Sensitivity coding circuit for an electronic instrument

• US 3,943,440 A
• Filed: 10/03/1974
• Issued: 03/09/1976
• Est. Priority Date: 10/03/1974
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Edwards, Allen P.
• Primary Examiner(s): Rolinec, R. V.
• Assistant Examiner(s): Karlsen, Ernest F.
• Application Number:
  US05/511,908
• Time in Patent Office: 523 Days
• Field of Search: 324/95, 324/115
• US Class Current: 324/95
• CPC Class Codes: G01R 15/09 Autoranging circuits
• CPC Class Codes: G01R 21/04 in circuits having distributed constants

Abstract

A power meter having a remote power transducer is provided with a circuit for measuring the value of a resistor in the transducer to indicate and automatically adjust the power measuring circuitry for the sensitivity of the transducer used.

Claims

1. A transducer sensitivity coding circuit for an electronic instrument having measurement circuits and a remote transducer unit connected to the electronic instrument by a cable, the electronic instrument employing different transducers for different measurement ranges, the transducer sensitivity coding circuit automatically providing information to the electronic instrument of the transducer sensitivity comprising:

a fixed value resistor mounted in the transducer unit having a value indicative of the sensitivity of a particular transducer unit;

a current supply circuit in the electronic instrument connected to the cable for supplying a current to the resistor to develop a resistor voltage across the resistor; and

comparator means in the electronic instrument, connected to the cable and the measurement circuits, for comparing the resistor voltage with a plurality of reference voltages for producing a signal indicative of the value of the resistor in the transducer unit to adjust the sensitivity of the measurement circuits.

2. A transducer sensitivity coding circuit as in claim 1 wherein the comparator means comprises:

a first reference voltage supply;

a first comparator having a first input connected to the resistor via the cable, having a second input connected to the first reference voltage supply, and having an output, for comparing the resistor voltage with the first reference voltage for giving a first output signal when the resistor voltage is greater than the first reference voltage and a second output signal when the resistor voltage is less than the first reference voltage;

a second reference voltage supply connected to the output of the first comparator for supplying a second reference voltage which has a first value in response to the first comparator first output signal and a second value in response to the first comparator second output signal; and

a second comparator having a first input connected to the resistor via the cable, having a second input connected to the second reference voltage supply, and having an output, for comparing the resistor voltage with the second reference voltage for giving a first output signal when the resistor voltage is greater than the second reference voltage and a second output signal when the resistor voltage is less than the second reference voltage.

3. A transducer sensitivity coding circuit as in claim 2 wherein the comparator means further comprises:

a third reference voltage supply connected to the outputs of the first and second comparators for supplying a third reference voltage which has a first value in response to the first comparator first output signal and the second comparator first output signal, a second value in response to the first comparator first output signal and the second comparator second output signal, a third value in response to the first comparator second output signal and the second comparator first output signal, and a fourth value in response to the first comparator second output signal and the second comparator second output signal; and

a third comparator having a first input connected to the resistor via the cable, having a second input connected to the third reference voltage supply, and having an output, for comparing the resistor voltage with the third reference voltage for giving a first output signal when the resistor voltage is greater than the third reference voltage and a second output signal when the resistor voltage is less than the third reference voltage.

4. A transducer sensitivity coding circuit as in claim 3 wherein the comparator means further comprises a fourth comparator having an input connected to the cable and having an output connected to the measurement circuits for producing a signal to indicate whether the resistor is connected to the cable.

5. A transducer sensitivity coding circuit as in claim 3 wherein:

the voltage that can be developed by the current supply circuit across a resistor having the highest of the plurality of values is V;

the first reference voltage is V/2;

the first value of the second reference voltage is V/4 and the second value of the second reference voltage is 3V/4; and

the first value of the third reference voltage is V/8, the second value of the third reference voltage is 3V/8, the third value of the third reference is 5V/8 and the fourth value of the third reference is 7V/8.