Voltage monitor with visible level indicator

• US 4,488,110 A
• Filed: 12/29/1980
• Issued: 12/11/1984
• Est. Priority Date: 12/29/1980
• Status: Expired due to Fees

• Current Assignee: Electro-Sensors Inc
• Original Assignee: Electro-Sensors Inc
• Inventors: Shirey, Thomas F., Serviss, William C., Young, Curtis H. Jr.
• Primary Examiner(s): Lynch, Michael J.
• Assistant Examiner(s): Snow, Walter E.
• Application Number:
  US06/220,999
• Time in Patent Office: 1,443 Days
• Field of Search: 324/133, 324/196, 324/158 MG, 324/433, 307/358, 307/362, 307/363, 330/69, 330/250, 330/251, 340/660, 340/661, 340/662
• US Class Current: 324/133
• CPC Class Codes: G01R 19/155 Indicating the presence of voltage

Abstract

There is provided a voltage monitor which monitors a first voltage. A means for providing a reference second voltage is provided. Also, a signal third voltage which is obtained from and is proportional to the first voltage is provided. A comparison amplifier for comparing the reference second voltage and the signal third voltage produces an output voltage which goes to a first polarity when the signal third voltage exceeds the reference second voltage and which goes to a second polarity when the signal third voltage is less than the reference second voltage. Also, there is provided at least one indicator and at least one driver amplifier which amplifies the output voltage and drives the indicator into a first state when the output voltage shows that the signal third voltage exceeds the reference second voltage, and drives the indicator into a second state when the output shows that the signal third voltage is less than the reference second voltage. The circuit is arranged so that the power supply voltage and current for all elements of the voltage monitor are taken from the first voltage to be monitored.

Claims

1. A voltage monitor which monitors a first voltage comprising:

(a) a means for providing a fixed reference voltage and an operational amplifier of variable gain with input from said fixed reference voltage whereby the output of said operational amplifier provides a variable reference second voltage, the reference second voltage being at a lesser voltage than said first voltage;

(b) a signal third voltage which is a fraction of said first voltage and is obtained by a voltage divider network from said first voltage;

(c) a comparison amplifier which has a first input to which said reference second voltage is connected and a second input to which said signal third voltage is connected, and an output terminal, the voltage of said output terminal depending upon the difference of the two voltages applied to the first and second inputs;

(d) polarity of said amplifier connected such that when said signal third voltage exceeds said reference second voltage then said output terminal of said comparison amplifier is driven toward ground, and when said signal third voltage is less than said reference second voltage then said output terminal of said comparison amplifier is driven toward power supply voltage;

(e) a first indicator;

(f) a second indicator;

(g) a first driver amplifier

(h) a second driver amplifier;

(i) said first driver amplifier and said second driver amplifier each having its input connected to said output terminal of said comparison amplifier, wherein said first driver amplifier drives said first indicator on when its input is driven toward ground potential and drives said first indicator off when its input is driven toward power supply voltage, and wherein said second driver amplifier drives said second indicator on when its input is driven toward power supply voltage and drives said second indicator off when its input is driven toward ground potential;

(j) power supply for said variable reference second voltage, said comparison amplifier, said first driver amplifier, said second driver amplifier, said first indicator, and said second indicator is taken from said first voltage to be monitored;

whereby the voltage monitor provides an indication of said first voltage to be monitored by turning on said first indicator and turning off said second indicator whenever said first voltage rises above a predetermined level, and turns on said second indicator and turns off said first indicator whenever said first voltage falls below said predetermined level, and further whereby said predetermined level of said first voltage is set by the value of said reference second voltage and the fraction of said first voltage at which said signal third voltage is set, and further whereby all power requirements of the voltage monitor are drawn from said first voltage.

2. A voltage monitor as claimed in claim 1, wherein said

means for providing a fixed reference voltage comprises an integrated circuit precision reference source.

3. A voltage monitor as claimed in claim 1, wherein said

means for providing a fixed reference voltage comprises a zener diode.

4. A voltage monitor as claimed in claim 1, wherein said

operational amplifier comprises an operational amplifier with a first input connected to said fixed reference voltage, and a second input connected to a first end of a fixed resistor and a first end of a variable resistor, the second end of said fixed resistor connected to ground and the second end of said variable resistor connected to the output of said operational amplifier,

whereby said fixed resistor and said variable resistor provide variable feedback for said operational amplifier, and further whereby said output of said operational amplifier provides a variable reference voltage.