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Transistor, relay or?.. for science experiment

kahax

Aug 28, 2018
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Dear forum

I am a researcher with the technical university of Denmark, my field is environmental engineering .

I am carrying out experiments to clean surface water sediments using bio-electrodes.
For this purpose I have assembled a data logger from basic arduino and breakout boards etc.
I am measuring voltage between 2 electrodes in comparison pairs, using ads1115's
Voltages are <1V (most of the time ca 0.0001-0.1V) at <2mA

I want to add the functionality to through code, break/open the circuit at a timing I choose (e.g. 1 time every day) in order to automatically measure open circuit potential, for 15 minutes and then close/reconnect the circuit again.

Open circuit potential I expect in the range of 0.3-0.8V

For this I as planning to use relays, but figure that might be overkill, and would consider using transistors.

It is important that I loose as little signal as possible when measuring.

I am a bit out of my field here, so I would greatly appreciate input :)

best regards
Karl
 

Harald Kapp

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Transistors are no good at switching these extremely low voltage levels. Even standard relays will not work reliably. Mercury wetted relays may be suitable.
A better option, imho, is to amplify the signal and switch the amplified signal. If that is not possible, use the wetted relays.
 

Harald Kapp

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You can't switch 0.0001-0.1V and expect reasonable measured values.
 

Harald Kapp

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You can't switch 0.0001-0.1V and expect reasonable measured values.
Sorry for being not really precise, the idea didn't find the way from head to keyboard: of course you can, but not using transistors. Use a wetted relay or amplify first, then switch. Or use an amplifier that can be turned on and off.
 
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