TDK / EPCOS Liquid Level Detection Special Sensor

B59050: Product series (PTC heating thermistor for liquid level detection)D1100: Structure code, stainless steel cylindrical probe with standard lead lengthB040: Nominal resistance code at 25°C, representing reference resistance of 60Ω

III. Core Electrical Specifications

Nominal resistance at 25°C (R₂₅): 60ΩResistance tolerance: ±30%Max operating voltage: 18V DCLeads: 2-pin through-hole, free-hanging mountingHousing material: Sealed stainless steel cylinder, waterproof and oil-resistantUnit weight: Approx. 630mgPacking: Bulk pack (standard packing quantity: 50 / 100 pcs)

Temperature & Operating Parameters

Non-powered static temperature range: -55℃ ~ +100℃Operating range under full load 18V power supply: 25℃ ~ +50℃Max surface temperature of powered probe: ＜90℃Stabilized response time: 60sRated service life cycles: 5000 cyclesApplicable liquid thermal conductivity: τ＞0.12 W/mK (engine oil, hydraulic oil, diesel fuel, etc.)

IV. Mechanical Dimensions

Probe: Slim sealed stainless steel cylindrical structureMounting method: Lead suspended type without fixed base, to be directly inserted into oil tanks / liquid containers

V. Working Principle & Application Scope

Working Principle

The PTC generates heat after power-on. When the probe is immersed in oil, heat is rapidly dissipated by the liquid, keeping the component at low resistance with high residual current.When the probe is exposed above liquid level (in air), poor heat dissipation leads to sharp temperature rise, the PTC resistance surges drastically and the current drops significantly. The back-end circuit judges the liquid level by detecting current variation.