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I have designed a circuit for an SGX EC410 oxygen sensor by using these application note -PAGE 4, FIGURE 4 - (http://www.sgxsensortech.com/content/uploads/2014/08/A1A-EC_SENSORS_AN2-Design-of-Electronics-for-EC-Sensors-V3.pdf). When I try to measure the biased voltage between working (SENS) and reference (REF) electrode, the value of -600 mV is held for about one second and goes down to few milli volts rapidly. The same happens when I connect the sensor without voltmeter. Am I doing something totally wrong, or the circuit is not quite right? enter image description here

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  • \$\begingroup\$ What OpAmps are you using? \$\endgroup\$ – user1582568 Feb 16 '16 at 15:13
  • \$\begingroup\$ @user1582568 There are two TLC2272cd dual operational amplifiers from Texas Instruments (IC1+IC2 and IC3+IC4). \$\endgroup\$ – Viktor Scherf Feb 16 '16 at 15:22
  • \$\begingroup\$ OK, those should be fine, I was wondering about bias current. Could it be that you are simply over range? Have you measured the voltage at the count electrode when the bias has disappeared? I will not be possible to measure the voltage at REF with a meter because as soon as you draw current from that node the voltage will be affected. \$\endgroup\$ – user1582568 Feb 16 '16 at 15:31
  • \$\begingroup\$ Maybe you can explain what should happen? \$\endgroup\$ – Andy aka Feb 16 '16 at 15:36
  • \$\begingroup\$ @user1582568 I have just measured the voltage at the count electrode with no bias (it is actually not zero, but something about 250 mV after long swing period) and that was the full supply voltage, e.g. +5V. The OpAmp is overloaded, right? \$\endgroup\$ – Viktor Scherf Feb 16 '16 at 16:21

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