43 CFR §3175.132

1. (a)The following reference test conditions must be maintained for the duration of the testing:
   1. (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. (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. (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. (4)The transducer must be isolated from any externally induced vibrations;
   5. (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. (6)The transducer must be isolated from any external electromagnetic fields; and
   7. (7)For reference accuracy testing of differential-pressure transducers, the downstream side of the transducer must be vented to the atmosphere.
2. (b)Before reference testing begins, the following pre-conditioning steps must be followed:
   1. (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. (2)The transducer must be exercised by applying three full-range traverses in each direction; and
   3. (3)The transducer must be calibrated according to manufacturer specifications if a calibration is required or recommended by the manufacturer.
3. (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.