P
Piyush Kamdi
Guest
i use the analog isolator from atlast scintific but it is quiet expensive so suggest me the cheap isolator circuit in india . (for ph probe )
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R
Ricky
Guest
On Monday, August 1, 2022 at 12:55:48 AM UTC-4, Piyush Kamdi wrote:
> i use the analog isolator from atlast scintific but it is quiet expensive so suggest me the cheap isolator circuit in india . (for ph probe )
By \"isolator\", I assume you mean a high input impedance amplifier? I know pH probe have a very high impedance, so nearly any current draw will create an error. I don\'t know how high the impedance needs to be. This may require a circuit with a bootstrap and guard rings. Do you have a schematic? Perhaps you can make your own. Have you looked for sample circuits?
--
Rick C.
- Get 1,000 miles of free Supercharging
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> i use the analog isolator from atlast scintific but it is quiet expensive so suggest me the cheap isolator circuit in india . (for ph probe )
By \"isolator\", I assume you mean a high input impedance amplifier? I know pH probe have a very high impedance, so nearly any current draw will create an error. I don\'t know how high the impedance needs to be. This may require a circuit with a bootstrap and guard rings. Do you have a schematic? Perhaps you can make your own. Have you looked for sample circuits?
--
Rick C.
- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
M
Martin Brown
Guest
On 01/08/2022 07:25, Ricky wrote:
Their OEM pH board doesn\'t look unreasonably priced to me:
https://atlas-scientific.com/embedded-solutions/ph-oem-circuit/
A working approximation is around 1G worst case.
You would probably get away without a guard band provided that the
humidity and ambient temperature isn\'t too high. Many opamps the input
bias current rises quickly with temperature above 25C ambient.
If you don\'t care too much about thermal drift or precision calibration
then almost any modern FET input opamp will be adequate in a unity gain
voltage follower configuration. eg #9.3 in TL071 datasheet
https://www.ti.com/lit/ds/symlink/tl071.pdf
Or a more recent automotive part like
https://www.ti.com/lit/ds/symlink/ina333-q1.pdf
If you do care about precision calibration and have to ask this question
then you are probably much better off with a commercial product.
--
Regards,
Martin Brown
On Monday, August 1, 2022 at 12:55:48 AM UTC-4, Piyush Kamdi wrote:
i use the analog isolator from atlast scintific but it is quiet
expensive so suggest me the cheap isolator circuit in india . (for
ph probe )
Their OEM pH board doesn\'t look unreasonably priced to me:
https://atlas-scientific.com/embedded-solutions/ph-oem-circuit/
By \"isolator\", I assume you mean a high input impedance amplifier? I
know pH probe have a very high impedance, so nearly any current draw
will create an error. I don\'t know how high the impedance needs to
be. This may require a circuit with a bootstrap and guard rings.
A working approximation is around 1G worst case.
You would probably get away without a guard band provided that the
humidity and ambient temperature isn\'t too high. Many opamps the input
bias current rises quickly with temperature above 25C ambient.
Do you have a schematic? Perhaps you can make your own. Have you
looked for sample circuits?
If you don\'t care too much about thermal drift or precision calibration
then almost any modern FET input opamp will be adequate in a unity gain
voltage follower configuration. eg #9.3 in TL071 datasheet
https://www.ti.com/lit/ds/symlink/tl071.pdf
Or a more recent automotive part like
https://www.ti.com/lit/ds/symlink/ina333-q1.pdf
If you do care about precision calibration and have to ask this question
then you are probably much better off with a commercial product.
--
Regards,
Martin Brown