Does anyone have a Labview code program (Ver 6i) which converts 4-20 mA signals to Ph measurements?

[Radgie Rabbit]

I would like to look at some Labview code that will convert a 4-20 mA signal into Ph measurements (Ph meaning the determination of a liquid being acid or alkali). I am using Labview 6i.

[Enrique]

Radgie;

I don't know much about ph sensors, but talking about sensors and measurements in general, I'll say that it is hard for somebody to just give a VI that do what you are asking without knowing the relationship (that is, the mathematical equation) between the electrical signal and the actual chemical value, in this case the ph.

For example, let say the relationship is lineal like:

ph = m*(Current) + b

Where m and b are constants, then you only need to implement that equation in LabVIEW. That should be very easy to do. I will encourage you to try to do it.

If you want somebody to give you the actual code, you need to provide us with the relationship between the ph and the current (or some pointer to where to look for that information).

Re
gards;
Enrique

[Process_Systems]

I am assuming that the 4-20 ma signal is linearly proportional to PH values. This is usually the case with 2-wire PH transmitters, which it sounds to me like you are using. If this is indeed the case, you simply need to subtract the 4 ma offset, and scale the remaining 16 ma proportionately to 0 to 14 ph. This also assumes that you have an analog input capable of dealing with a 4-20 ma. current input. If you have only voltage inputs, as most A/D cards have, then you have to use a shunt resistor across the input of the A/D convert it to a voltage signal.
Hope this helps.

Dave

[Radgie Rabbit]

This is simple! Your Ph probe will be linear ie: The Ph level from say 0 to 10 is directly proportional to 4 to 20mA. So... Ph 0 = 4mA, Ph 5 = 12mA & Ph 10 = 20mA. If you like I can write a simple code when I have time but do let me know how you get on.

Bye,Rabbit.