SWG Temperature compensation.

[JamesW]

The Pentair IntelliChlor salinity measurement is temperature compensated based on information from Pentair.

The Hayward AquaRite does not use conductivity. It uses the performance of the cell. I think that it definitely uses temperature in determining salinity.

The Jandy AquaPure and AutoPilot both use a trisensor that measures temperature ,flow and salinity based on conductivity.

Since they have the temperature, it really wouldn't make sense not to use it. Also, both are reasonably accurate over the normal temperature operating range.

Note that salinity measurements are not exact in any case. They can be up to 400 ppm over or under. Two different tests might be 800 ppm apart and still be considered to be ok.

 

[JoyfulNoise]

Can you post the information from Pentair either directly or through a link? None of their literature (at least the installation and owner manuals) talk about it in any meaningful way.

I would say that the salinity as registered on the EasyTouch panel has a fairly flat response to temperature in what would be considered a normal range, 75-90 deg F. However, outside those temperatures there's a definite drift in the output. So it would seem to me that they do some sort of compensation at and around the 77F point but it's not perfect.


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[JoyfulNoise]

Also, it looks like the only way to access the internal temperature data of the IC unit is to use an IntelliWand which will give you a diagnostic readout. It's too bad they concealed a lot of useful information from the user but I can understand it if they don't want people messing with the unit. I believe older units had the capability of adjusting the salinity output of the cell based on an external measurement but they discontinued that feature in later models. I have a version 3.01 cell and the front panel on the cell looks very different from the ver. 1.0 models.

 

[bdavis466]

I would say my IntelliChlor is not compensated and heres why:

Water temp is 55 degrees - Taylor says 4200 ppm, IC60 says 3625

When I heat the spa up to 80 degrees the IC60 says 4250, the next morning after it cools down, the cell reads 3625.

My cell was purchased at the end of 2014

 

[JamesW]

Maybe it's a new feature. Maybe the temperature sensor has failed. If you push the "More" button for about five seconds, the "Cold Water" led will go solid red if the temperature sensor is bad.

 

[JoyfulNoise]

I would say my IntelliChlor is not compensated and heres why:

Water temp is 55 degrees - Taylor says 4200 ppm, IC60 says 3625

When I heat the spa up to 80 degrees the IC60 says 4250, the next morning after it cools down, the cell reads 3625.

My cell was purchased at the end of 2014

Brian,

Can you read the version number off your cell? It's very handily placed on the bottom of the cell (DOH!!) for ease of access...

My cell is a 2013 model and is version 3.01

Matt


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[bdavis466]

It says 07/29/14. I didn't see a version but since its a little newer than yours...

I doubt the temp sensor is bad. The SWG is hooked to the IntelliPH and thats hooked to the Easytouch. The IntelliPH gives me a temperature reading that doesn't always correspond with what the Easytouch says.

 

[mas985]

I would say my IntelliChlor is not compensated and heres why:

Water temp is 55 degrees - Taylor says 4200 ppm, IC60 says 3625

When I heat the spa up to 80 degrees the IC60 says 4250, the next morning after it cools down, the cell reads 3625.

My cell was purchased at the end of 2014

I have read many posts where others have reported the same thing for the Intellichlor. So I came to the conclusion a long time ago that the Intellichlor did not compensate the salt readout for temperature.

However, I know for a fact that my unit, AqualLogic, does compensate for temperature because I have a spa and I can see that in the winter when water temps go from 55 to 102, that salt levels change by less than 200 ppm.

 

[skylar18]

I have a Jandy Aquapure and my salinity increases dramatically as the temperature goes up, in fact to almost 1000 ppm from mid winter to summer. My water range during the year seems to go from 51 degrees to 94 in July and August. It has always done that. This summer I replaced the sensor and I am seeing the exact same results. Beginning of October when water was in the mid 80's I was at 3300. No salt added or water overflow and right now I am hanging on at 2600 ppm. So I also assume at least mine is not compensating for temperature.

 

[JamesW]

It might be a new feature for the IntelliChlor. Perhaps an email to Pentair would help clarify.

For Jandy AquaPure and Autopilot, I have seen reasonably good accuracy across the normal temperature range. Again, asking the manufacturer should help.

Also, if they have the temperature information, why wouldn't they use it?

 

[JoyfulNoise]

I have an online ticket in with Pentair asking them this very question about their ICs. Hopefully they will respond with an adequate answer.


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[Pool Clown]

Is this thread just a conversation? Or is there a problem/question? I have no problem with it, just wondering...

