Humidity and Temperature Sensors for High Humidity & Condensation (AFTF-35 / KFTF-35)

July 6, 2026

Author: S. Becker

In cold storage facilities, fruit warehouses, or food processing plants, conventional humidity sensors quickly reach their limits. As soon as warm, humid air comes into contact with cold sensor components, condensation forms—leading to measurement errors or even sensor failures.

The condensation-protected humidity and temperature sensors AFTF-35 (surface-mounted) and KFTF-35 (duct-mounted) have been specifically designed for these conditions: stable readings even with extreme humidity fluctuations and temporary condensation.

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In a nutshell

When cold warehouse air meets warm outside air, the relative humidity quickly rises to 100% in certain areas—causing condensation. This is exactly why we developed the AFTF-35 and KFTF-35:

Reliable humidity measurement down to the 95–99% RH range.
An integrated heating element prevents condensation on the sensor
Suitable for cold storage facilities, fruit warehouses, and pharmaceutical logistics
Measured parameters: relative humidity, temperature, dew point, absolute humidity
Rugged industrial outputs: 0–10 V or 4–20 mA

The result: stable control variables even under real, dynamic operating conditions.

Why humidity measurement in cold stores is so challenging

In practice, it quickly becomes clear that the real challenge lies not in the stable, continuous operation of a cold storage facility, but in the transitional phases. It is precisely during these moments that conditions arise that overwhelm traditional humidity sensors.

A typical everyday scenario:

A warehouse door is opened > warm, humid outside air flows into the room > the cold air already in the warehouse is physically unable to absorb this Humidity

The result: Relative humidity rises locally to nearly 100% within a very short time. When the air exceeds the dew point, Humidity begins to condense, primarily on cold surfaces.

And this is exactly where the critical issue comes into play: The sensor itself is one of those cold surfaces.

You can think of it like a cold beverage bottle in the summer. The surrounding air “sees” the cold surface and releases Humidity in the form of condensation. For the sensor, however, this is not just a physical phenomenon—it’s a real measurement problem.

Impact on Measurement Technology

As soon as condensation forms on the sensor element, the measurement conditions change fundamentally:

The sensor surface is no longer surrounded by air, but by a film of water
The measured relative humidity no longer corresponds to the actual indoor air
The signal waveforms become sluggish or erratic

In building automation, this manifests itself quite specifically:

Measurements "stick" at 100% relative humidity.
Control loops respond with a delay or incorrectly
Dehumidification or ventilation is inefficient

Even more critical are the long-term effects:

Repeated condensation places mechanical and chemical stress on the sensor element
Deposits and residues from the air stick to the sensor
This results in drifting and premature failure

Particularly in applications such as fruit and vegetable storage, where stable climatic conditions directly affect product quality, this is not only a metrological problem but also an economic factor.

Why Standard Sensors Reach Their Limits Here

Conventional humidity sensors are generally designed for “normal” HVAC applications—that is, for stable conditions without persistent humidity spikes or condensation events. What they lack:

No active measures against condensation
The sensor element is located directly in the airflow
No distinction between sensor temperature and ambient temperature

This means that they function correctly as long as no condensation occurs. However, as soon as real-world operating conditions—with rapid changes in temperature and humidity—come into play, they operate outside their optimal range.

From a product manager's perspective, this can be clearly summarized as follows: The problem is not the maximum humidity—it is the dynamics and the phase changes between air and condensate.

It is precisely for these situations that specialized sensor technology is needed—technology that not only measures but also actively takes physical constraints into account.

The solution: Condensation-protected sensors with active heating

If you look at the effects described in practice, it quickly becomes clear that the problem cannot be solved simply by "better sensors" in the traditional sense. It is crucial to actively influence the physical boundary conditions - and this is precisely where dew-protected sensor technology comes in.

The AFTF-35 and KFTF-35 models take a deliberately different approach to standard sensors. Instead of just measuring passively, the measuring process is specifically stabilized.

The functional principle in detail

The core of the system is a slight, controlled overtemperature of the sensor element:

the humidity sensor is constantly operated approx. +3 K above the ambient temperature
As a result, its surface is always above the dew point
Condensate can hardly physically settle directly on the sensor

This sounds simple at first, but it has a decisive effect:
Even in critical conditions, the sensor remains in a defined, measurable state - namely dry.

