OpenHumidistat: Humidity-controlled experiments for everyone

Lars B Veldscholte; Sissi de Beer

doi:10.1016/j.ohx.2022.e00288

OpenHumidistat: Humidity-controlled experiments for everyone

HardwareX. 2022 Mar 9:11:e00288. doi: 10.1016/j.ohx.2022.e00288. eCollection 2022 Apr.

Authors

Lars B Veldscholte¹, Sissi de Beer¹

Affiliation

¹ Sustainable Polymer Chemistry Group, Department of Molecules & Materials MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.

Abstract

Humidity control is a crucial element for a wide variety of experiments. Yet, often naive methods are used that do not yield stable regulation of the humidity, are slow, or are inflexible. PID-based electropneumatic humidistats solve these problems, but commercial devices are not widespread, typically proprietary and/or prohibitively expensive. Here we describe OpenHumidistat: a free and open-source humidistat for laboratory-scale humidity control that is affordable (€500) and easy to build. The design is based around mixing a humid and dry air flow in varying proportions, using proportional solenoid valves and flow sensors to control flow rates. The mixed flow is led into a measurement chamber, which contains a humidity sensor to provide feedback to the controller, to achieve closed-loop humidity control.

Keywords: K d , Derivative gain; K ff , Feed-forward gain; K i , Integral gain; K p , Proportional gain; V ˙ , (Volumetric) flowrate; ADC, Analog-to-digital converter; CC, Creative Commons; CERN OHL, CERN Open Hardware License; CV, Control variable; Controller; DC, Direct current; DI, Deionized (water); EDA, Electronic design automation; Electronics; FC, Flow controller; FCE, Final control element; GNU GPL, GNU General Public License; HC, Humidity controller; Humidity; I/O, Input/output; IC, Integrated circuit; MOSFET, Metal-oxide-semiconductor field-effect transistor; PCB, Printed circuit board; PID; PID, Proportional, integral, derivative (control); PU, Poly(urethane); PV, Process variable; PVC, Poly(vinyl chloride); PWM, Pulse-width modulation; Pneumatics; RAM, Random-access memory; SMT, Surface-mount technology; SP, Setpoint; THT, Through-hole technology; UI, User interface; VCCS, Voltage-controlled current sink.