Masoneilan 12420 Digital Level Transmitter with HART and SIL 2
Overview
The Masoneilan 12420 is the basic transmitter model of the Baker Hughes 12400 Series digital level instruments. In the model code of the series, the third digit selects the action: 1 is the controller, 2 is a transmitter with a single output and 3 is a transmitter with adjustable switches and a second analog output. The 12420 is the second of these, a two-wire loop-powered displacer transmitter whose only analog output, AO_1, carries the level or interface signal together with HART communication.
Seven Star LLC is a trusted supplier for Masoneilan and quotes the Masoneilan 12420 for level service on separators, drums and tanks in Oman and the GCC. It is the model to choose when a plant wants a digital replacement for a pneumatic or older electronic displacer transmitter and does not need local switch outputs or a second signal. If those are needed, the 12430 is the correct model, and the options cannot be added on site later.
How the Masoneilan 12420 Measures Level
The Masoneilan 12420 uses the buoyancy principle. A displacer hangs in the liquid, and a change in level changes its apparent weight in direct proportion. That change loads a torque tube, the torque rod turns by a small angle, and a frictionless non-contacting sensor detects the resulting change in magnetic field. The sensor signal varies the current in the loop in proportion to the level in the vessel. Units are dry calibrated at the factory by weight simulation to the service specific gravity stated by the customer, or to a specific gravity of 1 when none was given.
Recalibration of the Masoneilan 12420 is recommended when the real specific gravity differs from the calibration value and is also needed when instrument performance is verified with liquid in the displacer chamber. The displacer is locked in the chamber for transport, so during set-up it must be released by unscrewing the M6 stem at the drain.
Safety Characteristics of the Masoneilan 12420
The SIL certification of the 12400 Series applies to the transmitter function, which makes the Masoneilan 12420 a natural choice for safety loops. The manual states that the instrument meets the architectural constraints for up to SIL 2 at a hardware fault tolerance of 0, as a type B device in low-demand mode. It can be configured as a SIL 2 device with the failsafe position at Fail Low, below 3.6 mA, or used without the SIL 2 device function activated. Hardware revision 1 or later and firmware revision 1.1.2 or later are required.
The safety failure rates are published in FIT, where one FIT is one failure per 10 to the power of 9 hours. With the SIL 2 feature activated the manual lists 23 FIT safe detected, 575 FIT safe undetected, 72 FIT dangerous detected and 147 FIT dangerous undetected. Without it the figures are 23, 480, 152 and 147. External leaks are 83 FIT in both cases. The assumptions include a proof test interval of one year or less, a safety accuracy of 2 percent of full span and a repair time of 24 hours. The hardware lock jumper must be in the secure position, which blocks any write from the pushbuttons, ValVue or a HART handheld.
Key Features
The features below are the ones that matter when specifying the Masoneilan 12420:
- Two-wire loop power with a single 4-20 mA output on AO_1 and HART communication on the same pair of wires.
- NAMUR NE 43 signalling, with 3.8 to 20.5 mA for the measurement and below 3.6 mA or above 21 mA for a severe fault.
- SIL 2 device feature that can be activated or deactivated from the configuration.
- Local LCD and three pushbuttons for set-up without a handheld, and ValVue or any HART handheld for remote configuration.
- Mean time between failures of 55.7 years, calculated to MIL-HDBK-217F.
- Response time under 60 ms, power-up time under 1 s and power interruptions of up to 100 ms without a reset.
- Specific gravity from 0.15 to 1.4 with the standard displacer.
Industrial Applications
The Masoneilan 12420 is used for liquid level and interface measurement where a DCS or safety system reads a single 4-20 mA signal. Typical duties are three-phase separators, flash drums, knock-out drums and storage vessels in oil and gas, refining and power generation. Because the signal is NAMUR compliant, the control or safety system can distinguish a real measurement from a fault condition.
The transmitter can be paired with a control valve and positioner in the same loop, for example the Masoneilan SVI3 digital valve positioner on a Masoneilan Camflex rotary control valve. Seven Star LLC can quote the level instrument and the valve together from the same manufacturer.
Related published Masoneilan pages: Masoneilan 10000 Series double-port valve.
Technical Specifications
The table lists published data for the Masoneilan 12420 from the instruction manual and safety guide, revision E.
| Parameter | Specification |
|---|---|
| Model | Masoneilan 12420 transmitter with single output AO_1 |
| Output | 4-20 mA with HART on AO_1 |
| Normal output signal | 3.8 to 20.5 mA; failsafe below 3.6 mA or above 21 mA |
| Supply voltage | 10 VDC minimum; 30 VDC maximum intrinsically safe; 40 VDC maximum flameproof |
| Maximum load | R max in ohms equals supply voltage minus 10 V, divided by the maximum current |
| Maximum power | 3 W inside the housing |
| Safety integrity | Up to SIL 2 at HFT 0, type B; hardware revision 1 and firmware 1.1.2 or later |
| MTBF | 55.7 years |
| Storage temperature | -50 degC to +93 degC |
| Accuracy | Head alone plus or minus 0.1 percent; with torque tube assembly plus or minus 0.5 percent |
| Enclosure | IP66/IP67 |
Related Masoneilan level instruments include the Masoneilan 12400 Series digital level transmitter and Masoneilan 12800 Series pneumatic level controller.
Request a Quote for Masoneilan 12420
To request pricing or support for the Masoneilan 12420, send a formal RFQ to the Seven Star LLC instrumentation division with the vessel connection, range, specific gravity, process temperature and pressure, and the hazardous area approval required. We will confirm the full model code and provide the Baker Hughes instruction manual from this page. In Oman and the GCC, Seven Star LLC supplies genuine products with manufacturer documentation.
- Instruction Manual Masoneilan 12420 Level Transmitter Instruction Manual Download
Masoneilan control valves and actuator series
The globe valve listing centers on the 21000 series, including the cryogenic version with extension bonnet, and the 41005 cage-guided series in high pressure, API 6A and VRT anti-cavitation executions. The 80385 and 80386 are three-way combining and diverting valves. Rotary products include the 35002 Camflex II and the 37002 MiniTork II butterfly control valve. Actuators cover spring-diaphragm, cylinder and rack-and-pinion designs, among them the 5A cylinder actuator for Camflex II. Masoneilan also makes pressure regulators, SVI digital valve positioners and displacer-type level instruments, and offers Lo-dB trim for noise control.Where Masoneilan valves are used
Throttling duty on steam, hydrocarbons, gas and water is the daily work of these valves: feedwater and steam conditioning in power plants, separator and compressor loops in gas processing, high pressure drop letdown, cryogenic service in LNG and air separation, and general flow, pressure and level control in refineries and chemical plants.Ordering Masoneilan valves and spare parts: what we need
For spare parts the serial number is decisive, since the factory record behind it lists trim, materials and actuator. Send a clear nameplate photo with serial number, model number, size and pressure class. For a new valve add the process data: fluid, inlet and outlet pressure, temperature, minimum, normal and maximum flow, required leakage class, fail position, air supply and control signal.Browse Masoneilan products by category: Control Valves, Valve Actuator, Regulators, Valve Positioner, Level Transmitter.
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