Humidity Sensors

Editor's Notes

• #2: This is a training module on Honeywell Humidity sensors.
• #3: Welcome to the training module on Honeywell Humidity Sensors. This training module introduces humidity sensor technology and their applications.
• #4: The technologies and situations most often associated with humidity sensors are: thermoset and thermoplastic sensors, bulk thermoplastic and bulk AlO 3 sensors, Lithium chloride sensors, and thermoset polymer capacitor sensors. Humidity sensors can be constructed from a variety of materials. However, the features and benefits of the material used influence the effectiveness of the sensor and the diversity of its applications.
• #5: Here is a comparison table for humidity sensors constructed from different materials. Thermoset and thermoplastic sensors (also referred to as thin film capacitance sensors) work on the rule that relative humidity changes the capacitance of a sensor in a measurable and consistent way. These capacitance based sensors can measure 0-100% with application temperatures ranging between -40 to 200 °F. Bulk Thermoplastic and Bulk AlO3 sensors (also called Bulk Polymer Resistance sensors) function on the basis that a change in resistance over a polymer element fluctuates with relative humidity in a measurable and consistent way. These sensors can typically measure 0-100% relative humidity with application temperatures between -20 to 140 °F. Lithium chloride film humidity sensors can contain a thin layer of lithium chloride that sits on an insulator, which has two palladium coils wound side-by-side. Because the film is hygroscopic, it will attract moisture from the surrounding atmosphere. When the humidity increases, there is a direct change in the resistance of the film between the two palladium coils.
• #6: The Thermoset Polymer Capacitor relative humidity sensor works through absorption. Water is absorbed down through the top of the sensor – through the porous platinum (top layer) – to effect the layer of thermoset polymer between the two layers of platinum.
• #7: This chart illustrate the primary features and benefits of the Honeywell thermoset polymer humidity sensors. The thermoset polymer relative humidity sensors use an industry-proven, thermoset polymer, three layer capacitance construction, platinum electrodes, and except for high temperature versions, on-chip silicon integrated voltage output signal conditioning. These humidity sensors are laser trimmed so that they eliminate calibration. Other features include low current/power design, stable low drift performance, fast response, high linearity, long term stability, etc.
• #8: In ATOM / Surface Transportation / Automotive On Board applications, manned space vehicles require systems to cool and dehumidify the cabin air. To do this they use a temperature and humidity control system. The system circulates and filters air, removes water in the form of humidity, and maintains a constant temperature. Any water that is collected goes to the water recovery and management system. Automotive HVAC control units rely on vital signals from different sensors to maintain a comfortable environment inside a vehicle. One of the conditions that is monitored is the amount of water vapor in the cabin air. Along with humidity as a comfort level, water vapor levels are important in the fogging up and defogging of the windshield. A humidity sensor inside the cabin of the vehicle continuously monitors the amount of water vapor present. This allows the HVAC unit to regulate the blow out air temperature, adjust blower speeds and open recirculation vents to control and help prevent windshield fogging.
• #9: In appliance consumer applications, the humidity sensor and control circuit monitors the ambient condition of the room air and controls the blower fan to maintain a constant humidity. There are a number of benefits for the use of humidity sensors in the areas of information technology. Because they are chemically resistant, humidity sensors are able to withstand the inks and chemicals used in the printing process. The stable, low drift performance of the sensors is called upon when doing long run productions. And even during those long run productions, the low power design ensures the sensors are energy efficient. For the medical instrumentation market, humidity sensors offer low, energy efficient, power design. Their fast response time works to ensure the patient’s physical comfort and well-being.
• #10: This table shows the humidity offerings from Honeywell. Each sensor is designed to provide enhanced sensitivity, response time, stability and reliability. Configured with integrated circuitry to provide on-chip signal conditioning offered on all products. Absorption-based humidity sensors provide both temperature and % RH. Packages are chemically resistant and operate in ranges of -40 °C to 85 °C performing in most harsh environments. These humidity sensors offer interchangeability of ±3 % accuracy for potential applications as diverse as heating, ventilation and air conditioning equipment (HVAC), refrigeration, office automation, and medical equipment.
• #11: For the HIH-4000-001 and HIH-4000-003, Honeywell recommends Mill-Max socket 310-93-132-41-001, or similar. For HIH-4000-002 and HIH-4000-004, Honeywell recommends Mill-Max socket 851-93-032-10-001 or similar.
• #12: You can answer the questions in the chart when deciding on a humidity sensor.
• #13: Thank you for taking the time to view this presentation on “ Humidity Sensors” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Honeywell site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility.