Hello everyone,
I recently bought an Arduino Mega and want to use it with a galvanic oxygen sensor that outputs 8-30 mV corresponding to the oxygen level present in the gas (0-100%).
The best I can do without an amplifier is to set the analog reference to 1.1 V, but then I only get a resolution of about 1.1 mV, which is too coarse for my liking. I would like to amplify the signal by 20x or 30x.
Can someone recommend me the best way to do this?
Thank you.
Google instrumentation amplifier
Is the sensor output ground referenced or differential?
aarg:
Is the sensor output ground referenced or differential?
Differential, I guess. Here is a diagram. The circuit board is already part of the sensor. For the external board I'm using a 10 kOhm resistance as indicated in the specs.
Please post a link to the product page for the sensor. Your guess is not helpful.
I've heard the TLV2462 is a good op amp.
You can use the Difference Amplifier schematic shown on page-1 of the LT1215 op amp
You would need a gain (A) of 375 to convert 12mV to 4.5V as preamplification for the A/D.
Rfeedback/RInput = 100k/11k yields a gain of 100 for the first three stages of non-inverting amplifier and
Rfeedback/RInput = 750k/10k for the last stage should work.
jremington:
Please post a link to the product page for the sensor. Your guess is not helpful.
Does this help? D-01 Spec
You can use the Difference Amplifier schematic shown on page-1 of the LT1215 op amp
You need to add a DC bias to that circuit, to establish a common mode Vref.
Instrumentation amps are for bridge circuits where a very large CMRR is required in the amp.
This is a galvanic sensor (ie it generates a voltage), not a bridge sensor like a strain guage.
A precision rail-to-rail opamp set to a gain of ~100 might be the way to go - you need
low offset voltage, and the non-inverting amplifier configuration to avoid loading down
the sensor.
If 30mV is full scale, an opamp with 250µV offset voltage represents about 1% error in O2
concentration. Opamps with offsets as low as 100µV are available, or even 0µV if you got
for a commutating-auto-zero style device (aka CAZ).
Actually, since the sensor has a current output, it might be easier to use the inverting configuration where the input resistor in figure 7 is omitted, and the amplifier input resistor of the same value 10k, performs the same function.
I would consider using one of these (or similar) Instrumentation breakout board
At 30 mv you have to be careful you don't have mixed materials in your signal path otherwise you may get some thermocouple action that will reduce your accuracy.
A "regular" opamp would be OK but it will need to be laid out well, paying attention to the grounds. You only need a gain of ~ 33 to boost it to 1v. Still unless you need a more cost effective design I think the instrumentation breakout will be the safest approach.
I've just updated a page here about using op amps.
Does this help? D-01 Spec
No, for me the link is not working. If you bought the sensor why not just link to the page or data sheet?
Or do it the right way and post it as an attachment?
FYI TI have a new "amplifier cookbook" you may find useful
Hi,
Dave Jones, YouTube EEVblog may have what you are after.
Even includes schematic.
Tom... 
this guy has x1000 DC PLL amplifier - LF442
https://radiolocation.tripod.com/NewDQandBeaconFiles/DQmainboardSchematic.htm
Santa has kinapped the OP!
Hi,
I hope the OP realises that those devices have a finite life, they are basically a zinc/air(oxygen) battery and when you buy one it is vacuum sealed.
The minute you open it it starts to work and age, even if you are not taking readings.
Many.. many.. (to many) years ago they were used in automotive IR Gas Analysers, the longest that I can remember one lasting was 12months.
Tom...
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