Torque spanners

Claim 2

A hand-held tool for tightening threaded fastenings, the tool comprising a housing, a bar mounted in said housing for limited movement relative thereto, a strain gauge mounted on said bar to measure bending moment in said bar and so provide an electrical output voltage dependent on the torque applied, an amplifier circuit mounted in said housing, and an indicating device mounted in said housing, said strain gauge forming part of a bridge circuit whose output feeds into said amplifier circuit, wherein said amplifier circuit comprises a first integrated circuit amplifier and a second integrated circuit amplifier, said first integrated circuit amplifier being arranged to amplify said output of said bridge circuit and having an output fed into said second integrated circuit amplifier, and said second integrated circuit amplifier being arranged to compare said output of said first integrated circuit amplifier against a preset trip voltage so that the output of said second integrated circuit amplifier will actuate said indicating device as soon as said output of said first integrated circuit amplifier is marginally greater than said preset trip voltage, thereby to indicate to the operator that the torque has reached a prescribed value.

Claim 3

A tool according to claim 1, wherein said indicating device is a light emitting diode.

Claim 4

A tool according to claim 1, wherein said indicating device is a relay coupled to a device for emitting an audible signal.

Claim 5

A tool according to claim 1, wherein means is provided for varying the amount of said preset trip voltage thereby to vary the prescribed value of torque.

Claim 6

A tool according to claim 4, wherein said means comprises a number of resistors in series across a supply voltage to provide a number of distinct points at different voltages, and a switch arranged to select one of these voltages as said trip voltage.

Claim 7

A tool according to claim 1, wherein negative feed-back is provided across one of the integrated circuit amplifiers, said negative feed-back being variable in amount to provide different values for the prescribed value of torque.

Claim 8

A tool according to claim 1, which is arranged to be powered by a battery mounted in said housing.

Claim 9

A tool according to claim 7, wherein said battery is a rechargeable battery.

Claim 10

A tool according to claim 1, wherein said bar has a socket of non-circular cross-section extending from said housing.

Claim 11

A tool according to claim 9, wherein said socket has a square cross-section.

Claim 12

A tool according to claim 9, further comprising an ON/OFF switch operated by said relative movement of said bar on application of torque by the operator.

Claim 13

A tool according to claim 1, wherein said indicating device is a milliameter.

Claim 14

A torque spanner comprising a housing, a bar mounted in said housing for limited relative movement, a strain gauge mounted on said bar to measure bending moment, in said bar, said bar having a socket of square cross-section extending from said housing, said strain gauge providing an electrical output voltage dependent upon the torque applied, an amplifier circuit mounted in said housing, an indicating device mounted in said housing, and a battery mounted in said housing, said strain gauge forming part of a bridge circuit whose output feeds into said amplifier circuit, wherein said amplifier circuit comprises a first integrated circuit amplifier and a second integrated circuit amplifier, said first integrated circuit amplifier being arranged to amplify said output of said bridge circuit and having an output fed into said second integrated circuit amplifier, and said second integrated circuit amplifier being arranged to compare said output of said first integrated circuit amplifier against a preset trip voltage so that the output of said second integrated circuit amplifier will actuate said indicating device as soon as said output of said first integrated circuit amplifier is marginally greater than said preset trip voltage, thereby to indicate to the operator that the torque has reached a prescribed value.

Claim 15

A torque spanner comprising a housing, a bar mounted in said housing for limited relative movement, a strain gauge mounted on said bar to measure bending moment, in said bar, said bar having a socket of square cross-section extending from said housing, said strain gauge providing an electrical output voltage dependent upon the torque applied, an amplifier circuit mounted in said housing, an indicating device mounted in said housing, and a battery mounted in said housing, said strain gauge forming part of a bridge circuit whose output feeds into said amplifier circuit, wherein said amplifier circuit comprises a first integrated circuit amplifier and a second integrated circuit amplifier, said first integrated circuit amplifier being arranged to amplify said output of said bridge circuit and having an output fed into said second integrated circuit amplifier, and said second integrated circuit amplifier being arranged to compare said output of said first integrated circuit amplifier against a preset trip voltage so that the output of said second integrated circuit amplifier will actuate said indicating device as soon as said output of said first integrated circuit amplifier is marginally greater than said preset trip voltage, thereby to indicate to the operator that the torque has reached a prescribed value.