General. The test of any meter or associated devices, or both, shall consist of a comparison of its accuracy with the accuracy of a working standard or may consist of other methods referenced in these regulations. Test Equipment Capacity. The test equipment shall be of sufficient capacity and ranges to test meters or associated devices, or both, under the conditions specified in Regulation .02 of this chapter. Accepted Good Practice. The Commission will use the applicable provisions of the publications listed in COMAR 20.55.02.02 as criteria of accepted good practice in the testing of meters. Bell Provers. Bell provers may be used to test diaphragm, rotary, and turbine type meters. A prover that is used to test rotary and turbine type meters shall be properly automated and have a satisfactory readout. The test shall consist of passing a specific volume of air through the prover and the meter. The accuracy or proof is either read or calculated from the prover scale or the readout. Working Standards Other Than Bell Provers. Approved working standards other than bell provers may be used to test diaphragm, rotary, and turbine type meters. The meter to be tested is connected to the approved working standard so that the same volume of air, either under pressure or vacuum, passes through both. The uncorrected accuracy is calculated or read directly from the readout on the working standard. Corrections shall be made for pressure and temperature differentials between the meter under test and the working standard to determine the corrected accuracy. Rotary Displacement Meters. Rotary meters on which an original test record of the differential pressures is established as soon as practicable, but not longer than 6 months, after installation may subsequently be tested by comparing the new differential pressures with the original test record. This subsequent test may be in lieu of normal testing with a meter prover or other approved working standard. In establishing the original test record, the pressure differential shall be recorded at two or more load levels, with the minimum being no less than 10 percent of the rated capacity at the operating pressure of the meter. The meters shall be given a differential pressure test at least once every 5 years. When the test differential pressure differs from the original test record by more than 50 percent, the meter may not be used for measurement for revenue billing purposes until, by cleaning or repairing, the differential pressure is not more than 50 percent in excess of the original test record. If the differential pressure cannot be brought within the above limits by cleaning or repairing, the meter shall be removed from service and replaced with an accurate meter. The differential pressure test may not be used as a periodic test on rotary meters on which the results of a differential pressure test would not be conclusive, such as meters connected to loads which are less than 10 percent of the rated capacity of the meters. Pressure Correcting Devices. The test of a pressure correcting device shall consist of driving the mechanism or by direct comparison of device measured pressure while the pressure element is actuated. A dead weight tester or regulated air or gas pressure may be used to actuate the pressure element. If regulated air or gas pressure is used, a pressure gauge having an accuracy of ±0.25 percent of full scale shall be used to indicate the pressure on the element. The accuracy is calculated by comparing the correction factor applied by the correcting device with the correction factor that should be applied for the pressure at which the test was made. Temperature Correcting Devices. The test of a temperature correcting device shall consist of driving the mechanism or by direct comparison of device-measured temperature while the temperature sensor is immersed in a temperature bath containing a precision thermometer that has an accuracy of ±0.5°F. Specific, reasonably constant temperatures are applied to the temperature sensor. The temperatures used may be the operating (flowing gas) temperature, ambient temperature, and an ice bath (32°F). The device shall be tested at not less than 2 points, preferably with temperatures at least 20°F apart. The accuracy is calculated by comparing the correction factor applied by the correcting device with the correction factor that should be applied for the temperature at which the test was made. Timing Devices. The test of a timing device shall consist of precisely synchronizing the timing device and the working standard at the start of the test time interval. At the end of the test time interval the working standard is stopped and the reading recorded. The accuracy is calculated by comparing the actual time elapsed with the test time interval. Use of Tolerances. All tolerances are to be interpreted as maximum permissible variation from the condition of zero error. In making adjustments, no advantage of the prescribed tolerance limits may be taken to set meters fast. Reading and Recording Data. Maximum Readability. In any test or calibration, the devices or instruments used in the test or calibration shall be read to the maximum degree of readability. Degree of Accuracy. The degree of accuracy achieved in the calculations involved in determining the accuracy of a meter, prover, device, or instrument in any test or calibration shall be consistent with the purpose for which the resultant accuracy is to be used. Recording. The final accuracy or proof shall be recorded to the nearest 0.5 percent. Overall Accuracies. The overall accuracy or proof of a meter and an associated device, which affects the meter readings for billing purposes, may not be more than 0.5 percent fast or more than 1.5 percent slow. Diaphragm Type Meters. Diaphragm meters