Typical accuracy envelope of electromagnetic flowmeter

Primary device

1. Required data

The following data shall be printed on the primary device or on the nameplate:

a) Instrument type and serial number;
b) Rated pressure and rated temperature:
c) Power supply: voltage, frequency and power (independent power supply).

2. Optional data

The following data may be provided optionally:

a) Enclosure protection level;
b) Nominal diameter;
c) Calibration factor;
d) Lining material;
e) Electrode material.

Note: If the size of the nameplate allows, additional information such as trademark, device weight, manufacturing date, flow direction arrow, etc. may also be included.

Secondary device

1. Required data

The following data shall be printed on the nameplate

a) Instrument type and serial number,
b) Power supply: voltage, frequency and power;
c) Output signal;
d) Limit load impedance.

2. Optional data

The following data may be provided optionally:

a) Enclosure protection level.

Note: If the size of the nameplate allows, additional information such as trademark, manufacturing date, etc. may also be included.

Calibration and test conditions

Wet calibration

The calibration coefficient shall be determined by wet calibration with water on the test device under reference (nominal calibration) conditions (see 9 2). The conditions for calibration shall make the measurement traceable to national or international standards, so that the calibration is for known uncertainties. For example, GB/T17612 and ISO 8316 give applicable calibration methods. GB/T 18659 also gives evaluation methods for electromagnetic flowmeters. When the secondary device is too large to be installed on the manufacturer's test device, or the test device flow is insufficient, another larger flow test device can be used. If this is not possible, the user's container or water tank can be used for on-site calibration, or another reference flowmeter in the system can be used for comparison. The total uncertainty shall be determined as specified in Chapter 10. The method based on magnetic induction intensity measurement and calculation of the primary device signal based on physical dimensions, which is usually called "dry calibration", is not within the scope of this standard.

Nominal calibration conditions

Nominal calibration conditions are those conditions that should be met during calibration. These nominal calibration conditions should be specified by the manufacturer. For comparison purposes. The flowmeter should be tested within the environmental range and flow conditions specified in GB/T18659. If the flowmeter has reached thermal equilibrium, when the influencing quantities remain within the operating limits specified by the manufacturer, it can usually be assumed that their influence on the metering characteristics of the flowmeter can be ignored.

Interpretation of results

1. Reference accuracy envelope

The manufacturer should provide the range of operating conditions and their influence on performance. For details on the relevant content of evaluating flowmeter performance, please refer to GB/T 18659. The current practice is to specify a reference accuracy envelope over a specified flow range. The typical reference accuracy envelope is shown in the figure.

Typical accuracy envelope

2. Accuracy under reference conditions

The accuracy of the flowmeter under reference conditions is determined by the combination of random and systematic uncertainties in the flowmeter signal and volume flow measurement. The upper and lower limits of the uncertainty of each data point should be within the accuracy envelope (chart) provided by the manufacturer.

Deviation from reference conditions

Deviation from reference test conditions may affect the performance of the flowmeter. Although these effects are usually compensated in the secondary device, the manufacturer should also specify an error limit for each influencing quantity.

Pressure test

As required, the primary device or measuring tube should be subjected to appropriate pressure specification standard tests. (end)