Calibration of liquid flow measuring instruments

Calibration of liquid flow measuring instruments

1. Scope

This calibration specification is applicable to the value transfer of liquid flow measuring instruments filled with closed pipelines. It includes the value transfer relationship, value transfer method, and optimal measurement capability between the main basic and derived quantities, liquid flow measuring reference instruments, liquid flow measuring standard instruments, and liquid flow working measuring instruments.

2. Overview

The national liquid flow measurement standard instrument is a set of primitive water flow standard devices, whose measurement values are determined by mass or volume, density, and time. The liquid flow measurement standard instrument consists of a transmission standard, a liquid flow standard device, a volume tube, and a standard meter method liquid flow standard device. The measurement values of the original liquid flow standard device and volume tube are derived from mass or volume, density, and time, and are linked to the national liquid flow measurement standard instrument through transmission or comparison by a transfer standard.

The measurement value of the standard meter method liquid flow standard device is transmitted from the national liquid flow measurement benchmark instrument, the original method liquid flow standard device, or the volume tube. Liquid flow working measuring instruments refer to various types of liquid flow meters (including velocity area method liquid flow devices), whose measurement values are transmitted from national liquid flow measurement reference instruments or liquid flow measurement standard instruments.

3Instructions for using liquid flow measurement standard instruments

3.1 Liquid flow transmission standard

The liquid flow transmission standard is a measuring standard instrument used to link the values of the reference device and various original liquid flow standard devices. It consists of a high-precision liquid flow meter and front and rear straight pipe sections. The instrument coefficient or indication of the transmission standard is obtained on the reference device and the original liquid flow standard device with an uncertainty of less than 0.1%. The weight of each device's measurement value is proportional to the reciprocal of the square of the device's uncertainty. The uncertainty of its instrument coefficient shall be analyzed according to the method specified in JJF 1059-1999.

3.2 Liquid Flow Standard Device

The liquid flow standard device consists of a liquid source, experimental pipelines, timers, commutators (only for static methods), working meters or scales, etc. It can also be configured with control and data acquisition and processing systems. The measurement range is determined by the measurement range of the working measuring instrument or scale, but the measurement time should be between (30~900) seconds. Its measuring instruments or scales, timers, commutators, etc. should be calibrated. The uncertainty of the device should be better than 0.5%, k=2。 When transmitting measurement values, the device still needs to be equipped with a flow integrator with counting function, a synchronous controller to synchronize the timer and counter with the commutator, a differential pressure transmitter, a thermometer, etc. These instruments should be calibrated according to the corresponding calibration cycle.

3.3 Volume tube

The volume tube consists of a measuring section, a displacement sensor, a detection switch for measuring the position of the displacement sensor, and auxiliary equipment. The flow range depends on the size of the standard volume. The volume of the measuring section of the volumetric tube is calibrated using standard measuring instruments, scales, and density meters with water or solid liquid as the medium. The measurement repeatability should be better than 0.02%, and the measurement uncertainty should be better than 0.05% (k=2).

3.4 Standard Table Method Liquid Flow Standard Device

The standard meter method liquid flow standard device consists of a liquid source, a test pipeline, a standard flowmeter, a timer, etc. It can also be configured with a control and data acquisition and processing system. The flow range depends on the combined flow rate of the standard flowmeter. Among them, the measurement value of the standard flowmeter is obtained by verifying or calibrating the liquid flow measurement reference instrument or liquid flow measurement standard instrument, and the measurement values of other auxiliary equipment should be traced separately. The uncertainty of the device is (0.1~1)%, k=2.

4. Model of liquid flow working measuring instrument

The main measuring instruments for liquid flow include differential pressure flow meters, velocity flow meters (including turbine flow meters, vortex flow meters, electromagnetic flow meters, ultrasonic flow meters, etc.), volumetric flow meters, mass flow meters, rotor flow meters, water meters, target flow transmitters, velocity area method flow standard devices, etc. The measurement value is transmitted from the liquid flow measurement reference instrument or liquid flow measurement standard instrument.

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