Voltage indicator using serial comparison voltage measurement

• US 5,998,985 A
• Filed: 02/20/1998
• Issued: 12/07/1999
• Est. Priority Date: 02/20/1998
• Status: Expired due to Fees

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: Gallavan, Michael F.
• Primary Examiner(s): Ballato, Josie
• Assistant Examiner(s): Brown, Khaled
• Application Number:
  US09/026,934
• Time in Patent Office: 655 Days
• Field of Search: 324/133, 324/122, 340/510, 340/511
• US Class Current: 324/133
• CPC Class Codes: G01R 13/405 using a plurality of active, i.e. light emitting, e.g. electro-luminescent elements, i.e. bar graphs
• CPC Class Codes: G01R 19/165 Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
• CPC Class Codes: G01R 19/2503 for measuring voltage only, e.g. digital volt meters (DVM's) G01R19/2506 - G01R19/257 take precedence
• CPC Class Codes: H03M 1/56 Input signal compared with linear ramp

Abstract

A voltage indicator using a serial or sequential comparison voltage measurement technique. Reference voltages generated by a voltage divider are applied to inputs of a multiplexer which is driven by a counter to select one reference voltage at a time in sequence to be presented via an output terminal to one input of a voltage comparator. An input signal to be measured is applied the other input of the comparator. When the input signal matches or exceeds the reference voltage at the output terminal of the multiplexer, the comparator switches, providing an enable signal to a one-of-N decoder. The one-of-N decoder is also driven by the counter, so that outputs of the decoder and corresponding inputs of the multiplexer are addressed simultaneously. The outputs of the one-of-N decoder are connected to LEDs which indicate the voltage level or magnitude. The voltage input signal may be applied via a conditioning amplifier that scales the input signal and an absolute value amplifier which provides an output in one polarity for comparison purposes. DC voltage polarity is detected and may be indicated by separate LEDs. Additionally, an AC/DC decode logic circuit may be provided to discern between AC and DC input voltages, and provide appropriate indication. While the preferred embodiment contemplates that both nominal AC and DC reference voltages may be provided by the same voltage divider, a gain control signal may be provided to change the gain of the absolute value amplifier by a ratio of √2 so that the same reference values may be used for both AC and DC measurements.

Claims

1. A voltage indicating circuit, comprising:

an input terminal for receiving an input voltage;

a multiplexer having a plurality of reference voltages applied to inputs thereof;

a one-of-N decoder having a plurality of indicator devices coupled to outputs thereof;

a control circuit for causing said multiplexer and said one-of-N decoder to operate in a sequence such that corresponding inputs of said multiplexer and outputs of said one-of-N decoder are simultaneously activated in pairs; and

a comparator coupled to said input terminal and to an output of said multiplexer for comparing said input voltage with said plurality of reference voltages and enabling said one-of-N decoder when said input voltage is at least in as great a magnitude as a reference voltage thereby to activate said plurality of indicator devices corresponding to said plurality of reference voltages.

2. A voltage measuring circuit in accordance with claim 1 further comprising an absolute value amplifier disposed between said input terminal and said comparator.

3. A voltage measuring circuit in accordance with claim 2 further comprising a polarity detector to determine the polarity of the input voltage and at least one polarity indicator to indicate the polarity detected.

4. A voltage measuring circuit in accordance with claim 1 further comprising an AC/DC decode logic circuit for discerning whether said input voltage is AC or DC, and providing appropriate AC or DC indication.