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The Honeywell VF20 NTC 20k immersion temperature sensor with a 65 mm probe measures the temperature of liquids without compromising the strength of the pocket. Designed for hot and cold water as well as HVAC pipework. Range −40 to +150 °C, IP65 protection. More information
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| IP Rating | IP 65 |
| Medium Temperature | -40...150 °C |
| Sensor type | NTC 20k |
| Stem length | 65 mm |
| Weight | 0.21 kg |
Honeywell VF20-5B65NW is an immersion temperature sensor without a thermowell, featuring an NTC 20k element and a 65 mm probe. It is used for measuring the temperature of liquids and air in heating, cooling and ventilation pipe systems. The thermowell (type WB50 or WS50) must be ordered separately.
The VF20-5B65NW is designed for systems operating with a controller or control unit requiring an NTC 20k input element. Typical applications include hot and cold water pipework, cooling circuits and ventilation ducting, where reliable measurement of the medium temperature at the thermowell installation point is required. Thanks to its IP65 rating, the sensor is also suitable for more humid environments such as plant rooms and machine rooms.
The terminal cover opens with a bayonet quarter-turn screw – no tools required and no need to remove the entire cover. The fixing holes for screwing to a wall or structure are accessible from the outside, so installation can be carried out by one person even in tighter spaces. The maximum cable length from the sensor to the controller is 200 m with a conductor cross-section of 1.5 mm².
The NTC 20k sensing element achieves an accuracy of ±0.2 K at 25 °C and a time constant τ63 of under 30 seconds when used with a brass or stainless steel thermowell. The terminals are non-polarised – reversing the wires will not cause a fault or short circuit. The plastic terminal housing meets UL94-V0 flammability class and is resistant up to +120 °C. The probe operating range is −40 to +150 °C.
Technical parameters:
No. The VF20-5B65NW is supplied without a thermowell – this must be ordered separately. For the 65 mm probe length, the compatible thermowells are WB50 (brass, nickel-plated, PN13 / max. 26 m/s) or WS50 (316Ti stainless steel, PN25 / max. 30 m/s). Both have an R 1/2" ISO thread and a tube diameter of ø 8 mm.
The sensor is compatible with any controller or control unit that accepts an NTC 20k input (20 kΩ at 25 °C). Typical examples include Honeywell SMILE and Excel series controllers, as well as compatible third-party systems. Before selecting, check that your controller actually requires NTC 20k – for NTC 10k or Pt 1000, VF10 and VF00 variants are available respectively.
The VF20-5B65NW sensor itself does not come into contact with the medium at all – measurement takes place through the thermowell. If you use the WS50 stainless steel thermowell (material 1.4571 / 316Ti), the assembly is also suitable for potable water systems. The WB50 brass thermowell is not certified for potable water.
The maximum cable length is 200 m. When using a 1.5 mm² conductor cross-section (AWG15), the error is approximately 0.06 °C for every 10 m – negligible for standard applications. In environments with high electromagnetic interference (EMI), use a screened cable and maintain a minimum separation of 15 cm from 230 V power cables. The terminals are non-polarised, so reversing the wires does not affect operation.
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