Schaller LF-TD 150 High-Temperature Humidity Transmitter

Overview

The Schaller LF-TD 150 is a high-temperature, industrial-grade humidity and temperature transmitter engineered for continuous, traceable monitoring in demanding thermal environments up to 150 °C. Unlike standard hygrometers limited to ambient conditions, the LF-TD 150 employs a capacitive polymer humidity sensor combined with a precision Pt1000 temperature element—both hermetically sealed within a stainless-steel probe body rated to IP65. Its measurement principle relies on dielectric constant changes in a moisture-sensitive polymer film, calibrated at six fixed RH points across the full 0–100 % range, ensuring long-term stability and minimal drift under thermal cycling. Designed for integration into process control systems, it delivers two independent, linearized 4–20 mA analog outputs—one for relative humidity (scaled 0–100 % RH) and one for temperature (scaled −20 to +150 °C)—enabling simultaneous, galvanically isolated acquisition without external signal conditioning.

Key Features

• Capacitive polymer humidity sensing technology with factory 6-point RH calibration traceable to national standards
• Stainless-steel probe (Ø12 mm × 750 mm) rated for continuous operation at up to +150 °C; electronics housing (70 × 32 × 120 mm) constructed from anodized aluminum
• Dual 4–20 mA outputs with independent scaling: RH output linearly spans 0–100 % RH; temperature output linearly spans −20 to +150 °C
• Operating temperature range: sensor head −20 to +150 °C; electronics unit −20 to +85 °C; supply voltage 12–29 VDC (24 VDC nominal)
• Robust mechanical design compliant with IP65 ingress protection; 5-pole sensor connector with 5-meter pre-terminated cable included as standard
• Optional field-installable modules: backlit LCD display (showing real-time RH and temperature), SPDT relay for programmable humidity threshold alarms, and digital communication interfaces including RS232, USB, Bluetooth, PROFINET, Ethernet, and Modbus RTU/TCP

Sample Compatibility & Compliance

The LF-TD 150 is compatible with gaseous media in non-corrosive, non-condensing environments—including dry air, nitrogen, compressed air, and inert process atmospheres typical of drying ovens, climate chambers, kilns, and sterilization tunnels. It is not intended for direct immersion or exposure to condensate, aggressive solvents, or particulate-laden exhaust streams without optional sintered stainless-steel filter caps (available upon request). The device complies with CE marking requirements under the EU Electromagnetic Compatibility Directive 2014/30/EU and Low Voltage Directive 2014/35/EU. Calibration documentation supports ISO/IEC 17025-compliant quality systems; its dual analog outputs are suitable for integration into FDA 21 CFR Part 11–compliant environments when paired with validated data acquisition software supporting audit trails and electronic signatures.

Software & Data Management

While the LF-TD 150 operates autonomously as a hardwired transmitter, its optional digital interfaces enable advanced configuration and diagnostics via Schaller’s proprietary PC software (compatible with Windows 10/11). Users may adjust zero/span offsets, configure relay thresholds, assign Modbus register mappings, and export calibration logs in CSV format. When connected via Ethernet or PROFINET, the device supports standard industrial protocols for seamless integration into SCADA, DCS, or MES platforms. All configuration changes are timestamped and stored in non-volatile memory. For GxP-regulated applications, optional firmware versions include configurable audit trail logging and user-access levels aligned with ALCOA+ data integrity principles.

Applications

• Real-time RH and temperature monitoring in industrial drying tunnels (wood, ceramics, pharmaceutical granules)
• Climatic chamber validation and routine performance verification per ISO 17025 and ASTM E2877
• Process humidity control in feed pelletizing, flour drying, and animal feed storage silos
• Environmental monitoring during thermal aging tests of polymers and composites
• Humidity supervision in cleanroom HVAC systems where elevated duct temperatures occur
• Validation of sterilization cycles (e.g., steam-free dry heat processes) requiring traceable temperature-humidity correlation

FAQ

Can the LF-TD 150 be used in saturated or condensing environments?
No. The sensor is designed for non-condensing gas-phase measurements only. Condensation will damage the capacitive polymer layer. Optional sintered stainless-steel filters mitigate dust but do not prevent liquid ingress.

Is NIST-traceable calibration documentation available?
Yes. Each unit ships with a factory calibration certificate listing six RH points (10%, 30%, 50%, 70%, 85%, 95%) and corresponding temperature points, referenced to accredited national metrology institutes. Full traceability documentation is available upon request.

What is the recommended recalibration interval?
Schaller recommends annual recalibration under normal operating conditions. In continuous high-temperature service (>120 °C), semi-annual verification is advised. Drift assessment can be performed in situ using a portable reference hygrometer meeting ISO 17025 accreditation.

Does the relay output support fail-safe logic (e.g., de-energized on alarm)?
Yes. The optional relay is configurable as normally open (NO) or normally closed (NC), with programmable hysteresis and delay timers to prevent chattering during transient excursions.

Can multiple LF-TD 150 units share a single Modbus network?
Yes. Units equipped with Modbus RTU or TCP support multi-drop configurations. Each device is assigned a unique slave ID (RTU) or IP address (TCP), enabling centralized polling and synchronized data logging.