagram showing a specific configuration of a conventional RMSDC converter 14. .

Claims (1)

[Scope of utility model registration request] 1. An RMSDC converter, which supplies a signal under test to an absolute value circuit through a range switching amplifier, and outputs the output of the absolute value circuit by an RMSDC converter including a multiplier and a low pass wave filter having an operational amplifier. In a digital multimeter that has a means for switching the high-speed mode and low-speed mode by converting the measured signal into a DC signal that is the effective value and supplying the output voltage of the RMSDC converter to the AD converter. A digital multimeter comprising a switch for connecting a capacitor inserted in a feedback loop of an operational amplifier between an output side of the operational amplifier and ground during operation in a high speed mode.