91.306 Dynamometer torque cell calibration.§ 91.306 Dynamometer torque cell calibration.
(a)(1) Any lever arm used to convert a weight or a force through a distance into a torque must be used in a horizontal position for horizontal shaft dynamometers (±five degrees). For vertical shaft dynamometers, a pulley system may be used to convert the dynamometer's horizontal loading into the vertical plane.
(2) Calculate the indicated torque (IT) for each calibration weight to be used by:IT = Moment Arm (meters) × Calibration Weight (Newtons)
(3) Attach each calibration weight specified in § 91.305(b)(2) to the moment arm at the calibration distance determined in paragraph (a)(2) of this section. Record the power measurement equipment response (N-m) to each weight.
(4) Compare the torque value measured to the calculated torque.
(5) The measured torque must be within two percent of the calculated torque.
(6) If the measured torque is not within two percent of the calculated torque, adjust or repair the system. Repeat steps in paragraphs (a)(1) through (a)(6) of this section with the adjusted or repaired system.
(b) Option. A master load-cell or transfer standard may be used to verify the torque measurement system.
(1) The master load-cell and read out system must be calibrated with weights specified in § 91.305(b)(2).
(2) Attach the master load-cell and loading system.
(3) Load the dynamometer to a minimum of three equally spaced torque values as indicated by the master load-cell for each in-use range used.
(4) The in-use torque measurement must be within two percent of the torque measured by the master system for each load used.
(5) If the in-use torque is not within two percent of the master torque, adjust or repair the system. Repeat steps in paragraphs (b)(2) through (b)(4) of this section with the adjusted or repaired system.
(c) Calibrated resistors may not be used for dynamometer torque transducer calibration, but may be used to span the transducer prior to engine testing.
(d) Other engine dynamometer system calibrations such as speed are performed as specified by the dynamometer manufacturer or as dictated by good engineering practice.