Timeline for Considerations for PCB guard ring trace for PH probe
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
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| Jun 7, 2021 at 20:44 | comment | added | Voltage Spike♦ | Only the input trace needs to be guarded, including the other trace will introduce a small amount of offset error from leakage current from that trace. | |
| Jun 7, 2021 at 20:42 | comment | added | Andy | Should I be guarding the reference electrode terminal (probe GND if you want to call it that) as well? | |
| Jun 7, 2021 at 20:38 | comment | added | Andy | @VoltageSpike Amplifier is unity gain, so no resistors. I like your bottom side guard ring implementation. Thanks, I will use that. | |
| Jun 7, 2021 at 18:28 | history | edited | Voltage Spike♦ | CC BY-SA 4.0 |
added 119 characters in body
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| Jun 7, 2021 at 18:28 | comment | added | Kuba hasn't forgotten Monica | I'm in full agreement - just trying to make it clear for those who might be used to treating FR-4 as an ideal insulator: with that mindset, your solution is pure magic, but as soon as you can see the virtual lattice of resistors formed by the FR4, it starts making sense :) | |
| Jun 7, 2021 at 18:25 | comment | added | Voltage Spike♦ | I guess it depends on how accurate you want need your input bias current and how much errror your application can tolerate. There are differences between a pA level amp or an fA level amp. to get pA's through fr4 you only need 100mV's on the other side. Anyway most pH meters have an impedance much greater than 10^8 so everything becomes a source of error (the two currents will add). | |
| Jun 7, 2021 at 18:18 | comment | added | Kuba hasn't forgotten Monica | I'd explicitly add the driving principle behind your solution: you are considering the PCB material to be a weak bulk conductor, sort of like the black antistatic conductive foam. This requires a bit of an adjustment of the mental model for someone unused to thinking that way. It also informs any simulation efforts (mental or otherwise) in determining the best shape of the guard plane. | |
| Jun 7, 2021 at 18:06 | history | answered | Voltage Spike♦ | CC BY-SA 4.0 |