Mobrey DMS Series Vibrating Fork Level Switch for Solids

Vibrating fork level switch for powders, granules and bulk solids

The Mobrey DMS series vibrating fork level switch gives single point level switching for dry solids such as powders, pellets, granulates, grains, flour, fly ash, cement and sand, coal and slag, and aggregate. The forks are kept vibrating by the electronics. When the medium reaches and covers the forks, the vibration is damped or stops, the electronics detect the change and switch the output relay after a configurable time delay. The forks vibrate again once the medium releases them.

The housing is robust aluminium with IP67 protection, there is a plastic housing option, and a flameproof Ex d version is offered. Forks can be covered in plastic for aggressive media, and insertion lengths reach 3000 mm. An internal switch selects high or low level action, and a bi-colour green and red LED shows the state.

Technical specifications

Models and ordering code

Table 2 selects the process connection: 1 inch BSP (FPB) or 1 inch NPT (FNB) for the L and G types, 1 1/2 inch BSP (NPB) or NPT (NNB) for the B and U types, and flanges in stainless steel, DN50 PN40 or PN25 (KKF), 2 inch ANSI 600 RF (KCF), JIS 40K 50A (HJF) or PP flanges DN50 PN16 (KKP), 2 inch ANSI 150 RF (KCP) and JIS 10K 50A (HJP). Housing codes are C aluminium alloy IP67, H aluminium alloy ATEX flameproof, and W plastic PBT fibreglass reinforced. Insertion length codes include 01 for the standard 125 mm (L and G) or 137 mm (B and U) in stainless steel, 02 for 300 mm or 175 mm, and XX for a customised length. Contact codes are 0 for one SPDT 8 A, 1 for two SPDT, and 2 for one SPDT 8 A Ex d.

Installation notes

The instrument can be mounted in any position, but vertical mounting at the top of the vessel is recommended for light, free flowing solids. If side mounting is used, choose a position where the forks are freed from the medium easily and protected from deposits. The fork position is marked on the hexagon.

Key features of the DMS series

• Works on light bulk solids down to a density of 0.01 kg/dm³, which covers fluffy powders that defeat many paddle switches.
• No moving parts outside the fork, so there are no bearings or shaft seals to wear on abrasive media.
• Configurable switching delay to ignore material falling past the forks during filling.
• Fail-safe high or low selection by an internal switch, with a green and red LED for local status.
• Universal power supply of 20 to 255 Vac or 20 to 60 Vdc, with one or two SPDT relay outputs.
• Extended insertion lengths from 300 to 3000 mm for top mounting in tall silos.

Selection guidance

Start with the switching job. For high level protection against overfilling, a short fork mounted through the silo roof or high on the side wall is the usual choice; for low level or empty detection, a side-mounted fork near the discharge cone is typical. Tube extensions let a top-mounted switch reach a specific level without a side nozzle. The material should then be checked against the minimum density, and any tendency to bridge, build up or stick to the forks should be considered. For sticky or aggressive products, the plastic-coated forks can reduce adhesion and chemical attack. Process temperature, pressure and the type of connection follow from the vessel design, and hazardous areas involving combustible dust require the appropriate certified housing.

Installation and maintenance

• Mount side-wall switches with the forks angled slightly downward so material can slide off, and position the fork faces vertically to reduce buildup.
• Keep the forks out of the filling stream and away from the discharge flow to avoid false switching and mechanical damage.
• Provide a protective baffle above the forks where heavy lumps can fall onto them.
• Seal unused cable entries and use suitable glands to maintain the IP67 rating.
• Test the switch periodically by covering the forks or using the built-in function, and check the forks for buildup during silo inspections.

Applications in Oman and the GCC

Cement plants, ready-mix concrete batching plants, flour mills, plastic compounding and fertilizer facilities in the region all use silos and hoppers that need reliable level switching. Cement and fly ash are common duties, and a fork switch prevents overfilling and silo pressurization during pneumatic truck deliveries. High summer temperatures and dust are routine conditions for these plants, so the -40 °C to +70 °C ambient rating and the robust aluminium housing are useful. Outdoor switches mounted on silo roofs benefit from a sunshade and careful sealing of cable entries against wind-blown dust and humidity.

What to include in your RFQ

• Material to be detected, with bulk density and particle size.
• Mounting position (side or top) and required insertion length.
• Process connection type and size, process temperature and pressure.
• Power supply and number of relay outputs.
• Housing type and any hazardous-area certification needed.

Documents and quotation

Confirm the bulk solid, density, particle size, process temperature and pressure, mounting position and insertion length, supply voltage, and whether a zone 20 or 21 certified version is required.

The manufacturer document is attached to this page and listed below. Seven Star LLC is an independent supplier in Muscat and can quote against the model code, quantity and delivery location. Browse more instruments in Level Instrumentation, or see the Mobrey brand page.