Karrie SD360 Series DC LVDT Linear Position Sensor

Overview

The Karrie SD360 Series DC LVDT (Linear Variable Differential Transformer) is an industrial-grade linear position sensor engineered for high-reliability operation in demanding hydraulic and electro-hydraulic control systems. Unlike AC-operated LVDTs requiring external signal conditioning, the SD360 integrates a built-in DC-to-DC converter and analog signal conditioning circuitry—enabling direct DC excitation and standardized voltage or current output. Its operating principle relies on electromagnetic coupling between a primary coil and two secondary coils wound symmetrically around a precision-machined ferromagnetic core. As the core moves axially within the coil assembly, differential voltage induced across the secondaries varies linearly with displacement—converted internally to a robust 2–10 V DC or 4–20 mA analog output. Designed specifically for proportional and multi-way hydraulic valves, the SD360 delivers stable metrological performance under sustained static pressure up to 350 bar, making it suitable for integration into closed-loop servo-control architectures where positional fidelity, long-term repeatability, and environmental resilience are critical.

Key Features

• Stainless steel hermetically sealed housing with IP67 ingress protection—resistant to dust, moisture, and transient submersion.
• Pressure-isolated core architecture utilizing a hardened stainless steel pressure tube, enabling safe operation in direct contact with hydraulic fluid at up to 350 bar static pressure.
• Dual-output capability: user-selectable 2–10 V DC (high-impedance, low-noise) or 4–20 mA (loop-powered, noise-immune, ideal for long cable runs).
• Field-adjustable zero offset and gain via onboard potentiometers—facilitating system-level calibration without disassembly or external instrumentation.
• Compact 36 mm outer diameter form factor with M12-4 waterproof connector—optimized for space-constrained valve manifolds and embedded OEM installations.
• Wide operating temperature range (−25 °C to +85 °C) and low thermal coefficient (<0.05 %/°C), ensuring minimal drift across ambient and fluid-temperature fluctuations.
• Compliant with IEC 61000-6-2 (immunity) and IEC 61000-6-3 (emission) standards—validated for use in electrically noisy industrial environments including mobile hydraulics and power generation facilities.

Sample Compatibility & Compliance

The SD360 is compatible with standard hydraulic fluids (mineral oil, HFD-U, and biodegradable esters) when installed with its integrated pressure-isolation tube. It does not require fluid compatibility certification beyond standard ISO 4406 cleanliness class 18/16/13, as internal electronics remain fully isolated from process media. The sensor meets mechanical and electrical requirements outlined in ISO 13849-1 (PL d) for safety-related parts of control systems, and its construction adheres to RoHS 2011/65/EU and REACH (EC 1907/2006) directives. While not intrinsically safe certified, it is suitable for Zone 2/Class 1 Division 2 environments when installed per manufacturer-specified mounting torque and cable routing guidelines. No special calibration certificates are required for routine use; however, traceable NIST-calibrated verification reports are available upon request for GLP/GMP-aligned applications.

Software & Data Management

The SD360 operates as a standalone analog transducer and requires no firmware, driver software, or configuration tools. Its analog outputs interface directly with PLC analog input modules (e.g., Siemens S7-1200 AI, Allen-Bradley 1769-IF4), data acquisition systems (NI CompactDAQ, Keysight DAQ970A), or distributed I/O networks (EtherCAT, CANopen via analog gateway). For predictive maintenance workflows, the 4–20 mA output can be logged alongside pressure, flow, and temperature channels in SCADA platforms such as Ignition or Siemens WinCC. Although the sensor itself provides no digital diagnostics, its stable linearity (±1.0%) and low hysteresis (<0.1% FS) support trend-based health monitoring—deviations exceeding ±2% full-scale output over time may indicate mechanical wear, seal degradation, or mounting misalignment, triggering scheduled inspection protocols.

Applications

• Proportional spool position feedback in industrial and mobile hydraulic valves (e.g., Bosch Rexroth 4WRA, Parker D1VW).
• Actuator stroke monitoring in hydroelectric turbine guide vanes and wicket gate control systems.
• Real-time displacement sensing in armored vehicle suspension damping units and fire-control stabilization platforms.
• Bridge expansion joint displacement tracking under dynamic load and thermal cycling conditions.
• Brake pedal travel measurement and redundancy verification in commercial rail braking systems compliant with EN 50126/128/129.

FAQ

What is the maximum allowable static pressure for continuous operation?
The SD360 is rated for continuous operation at 350 bar static pressure when correctly installed with the pressure-isolation tube engaged and hydraulic connections torqued to specification.
Can the sensor be used in submerged applications?
Yes—the IP67-rated housing and M12-4 connector permit temporary immersion up to 1 m for 30 minutes; however, prolonged submersion or dynamic fluid flow across the connector face is not recommended without supplemental sealing.
Is field recalibration possible without specialized equipment?
Yes—zero and gain adjustments are accessible via front-panel potentiometers using a non-metallic calibration tool; no external power supply or signal generator is required beyond the nominal 24 V DC supply.
Does the sensor comply with FDA or pharmaceutical industry requirements?
No—the SD360 is not constructed with FDA-compliant materials nor validated for clean-in-place (CIP) or sterilization cycles; it is intended for industrial hydraulic, not sanitary process, applications.
What is the expected service life under cyclic loading?
Rated for >100 million full-stroke cycles at rated pressure and temperature, assuming proper alignment, absence of side-loading, and adherence to specified mounting tolerances (≤0.1 mm radial runout).