Abstract
Stable and precise control of humidity is imperative for a wide variety of experiments. However, commercially available humidistats (devices that maintain a constant humidity) are often prohibitively expensive. Here, we present a simple yet effective humidistat for laboratory-scale applications that can be easily and affordably (<€250) constructed based on an Arduino Uno as microcontroller, a set of proportional miniature solenoid valves, a gas washing bottle, and a humidity sensor. The microcontroller implements a PID controller that regulates the ratio of a dry and humid airflow. The design and implementation of the device, including a custom driver circuit for the solenoids, are described in detail, and the firmware is freely available online. Finally, we demonstrate its proper operation and performance through step response and long-term stability tests, which shows settling times of approx. 30 s and an attainable relative humidity range of 10–95%
Highlights
Careful control of the humidity in a sample chamber is necessary for numerous experiments ranging from controlling molecular charge transport [1] to designing state-of-the-art sensors [2]
Relative humidity is a dimensionless number representing the ratio of the partial pressure of water vapour with respect to its saturation pressure: Φ
When the humidity is pushed beyond 100%, the dew point is reached and water vapour will condense into a liquid
Summary
Careful control of the humidity in a sample chamber is necessary for numerous experiments ranging from controlling molecular charge transport [1] to designing state-of-the-art sensors [2]. Relative humidity is a dimensionless number representing the ratio of the partial pressure of water vapour with respect to its saturation pressure: Φ. It is typically expressed as a percentage and ranges from 0 to 100%. When not further specified, ‘humidity’ usually refers to relative humidity Another technique that is commonly utilised is local heating of a water bath in an enclosed chamber [6,7]. The lack of closed-loop control combined with its susceptibility to external disturbances and long response times renders this set-up very arduous to control manually.
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