1. Calibration basis ( reference ) : J JG10 29-20 07

2. Calibration location: Gas flow station

3. Standard Instruments

Critical flow Venturi nozzle gas flow standard device (referred to as the device) U = 0.33% ( k = 2).

    The critical flow Venturi nozzle gas flow standard device mainly consists of a nozzle, a stagnation container, a temperature and humidity measuring instrument for measuring the stagnation of the nozzle upstream, a pressure measuring instrument, a pipeline, a temperature and pressure measuring instrument at the flow meter to be calibrated, a timer, a control system for controlling the equipment in the device and for data acquisition and processing, and some other auxiliary equipment, as shown in Figure 1.

Figure 1 Critical flow Venturi nozzle gas flow standard device

1. Calibration method

1) Preparation before calibration

Confirm whether the test environment conditions are met: the ambient temperature is generally (5~45)℃; the relative humidity is generally 35%~95%; the atmospheric pressure is generally (86 ~ 106) kPa. Start the device calibration system software, enter the calibration task interface, determine the calibration project according to user requirements, fill in the basic information of the flow meter to be calibrated, and set related parameters.

Calibration task interface

Set the relevant parameters to form a table and confirm the table contents.

2) Appearance inspection

Random Documents: The flow meter should have an instruction manual. The instruction manual should include the name, model, manufacturer, measuring medium, working pressure range, working temperature range, applicable diameter, flow range, cut-off flow rate (if the flow meter has this indicator), explosion-proof grade and explosion-proof certificate number (for use in flammable and explosive environments), protection level, etc.

Marking and nameplate: The flow meter body should have a clear flow direction marking. The flow meter should also have a nameplate. The nameplate should generally indicate the name, model, factory serial number, medium used, flow range, caliber, accuracy level, maximum working pressure, manufacturer and manufacturing date, and other technical requirements.

Appearance: Newly manufactured flowmeters should have good surface treatment and should be free of burrs, scratches, cracks, rust, mildew, and coating peeling. The sealing surface should be flat and free of damage.

The welding of the flow meter body and the vortex generator should be smooth and clean, without any cold welding or desoldering.

The flow meter connectors must be firm and reliable and must not become loose or fall off due to vibration.

The flow meter buttons should have a moderate feel and no sticking.

3) According to the requirements of the regulations: the flow direction marked on the flow meter should be consistent with the flow direction of the fluid, the flow meter should be consistent with the axial direction of the device calibration pipeline, and the installation position should meet the requirements of the front and rear straight pipe sections in the manual. There should be no leakage in the connection between the flow meter and the device calibration pipeline, and the sealing gasket at the connection should not protrude into the pipeline. Install the flow meter into the pipeline and install the pressure tube in the pressure hole downstream of the flow meter. After confirming that the calibrated flow meter meets the installation requirements, connect the output signal of the calibrated flow meter to the flow calibration system and turn on the power of the flow meter. The numbers displayed on the flow meter should be eye-catching and neat, and the text symbols and logos indicating the functions should be complete, clear and correct. The various markings on the flow meter are correct; the protective glass of the flow meter display numbers should have good transparency and no defects that distort the readings or hinder the display. Check the relevant parameters of the flow meter according to the method specified in the flow meter manual.

4) Run the instrument at 70% to 100% of the maximum flow rate for 5 minutes until the fluid temperature, pressure, and flow rate stabilize before calibrating.

5) K-factor calibration

On the calibration interface of the calibration system, adjust the flow rate to the specified calibration flow rate point. After the pressure, temperature, and back pressure ratio stabilize, click Start Calibration. The system will measure the nozzle flow rate and the pulses of the flowmeter being tested. After the set measurement time, the device will display the nozzle flow rate, measurement time, and the accumulated pulse count of the flowmeter being tested. The coefficient of the flowmeter being calibrated for that flow point will be calculated. Repeat this process three times to complete the measurement of one flow point. Repeat the above steps until all specified flow points are calibrated.

