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p-Type Metal Oxide Sensor Overview

p-Type Metal Oxide Sensor Overview
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p-Type Metal Oxide Sensor Overview Alphasense introduces a new class of metal oxide gas sensors. Commercially available metal oxide sensors are based on n-type metal oxides: SnO2 or WO3. With low base resistance, those n-type sensors are simple to manufacture and operate at lower temperatures, but suffer from three problems: • baseline drift • humidity sensitivity • negative response to gases (potentially an unsafe response) Developed over many years, our p-type metal oxide gas sensors offer the following benefits: • stable baseline • low humidity sensitivity • positive response to gases (safer response) Three sensors have been developed for specific markets: • H2S detection at high temperatures (up to 120°C) for oil and gas applications • Volatile Organic Compounds (VOCs) detection for low cost IAQ applications • CO detection for extreme temperature or humidity enviroments Each sensor type can be supplied in three housings (see figures 1,2, 3 & 4 for housing dimensions) • TO-5 metal can, the most common format • Plastic 6-pin housing - frequently used with other metal oxide gas sensors • Ex housing* - stainless steel 316 housing with UL, CSA, ATEX and IECEx approvals, unique for metal oxides, allowing use in hazardous areas without the need for an IS circuit * Refer to the following pages for Ex specifications and housing dimensions. Table 1 Housing options ** Alphasense p-type sensors can be operated at constant heater voltage/ constant temperature (400°C), but performance is improved when the sensors are refreshed periodically at a higher temperature (525°C). Typical sense:refresh time ratio is 5:1, however with application optimisation even higher sensitivities can be achieved. Refer to our Application Notes for more information. Alphasense Ltd, Sensor Technology House, 300 Avenue West, Skyline 120, Great Notley. CM77 7AA. UK Telephone: +44 (0) 1376 556 700 Fax: +44 (0) 1376 335 899 E-mail: sensors@alphasense.com Website: www.alphasense.com

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p-Type Metal Oxide Sensor Overview Technical Specification Figure 1 Schematic Diagram (TO-5 Housing, 12.3mm can) Sensing area do not obscure Pins 1 & 3 Heater Pins 2 & 4 Detector All dimensions in millimetres (± 0.1mm) Side View Bottom View Figure 2 Schematic Diagram (TO-5 Housing, 7.7mm can) Pins 1 & 3 Heater Pins 2 & 4 Detector All dimensions in millimetres (± 0.1mm) Side View Bottom View Figure Schema hematic Diag Figure 3 Schematic Diagram (Plastic Housing) Sensing area do not obscure Pins 1 & 4 Detector Pins 2 & 5 Heater Pins 3 & 6 Detector Side View Bottom View

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p-Type Metal Oxide Sensor Overview Sensing area do not obscure Pins 1 & 4 Detector Pins 2 & 5 Heater Pins 3 & 6 Detector Side View Bottom View Figure 5 Basic Measuring Circuit for TO-5 package Pins on the measuring circuit correspond with the pin numbers in Figure 1 & 2 When the sensor is connected in this half Wheatstone bridge configuration, V0 increases as the sensing material resistance increases. Heater Voltage Circuit Voltage Figure 6 Resistance/temperature for Alphasense Metal Oxide Gas Sensor heaters 35 Sensing temperature (400 o C) and reset temperature (525 o C) variances should...

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p-Type Metal Oxide Sensor Overview Technical Specification SPECIAL CONDITIONS FOR SAFE USE (denoted by X after the certificate number) The non-metallic parts of the Flameproof Sensor Housings shall only be installed in enclosures that offer protection from mechanical impact damage and shall not be exposed to ultraviolet radiation. The final installation of the Flameproof Sensor Housings shall ensure that any likely damage from dropping the complete device has been considered. The Flameproof Sensor Housings shall only be connected to an electrical supply that is certified as compliant with...

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