Masoneilan 496 Series Electric Rotary Position Switches and Transmitters

Overview

The Masoneilan 496 Series from Baker Hughes is a family of rotary position switches and position transmitters that report the stroke position of a control valve. Depending on the model code, a 496 instrument can be configured as an electromechanical limit switch, as a proximity switch or as an opto-electronic position transmitter with a 4-20 mA output, and the same explosion-proof housing is used for all of them. Mounted on the shaft or linkage of a valve actuator, it tells the control room or the plant interlock system when a valve has reached open, closed or an intermediate position, which is essential for sequencing, permissives and shutdown verification.

Seven Star LLC is a trusted supplier for Masoneilan and supplies the Masoneilan 496 Series to refineries, gas plants, power stations and process facilities across the Sultanate of Oman and the GCC. Because the numbering system covers many switch and transmitter combinations with different certifications, our instrumentation team in Muscat confirms the model code, hazardous area approval and stroke type with each customer, and provides the Baker Hughes technical specification so that the selection is documented.

Operating Principle of the Masoneilan 496 Series

In the electromechanical versions of the Masoneilan 496, an adjustable cam on the shaft operates one, two or four microswitches. The cam is turned by the valve through a direct rotary coupling or through a linkage for linear stems, so the switch contacts change state at set positions of travel. Single-pole double-throw and double-pole double-throw microswitches are offered, with silver-plated contacts. The proximity versions replace the contacts with one or two detectors that act by flux variation through an oscillator and amplifier, which operates a power relay located outside the hazardous area.

The 496-8 transmitter uses an optical principle. A prism driven mechanically by the valve follows the travel through gears, and an LED fixed to the housing sends a light beam that the prism reflects onto a stationary disc with three tracks: one resistive, one conductive and a photosensitive track between them. The reflected beam bridges the two tracks and acts as a potentiometer slider, and the resulting variable voltage is converted electronically into a 4-20 mA signal. Baker Hughes describes this detector as frictionless, non-sparking and free from electrical noise, insensitive to vibration and with a long life.

Engineering Design of the Masoneilan 496 Series

The body and cover of the Masoneilan 496 are aluminium with an anti-corrosion treatment and an epoxy or polyurethane paint finish, with 316L stainless steel with passivation as an option. The shaft is stainless steel, O-ring seals are Buna N and no copper or copper-bearing alloy is exposed to the atmosphere. The enclosure rating is IP66 and IP67 to EN 60529, the electrical connection is 3/4 inch NPT, and other thread types are possible with adaptors or reducers. A three-output cable of type Y237 is available where separate cables are needed for additional functions.

The model code is a compact configuration key. In the European design the first digit gives the instrument type (1 or 2 electromechanical single-pole switches, 4 or 5 proximity detectors, 6 or 7 double-pole switches and 8 for the opto-electronic transmitter), and the second part gives the protection concept: 55 weatherproof, 57 explosion-proof for gas and dust, and 58 intrinsically safe. For the 496-8 an optional extra switch can be added after a slash. Stroke is a maximum of 90 degrees rotary, or 12 to 102 mm of linear travel through a linkage, and rotary or linear travel must be specified when ordering separate instruments.

Key Features

These capabilities allow the Masoneilan 496 Series to cover most valve position feedback requirements with one housing style:

• Choice of one or two electromechanical switches, double-pole switches, proximity detectors or a 4-20 mA position transmitter.
• Explosion-proof and intrinsically safe versions with ATEX, US and Canadian approvals, plus other local approvals on request.
• Aluminium housing with optional 316L stainless steel, IP66 and IP67 enclosure rating and Buna N seals.
• Rotary travel up to 90 degrees or linear travel of 12 to 102 mm through a linkage.
• Temperature range from -55 to +85 degrees Celsius for switches and -40 to +80 degrees Celsius for the transmitter.
• Opto-electronic transmitter with linearity of 0.5 percent or better, hysteresis and repeatability of 0.1 percent or better, and zero and span potentiometers.
• Transmitters can be fitted with one or two micro-switches or proximity detectors for on-off indication.
• Differential gap of 1.5 percent of full scale on rotary valves, with low repeatability of 0.2 percent on the switches.

Industrial Applications

Baker Hughes lists the Masoneilan 496 Series for power generation, refining, petrochemicals and midstream and upstream oil and gas, with typical applications on steam turbine generators, condensers, cooling towers, distillation units and compression systems. The switches provide open and closed limit signals for isolation and shutdown valves, while the transmitter gives a continuous valve position signal for control room display and valve diagnostics. In Oman, typical installations are process valves in coastal refineries and gas plants, and on cooling-water and utility valves in power and desalination stations.

In Oman and the GCC, Seven Star LLC supplies the Masoneilan 496 Series with the valves and actuators that carry it. Typical companions are the Masoneilan Type 87/88 spring-diaphragm actuators, the Masoneilan Camflex II 35002 rotary control valve and the Masoneilan 41005 cage-guided control valve. We can advise which housing and approval combination suits each location, particularly where the area classification requires an explosion-proof or intrinsically safe version.

Technical Specifications

The table summarises the published data for the Masoneilan 496 Series, covering every Masoneilan 496 model code, from the Baker Hughes technical specification. The ambient range and ratings available depend on the internal element and approval, so please consult the manual for the exact model.

Related Masoneilan positioners include the Masoneilan SVi1000 digital valve positioner, Masoneilan 4700P/4800P pneumatic positioner and Masoneilan 4700E/4800E electropneumatic positioner.

Request a Quote for Masoneilan 496

To request pricing or technical support for the Masoneilan 496 Series, send a formal RFQ to the Seven Star LLC instrumentation division stating the model code, rotary or linear stroke, switch or transmitter function and hazardous area approval. We can confirm the correct configuration, advise on availability and lead time and provide the Baker Hughes technical specification from this page. In Oman and the GCC, Seven Star LLC delivers genuine products with manufacturer documentation and local engineering support.