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I am going trying to interface with a ph sensor. For this work I realize I need to connect to an amplifier for an impedance buffer. After searching I found some op amps that have high impedance, which one is the best for this work and have best voltage accuracy?

What should I look for in an amplifier for sensors such as this?

Voltage Spike
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Rashid
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  • I've never done one, but how about the INA116... femto amp instrument amp. – George Herold Mar 10 '17 at 20:08
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    I am going on a road trip... which car will work best for this, a Honda, a Toyota, a Buick.... Seriously mate, I don't mean to be rude, but you don't even give us the specs for the ph probe or what voltages you want to use.. How is anyone supposed to answer that if they don't work for one of those chip manufacturers. – Trevor_G Mar 10 '17 at 20:09
  • How on earth did the TL082 even get on that list? –  Mar 10 '17 at 20:16
  • most of ph sensor have a voltage betwwen -500 to 500 mv and i want to change it to 0 to 5 v, you are right but if somebody work with ph sensor , he know witch one is better – Rashid Mar 10 '17 at 20:17
  • That only helps a little bit Rashid, would need the spec of the chosen device to figure out impedences, what if needs in the way of power etc, Also need to know what you want to run this from... 5v, 9V, +/-12v etc etc... There are a myriad of op-amps that will do what you want equally well. You need to narrow down the options. – Trevor_G Mar 10 '17 at 20:26
  • *he know witch one is better* By **specifying** your requirements, at the moment there are a lot of things you have not specified like bandwidth, noise, offset, accuracy. Not clear what sensor you're using either. Not clear where the amplified signal is going. If you'd go to a professional design house to design this amplifier they'd laugh in your face and send you on your way because they have nothing useful to work with. – Bimpelrekkie Mar 10 '17 at 20:33
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    *and have best voltage accuracy?* All beginner designers always want "the best". OK, that will cost $ 100000 and it needs a constant flow of liquid helium. Now do you still want "the best" or can you tell what you actually need ? – Bimpelrekkie Mar 10 '17 at 20:35
  • I edited the question to better the question – Voltage Spike Mar 10 '17 at 20:37

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Since you haven't listed the pH sensor your trying to interface to, I'll comment on what is involved:

1) The input impedance of the amplifier needs to be higher than the source impedance of the pH sensor. Another way of saying this is the output current of the pH sensor needs to be higher than the input current of the amplifier. Find the pH probe datasheet and look for an impedance or current number, then size your amplifier impedance or current.

2) Leakage currents are a problem. When resistances are similar, every material becomes a conductor. Teflon, Kapton and a few other materials have high resistances. Usually a guard trace or ring is used so even if the material (like FR4 which would leak a large portion of the current from the trace) the voltage is the same as the input so there is minimal leakage current. You can build your own guard ring by matching the voltage of the input with a buffer amplifier from the output. Kind of like this example

The best one is going to have the highest impedance, it will be easier to interface to something like the INA116 which already has guard ring buffers built into the amplifier. There are a few others that do this also.

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Voltage Spike
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