Torque Measurement with Increased Accuracy at Lower Torque Values

1 . An apparatus for determining a torque value of an applied torque, the apparatus comprising:

an amplifier configured to receive an analog electrical signal that varies in voltage with the applied torque, and increase an amplitude of the analog electrical signal to produce an amplified, analog electrical signal, the amplifier having a gain that is controllable and set based on a measured torque;

an analog-to-digital converter configured to convert the amplified, analog electrical signal to an equivalent digital electrical signal; and

processing circuitry configured to determine the torque value of the torque applied to the fastener from the equivalent digital electrical signal, and output an indication of the torque value.

2 . The apparatus of claim 1 , wherein the apparatus is an electronic torque wrench, torque tester, torque meter or torque transducer.

3 . The apparatus of claim 1 , wherein the apparatus further comprises:

a strain gauge assembly configured to measure the applied torque, and produce the analog electrical signal that varies in voltage with the applied torque.

4 . The apparatus of claim 1 , wherein the amplifier is a programmable-gain amplifier (PGA) or a variable-gain amplifier (VGA).

5 . The apparatus of claim 1 , wherein the equivalent digital electrical signal includes digital data points, and the processing circuitry configured to determine the torque value includes the processing circuitry configured to:

determine a subset of the digital data points in a moving sample window; and

calculate the torque value from a rolling average of the subset of the digital data points in the moving sample window.

6 . The apparatus of claim 1 , wherein the apparatus further comprises a digital display, and the processing circuitry is configured to output the indication of the torque value to the digital display that is configured to display the torque value.

7 . The apparatus of claim 1 , wherein the processing circuitry is configured to set the gain of the amplifier based on the measured torque, the gain set to a higher value when the measured torque lies at a lower end of a range of torque values, relative to when the measured torque lies at an upper end of the range.

8 . The apparatus of claim 7 , wherein the lower end of the range is below a rated torque range of the apparatus, and the upper end of the range is within the rated torque range.

9 . The apparatus of claim 8 , wherein the gain of the amplifier is set above a predefined gain value gain when the measured torque is below the rated torque range, and set to gain when the measured torque is within the rated torque range.

10 . The apparatus of claim 9 , wherein below the rated torque range includes a first subrange of torque values, and a second subrange of torque values that are greater than the torque values of the first subrange, and

wherein the gain of the amplifier is set to a first value above gain when the measured torque lies within the first subrange, and set to a lower, second value above gain when the measured torque lies within the second subrange.

11 . The apparatus of claim 1 , wherein the processing circuitry is configured to determine the torque value further from a calibration function that maps the equivalent digital electrical signal to the torque value.

12 . The apparatus of claim 11 , wherein the processing circuitry is configured to set the gain of the amplifier to a value from a plurality of predefined gain values, and

wherein the calibration function is a linear function selected from a plurality of linear functions for respective ones of the plurality of predefined gain values, and the plurality of linear functions include respective line segments for respective intervals of torque values over which the gain of the amplifier is set to respective ones of the plurality of predefined gain values.

13 . A method of determining a torque value of an applied torque, the method comprising:

receiving an analog electrical signal that varies in voltage with the applied torque;

applying the analog electrical signal to an amplifier that increases an amplitude of the analog electrical signal to produce an amplified, analog electrical signal, the amplifier having a gain that is controllable and set based on a measured torque;

converting the amplified, analog electrical signal to an equivalent digital electrical signal using an analog-to-digital converter; and

determining the torque value of the torque applied to the fastener from the equivalent digital electrical signal; and

outputting an indication of the torque value.

14 . The method of claim 13 , wherein the method further comprises:

measuring the applied torque, and producing the analog electrical signal that varies in voltage with the applied torque.

15 . The method of claim 13 , wherein the analog electrical signal is applied to the amplifier that is a programmable-gain amplifier (PGA) or a variable-gain amplifier (VGA).

16 . The method of claim 13 , wherein the equivalent digital electrical signal includes digital data points, and determining the torque value includes:

determining a subset of the digital data points in a moving sample window; and

calculating the torque value from a rolling average of the subset of the digital data points in the moving sample window.

17 . The method of claim 13 , wherein the indication of the torque value is output to a digital display that displays the torque value.

18 . The method of claim 13 , wherein the method further comprises setting the gain of the amplifier based on the measured torque, the gain set to a higher value when the measured torque lies at a lower end of a range of torque values, relative to when the measured torque lies at an upper end of the range.

19 . The method of claim 18 , wherein the applied torque is by an electronic torque wrench, the lower end of the range is below a rated torque range of the electronic torque wrench, and the upper end of the range is within the rated torque range.

20 . The method of claim 19 , wherein the gain of the amplifier is set above a predefined gain value gain when the measured torque is below the rated torque range, and set to gain when the measured torque is within the rated torque range.

21 . The method of claim 20 , wherein below the rated torque range includes a first subrange of torque values, and a second subrange of torque values that are greater than the torque values of the first subrange, and

wherein the gain of the amplifier is set to a first value above gain when the measured torque lies within the first subrange, and set to a lower, second value above gain when the measured torque lies within the second subrange.

22 . The method of claim 13 , wherein the torque value is determined further from a calibration function that maps the equivalent digital electrical signal to the torque value.

23 . The method of claim 22 , wherein the method further comprises setting the gain of the amplifier to a value from a plurality of predefined gain values, and

wherein the calibration function is a linear function selected from a plurality of linear functions for respective ones of the plurality of predefined gain values, and the plurality of linear functions include respective line segments for respective intervals of torque values over which the gain of the amplifier is set to respective ones of the plurality of predefined gain values.