SIEMENS QAF64.2-J Frost Protection Sensor, Continuous and 2-Point (S55700-P155)

Frost protection sensor for air ducts, heat exchangers, and air heaters. It combines a continuous DC 0...10 V output with a 2-point relay output to monitor and protect against freezing conditions. The sensor uses an NTC thermistor element with a 3000 mm capillary tube for flexible installation.

Advantages

Dual output modes allow integration with various control systems. The adjustable setpoint range of 2...15 °C and fixed 1 K switching differential provide reliable frost detection. The copper sensor tube ensures accurate temperature sensing, and the IP54 housing protects against dust and water splashes.

Suitable for

• Air duct frost monitoring
• Heat exchanger freeze protection
• Air heater safety control

Key specifications

• Sensor element: NTC thermistor
• Continuous output: DC 0...10 V, measuring range -20...20 °C
• Switching output: 2-point relay, change-over contact (SPDT), AC 250 V, 5 (2) A
• Setpoint range: 2...15 °C, adjustable; switching differential: 1 K fixed
• Supply voltage: AC 24 V / DC 13.5...35 V; power consumption max. 1 VA
• Capillary tube length: 3000 mm; sensor tube material: copper
• Protection class: IP54; operating temperature: -20...50 °C; humidity: 5...95% r.h. non-condensing

Recommendations

Install the sensor tube in the coldest part of the duct or coil. For best accuracy, ensure the capillary tube is not kinked and the housing is mounted away from direct heat sources.