LEFOO TSD Dual-Bulb Temperature Difference Controller
LEFOO TSD is a dual-bulb temperature difference controller for two separate temperature bulbs. The distinction between a flow, pressure, temperature, protective or remote-actuator contact matters when selecting replacements.
Model Identification & Key Specifications
Original Manufacturer Data
TSD has two thermal bulbs to compare temperature DIFFERENCE between two media, rather than two unrelated single-temperature alarms. TSD40 setting difference 0–15°C, max action differential ≤3°C and working −25…40°C, bulb ceiling 60°C; TSD100 is 5–25°C, ≤5°C, 20…100°C working and bulb up to 150°C. Interchanging TSD40 and TSD100 for high-temperature ventilation is unsafe; choose correct material and control contact load.
Match the original sensor bulb and mounting, ambient/media operating range, automatic/manual reset circuit, inductive load and exact order code. A thermal trip is not identical to a pressure trip. Verify the exact order code and use model-matched manufacturer documentation and photographs.
AirAlign Engineering & Variant Comparison
TSD compares temperatures and trips on their DIFFERENCE; unlike TSH it is not simply two independent over-temperature safety limits. TSD40 and TSD100 have different bulb maximum temperatures and cannot be swapped in a hot-water heat exchanger without confirming their range.
Always identify whether the part measures a continuously variable signal, provides a discrete protective trip or controls an operating cycle. Component substitution should preserve sensing topology, switching hysteresis, reset and energized/deenergized states. Enclosure and cable routing must be assessed within the actual equipment, not only against a standalone catalogue illustration.
Installation and Integration Checks
Check supply voltage, relay versus transistor wiring, contact NO/NC state and peak inductive duty. Signal outputs are not equivalent to motor-control contacts.
Distinguish temperature difference from independent thermal limits, and paddle/piston/calorimetric flow measurement from pressure differential. Match actual calibration media.
Mount as specified for the device’s reference sensor or mechanical paddle; verify working medium, housing, ingress protection, maximum process temperature and cable/port fittings.
Confirm applicable safety function and approvals for the exact order-code revision. Match any applicable CE, UL or TÜV documentation to the exact device configuration.
Related Products
LEFOO TS · LEFOO TSH · LEFOO manufacturer profile
Official Manufacturer Sources
Independent AirAlign engineering page. Device-specific maker photo and current exact-variant third-party approvals require separate verification.
TSD — true temperature difference between two bulbs
TSD compares temperatures at two separately routed capillary bulbs rather than measuring one absolute room temperature. Mount each bulb where the intended thermal source and sink are representative, and distinguish the TSD40 difference range from TSD100 options. A differential switch can be useful for circulation/heat transfer, but a misplaced sensor can reverse the control decision. Verify SPDT contact and hysteresis with controlled temperatures at both bulbs.