Electrochemical Figaro TGS5042 Carbon Monoxide Sensor & Op Amp

Discussion in 'General Electronics Chat' started by Sam Matthews, May 1, 2016.

  1. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
    I'm currently trying to set a circuit up for a Figaro TGS5042 Carbon Monoxide sensor using an Op Amp in a non-inverting configuration but having no luck what so ever, i think anyway.

    I have configured my circuitry in two separate ways trying to figure this out. I have recently found a little 'review/guide' blog post which I've read through with no joy either, here. This is my Op Amp datasheet. Am i correct in expecting to receive 0V on the output pin when there is nothing detected, presuming that there is 0mV or 0mA over the sensor, just like the video in the linked blog post shows?

    So, the first circuit i tried is that specified by the datasheet;


    All i'm getting here is a voltage readout on the output pin in relation to gnd is 4.35v with no movement what so ever.

    So i then go on to consider his own circuit of;


    Still nothing. And more specifically, i get the same reading of 4.35v.

    So, thinking i have a faulty sensor here i go and make the very basic 'poor' circuit of just the sensor and a resistor (Page 2, Figure 2b in this app note). I do get some life, in fact with a 1k resistor i get 1.5mV after 2 minutes of burning paper exposure. I then let it settle down over 10 minutes to which it reads 0.3mV. It is safe to say the sensor is in working order.

    I then go ahead and create the following circuit, exactly to this image;


    However, the multimeter in this simulation is showing 2.47V where in the exact setup to compare the simulation to my circuit i get 4.2V without the sensor attached.

    I do suspect this to be an incorrect op amp selection as the app note for the figaro sensor does specify a rail to rail op amp, however the op amp they show doesn't state it is a rail to rail device.

    Would the slew rate of the op amp have any effect on this?

    I also am very aware, although not sure how to calculate exact figures, that with this op amp not being a rail to rail device it will not allow the output voltage to go close to V- or V+ (GND or 5V in this case).