The KOBOLD MM is a magnetic float level sensor that provides continuous level indication and monitoring of compatible liquids. It works on the float principle with magnetic transmission in a 3-wire potentiometer circuit, and its simple construction uses only one moving part, the float, a design intended for reliable operation. The MM is built for measured-value data acquisition across a wide range of sensors, materials, designs, and connections, so one product family can cover many level applications. Measuring lengths run from 11.8 in (300 mm) to 236 in (6000 mm), with wetted parts in 316L stainless steel, polypropylene (PP), PVC-U, or PVDF. Level indication stays constant regardless of conductivity, pressure, and temperature, and the output signal is directly proportional to the liquid level. The MM is made in the USA.
How the MM Magnetic Float Level Sensor Works
A ring magnet inside the float travels along a guide tube as the liquid level changes. The magnet actuates a chain of reed contacts wired to a bank of resistors, producing a resistance that corresponds to the level height, similar to the wiper on a resistance potentiometer.
That resistance can be read directly as a 3-wire potentiometer output or converted by an optional transmitter into a signal proportional to level, and it can also drive local analog or digital indication.
Measuring Range, Accuracy, and Resolution
Measuring lengths run from 11.8 in (300 mm) to 236 in (6000 mm). The upper limit depends on float material: 236 in (6000 mm) with 316L stainless steel floats, up to 197 in (5000 mm) with the larger PP, PVC-U, and PVDF floats, and 79 in (2000 mm) with the compact PP and PVC-U floats.
Accuracy is 0.5% for measuring lengths under 6.2 ft (1900 mm), and resolution is 0.39 in (10 mm) along the measuring chain.
Pressure and Temperature Ratings
The MM is rated to a maximum pressure of 435 psi (30 bar) and a maximum temperature of 265°F (129°C). Both limits depend on the float and material selected, with 316L stainless steel floats carrying the highest ratings and the plastic floats carrying lower ceilings.
Typical float temperature ranges are -4 to 265°F for 316L stainless steel, 14 to 250°F for PVDF, 14 to 175°F for PP, and 32 to 140°F for PVC-U. Nominal float pressure ratings at 70°F run from 30 psi up to 435 psi depending on the float.
Wetted Materials and Float Selection
Wetted parts are available in 316L stainless steel, polypropylene (PP), PVC-U, or PVDF, so the MM can match a range of chemical compatibility needs. Eight float designs are offered in cylinder and ball forms, each with a specified minimum liquid specific gravity.
Minimum liquid specific gravity ranges from 0.4 for the low-density PP float to 0.85 for the PVDF float, so the float is chosen to suit the density of the measured liquid. Floats can be removed on all MM models.
Process Connections and Installation
Process connections include 3/8 in to 2 in NPT threads and ANSI 1 1/2 in to 4 in flanges. The sensor mounts vertically and may not deviate more than 30 degrees from vertical, and the float must be able to move freely with adequate clearance from tank walls.
The guide tube should not be bent or subjected to hard impacts, which can damage the internal reed contacts, and the unit should not be installed near strong magnetic fields. Protection is IP65 (IP68 is possible with housing types L, C, and E).
Output Signals, Displays, and Electrical Options
The MM offers a resistance (3-wire potentiometer) output or transmitter outputs: 4-20 mA 2-wire, 4-20 mA HART, and PROFIBUS or Fieldbus. Local LCD and LED displays are available, including a touch-screen LCD and versions with relay outputs.
Resistance outputs operate at up to 24 Vdc, 4-20 mA and HART transmitters at 8 to 35 Vdc, and PROFIBUS or Fieldbus at 9 to 32 Vdc. Connection heads are offered in aluminum, PA, PP, ABS, PVDF, or stainless steel.
Hazardous-Area and Optional Versions
For classified areas, the MM is available with ATEX approvals for intrinsically safe (Ex ia) and explosion-proof (Ex d) operation, certified under LOM 06ATEX2054X and LOM 14ATEX2075X. Intrinsically safe versions install through an isolating switch amplifier between the hazardous zone and the safe area.
Options on request include a Pt100 (3-wire) temperature sensor, a temperature switch with a normally closed contact at 150°F, 175°F, or 220°F, and interface level measurement at a density difference of 150 g/l.
Applications
The MM is applied in wastewater and purification plants, feed and batching tanks, chemical tanks, general manufacturing, power plants, and the pharmaceutical and food and beverage industries. It is intended for clean liquids that let the float move freely, without large particles, suspended solids, or a tendency to crystallize.
Common Questions about MM - Reed Chain Level Sensor
Inside the guide tube sit a reed contact chain and a resistor chain. As the float rises and falls, its magnet closes reed switches along the chain, and the tapped resistance changes in step with the height of the liquid, working much like the slider of a potentiometer.
The longest span is 236 in (6000 mm), available with 316L stainless steel floats. Versions using the larger plastic floats extend to 197 in (5000 mm), while compact plastic floats are offered to 79 in (2000 mm). The shortest measuring length is 11.8 in (300 mm).
The MM provides 0.5% accuracy on spans shorter than 6.2 ft (1900 mm). Resolution along the chain is 0.39 in (10 mm), and because the output tracks the float position directly, the reading stays proportional to liquid level for both indication and control.
Peak ratings are 435 psi (30 bar) and 265°F (129°C), reached with 316L stainless steel floats. Plastic floats carry lower ceilings: PVDF to 250°F, PP to 175°F, and PVC-U to 140°F. The correct rating depends on the float and material you select.
Fluid-contact parts come in 316L stainless steel, PP, PVC-U, or PVDF. Eight float designs span cylinder and ball shapes, each rated for a minimum specific gravity from 0.4 to 0.85. Every MM model has a removable float, which helps with cleaning and service.
Signal choices are a resistance output (3-wire potentiometer) or a transmitter delivering 4-20 mA 2-wire, 4-20 mA HART, or PROFIBUS/Fieldbus. For local reading, LCD and LED displays are offered, including a touch-screen LCD and a version with relay outputs. Heads come in metal or plastic.
Yes. ATEX versions cover both explosion-proof (Ex d) and intrinsically safe (Ex ia) protection, with certificates LOM 06ATEX2054X and LOM 14ATEX2075X. Intrinsically safe units are wired through an isolating barrier that separates the classified zone from the safe side.
Available on request are a Pt100 (3-wire) element, interface sensing between two liquids at a 150 g/l density difference, and a normally closed temperature switch set to 150°F, 175°F, or 220°F. One device can then cover more than level alone.
An MM code combines the float type (for example M08, M10, or M20), the process connection (N10 for 3/8 in NPT, N15 for 1/2 in NPT), the head or fitting code, the output (P, S, Y, 2 for resistance; M, H, F for a transmitter), and an ATEX code (0 none, E for Ex ia, F for Ex d). Always specify length L.