pH Value assigned to L1 need 0-10v clarification

Morning all,

I'm trying to figure out how the 1-10v logic interacts with the pH. I was hoping that the analog voltage would be linear based on the pH reading but when I probe the 1-10v and ground on the L port of the break out box and place the pH probe in various solutions the output voltages doesn't make sense.

I also realize that "Nominal value" and "Hysteresis" change how the 1-10v reference is read. I have read this article by @sibylle and tried to apply the temperature explanation to pH but there are more questions than answers.

Let me give you a brief run down of what I'm trying to accomplish. I have an arduino that I want to read the pH from the GHL in the format of 0-5v so that I can take that signal and give it a value so that the arduino can take action based on pH. But I don't know the limitations of how the profilux sends this signal and how changing the "Nominal value" and "Hysteresis" effect the value.

My hypothesis is that "Nominal value" is the 0 point and as I move away from the "Nominal value" the voltage increases. If this is true, does it increase the same in both directions? And how does "Hysteresis" play a role in the output? What pH range do you get the full 0-10v reference?

I'm not sure if this is something that has been addressed in previous threads, if it has, I couldn't find anything. Can someone point me in the right direction with information on the subject?

Hi,

Yes, "The selected controller outputs then a voltage that is proportional to the control deviation (= deviation from nominal value to actual value) at this interface."

Gaël

Can you expand on this by giving examples? I can't wrap my mind around what you're telling me?

Quote:

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Originally Posted by itsmorefun

Hi,

Yes, proportional to the control deviation (= deviation from nominal value to actual value) at this interface."

Gaël

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proportional how? in both directions? And what is the range of the 0-10v output? How far is the deviation before we go from 0 - 10v?

Yes in both directions
The range seem defined by hysteresis.

with nominal value = 8.0 and hysteresis = 0.1 and current ph = 8.1 you will get 5v
with nominal value = 8.0 and hysteresis = 0.1 and current ph = 8.0 you will get 0v
with nominal value = 8.0 and hysteresis = 0.1 and current ph = 7.9 you will get -5v

with nominal value = 8.0 and hysteresis = 0.05 and current ph = 8.1 you will get 10v
with nominal value = 8.0 and hysteresis = 0.05 and current ph = 8.0 you will get 0v
with nominal value = 8.0 and hysteresis = 0.05 and current ph = 7.9 you will get -10v

Gaël

Thank You Gaël,

That seems to help a lot. However, I'm not experiencing the -10v when you go below nominal value. It's + in both directions.

it is indeed logical not to send a negative voltage in 0-10 volts I think it is implemented in the same way as for the temperature, when it is negative the relay is activated. see if the relay output activates when it is negative.

Gaël

Quote:

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Originally Posted by itsmorefun

it is indeed logical not to send a negative voltage in 0-10 volts I think it is implemented in the same way as for the temperature, when it is negative the relay is activated. see if the relay output activates when it is negative.

Gaël

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That was a piece of the puzzle I was unaware of. It does send 0.5v to relay1 when it's above nominal value and 0v when below. Am I correct to assume that 0.5v is the relay output when on?

Relay 1: max. 100mA (open collector: active = GND, inactive = floating)
GND = Ground = 0V, outputs with clamp diode to GND.

Gaël

Oh... Got it.

Gaël, thanks so much for helping me understand this.

Jimmy

It appears that this won't work for what I'm trying to achieve.

@itsmorefun is there another way to get 0-10v to send a signal based on pH value? For example if pH = 8.00 can I program profilux to send 45% of the 0-10v range? Which is 4.5v. And when the pH moves up an increment of 0.01 (to 8.01) can I have profilux change the output to 4.6v?

Even if it's time consuming to program... Is it possible? If so how?

Hi,

Set U Min to 0 et U Max to 5
Increase Hysteresis for higher range.

For exemple, with U Min set to 0v et U Max set to 5v and pH hysteresis set to 1pH:
with nominal value = 8.0 and current ph = 9.5 you will get 5v
with nominal value = 8.0 and current ph = 8.0 you will get 0v
with nominal value = 8.0 and current ph = 6.5 you will get -5v

But as 1 is max allowed value for hysteresis we can't get higher range than 1.5pH for 10V (reduced to 5v in your case)

Gaël

I see how my example could be construed as trying to achieve 0-5v. I've already decided I'm going to use a voltage divider to prevent damage of the arduino. Let's forget about U and U max for a moment. I want 1-9v to provide a pH range from 7.65-8.46. That a scale of 0.1v = 0.01pH.

Example, when pH = 8.30 the output voltage would read 7.5v. another example, when pH = 8.00 the output voltage would read 4.5v.

Can this be done with programmable logic? Or any other way?

Hi,
Sorry, I already told you what can be done.
Forget programmable logics, they can't do that and can only be applied to switchable channels.

Gaël