Question for those who have experience using pH Sensors.

I've been looking at the Atlas Scientific pH Probe and EZO pH circuit.
• 1 EZO™ pH Circuit
• 1 scientific grade silver / silver chloride pH Probe.

Q...How accurate/sensitive are the pH probes to temperature of the liquid?
example if the fluid was 2celcius at night and 22celcius in the afternoon would the pH reading fluctuate due to temperature difference. If compensation is needed ... is it handled by the EZO circuit or can I write it into the sketch (assuming I put a temp probe in the water also)

Q.. If a probe was exposed to water 24/7... how often would it need to be calibrated?
Q.. If a probe was exposed to water 24/7... how often would it need to be replaced?

At the water treatment facility I work at I am monitoring 6 different tanks for HIGH LIQUID LEVEL . I've built a project that monitors the 6 different float sensors and sends SMS messages via a Sim900 GPRS shield to alert us to possible overflows. I would like to add monitoring of pH to a few of these tanks as well.

Incase you get the feeling your drinking water quality is in the hands of a electronic hobbyist. My pH and TANK HIGH LEVEL monitoring projects are redundant to actual procedure & processes within the treatment plant. We are not dependent on home brew telemetry alarms... but we are having fun and learning a lot.

Thanks in advance for sharing your pH sensor experience,
Marty

SCFalconry:
Q…How accurate/sensitive are the pH probes to temperature of the liquid?
example if the fluid was 2celcius at night and 22celcius in the afternoon would the pH reading fluctuate due to temperature difference. If compensation is needed … is it handled by the EZO circuit or can I write it into the sketch (assuming I put a temp probe in the water also)

Yes, pH is temperature dependent and so is your measurement of it. You’ll need to have some programming to compensate if your temperature is fluctuating that much.

SCFalconry:
Q… If a probe was exposed to water 24/7… how often would it need to be calibrated?

That depends on what’s in the water and how accurate a reading you want and what type of probe you have. A double junction probe will stay good longer than a single junction probe which will stay good longer than a wick junction probe. When pH measurements are critical in the lab we calibrate before every measurement or set of measurements. In my aquarium at home where I can be a little looser with the accuracy I calibrate once a month. The real trick is to look at your readings vs. what you expect and work out what you need for your particular situation. There’s no “rule of thumb” to follow.

SCFalconry:
Q… If a probe was exposed to water 24/7… how often would it need to be replaced?

Again that depends on what is in the water you’re measuring and the type of probe. They’re not all created equal.

Delta_G:
Yes, pH is temperature dependent and so is your measurement of it. You'll need to have some programming to compensate if your temperature is fluctuating that much.

DELTA_G ... Thank you for your reply.

I'm about to order probe and sensor board... so not having any practical experience with ARDUINO pH sensors.... how much compensation will be normal for that wide of a temperature swing?
If the reading varied by +/-0.2pH over a 20degree range... that would be precise enough for me. (6.5pH at 2celcius & 6.9pH at 22celcius) However if it is typical for the error to be much greater than that due to temperature alone... that would cause concern. What do you or others feel is typical error due to temperature fluctuation?

Delta_G:
Again that depends on what is in the water you're measuring and the type of probe. They're not all created equal.

Do you have any recommendations on which probes are more durable or accurate?

SCFalconry:
What do you or others feel is typical error due to temperature fluctuation?

It's not about how anyone feels. It's chemistry. It depends on the nature of what you are taking the pH of. There are equations to calculate the difference but it is much more common just to take a series of measurements and see what it is for your solution. It all depends on ionic strength and a bunch of other stuff that's easier to measure than to calculate.

SCFalconry:
Do you have any recommendations on which probes are more durable or accurate?

Not without knowing what you are trying to measure the pH of. I would stick with double glass junction probes if you intend on constant monitoring. Avoid the refillable kind if the level of the liquid could change and get into the refill hole. Other than that it all depends on what you want to measure.

SCFalconry,

take in account that some pH probe manifacturer sells automatic systems were the probe move inside the thank and, after the measure, retract. The probe stay in another little tank filled with a special solution and there is also a cycle that change this solution with buffers, usually pH 7 and pH4 or pH10 depending on what you are measuring.

So, as Delta_G wrote, it depends a lot in liquid type and chemistry, your budget, the precision that you want to achieve and so on. Take a look to a manufacturer web site and you will find a lot of probes.