Multimeter with filtered measurement mode

A multimeter with filtered measurement mode is disclosed. The multimeter includes a signal conditioning circuit, a low-pass filter, a microprocessor, a measurement circuit, a root-mean-square (RMS) converter, a display unit, and an external rotary switch. The signal conditioning circuit receives a control signal to select an operation mode of the multimeter. The low-pass filter is electrically connected to the signal conditioning circuit. The microprocessor is electrically connected to the signal conditioning circuit. The measurement circuit is electrically connected to the microprocessor and the RMS converter to measure a signal outputted from the RMS converter. The display unit is electrically connected to the microprocessor and the measurement circuit. Also, the external rotary switch is optionally connected to the microprocessor. Whereby rotating the external rotary switch to generate the control signal and perform a low-pass filtering mode to communicate the low-pass filter with the RMS converter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multimeter, and more particularly to a multimeter with a filtered measurement mode.

2. Description of Prior Art

Digital multimeters measure a wide range of electrical parameters, such as AC and DC currents and voltages, and resistance.

However, there are a number of measurement situations confronting the technician in which it is extremely difficult to make accurate measurements. For example,

2. uninterruptible power sources; and

3. switching power supplies use pulse-width modulation using high frequency and high voltage pulses to generate pulse-width modulated pulses, or lower frequency sinusoidal signals.

However, the measured root-mean-square (RMS) voltage value is substantially larger than the actual RMS voltage value to cause significant distortion because the measured RMS voltage value contains the high-frequency component, which is caused from factors such as voltage spikes, noise, and switching transients. Hence, a low-pass filter, installed in the multimeter, is used to filter out unnecessary high-frequency component of the voltage signal to acquire correct RMS voltage value.

The U.S. Pat. Nos. 7,342,393 and 7,034,517 both disclosed a multimeter with a filtered measurement mode, and the multimeter has the above-motioned low-pass filtering function to filter out unnecessary high-frequency component of the voltage signal to acquire correct RMS voltage value. However, the disclosed multimeter has a single button on the panel to select an operation of low-pass filtering mode. Also, users can recognize that the low-pass filtering mode is operated while a symbol of using a low-pass filtering mode, such as “LO”, is shown on a view screen of the multimeter. The low-pass filtering mode is canceled and the symbol “LO” is not shown when the single button is pressed again. However, such operation is not simple and convenient.

In practically, users have to carefully check whether the symbol “LO” is shown or not before operating the low-pass filtering mode in order to avoid misemploying the multimeter to acquire unwanted measured results.

SUMMARY OF THE INVENTION

In order to improve the disadvantages mentioned above, the prevent invention provides a multimeter with a filtered measurement mode.

In order to achieve an objective mentioned above, the multimeter with a filtered measurement mode includes a signal conditioning circuit, a low-pass filter, a microprocessor, a measurement circuit, a root-mean-square (RMS) converter, a display unit, and an external rotary switch. The signal conditioning circuit receives a control signal to select an operation mode of the multimeter. The low-pass filter is electrically connected to the signal conditioning circuit. The microprocessor is electrically connected to the signal conditioning circuit. The measurement circuit is electrically connected to the microprocessor and the RMS converter to measure a signal outputted from the RMS converter. The display unit is electrically connected to the microprocessor and the measurement circuit. Also, the external rotary switch is optionally connected to the microprocessor. Whereby rotating the external rotary switch to generate the control signal and perform a low-pass filtering mode to communicate the low-pass filter with the RMS converter.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. Other advantages and features of the invention will be apparent from the following description, drawings and claims.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to the drawing figures to describe the present invention in detail. Reference is made toFIG. 1which is a block diagram of a first embodiment of a multimeter with a filtered measurement mode according to the present invention. The multimeter with a filtered measurement mode20is applied to a measured object10. The multimeter with a filtered measurement mode20includes a signal conditioning circuit202, a low-pass filter204, a microprocessor210, a measurement circuit212, a root-mean-square (RMS) converter208, a display unit24, and an external rotary switch22.

The low-pass filter204is electrically connected to the signal conditioning circuit202. The microprocessor210is electrically connected to the signal conditioning circuit202. The measurement circuit212is electrically connected to the microprocessor210and the RMS converter208. The display unit24is electrically connected to the microprocessor210and the measurement circuit212. Also, the external rotary switch22is optionally connected to the microprocessor210.

The signal conditioning circuit202receives a control signal to select an operation mode of the multimeter with a filtered measurement mode20. The operation mode includes measuring AC (or DC) currents, voltages, resistance, and so on. The measurement circuit212is used to measure a signal outputted from the RMS converter208. By rotating the external rotary switch22to generate the control signal, which is generated by the microprocessor210, to perform a low-pass filtering mode to communicate the low-pass filter204with the RMS converter208. Reference is made toFIG. 4which is a front view of the multimeter with the filtered measurement. The external rotary switch22is rotated to the low-pass filtering mode (namely, the VFD range is selected as shown inFIG. 4) to communicate the low-pass filter204with the RMS converter208.

Reference is made toFIG. 2, which is a block diagram of a second embodiment of the multimeter with the filtered measurement mode. The connection relationship of the components of the second embodiment is similar to that of the first embodiment. The main difference between the second embodiment and the first embodiment is that: the second embodiment further includes a signal switch206, which is optionally connected to the external rotary switch22. By rotating the external rotary switch22, the signal switch206is switched to perform a low-pass filtering mode to communicate the low-pass filter204with the RMS converter208.

Reference is made toFIG. 3, which is a block diagram of a third embodiment of the multimeter with the filtered measurement. The connection relationship of the components of the third embodiment is similar to that of the first embodiment. The main difference between the third embodiment and the first embodiment is that: the third embodiment further includes a signal switch206, which is electrically connected to the microprocessor210. By rotating the external rotary switch22, the microprocessor210controls the signal switch206to perform a low-pass filtering mode to communicate the low-pass filter204with the RMS converter208.

In conclusion, the main difference between the first embodiment, the second embodiment, and the third embodiment is that:

1. In the first embodiment, the external rotary switch22is directly used to communicate the low-pass filter204with the RMS converter208.

2. In the second embodiment, the external rotary switch22is used to control the signal switch206to communicate the low-pass filter204with the RMS converter208.

3. In the third embodiment, the external rotary switch22is used to control the microprocessor210, and then the microprocessor210controls the signal switch206to communicate the low-pass filter204with the RMS converter208.

The multimeter of the present invention is more advantageous than the prior art multimeter is to provide a simple operation. Namely, the external rotary switch22is only used to perform a low-pass filtering mode. On condition that the external rotary switch22is rotated to the VFD range (low-pass filtering mode is enabled), users can operate the multimeter with a filtered measurement mode20to the low-pass filtering mode.

In the above-mentioned embodiments, the display unit24does not need to show any symbol to indicate that the external rotary switch22is rotated to the low-pass filtering mode. However, operating the prior art multimeter in a low-pass filtering mode, users have to carefully check whether a symbol of using a low-pass filtering mode is shown on a displayer of the multimeter. Accordingly, users can correctly operate the multimeter to acquire the wanted measured results when users easily confirm that the VFD range (low-pass filtering mode range) is selected.