Yokogawa RAMC flowmeter selection and troubleshooting

When multiple rotor flow meters are installed in parallel, the distance between the center axes of the pipes should be at least 300 mm, and the distance from other ferromagnetic materials should be at least 250 mm, while avoiding static magnetic fields from approaching the instruments. This requirement is easily overlooked on site: if several flow meters are installed side by side on narrow metal supports, magnetic coupling may interfere with each other, manifested as pointer shaking or limit switch misoperation. The installation position should also avoid strong vibration and external heat sources. The indicator should not be insulated, and the insulation material should only cover the measuring tube and connecting part, not the indicator, otherwise the internal temperature of the electronic transmitter will exceed the allowable range.

Transmitter, communication and limit switch

Electronic transmitters are divided into four types: - E, - J, - P, and - F. -E is a standard 4-20 mA two-wire system with a power supply of 14-30 V DC. The 20 mA point can be selected between 60% and 100% at the end of the range. The load resistance is ≤ (U-14V)/20 mA, with linearity ± 0.2%, hysteresis ± 0.1%, and repeatability ± 0.1%. The fault output is less than 3.6 mA, which complies with NAMUR NE43. -J is HART version 7, with a load of 230-600 Ω, and the fault output can be less than 3.6 mA or greater than 21 mA. - P is Profibus PA, and - F is FOUNDATION Fieldbus, both of which are two-wire buses that do not distinguish polarity. The bus power supply is 9-32 V DC, with a current of about 14 mA and a fault additional current FDE of about 10 mA. It supports AI and TB blocks, and Profibus PA also supports Condensed Status and I&M functions. During on-site debugging, the HART controller or bus host should be able to read the internal temperature. The internal temperature measurement range of the transmitter is -25 to+70 ° C, with an accuracy of ± 5 ° C, which can be used to determine whether the indicator is overheated.

Limit switches are divided into standard version and fail safe version. The standard version/K1~/K3 uses SC3.5-NO inductive proximity switches with signals of ≤ 1 mA or ≥ 3 mA; the fail safe version/K6~/K10 uses SJ3.5-SN/S1N, also powered by 8 V DC and ≤ 1 mA or ≥ 3 mA. According to IEC 61508, the fail safe limit switches/K6~/K10 can be used for SIL2 safety functions, and the standard limit switches/K1~/K3 can be used for SIL1; The safety indicators of ISO 13849-1 can also be provided. The hysteresis of the limit switch is approximately 0.8 mm for pointer movement and 0.8 mm for float movement, with a minimum distance of not less than 2 mm between the two contacts. If the process requires "fault safety", it must be selected from/K6 to/K10 and matched with corresponding power modules:/K6 or/K7 with/W4E,/K8,/K9 or/K10 with/W4F. Standard limit switches can be equipped with relay power supplies such as/W1A,/W1B,/W2A,/W2B,/W4A,/W4B, etc. The common problem on site is the drift of the limit switch action point. First, check whether the float is jumping, whether the medium contains bubbles or dirt, whether the contact distance is too close, and then check the power module and wiring.

Dangerous area certification and explosion-proof selection

There are many hazardous area options for RAMC, and when selecting, one should not only focus on the word "explosion-proof", but also distinguish between intrinsic safety "ia", explosion-proof "db", dust-proof "tb", as well as complete instrument certification and component certification. Common options for intrinsically safe electronic transmitters include/ KS1（ATEX）、/ES1（IECEx）、/FS1（FM/UL）、/NS1（NEPSI）、/GS1（EACEx）、/US1（INMETRO） Wait; Limit switches of intrinsic safety type are also combined with corresponding certifications according to/K1~/K10. The complete RAMC explosion-proof type includes/ KF1（ATEX）、/EF1（IECEx）、/NF1（NEPSI）、/GF1（EACEx）、/UF1（INMETRO） Usually only equipped with housing 91 aluminum shell, indicator temperature -20~+60 ° C, cable connector standard M20 × 1.5, optional 1/2-14 NPT. Mechanical non electrical certifications include/KC1 (ATEX) and/GC1 (EACEx), which are only applicable to mechanical indicator type T and do not come with limit switches.

When designing an intrinsic safety system, physical parameters such as UI, II, PI, CI, LI, and maximum ambient temperature of/KS1,/ES1,/US1,/FS1,/NS1,/GS1 must be checked. The safety output of associated equipment must not exceed these values. Explosion proof type also needs to check the temperature group and the highest process temperature. For example, T6 usually corresponds to a lower process temperature, while T1-T3 can correspond to higher temperatures, according to the certification certificate and temperature classification table. When replacing transmitters or limit switches on site, intrinsic safety components cannot be directly replaced with explosion-proof components, nor can explosion-proof enclosures be replaced with non explosion-proof enclosures; Cable joints, plugs, and grounding must remain certified.