Yokogawa RAMC flowmeter selection and troubleshooting

Yokogawa RAMC flowmeter selection and troubleshooting

In chemical, petrochemical, water treatment, and situations where opaque, corrosive, or turbulent fluids need to be measured, short tube rotor flow meters are still the most intuitive and economical type of flow instrument on site. The Yokogawa Rota RAMC series adopts a vertical installation and upward flow measurement method. The float is guided concentric inside a special conical metal tube, and its position is transmitted to the indicator through magnetic coupling. Therefore, mechanical indication can be achieved without the need for power supply, with low pressure loss and suitable for long-term online operation. For engineers, the difficulty of RAMC is usually not whether it can be measured, but whether the process connection, temperature and pressure boundary, liquid material, limit switch, intrinsic safety or explosion-proof certification, installation of straight pipe sections, and gas application back pressure are all confirmed clearly at once when selecting. Taking on-site selection, installation, and troubleshooting as the main line, combined with key data in technical materials, a set of practical reference ideas is provided below.

Measurement principle, range and accuracy boundary

RAMC belongs to variable area flow meters. The fluid passes through a conical measuring tube from bottom to top, and the float is lifted by the fluid and stabilized at a certain height, which corresponds to the flow rate. The magnet inside the float is coupled with the magnet inside the indicator, and the pointer directly displays the flow value. Mechanical indicator type does not require power supply, especially suitable for sites without power supply or where electrical introduction is not allowed; The electronic transmitter type adds 4-20 mA, HART 7, Profibus PA or FOUNDATION Fieldbus output on the basis of mechanical indication, and is equipped with an 8-bit 7-segment LCD display, which can display total amount, instantaneous flow rate, percentage, and different volume or mass flow units.

The flow range provided in the technical data is closely related to the density and viscosity of the medium: water is approximately 0.0025-130 m ³/h, and air is approximately 0.075-1400 m ³/h at 20 ° C and 1 bar abs. The range ratio is approximately 10:1, but the specific measurable range must be calculated using Yokogawa selection software based on actual density, viscosity, temperature, and pressure, not just the caliber. In terms of accuracy, the stainless steel measuring tube DN15-DN100 is ± 1.6% (according to VDI/VDE 3513 sheet 2, qG=50%), and DN125-DN150 is ± 2.5%; The PTFE lining for DN15 to DN100 is ± 2.5%. It should be emphasized that the accuracy varies with the percentage of flow rate, and the relative error in the low flow range will significantly increase. Therefore, when selecting, the normal operating point should be placed in the later range as much as possible, rather than operating at the lower limit of the range for a long time.

Process connection, temperature and pressure, and material selection

The process connections of RAMC are very diverse, with stainless steel options including EN 1092-1 flange (DN100~DN150 PN16, DN15~DN100 PN40, DN50~DN80 PN63), ASME B16.5 flange (1/2~6 in Class 150/300/600 raised face), DIN11851 external thread, NPT or G internal thread, DIN 32676 TRI-CLAMP clamp, Rosista flange, etc; PTFE lining type corresponds to D2PF, D4PF, A1PF, A2PF and other connections. The process pressure depends on the connection form, with a high standard coverage range and special requirements up to 700 bar; In terms of process temperature, stainless steel parts for liquid contact are between -196 ° C and+400 ° C, while PTFE parts for liquid contact are between -80 ° C and+130 ° C. When selecting, it is necessary to check the pressure temperature rating at the same time, and not only consider the room temperature pressure resistance.

The main materials for liquid contact are stainless steel 1.4401/1.404/316/316L and PTFE, and the R4/T4 connecting gasket is Arame fiber and NBR adhesive. If the medium has strong corrosiveness, it should be confirmed whether the liquid receiving parts and gaskets are compatible, and if necessary, PTFE lining or special alloy should be selected. The technical data also indicates that the measuring tube is supplied according to PED module H, fluid group 1, and category III; Heating options/T1~/T6 are classified according to Art. 4 section 3, fluid group 2, and Table 2 containers. For on-site engineers, this means that high-temperature or heat tracing applications cannot only rely on the temperature of the instrument body, but also need to verify the heat transfer between the heating jacket and the indicator.

Installation conditions: Vertical, straight pipe section and magnetic interference

RAMC must be installed on a vertical pipeline with an upward flow direction. It is recommended that the inlet straight pipe section be no less than 5 × DN and the outlet straight pipe section be no less than 3 × DN, especially for RAMC08 and above diameters. If it is expected that the medium will deposit dirt, it is recommended to install a bypass pipe for online cleaning without interrupting the process. Special attention should be paid to float jumping in gas applications: the operating pressure should be at least 5 times the pressure loss, otherwise the float is prone to up and down oscillation and unstable readings; If necessary, a float damping structure can be used.