I'm curious about a discussion of the fact that most, if not all SWCGs' shut themselves off at a predetermined (low) temp. This is a good thing.

You wouldn't want the unit generating Cl at those temps. Your pool requires a lot less Cl at those temps, and i don't think you would be able to get the unit to throttle back enough to keep the pool from "gaining" chlorine anyway. Either get a floater, erosion feeder, or hand apply chlorine. Hand apply would only require attention 2, maybe 3 times a month (in my area).

My two cents: I think the manufacturer wouldn't want to, or wouldn't want to pay for (i mean pass the cost to you) the technology for the units to be able to adjust salinity readings for temp deviation for the reasons above. And because it would be just another component either hardware or software that they would have to deal with when it went askew. And it would go askew!

Experiment:
Try calibrating your water temp sensor during the dead of winter, then go back and check it in the summer and see how far its off. I doubt you want to pay for a real good quality temp sensor that will remain stable throughout the temp range that you want. The manufacturer is betting you wont, since it would probably be 3 to 4 times more than you are paying now. It would be even more to get that in your SWCG. Besides, how crucial is it to know how CCCOLD your pool is? I believe manufacturers believe having a sensor with a stable range of +/- 40 degrees is "good enough" for the pool industry...

 

[JamesW]

Builder put too much salt in my pool... - Page 2

The issue arose in the above thread. I started this so as not to hijack that thread.

The low temperature cutoff is because the process becomes much less efficient at lower temperatures. Oxygen begins to be generated instead of chlorine.

I think that temperature is factored into the salinity for the major brands. They have the temperature information, so it really wouldn't make sense that they wouldn't use it. It's a minor software difference. There should be no extra cost.

Pentair says that the Intellichlor is. Why some units seem to be inconsistent, I don't know.

Also note that pretty much any halfway decent salinity tester will have temperature compensation.

 

[needsajet]

I'm following this thread because I don't know how the SWG controller senses salt, temp and flow. I had just wildly guessed it was by the extent and rate of changes in the current going to the plates and the pump. I'd love to understand this all way better, so I know what's going to fail, lol! I'm definitely happy and content that it handled the faults I could throw at it.

 

[JoyfulNoise]

Looking at this source, one finds a charts of conductivity versus standard solutions and TDS values. This European Standard document is the same as the ISO 7888:1985 standard on how to measure solution conductivity and compensate for temperature. The standards all use a simple linear model of compensation - if you know the conductivity at one temperature (25C or 77F) and the temperature coefficient of conductivity, then you can simply extrapolate the value at any other temperature. This linear method is only accurate over very small temperature ranges but is very easy to implement as an automated process. As an interesting side-note, This document describes the fundamental conductivity of pure water and, on page 4, gives the coefficients for a 4th order polynomial expansion of conductivity versus temperature.

With all that said, my guess is that the SWG manufacturers, at best, use a simple linear model for temperature compensation which is easy to implement and wouldn't really require any kind of recalibration in the field. The deviations from actual values on either side of 77F (25C) will grow with the magnitude of the temperature difference but all of that probably falls well within their quoted specs. For example, the Pentair manual claims that their SWG salinity measurement error is +/-500ppm to the actual value. That's a pretty big error considering the Taylor test is a lot closer to the mark at +/-200ppm (+/- 1 drop) and can be made more accurate by simply using a larger water sample.

 

[Pool Clown]

Me thinks you guys have too much time on your hands...

Pentair manual claims that their SWG salinity measurement error is +/-500ppm to the actual value. That's a pretty big error considering the Taylor test is a lot closer to the mark at +/-200ppm (+/- 1 drop) and can be made more accurate by simply using a larger water sample.

Again, If you want a more accuracy, or rather less error, you would have to pay for it. Not to say that it would cost (the manufacturer) more.

With an acceptable range of 2800-4500ppm (iC40), the SWCG can afford that much error and still function. Maybe what Pentair calls error is actually the deviation you get with temperature change.

 

[mas985]

Maybe what Pentair calls error is actually the deviation you get with temperature change.

I calibrated my own cell (T15) some time ago and this is the formula I came up with:

salt ppm = 2300 + 17000 * mhos - 42 * DegF

(mhos = amps / voltage)

This matches the readout fairly well. But as you can see, there would be a 42 ppm error per degree if they didn't compensate for temperature (assuming they do calibrate for at least a single temperature). Not sure if the T15 equation is similar to the IC40 but a +-500 ppm error is about +- 12 degF change.

