Accuracy of Measurement

• Coriolis Mass Flow Meters
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• General Specifications
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• Accuracy of Measurement

Coriolis Mass Flow Meters – Accuracy of Measurement

1. The following flow ranges are provided for water with a temperature range of 20 to 25 ºC, a pressure range of 0.1 to 0.2 MPa, and a density of 1,000 kg/m3 under standard conditions. However, for liquids with a different density, it is necessary to calculate the volumetric flow range by dividing the flow range limits under standard conditions by the actual density value of the liquid.
2. In order to ensure accurate measurements, the coriolis mass flowmeter has a low flow cutoff value. When the measured flow rate falls below this value, the device will indicate zero flow and pause the accumulation of mass and volume. This cutoff value is set to 1% of the maximum flow rate, but it can be easily adjusted through the menu display or using Modbus. By customizing this value, users can fine-tune the performance of the coriolis mass flowmeter to suit their specific needs and applications.
3. Coriolis flow meters are capable of measuring flow rates up to 1% of the maximum full flow range, but accuracy may not be guaranteed within the range of 1% to 2% of the lower limit of the full flow range. It should be noted that this potential measurement error can be estimated using the following formula 1.1.
4. Medium density measurement range is 200…3000 kg/m³.

Relative basic error of measurement of mass flow (mass) on pulse and digital output signals (δ_M) calculated as

δ_M = ± [δ₀ + (Z / Q_M) *100%],

1.1) where δ₀ – accuracy class, %;

Z – zero stability (according to Table 1.2), kg/h;

Q_M – measured mass flow rate, kg/h.

Note – For the accuracy flow range, corresponding to a given accuracy class (according to Table 1.2), the value of Z is assumed to be 0.

Absolute basic error of measurement of medium density (∆ρ) is ± 1 kg/m³.

Absolute basic error of measurement of medium temperature is ± 1 °C.

Additional error of measurement of density, caused by a change of medium temperature is ±0.03 kg/m³ for every 10 ºC of deviation from the density calibration temperature.

Additional error of measurement of density, caused by a change of pressure is ±0.015 kg/m³ for every 100 kPa of deviation from the density calibration pressure.

Relative basic error of measurement of volumetric flow (volume) on pulse and digital output signals (δ_V) calculated as

δ_V = ± [δ₀ + (∆ρ / ρ) *100% + (Z / Q_V) *100%],

1.2) where δ₀ – accuracy class, %;

∆ρ – absolute basic error of measurement of medium density, kg/m³;

ρ – measured medium density, kg/m³;

Z – zero stability (according to Table 1.2), L/h;

Q_V – measured volumetric flow rate, L/h.

Note – For the accuracy flow range, corresponding to a given accuracy class (according to Table 1.2), the value of Z is assumed to be 0.

Relative basic error of measurement of mass flow (mass) on current output signal (δ_IM) calculated as

δ_IM = ± [|δ_M| + 0.2*I_max / (4+16*Q_М / Q_Мmax)],

1.3) where δ_M – Relative basic error of measurement of mass flow (mass), %;

I_max = 20 mA – maximum value of current output signal;

Q_М – measured mass flow rate, kg/h;

Q_Мmax – upper limit of the full mass flow range, kg/h.

Relative basic error of measurement of volumetric flow (volume) on current output signal (δ_IV) calculated as

δ_IV = ± [|δ_V| + 0.2*I_max / (4+16*Q_V / Q_Vmax)],

1.4) where δ_V – Relative basic error of measurement of volumetric flow (volume), %;

I_max = 20 mA – maximum value of current output signal;

Q_V – measured volumetric flow rate, L/h;

Q_Vmax – upper limit of the full volumetric flow range, L/h.

The precision of mass (volumetric) flow rate measurement can be affected by changes in the medium’s temperature. Specifically, there is an additional error of measurement caused by a deviation from the zero calibration temperature, which results in an accuracy loss of ±0.05% of the maximum flow rate for every 10ºC of variation.

The accuracy of mass (volumetric) flow rate measurement is affected by pressure changes, with an additional measurement error of ±0.02% of the maximum flow rate for every 100 kPa deviation from the zero calibration pressure.

To ensure accurate measurements amidst fluctuations in temperature and pressure, it is essential to perform a zero calibration while operating under current temperature and pressure conditions. This zero point adjustment process is elaborated in paragraph 2.5.4 of the guidelines.