§ 3175.131 General requirements for transducer testing. ( a ) All testing must be performed by a qualified test facility.
( b ) *Number and selection of transducers tested.* ( 1 ) A minimum of five transducers of the same make, model, and URL, selected at random from the stock used to supply normal field operations, must be type-tested.
( 2 ) The serial number of each transducer selected must be documented. The date, location, and batch identifier, if applicable, of manufacture must be ascertainable from the serial number.
( 3 ) For the purpose of this section, the term “model” refers to the base model number on which the BLM determines the transducer performance. For example: A manufacturer makes a transmitter with a model number 1234-XYZ, where “1234” identifies the transmitter cell, “X” identifies the output type, “Y” identifies the mounting type, and “Z” identifies where the static pressure is taken. The testing under this section would only be required on the base model number (“1234”), assuming that “X”, “Y”, or “Z” does not affect the performance of the transmitter.
( 4 ) For multi-variable transducers, each cell URL must be tested only once under this section. For example: A manufacturer of a transducer measuring both differential and static pressure makes a model with available differential-pressure URLs of 100 inches, 500 inches, and 1,000 inches, and static-pressure URLs of 250 psia, 1,000 psia, and 2,500 psia. Although there are nine possible combinations of differential-pressure and static-pressure URLs, only six tests are required to cover each cell URL.
( c ) *Test conditions—general.* The electrical supply must meet the following minimum tolerances: ( 1 ) *Rated voltage:* ±1 percent uncertainty;
( 2 ) *Rated frequency:* ±1 percent uncertainty;
( 3 ) Alternating current harmonic distortion: Less than 5 percent; and
( 4 ) *Direct current ripple:* Less than 0.10 percent uncertainty.
( d ) The input and output (if the output is analog) of each transducer must be measured with equipment that has a published reference uncertainty less than or equal to 25 percent of the published reference uncertainty of the transducer under test across the measurement range common to both the transducer under test and the test instrument. Reference uncertainty for both the test instrument and the transducer under test must be expressed in the units the transducer measures to determine acceptable uncertainty. For example, if the transducer under test has a published reference uncertainty of ±0.05 percent of span, and a span of 0 to 500 psia, then this transducer has a reference accuracy of ±0.25 psia (0.05 percent of 500 psia). To meet the requirements of this paragraph (d), the test instrument in this example must have an uncertainty of ±0.0625 psia or less (25 percent of ±0.25 psia).
( e ) If the manufacturer's performance specifications for the transducer under test include corrections made by an external device (such as linearization), then the external device must be tested along with the transducer and be connected to the transducer in the same way as in normal field operations.
( f ) If the manufacturer specifies the extent to which the measurement range of the transducer under test may be adjusted downward (i.e., spanned down), then each test required in §§ 3175.132 and 3175.133 must be carried out at least at both the URL and the minimum upper calibrated limit specified by the manufacturer. For upper calibrated limits between the maximum and the minimum span that are not tested, the BLM will use the greater of the uncertainties measured at the maximum and minimum spans in determining compliance with the requirements of § 3175.31(a).
( g ) After initial calibration, no calibration adjustments to the transducer may be made until all required tests in §§ 3175.132 and 3175.133 are completed.
( h ) For all of the testing required in §§ 3175.132 and 3175.133, the term “tested for accuracy” means a comparison between the output of the transducer under test and the test equipment taken as follows: ( 1 ) The following values must be tested in the order shown, expressed as a percent of the transducer span: ( i ) (Ascending values) 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100; and
( ii ) (Descending values) 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, and 0.
( 2 ) If the device under test is an absolute-pressure transducer, the “0” values listed in paragraphs (h)(1)(i) and (ii) of this section must be replaced with “atmospheric pressure at the test facility;”
( 3 ) Input approaching each required test point must be applied asymptotically without overshooting the test point;
( 4 ) The comparison of the transducer and the test equipment measurements must be recorded at each required point; and
( 5 ) For static-pressure transducers, the following test point must be included for all tests: ( i ) For gauge-pressure transducers, a gauge pressure of −5 psig; and
( ii ) For absolute-pressure transducers, an absolute pressure of 5 psia.