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 )
about isolator for PH probe
Started by ●August 1, 2022
Reply by ●August 1, 20222022-08-01
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 - Tesla referral code - https://ts.la/richard11209
Reply by ●August 1, 20222022-08-01
On 01/08/2022 07:25, Ricky wrote:> 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
