AUTOMATIC ZERO DEVICE

• US 3,784,912 A
• Filed: 08/11/1972
• Issued: 01/08/1974
• Est. Priority Date: 08/11/1972
• Status: Expired due to Term

• Current Assignee: Harold R Van Aken
• Original Assignee: Harold R Van Aken
• Inventors: Van Aken, Harold R.
• Primary Examiner(s): Strecker, Gerard R.
• Assistant Examiner(s): Karlsen, Ernest F.
• Application Number:
  US05/279,960
• Time in Patent Office: 515 Days
• Field of Search: 324/130,99D,99R 330/9
• US Class Current: 324/130
• CPC Class Codes: G01R 17/06 Automatic balancing arrangements

Abstract

An automatic zeroing device for use with a measuring instrument is described. The device automatically causes the instrument to read a predetermined value, termed the zero value, in response to an input signal, regardless of the value of the input signal. The device is based on a modification of a digital to analog converter in a feedback loop which also includes a summing amplifier, receiving the input signal and a zeroing signal, and a comparator. The digital to analog converter produces the zeroing signal in response to the comparator output.

Claims

1. A device for automatically causing a voltage responsive measuring instrument to register a predetermined reading in response to an input signal having a value other than that corresponding to said predetermined reading comprising:

a. a summing amplifier receiving said input signal and a varying zeroing signal;

b. a comparator, one input of which receives the output of said summing amplifier, a second input receiving a signal corresponding to said predetermined reading;

c. a pulse source responsive to said comparator for producing pulse signals when the summing amplifier output does not correspond to said signal which corresponds to the predetermined reading;

d. a digital to analog converter comprising a counter, incremented in response to said pulse signals, a resistive ladder network, transistor switches coupled between the stages of said counter and selected resistors of said ladder network for selectively switching said resistors into or out of said ladder network in response to the count in said counter and a ladder network summing amplifier, an input of which is coupled to said ladder network, its output supplying said zeroing signal, said zeroing signal being incrementally varied in response to the count in said counter;

e. said pulse source ceasing to produce pulse signals in response to correspondence between said summing amplifier output and said signal which corresponds to the predetermined reading, said counter storing the count which resulted in said correspondence.

2. The device of claim 1 further including a trigger means for initiating a zeroing operation, said trigger means comprising a manually operable switch and means responsive to the closing of said switch for resetting said counters and for supplying an enabling signal to said pulse source, said enabling signal when combined with the comparator output when the input signals thereto do not correspond, triggering said pulse source into operation.