Calibration interface

2. Calibration records

1) Save calibration records in file format

After the calibration is completed, the software system automatically generates and displays the calibration record. As shown in the following figure:

Click the "Save" button of the calibration record file marked in the figure below and confirm, and the calibration record will be saved and saved in the database of the system software.

2) Calibration record management

In the calibration record query interface, you can query and delete the calibration records saved in the access database.

Calibration record query interface and calibration record search condition input interface

4. Data Processing -Error Calculation

_coefficient Kij calculated according to formula (1) for each calibration should meet the requirements for flow meter error limits in Table 1 of JJG10 29-2007.

  (1)

Where: K _{i j} is the instrument factor measured at the i-th measuring point for the jth time, and the unit is 1/ m ³ ;

  N _{i j} is the number of pulses of the flow meter measured at the jth time at the i-th measuring point;

  V _{si j} is the actual gas volume value measured by the device at the i-th measuring point for the jth time and corrected to the measured flow meter, in units of m ³ .

Ki for each calibration point according to formula (2) _:

  (2)

Where: Ki _is the average instrument factor of the i-th measuring point, the unit is 1 / m3 ^;

  n is the number of calibrations for each flow calibration point.

Calculate the flow meter's instrument coefficient K according to formula (3):

   (3)

Where: ( Ki _{) max} , ( Ki ) _min is the maximum and minimum value of the K coefficient _of each calibration flow point within the range of qt≤qx≤qmax

Relative indication error of pulse output flowmeter:

In the range of qt≤qx≤qmax,
          (4)

In the range of qmin≤qx≤qt,
              (5)

5. Uncertainty Assessment

1. Measurement basis

JJG 1029-2007 Vortex Flowmeter.

2. Measurement data

Table 1 Vortex flowmeter measurement data

3. Uncertainty analysis

The main sources of the composite standard uncertainty of the instrument factor are the relative uncertainty introduced by the standard device and the relative uncertainty introduced by the measurement repeatability.

(6)

3.1 Uncertainty introduced by gas flow meter measurement repeatability u _r ( s )

the input quantity Ni (number of pulses ^{in a single measurement) is mainly introduced by} _the measurement repeatability of the vortex flowmeter. Selecting Qmax flow rate as 300 m3 /h, the measurement is repeated 3 times under repeated conditions, and the repeatability is s=0.813%.

Therefore the mean experimental standard deviation is:

Uncertainty introduced by the sonic nozzle gas flow standard device u _r ( )

The sonic nozzle gas flow standard device is traceable to the superior metrology agency, the China Institute of Metrology. The uncertainty of the standard device, U _{r, can be known from the certificate.} =0.33 % ( k =2), then the absolute uncertainty introduced by the sonic nozzle gas flow standard device is u _r ( ) = 0.33 %/2= 0.165%

4 Evaluation of combined standard uncertainty

4.1 Summary table of standard uncertainty

Table 2 Summary of standard uncertainties

Since the above input uncertainty components are independent of each other in batches, the combined standard uncertainty is:

5 Evaluation of expanded uncertainty

Taking coverage factor k = 2, U _rel ≈ 0.1.00%

6 Reporting and Expression of Measurement Uncertainty

of the vortex flowmeter at the flow point of 300 m ³ /h is K =8912.48 (1/ m ³ ), and the relative uncertainty is: U _rel ≈1.00%, k =2.

7. Evaluation of measurement uncertainty in vortex flowmeter calibration using a sonic nozzle gas flow standard device

Within the flowmeter range, three flow points of 0.4 Q max, 0.2 Q max and Q min are selected _for calibration _, and their _instrument factors are _K ( 0.4 Q max ₎ = 9009.29 (1/ m3 ), K (0.2 Q _max ) = 8934.24 (1/ m3 ⁾ , and K ⁽ Q min _{) =} 9036.78 (1/ m3 ⁾ , respectively. The measurement uncertainties are shown in Table 3.

Table 3 Measurement uncertainty

5. Calibration results:

Critical Flow Venturi Nozzle Gas Flow Standard Device for Calibration of Flow Meters