Section 3175.132 - Testing of reference accuracy(a) The following reference test conditions must be maintained for the duration of the testing: (1) Ambient air temperature must be between 59 °F and 77 °F and must not vary over the duration of the test by more than ±2 °F;(2) Relative humidity must be between 45 percent and 75 percent and must not vary over the duration of the test by more than ±5 percent;(3) Atmospheric pressure must be between 12.46 psi and 15.36 psi and must not vary over the duration of the test by more than ±0.2 psi;(4) The transducer must be isolated from any externally induced vibrations;(5) The transducer must be mounted according to the manufacturer's specifications in the same manner as it would be mounted in normal field operations;(6) The transducer must be isolated from any external electromagnetic fields; and(7) For reference accuracy testing of differential-pressure transducers, the downstream side of the transducer must be vented to the atmosphere.(b) Before reference testing begins, the following pre-conditioning steps must be followed: (1) After power is applied to the transducer, it must be allowed to stabilize for at least 30 minutes before applying any input pressure or temperature;(2) The transducer must be exercised by applying three full-range traverses in each direction; and(3) The transducer must be calibrated according to manufacturer specifications if a calibration is required or recommended by the manufacturer.(c) Immediately following preconditioning, the transducer must be tested at least three times for accuracy under § 3175.131(h) . The results of these tests must be used to determine the transducer's reference accuracy under § 3175.135 .