C-RQ-0600R-SHS-RHT, temperature and humidity measurement and dew point monitoring

The C-RQ-0600R-SHS-RHT module enables you to measure room temperature and relative humidity while also monitoring (via a sensor connected to the AI2 input) the dew point of cooling ceilings and measuring floor temperature (AI1). The module (module housing) is available in a variety of designs (Logus, ABB, Unica, etc.).

To prevent condensation, we use a special SHS-A4L sensor with a resistive response that is sensitive to high humidity. Typical applications include cooling ceilings, control cabinet enclosures, and similar structures where we need to prevent condensation from forming on walls and other surfaces.

The sensor can withstand humidity of up to 100% for short periods, but must not be exposed to continuous condensation. 

Secure the sensor to the supply pipe (the coldest part of the system) with a cable tie, or screw it onto the surface being monitored. It is best to apply thermal paste to the contact surfaces between the sensor and the substrate. Protect the sensor from damage and contamination (staining, etc.).

There must be a small opening in the plaster beneath the sensor so that air from the room can reach the sensor and the sensor can accurately measure the humidity at the location of the system pipe.

Input AI2 is designated for evaluating dew point using the SHS sensor; with this module variant, it cannot be used to connect other sensors. Unlike standard AI inputs, this input is configured to ensure that the limit parameters specified by the sensor manufacturer are not exceeded.

The AI2 input must be set in the module configuration to a resistance measurement range of up to 160 kΩ.  The risk of condensation is evaluated in the user program; the measured resistance value of the sensor corresponds approximately to the relative humidity as shown in the following table:

Fig. 1 Example of connecting an SHS dew point sensor to the module

Notes:

1. The sensor’s connection cable can be extended up to approximately 30 m. Use a shielded cable, such as SYKFY 2x2x0.5 or J-Y(St)Y 1x2x0.6.
2. When installing the sensor, ensure a high-quality conductive connection to the measured surface and take care not to damage the sensor’s active surface.

SHS-A4L Dew Point Sensor

The SHS-A4L humidity sensor is a miniature resistive dew point sensor used to detect and/or prevent condensation.
In the low humidity range, up to 75% RH, the resistance (R) versus % RH curve has a flat slope, i.e., low sensitivity to changes in humidity. At 80% RH and above,
the sensor’s resistance begins to increase exponentially as humidity rises.
This behavior ensures very easy signal evaluation and a stable switching point near the dew point threshold (high % RH values).

SHS-A4L Sensor Specifications:

The following graph shows an example of how the sensor's resistance varies with relative humidity