I.Overview
The All Gas/VOC sensor is a solid-state polymer gas sensor designed for comprehensive measurement of multiple volatile organic compounds (VOCs) and toxic gases. It operates on the principle of solid-state polymer electrochemistry, which is analogous to the reaction mechanism of traditional liquid-phase electrochemistry. The core components are manufactured using a printing process, which significantly enhances product consistency and production yield.
The sensor consists of three electrodes: the SE (Sensing Electrode) serves as the working electrode, the CE (Counter Electrode) as the counter electrode, and the RE (Reference Electrode) as the auxiliary electrode. The reference electrode maintains a stable potential and is connected to the working electrode, enabling accurate measurement of the working electrode's potential and its changes.
The sensor typically operates in two main application modes:
1. Comprehensive Measurement: This refers to measuring the total quantity of multiple toxic gases and volatile organic compounds (VOCs). The gas concentration detected by the sensor represents the comprehensive total concentration, and it cannot distinguish the concentration value of each individual gas.
2. Single Gas Measurement: This involves measuring the concentration of a single target gas in a single environment (i.e., only one gas is present in the environment at the same time).
IV. Calibration
1.Comprehensive Measurement Calibration Method--When the sensor is used for comprehensive measurement, the calibration gas shall be selected according to the specific gas to be measured and the test purpose.
1.1 Determine the gas with the highest concentration in the mixed gas environment, and use the standard gas of this gas to calibrate the sensor.
1.2 Determine the gas with the highest hazard level in the mixed gas environment, and use the standard gas of this gas to calibrate the sensor.
1.3 If there is a specified target gas to be measured according to the measurement requirements, use the standard gas of the specified gas to calibrate the sensor.
1.4 When the above conditions cannot be determined, carbon monoxide gas can be used for calibration using a 1:2 ratio method to ensure the response sensitivity to most gases.
2.Single Measurement Calibration Method
When the sensor is used for single measurement, calibrate it with the standard gas concentration of the gas to be measured.
Normal Reaction State of Ethanol in the All Gas Sensor-When ethanol (alcohol) gas enters the sensor, a chemical reaction occurs on the SE working electrode. The CE counter electrode and RE reference electrode do not come into contact with the ethanol (alcohol) gas. When an appropriate amount of ethanol gas enters, all the gas reacts completely on the SE working electrode. At this point, the sensor’s measurement state is optimal.The reaction of ethanol in the sensor is a positive reaction, and the output signal is a positive value.
Reaction State of High-Concentration Ethanol in the All Gas Sensor-When high-concentration ethanol gas or pressurized gas is directly directed at the air inlet, a large amount of ethanol gas enters the sensor. The SE working electrode cannot complete the reaction within a short time, or due to pressure, the gas may enter the RE reference electrode. This causes the signal to switch from positive to negative.If the concentration exceeds 1500ppm and the gas is continuously introduced for 2 hours, the sensor requires at least 10 hours of recovery time before normal measurement can resume for the second time.
If the measurement is specifically for ethanol (alcohol), it is recommended to use a dedicated alcohol sensor. If comprehensive measurement is still required and occasional alcohol detection is needed, use ethanol gas with a concentration below 100ppm for calibration, at a flow rate of 300ml/min and a maximum continuous gas supply of 3 minutes. During calibration, avoid directing gas with flow rate directly at the air inlet; instead, use a side (90-degree angle to the air inlet) to allow the sensor to measure in a diffusive state and prevent flow (flow impact). For special applications, please consult our company separately.
Non-Conventional Testing/Calibration Cases-When ethanol standard gas is unavailable for sensor testing/calibration and liquid alcohol must be used, note the following: When a cloth or other material is soaked in liquid alcohol and placed in a plastic or glass sealed bag/container, the concentration in the enclosed space at room temperature (25°C) can instantly vaporize to 600,000ppm, and the vapor concentration will be higher at temperatures above 25°C. Therefore, do not directly place the alcohol-soaked cloth or material for sensor testing. If this method must be used for relative calibration/testing, dilute the gas before measurement: Prepare a syringe, a sealed bag/container, and calculate the volume of the sealed bag/container. Determine the dilution ratio based on the target concentration (100ppm or below). Use the syringe to extract a pre-calculated volume of gas from the 600,000ppm vapor bag and inject it into another sealed bag/container for dilution. Place the sensor to be tested into the dilution bag/container in advance, and position it according to the specific gravity of ethanol gas relative to air.
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