We are manufacturer of Solar Inverter in China,OEM and ODM are acceptable, if you want to buy Off Grid Hybrid Inverter,Solar Power Inverter, please contact us.
Solar Power Inverter,Solar Inverter,Hybrid Inverter,Solaredge Inverter,Solar Power Inverter suzhou whaylan new energy technology co., ltd , https://www.xinlingvideo.com
Rotary piston flowmeters are a type of volumetric flowmeter known for their reliable operation, high measurement accuracy, and minimal pressure loss. These devices are particularly effective when the medium has a viscosity greater than 50 cp, as changes in viscosity do not significantly affect measurement accuracy. They are ideal for measuring both instantaneous and cumulative flow rates of liquid media that do not contain solid particles.
Over time, these instruments may require repairs, and calibration data often reveals that many units have gone out of tolerance. This article aims to analyze the measurement principle and structural composition of rotary piston flowmeters to identify the root causes of measurement errors and explore practical correction methods.
**Analysis of Measurement Principle**
The rotary piston flowmeter operates based on the continuous filling and emptying of a measuring chamber (V1 + V2), as illustrated in Figure 1. The measuring mechanism includes a cover, a rotating piston, and a partition plate. The slotted piston features two upper and lower piston pins, while the partition plate is radially positioned between the inlet and outlet. The measuring chamber pin is concentric with the guide ring.
During operation, the slot of the slotted piston moves linearly along the diaphragm, while the piston pin rotates around the guide ring. Since the volume of the measuring chamber remains constant, the instantaneous flow rate depends solely on the rotational speed of the piston, and the cumulative flow rate is determined by the number of revolutions.
**Measurement Error Generation and Correction**
**1. Errors Caused by Changes in Measuring Chamber Volume**
During use, pressure fluctuations in the pipeline can cause the piston to rotate too quickly, leading to impacts on the partition plate and potential bending or cracking of the diaphragm. This can result in misalignment of the piston, causing excessive wear on the inner walls of the measuring chamber, the piston’s end faces, and the partition plate. In such cases, grinding of the measuring chamber and piston is necessary to restore free rotation and re-measure the flow.
However, repeated grinding alters the dimensions of the measuring chamber. For example:
- Before grinding: V = (V1 + V2) = [(D² - d²) + (D1² - d1²)]
- After grinding: D and D1 increase, while d and d1 decrease, resulting in a new volume V’ = V + ΔV.
This change in volume leads to a deviation in the measured flow rate. If left uncorrected, this error can accumulate over multiple inspections, exceeding the device’s accuracy range.
To correct this, two main approaches are commonly used:
**(a) Gear Replacement Based on Calibration Data**
Many flowmeters use a gear system to transmit signals. By replacing the paired gears with those calibrated to account for the volume change, the error can be corrected. For instance, if a flowmeter with an accuracy of 0.5% shows a calibration error of -1.27%, the gears can be replaced with ones that adjust the ratio accordingly, restoring the meter's accuracy.
**(b) Coefficient Adjustment via System Configuration**
Modern control systems, such as distributed control systems (DCS) or KMM digital regulators, allow for coefficient adjustments. By modifying the ratio factor (k), the measured value can be adjusted to reflect the actual flow. For example, if the measured flow is 2.5 m³/h but the actual value is 2.465 m³/h due to temperature changes, the system can be configured to apply a correction factor and display the accurate value.
**2. Errors Caused by Temperature-Induced Density Changes**
Temperature variations can significantly impact the density of liquid media, even though pressure effects are negligible. For example, ethylene glycol at 180°C has a density of 986 kg/m³, while at 165°C, it increases to 1000 kg/m³. If the mass flow rate is kept constant, the volume flow rate will change, leading to inaccurate readings.
In chemical processes where mass flow is critical, it is essential to account for these temperature-induced density changes. Unlike mechanical errors, these cannot be corrected by gear replacement or coefficient adjustment. Instead, the setpoint must be manually adjusted to maintain accurate measurements.
**Conclusion**
This article has explored the measurement principles and common sources of error in rotary piston flowmeters, including volume changes from wear and temperature-induced density shifts. Practical correction methods—such as gear replacement, coefficient adjustment, and manual setpoint recalibration—can help restore accuracy and ensure reliable performance in industrial applications. These solutions are simple to implement and can significantly improve the long-term reliability of flow measurement systems.