may not be placed or left in service unless found upon test to comply with the following: The meter may not be more than 0.5 percent fast nor more than 1.5 percent slow at check flow or at full rated flow. The proof at full rated flow may not differ from the proof at check flow by more than 1 percent. When air is used for testing meters, the rate of flow shall be adjusted to compensate for the difference in the specific gravity of air and the specific gravity of gas. Rotary Type Meters. Rotary type meters shall be tested at not less than 15 percent of full rated flow. A utility may not install a rotary meter which is more than 0.5 percent fast or more than 1.5 percent slow at the points of test. Turbine Type Meters. Turbine type meters shall be tested at not less than 15 percent of full rated flow. The meters may not be more than 0.5 percent fast or more than 1.5 percent slow at the points of test. Pressure Correcting Devices. Pressure correcting devices may not be more than 0.5 percent fast or more than 1.5 percent slow in the pressure range for which the instrument is intended to be used. Temperature Correcting Devices. Temperature correcting devices may not be more than 0.5 percent fast or more than 1.5 percent slow at the points at which they are tested. Timing Devices. Timing devices may not have an error more than 0.25 percent. Meter Condition. Before a meter may be installed for revenue billing purposes the utility shall inspect and test the meter, and adjust it if necessary, so that its proof is within the tolerances specified in Regulation .02. Sample Testing New Meters. New meters may be sample tested for proof in accordance with a utility's sample plan of testing acceptable to the Commission. Leak Test. The meter may not leak when subjected to pressure and checked for leaks by: Immersion; Soap test; or A pressure drop test of a type acceptable to the Commission. Tinned Steel Case Meters. Each meter shall be subjected to an internal pressure of at least 2 psig when testing for leaks. Iron or Aluminum Case Meters. Iron or aluminum case meters shall be tested at a pressure at least 50 percent above operating pressure. The meters may be sample tested in accordance with the plan described in §B. If one or more meters in the sample is found to leak, additional testing shall be done as described in §B. Commission Test. A representative of the Commission will check the condition of meters in the meter shop of the utility from time to time by testing random samples of meters ready for installation. Re-test. When any meter is inactive, whether installed in service or not, for a period of 2 years or longer, it shall be tested, and adjusted if necessary before being placed in service again. Request For Test. Upon request by a customer and at no charge, the utility shall make a test of the accuracy of registration of the meter serving the customer, provided that these tests need not be made more frequently than once in 18 months. Customer May Observe. The customer, or his representative, may be present when the meter is tested. Report to Customer. A report of the results of the test shall be made to the customer within a reasonable time after the completion of the test, and a record of the report, together with a complete record of the test, shall be kept on file at the office of the utility for at least 3 years. Application For Test. Upon written application to the Commission by a customer or a utility, a test will be made of the customer's meter as soon as practicable by a representative of the Commission, provided that these tests need not be made more frequently than once in 18 months. Deposit For Test. The application shall be accompanied by a deposit as indicated: Gas meter—$10. Notice to Utility. On receipt of the request from a customer, the Commission will notify the utility and the utility may not knowingly remove or adjust the meter until instructed by the Commission. The utility shall furnish to the Commission's representative such reasonable assistance as may be required to make the test. Customer May Observe. The customer, or his representative, may be present when the meter is tested. Report to Customer. A written report of the results of the test will be sent to the customer and to the utility. Disposition of Deposit. If the meter is found to over-register more than 2 percent, calculated in accordance with COMAR 20.55.04.05D and Regulation .02B(3) of this chapter, the deposit shall be refunded by the Commission and the utility billed the amount of the deposit. If the meter is found to be not more than 2 percent fast, the deposit will be retained and disposed of according to law. Meters or associated metering devices, or both, shall be tested before they are adjusted, repaired, or retired. Test Program. A utility in-service performance test program shall be designed to automatically adjust the number of meters required to be tested by a utility based solely on the performance of the utility's meters. In-service performance tests shall be made in accordance with the requirements of COMAR 20.55.02.02B. Location of Tests. In-service performance tests may be made on the customer's premises, in the utility's shop, or in an approved meter shop. Analysis of Meter Tests. By Commission. The Commission will review the annual reports of meter test results. By Utility. Each utility shall analyze its meter test results for the purpose of identifying the meter types which have poor accuracy characteristics. Public Utilities Article, §§2-121, 5-101, 7-301, and 7-302, Annotated Code of Maryland Effective date: July 1, 1964 (Order No. 55567) Chapter revised effective October 21, 1974 (Order No. 60922) Regulation .05A, B amended effective May 5, 1986 (13:9 Md. R. 1032) Chapter revised effective February 7, 2000 (27:2 Md. R. 146)