Product manual

8
1130_0_Product_Manual - March 26, 2010 8:07 AM
Technical Information
Measuring the pH
TodeterminethepHofasolution,makesuretheDIPswitchontheboardisippedtothepHside.Giventhe
SensorValue from the Phidget InterfaceKit, the following formula can be applied:
pH = 0.0178 * SensorValue - 1.889
This formula assumes that the solution is at 25 degrees Celsius. Depending on the temperature of the solution and
on the actual pH level, the SensorValue can change dramatically. To incorporate temperature (in degrees Celsius) for
added accuracy, the following formula can be used:
pH = 7 - (2.5 - SensorValue / 200) / (0.257179 + 0.000941468 * Temperature)
The following example is to give an idea of how the temperature affects the SensorValue. A solution with a pH
of 2 at a temperature of 25 degrees Celsius yields a SensorValue of 219. At 100 degrees Celsius, the SensorValue
decreases to 148, and at 0 degrees celsius, the SensorValue reports 242. A solution with a pH of 8 with a
temperature of 0, 25 and 100 degrees Celsius gives a SensorValue of 551, 556 and 570, respectively. It can be
seen that the temperature has a greater affect on solutions that have a pH further away from the reference pH of
7. Additionally, temperature affects the impedance of the glass electrode, and can result in increased errors if not
properly calibrated.
Measuring Oxidation/Reduction Potential (ORP)
TodeterminetheORPofasolution,makesuretheDIPswitchontheboardisippedtotheORPside.Giventhe
SensorValue from the PhidgetInterfaceKit, the following formula can be applied:
ORP (V) = (2.5 - SensorValue / 200) / 1.037
ORP electrodes give a typical range of -2V to 2V, where the positive values are for oxidizers and the negative values
are for reducers.
Words of Caution
The pH Adapter Board should be used to measure solutions that are ‘electrically quiet’.
Measuring pH in electrically noisy environments such as tanks with mixing pumps, and even other measuring
devices, is not recommended.
Choosing Electrodes
Review the data sheet for the electrode you have selected for your application to ensure that it complies with the
devicespecicationsofthepHAdapterBoard.Theimportantspecicationistheoutputvoltageoftheelectrode.
Many electrodes will work but it is important to verify compliance before connecting an electrode to the Adapter
Board. We have reviewed the following electrodes, and found that they can be used with the pH Adapter Board.
This is by no means a comprehensive list, but can be used as a comparison with other electrodes if necessary.
Manufacturer Web Page Part Number
Omega www.omega.com PHE13XX, PHE14XX,
ORE1311, ORE1411
Cole - Parmer www.coleparmer.com EW-59001,
EW-27003
Mettler - Toledo www.mt.com InLab (BNC) Series
Other Interfacing Alternatives
If you want maximum accuracy, you can use the RawSensorValue property from the PhidgetInterfaceKit. To adjust a
formula, substitute (SensorValue) with (RawSensorValue / 4.095)
If the sensor is being interfaced to your own Analog to Digital Converter and not a Phidget device, our formulas can
bemodiedbyreplacing(SensorValue)with(Vin*200).Itisimportanttoconsiderthevoltagereferenceandinput
voltage range of your ADC for full accuracy and range.