At the same time, heating alone would falsify the measurement, as the relative humidity is temperature-dependent. This is precisely why the second component of the system is so important:

A separate, unheated temperature measuring element records the real ambient temperature
the electronics link both pieces of information (sensor status + environment)
The actual relative humidity is calculated correctly from this

Typical applications

Condensation-protected humidity sensors demonstrate their greatest value particularly in the areas of food storage and agricultural processes. The reason is always the same: high humidity, low temperatures, and dynamic operating conditions all come into play—precisely the conditions under which conventional sensors become unstable.

In Fruit and Vegetable Storage Facilities Moisture is not a secondary factor, but a key variable determining quality and shelf life. Read here More about this.
Even in the context of the Vegetable Farming – especially under controlled conditions – humidity is a crucial factor. Learn more more.
In the Food Industry There are additional factors at play that are often underestimated. You can read about what they are in the next blog post.
Also in the Pharmaceutical and Logistics Industries Similar conditions apply—though with even stricter requirements for the traceability of the measured values. More on that.

AFTF-35 vs. KFTF-35 – Which model is best suited for fruit storage?

Depending on the system, both room sensors and duct sensors can be used in fruit storage facilities. The key factor is where the measured value is needed for control purposes:

AFTF-35 (Surface-Mounted Sensor)

Wall mounting in rooms
Ideal for warehouses and cold storage rooms
Direct measurement of indoor air

Typical applications: Cold storage facilities, fruit storage facilities, vegetable storage facilities

The AFTF-35 is suitable for direct measurement of the ambient air in storage areas. It is typically installed on a wall or mounting surface and provides readings at the location where the storage environment is to be evaluated or controlled. It is important to choose a location with representative airflow—not directly at the door, not immediately next to the evaporator, and not in dead zones behind stacks.

KFTF-35 (Duct Sensor)

Installation in Air Ducts
includes mounting flange
for ventilation and air conditioning systems

Typical applications: Supply air/exhaust air measurement, HVAC systems, centralized humidity control in (food) processing facilities and the pharmaceutical industry

Both provide standard signals and can be easily integrated into GLT/DDC.

Our KFTF-35 is used in ventilation or air-conditioning ducts. It is ideal when humidity and temperature measurements need to be taken in the supply or exhaust air, for example in central ventilation units, recirculation systems, or systems with controlled air treatment.

Which metrics are really relevant?

In addition to relative humidity, the sensors also provide parameters such as dew point, absolute humidity or mixing ratio, which are often much more meaningful in practice. These values are calculated internally and output directly as a standard signal. This makes climate control much more precise and stable, especially in sensitive storage processes.
Further parameters:

Dew point → decisive for condensation risk
absolute humidity (g/m³) → important for storage strategies
Mixing ratio (g/kg) → for process optimization
Wet bulb temperature → for energy considerations

These values are calculated internally and provided via additional outputs.

Practical benefits:

Better control strategies instead of pure RH consideration
more stable storage conditions
Less spoilage and loss of quality

Important influencing factors for selection and installation

The measurement quality depends heavily on the installation situation:

Positioning
- not directly in the airflow of doors
- No direct proximity to sources of cold

Consider dynamics
Frequent door openings = high moisture jumps
→ Heated sensor is absolutely essential

Maintenance
- Check sintered filter regularly
- Contamination influences measuring behavior

Signal integration
- 0-10 V or 4-20 mA for BMS
- Several outputs can be used in parallel

Select suitable humidity sensors for high humidity now

If your application is characterized by temperature fluctuations, high humidity or condensation risks, classic humidity sensors quickly reach their limits - especially when measured values need to be permanently stable and suitable for control. This is precisely where the AFTF-35 and KFTF-35 come in: They provide reliable signals even under real, dynamic conditions and ensure that your BMS or control system is not "flying blind".

In concrete terms, this means for you:

Stable measured values even with moisture peaks and condensation
Significantly lower failure and maintenance rates during operation
More precise control of cooling, ventilation and dehumidification

Choose the right variant depending on the installation situation:
On-wall sensor (AFTF-35) for on-wall/room applications or duct sensor (KFTF-35) for installation in ventilation systems.

This ensures that your moisture measurement works reliably even under demanding conditions - and that your system can be operated stably and economically in the long term.

Discover sensors for high humidity applications now