 

[JoyfulNoise]

So I finally got a response, but it would seem to leave a bit open to interpretation -

This was my e-mail inquiry to Pentair -

Dear Pentair,

I just want to say there is nothing wrong with my unit, it is working fine. I have a technical question regarding HOW the unit reports salinity. I have an IC-40 (S/Nxxxxxxxxxxx, ver 3.01) and an EasyTouch8 automation system. I want to know if the salt level output that is reported on the EasyTouch is compensated for water temperature. We all know that the IC does not actually measure chloride concentration directly but it infers the value from the measured electrical conductivity of the water similar to how an electronic TDS meter works. Also, the conductivity of water changes with temperature - warmer water is more electrically conductive than colder water. I have also noticed that, when my IC is generating chlorine (water is warmer than the 52F cold water cutoff) that the reported salinity level is lower when the water is cold as opposed to when it's swim season and the water is at a higher temperature. I measure my salt level exactly using a chemical measurement from the Taylor Technologies K-1766 Salt Test kit. Therefore, I know that my ACTUAL salt concentration has not physically changed, it's just the temperature of the water that is changing and therefore affecting the output salinity level as-reported by the unit.

I have had discussions with people and some say that the Pentair IntelliChlor's are compensated for temperature. However, the fact that the salinity output changes with water temperature would seem to suggest that the IntelliChlor's salt readout is not compensated for temperature drift.

Can someone from the technical or engineering area of Pentair say definitively what is going on?

This was the response from Bill Fann -

Matthew, You are right in all of facts of how the cell works. The easytouch reads what the cell reads with water temp and salt in the pool. That is why we say to have 2800 to 4200 PPM of salt to compensate for the water temp.


Please reference case number TSXXXXXXXXX in all correspondence.

Thank you,
Bill Fann
Pentair Water Pool and Spa Inc

SO make of that what you will but it sounds like the IC units are either not compensated for temperature drift OR, if they are, it's probably a one-time factory calibration using a simple linear fit to make the salinity output behave flat around the 77F (25C) point.

And, to muddy the water's further, there is more complexity with salinity-temperature measurements. First, pure water does change it's conductivity with temperature BUT once you start adding salts to the water, the temperature effect of the water itself is washed out by the presence of ionic species. Also, based on the ISO standards, an electrical conductivity measurement is SUPPOSED to be made using a platinized metal electrode (either a platinum wire or a copper wire coated with platinum). As far as I can tell when I opened the IC the last time, the "salinity" probe looked like it was just two bare metal conductors (maybe copper?) separated by about an inch distance. The problem with using something like a copper electrode is that it will erode (dissolve) when a test voltage/current is applied as it is basically going to act like a miniature electrochemical cell. So that, in itself, would add some error & drift to the measurement.

In Summary - Take the salinity output with a grain of salt (haha, pun intended ), get yourself a K-1766 for routine measurements and keep the salt at a level that makes the SWG happy (all green lights).

 

[Pool Clown]

I believe this.

it sounds like the IC units are either not compensated for temperature drift OR, if they are, it's probably a one-time factory calibration using a simple linear fit to make the salinity output behave flat around the 77F (25C) point.

I'll admit, i don't know anything "outside" of the working limits of these things for the simple reason that, at the end of the day, it is information that i have no application for. Not to say that it isn't interesting, but i have never needed this info because a customer started asking. The only info i have ever needed with respect to teaching customers is that it shuts itself off in the winter to protect itself (customers like that wording because they wouldn't want the unit to harm itself.) and you have to chlorinate in another manner until spring.

Think of it as a hibernation of the cell...

 

[JoyfulNoise]

I believe this.



I'll admit, i don't know anything "outside" of the working limits of these things for the simple reason that, at the end of the day, it is information that i have no application for. Not to say that it isn't interesting, but i have never needed this info because a customer started asking. The only info i have ever needed with respect to teaching customers is that it shuts itself off in the winter to protect itself (customers like that wording because they wouldn't want the unit to harm itself.) and you have to chlorinate in another manner until spring.

Think of it as a hibernation of the cell...

The reason why discussion like this come up from time to time is because the general pool user gets confused by the salinity output of these units. Every pool season you will find posts by new TFP'ers about how they saw their salinity drop as the weather cooled off and then blindly added salt to compensate only to turn around the next spring and find their pools over salted. I know, because as a pool noob, I made this very mistake ! The temperature behavior of these units is rarely, if at all, discussed in the owner manuals and most PBs have no clue either. So owners are left confused by these systems.

Once you explain to people that the units tend to drift with temperature, most get the concept and then want to know why. Having a thread like this can be helpful in pointing them towards "further reading" on the subject.


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