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Thread: Ph probe reads lower than my measured values.

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    Ph probe reads lower than my measured values.

    Up and running after lightning destroyed my pentair automation system. Intellichem and easy touch boards are new as is my vf drive.

    fc 4
    ta 125
    cya 30
    ph measured 7.8
    ch 250

    Noticed the value from my PH probe was always reading about one entire unit lower than the intellichem reading. Measured 7.8 by strip and taylor test kit, but intellichem reads 6.8 with a .3 up tweak

    Pentair tech just came out and replaced the PH probe yesterday , but the readings are identical. from the screen logic graph It almost looks like it is reading backwards-- yet the connections are correct. ph feed indicates 94 % activity, but the level is set to 7.5 and it is not dispensing muriatic acid.

    F/C has been rock stable at an orp setting of 650.

    While I have heard concerns about the intellichem usualy the concern is ORP and ph is ok. I would appreciate it if anyone has any suggestions as to why the ph reading and measured are so different.

    Many thanks
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    " A little knowledge is a dangerous thing"
    19,000 gallon sylvan pool, Easytouch 2 4p automation, Screenlogic interface, Intelliflo VF 3050 pump, Intellichem with Intellichlor 40 chlorinator/Muriatic acid, Raypac millivolt natural gas heater.Polaris pool cleaner with booster pump.Coverstar automatic cover hydraulic mechanism with PCS cover. Wet edge Luna quartz finish 2016. Northeast climate.

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    Mod Squad Bama Rambler's Avatar
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    Re: Ph probe reads lower than my measured values.

    Did they calibrate the pH to a standard solution?
    Dave J. TFP Moderator
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    Re: Ph probe reads lower than my measured values.

    No, They just changed the probe, came out when I was not there. I was disappointed that the did not schedule the appointment with me and look at the screen logic record as well. Had asked them to upgrade my intellichem software and while they said they would they did not do that either.

    Thank you for responding.
    " A little knowledge is a dangerous thing"
    19,000 gallon sylvan pool, Easytouch 2 4p automation, Screenlogic interface, Intelliflo VF 3050 pump, Intellichem with Intellichlor 40 chlorinator/Muriatic acid, Raypac millivolt natural gas heater.Polaris pool cleaner with booster pump.Coverstar automatic cover hydraulic mechanism with PCS cover. Wet edge Luna quartz finish 2016. Northeast climate.

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    Patrick_B's Avatar
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    Re: Ph probe reads lower than my measured values.

    This seems strange to me. Isn't cal to a standard buffer the norm with these pool pH controllers? It certainly is in my business and we do three point cals to 4, 7, and 10. This way, the controller can set a reference curve so it can be accurate.
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    Mod Squad Bama Rambler's Avatar
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    Re: Ph probe reads lower than my measured values.

    Any time a probe is changed out the new one should be calibrated. Preferably to 3 standards, but at least two.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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    Re: Ph probe reads lower than my measured values.

    the intellichem goes through its own calibration sequence on startup . Is that good enough ?
    " A little knowledge is a dangerous thing"
    19,000 gallon sylvan pool, Easytouch 2 4p automation, Screenlogic interface, Intelliflo VF 3050 pump, Intellichem with Intellichlor 40 chlorinator/Muriatic acid, Raypac millivolt natural gas heater.Polaris pool cleaner with booster pump.Coverstar automatic cover hydraulic mechanism with PCS cover. Wet edge Luna quartz finish 2016. Northeast climate.

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    Patrick_B's Avatar
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    Re: Ph probe reads lower than my measured values.

    Quote Originally Posted by Bama Rambler
    Any time a probe is changed out the new one should be calibrated. Preferably to 3 standards, but at least two.
    No different than ours that control acid/caustic feed, we just do it on a much different scale. There are units that don't require it, but guess what we think of them usually.
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    Mod Squad Bama Rambler's Avatar
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    Re: Ph probe reads lower than my measured values.

    Quote Originally Posted by dradam
    the intellichem goes through its own calibration sequence on startup . Is that good enough ?
    I wouldn't think it's a proper calibration. The reason for calibrating to standard buffers is because each probes glass has a slightly different impedence and if you don't calibrate the electronics to that impedence, it can never know what the pH really is. There are probes that have electronics built into the probe that supply that info to the instrument but they're a little more expensive than you'd put on a pool.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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    Re: Ph probe reads lower than my measured values.

    Thank you,

    I just got off the phone with the company that brought out the new probe. They are going to check it out again.

    Many thanks
    " A little knowledge is a dangerous thing"
    19,000 gallon sylvan pool, Easytouch 2 4p automation, Screenlogic interface, Intelliflo VF 3050 pump, Intellichem with Intellichlor 40 chlorinator/Muriatic acid, Raypac millivolt natural gas heater.Polaris pool cleaner with booster pump.Coverstar automatic cover hydraulic mechanism with PCS cover. Wet edge Luna quartz finish 2016. Northeast climate.

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    Patrick_B's Avatar
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    Re: Ph probe reads lower than my measured values.

    Quote Originally Posted by Bama Rambler
    There are probes that have electronics built into the probe that supply that info to the instrument but they're a little more expensive than you'd put on a pool.


    You could say that.
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