Recording from Figaro Gas Sensors

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Figure 1. The Chart software gives a continuous live display of the gas concentration

The e-corder can be connected to a Figaro sensor to record gas concentration.

Introduction

Figaro Engineering manufacture a range of sensors for measuring different gasses. The e-corder can provide the 5 V required to power the sensor and measure the signal produced. The Chart software is used to calibrate and monitor the signal. The gas concentration is displayed in real time as in Figure 1.

Equipment Required

The following equipment is required:

Experimental Setup

The sensing element inside the Figaro sensor is comprised of a metal oxide semiconductor layer formed on an alumina substrate of a sensing chip together with an integrated heater. In the presence of a detectable gas, the sensor's conductivity increases depending on the gas concentration in the air. The gas sensor cable from eDAQ can convert the change in conductivity to an output signal which corresponds to the gas concentration. This signal is record by the e-corder.

The sensor requires two voltage inputs, which are supplied by the e-corder: the heater voltage and the circuit voltage. The heater voltage is applied to the integrated heater in order to maintain the sensing element at a specific temperature which is optimal for sensing. Circuit voltage is applied to allow measurement of voltage across a load resistor which is connected in series with the sensor.

The Arithmetic calculation function in the Chart software is used convert measured voltage to sensor resistance. For example, for the TGS 2620 ethanol sensor, Equation 1 is used. When the ambient temperature and humidity is taken into account, the Sensor resistance can be converted to the concentration of the gas.

        R_s = \tfrac{V_C - V_{RL}}{V_{RL}} \times R_L          Equation 1.

where sensor resistance (Rs), circuit voltage (VC), measured voltage (VRL) and load resistor (RL)

Figure 2. The ethanol in the flask is heated by the hotplate. The ethanol vapour travels through the tubing to the Figaro TGS 2620 sensor