# Title 40

## SECTION 1065.310

### 1065.310 Torque calibration.

§ 1065.310 Torque calibration.(a) *Scope and frequency.* Calibrate all torque-measurement
systems including dynamometer torque measurement transducers and
systems upon initial installation and after major maintenance. Use
good engineering judgment to repeat the calibration. Follow the
torque transducer manufacturer's instructions for linearizing your
torque sensor's output. We recommend that you calibrate the
torque-measurement system with a reference force and a lever
arm.

(b) *Recommended procedure to quantify lever-arm length.*
Quantify the lever-arm length, NIST-traceable within ±0.5%
uncertainty. The lever arm's length must be measured from the
centerline of the dynamometer to the point at which the reference
force is measured. The lever arm must be perpendicular to gravity
(i.e., horizontal), and it must be perpendicular to the
dynamometer's rotational axis. Balance the lever arm's torque or
quantify its net hanging torque, NIST-traceable within ±1%
uncertainty, and account for it as part of the reference
torque.

(c) *Recommended procedure to quantify reference force.* We
recommend dead-weight calibration, but you may use either of the
following procedures to quantify the reference force,
NIST-traceable within ±0.5% uncertainty.

(1) *Dead-weight calibration.* This technique applies a
known force by hanging known weights at a known distance along a
lever arm. Make sure the weights' lever arm is perpendicular to
gravity (i.e., horizontal) and perpendicular to the dynamometer's
rotational axis. Apply at least six calibration-weight combinations
for each applicable torque-measuring range, spacing the weight
quantities about equally over the range. Oscillate or rotate the
dynamometer during calibration to reduce frictional static
hysteresis. Determine each weight's reference force by multiplying
its NIST-traceable mass by the local acceleration of Earth's
gravity, as described in § 1065.630. Calculate the reference torque
as the weights' reference force multiplied by the lever arm
reference length.

(2) *Strain gage, load transducer, or proving ring
calibration.* This technique applies force either by hanging
weights on a lever arm (these weights and their lever arm length
are not used as part of the reference torque determination) or by
operating the dynamometer at different torques. Apply at least six
force combinations for each applicable torque-measuring range,
spacing the force quantities about equally over the range.
Oscillate or rotate the dynamometer during calibration to reduce
frictional static hysteresis. In this case, the reference torque is
determined by multiplying the force output from the reference meter
(such as a strain gage, load transducer, or proving ring) by its
effective lever-arm length, which you measure from the point where
the force measurement is made to the dynamometer's rotational axis.
Make sure you measure this length perpendicular to the reference
meter's measurement axis and perpendicular to the dynamometer's
rotational axis.