Humidity transmitters for humidity and temperature – precision saves money

Compliance with pre-defined climatic values is a decisive factor when it comes to ensuring product quality. However, it is essential for us humans too. In building automation in particular, failure to comply with specified measuring values can have a decisive impact on our health and well-being.
It can also have a negative effect on product quality if, for example, a drying process is not properly monitored or carried out.

Inappropriate environmental conditions can therefore have an enormous impact on the quality of products. The humidity transmitters from Testo offer reliability in monitoring, which not only saves time, but also money.

The advantages of Testo humidity transmitters

  • Optimum calibration concept for humidity transmitters due to the adjustability of the entire signal chain, including analog adjustment
  • High-precision testo humidity sensor with long-term stability
  • P2A software for parametrization, adjustment and analysis saves time and money during commissioning and maintenance of humidity transmitters
     

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Overview of humidity transmitters

Humidity measurement – special probes for extreme conditions

Humidity transmitter

testo 6614 – probe for high humidity

Measuring humidity in the high humidity range is one of the most difficult measuring tasks to undertake. Unstable measuring values, delayed signal response and sometimes even sensor corrosion are not uncommon if a special solution is not applied.

For these applications, Testo has developed a special, heated humidity sensor with the testo 6614. This creates a microclimate inside the filter that is 5 Kelvin above the process conditions. The significantly lower relative humidity in the microclimate greatly improves the sensor response as well as noticeably reducing the likelihood of corrosion.

Parallel to the heated humidity sensor, the testo 6614 also has an additional temperature probe. This measures the actual process temperature; on this basis the correct process humidity is calculated in the microprocessor of the measurement transmitter, and displayed.

testo 6615 – probe for trace humidity

Measuring humidity in the lowest humidity ranges is also very challenging. If “normal” polymer humidity sensors are used here, the error, measured in dewpoint degrees, soon shows high values.

For challenging trace humidity measurements, Testo has developed the testo 6615, which has an integrated trace humidity self-adjustment feature. This ensures that even the smallest deviations are corrected cyclically, even down to trace humidity levels of -60° dewpoint!

testo humidity transmitter

testo 6617 – humidity probe with early warning function for aggressive environments

Humidity measurement in environments with corrosive media is often associated with only a short useful life of the sensors. Testo has also developed a reliable solution to this problem: Cover electrode monitoring.

This enables the first signs of corrosion to be detected and reported early on. This early warning function allows the measuring probe to be replaced before the measurement malfunctions or is even interrupted. This guarantees optimum system availability.

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Dew point transmitter

testo humidity transducer

The Testo humidity sensor: The core element of the high-quality humidity transmitter

The Testo humidity sensor has been in use for more than 20 years now and continuously improved, and from the very beginning, the focus has been on the two accuracy parameters - measurement uncertainty and long-term stability: A moisture-sensitive polymer serves as the dielectric between two capacitor electrodes.

The special feature, though, lies in the perfect way the individual layers are designed. This is evident particularly in the top electrode, which has to perform two tasks that, at first glance, appear contradictory: it must be completely permeable to the water vapour that is to be led to the polymer dielectric, but at the same time it must be impervious, smooth and repellent to condensate, oil and dirt in order to protect the sensor.

These roles have, after some considerable research, been optimally combined in the Testo humidity sensor. This structure, and the high stability in Testo’s production and calibration, make it possible to guarantee a measurement uncertainty of +/- 2 %RH for Testo humidity transmitters, or optionally even +/-1 %RH.

In addition, the humidity sensor has great long-term stability. This was demonstrated in an inter-laboratory test, in which several humidity sensors from Testo were tested by a number of international calibration laboratories (PTB, NIST, etc.), whereby the +/- 1 %RH limit was not exceeded even without recalibration.

The more accurate the humidity measurement, the lower the operating costs of the air conditioning system. In accordance with international standards (ASHRAE Fundamentals, DIN 1946, etc.), air conditioning systems are required to deliver air humidity levels of between 30 and 65 %RH. Higher humidity levels must be brought into the target range via dehumidification, and lower humidity levels via humidification.

If a humidity transmitter with a total measurement error of +/- 2 %RH (measurement uncertainty including long-term drift) is used for humidity measurement, the operating costs are noticeably lower than if a typical climate transmitter with a total measurement error of +/- 6 %RH (uncertainty including long-term drift) is used.

This comparison stands out even more starkly in favour of the high-quality humidity transmitter if the %RH target range to be achieved is more narrowly defined, e.g. for cleanroom applications.

Dew point transmitters

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1 Top electrode

  • Allows moisture to penetrate to the dielectric layer
  • Repels condensate and impurities
     

2 Carrier

  • Ceramic substrate for mechanical protection
     

3 Connectors

  • Special anti-corrosion design
     

4 Bottom electrode
 

5 Dielectric layer

  • Polymer, dielectric constant continually changes with the relative humidity

Overview of the benefits of Testo humidity transmitters:
 

  • Fast and effective measurement of humidity values
  • Easy handling of the humidity transmitters
  • Precise measurements
  • Calculation and output of relative and absolute humidity and dewpoint values
  • Self-monitoring and an early warning function ensure high system availability