Apparatus for use in a DMM for measuring the battery voltage of the DMM

• US 6,242,920 B1
• Filed: 09/18/1998
• Issued: 06/05/2001
• Est. Priority Date: 09/18/1998
• Status: Expired due to Fees

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Brooks, James R., Nelson, Theodore G.
• Primary Examiner(s): BROWN, GLENN WARNER
• Application Number:
  US09/156,319
• Time in Patent Office: 991 Days
• Field of Search: 324/426, 324/427, 324/433, 324/115
• US Class Current: 324/427
• CPC Class Codes: G01R 15/125 for digital multimeters
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3835 involving only voltage measurements

Abstract

A circuit for use in a DMM utilizes an auxiliary A/D converter to measure the battery voltage of the DMM and displays the result on the LCD display screen of the DMM. The user receives a numeric indication of the battery voltage measured, rather than a simple good/bad or bar graph indication. The voltage measured provides the user with a quantitative indication which allows the user to determine how close the battery is to being exhausted. Thus, the user can be made aware of a weakened state of the battery before operation of a backlight further drains the battery to an unacceptably low level.

Claims

1. A digital multimeter, comprising:

a battery for providing operating power to said multimeter;

an input for receiving an external analog signal to be measured;

a first A/D converter coupled to said input for converting said external analog signal to digital data;

a controller coupled to said first A/D converter for receiving said digital data;

a display device, coupled to said controller, for displaying digits representative of the value of said digital data; and

a second A/D converter coupled to said battery for measuring a voltage level present on a terminal of said battery;

said second A/D converter being coupled to said controller and providing numerical data representative of said voltage present on said terminal of said battery, said controller causing said numerical data to be displayed on said display device.

2. The digital multimeter of claim 1 further comprising:

a circuit for increasing the magnitude of the battery voltage for providing operating power to said first A/D converter and extending the dynamic range of said first A/D converter.

3. The digital multimeter of claim 2 wherein said second A/D converter is formed within an integrated circuit including said controller and exhibits a dynamic range encompassing an expected range of battery voltages.

4. An electronic test and measurement instrument, comprising:

a battery exhibiting a given voltage for providing operating power to said instrument;

an input for receiving an analog signal to be measured;

a first A/D converter coupled to said input for converting said signal to digital signal to digital data, said first A/D converter being biased about a midpoint of said given voltage in order to measure both positive and negative polarities of said analog signal;

a controller coupled to said first A/D converter for receiving said digital data;

a display device, coupled to said controller, for displaying digits representative of the value of said digital data; and

a second A/D converter coupled to said battery for measuring a voltage level present on a terminal of said battery;

said second A/D converter being coupled to said controller and providing numerical data representative of said voltage present on said terminal of said battery, said controller causing said numerical data to be displayed on said display device.

5. The instrument of claim 4 further comprising:

a circuit for increasing the magnitude of the battery voltage for providing operating power to said first A/D converter and extending the dynamic range of said first A/D converter.

6. The instrument of claim 4 wherein said second A/D converter is formed within an integrated circuit including said controller and exhibits a dynamic range encompassing an expected range of battery voltages.

7. A digital multimeter, comprising:

a battery having a given terminal voltage, said terminal voltage being subject to a decrease in magnitude over time;

a first A/D converter for use in measuring external signals;

a second A/ID converter for monitoring said terminal voltage of said battery

a display device for displaying numerical information; and

a controller for reading data from said first and second A/D converters and causing a display on said display device of numerical data representative of said data read from said first and second A/D converters.

8. The digital multimeter of claim 7, further comprising:

a circuit for increasing the magnitude of the battery voltage for providing operating power to said first A/D converter and extending the dynamic range of said first A/D converter.

9. The digital multimeter of claim 7, wherein said second A/D converter is formed within an integrated circuit including said controller and exhibits a dynamic range encompassing an expected range of battery voltages.