DEVELOPMENT OF AN AFFORDABLE AND RELIABLE pH SENSOR
NG KEEN YUNG(18)
Type of project
-Improve a product or process: Industrial and applied research
e.g. Development of a SMART and GREEN energy system for households
A. QUESTION OR PROBLEM BEING ADDRESSED
Acidity is an important factor affecting the conductivity of aqueous solutions (Covington, Bates and Durst, 1985). However, we need to define the acidity. Thus, we have a pH scale and pH.
The concept of pH was first introduced by Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909 (Sørensen, 1909) and revised to the current symbol pH at 1929 to keep it consistent with definition and measurements of electrochemical cells. The meaning of pH has been widely disputed. As Nørby (2000) reported, “Current usage in chemistry is that p stands for “decimal cologarithm of”, as also in the term pKa, used for acid dissociation constants.” (p. 25)
The pH scale is traceable to a set of standard solutions whose pH is established by international agreement (Covington, Bales and Durst, 1985) The pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution.
This definition is adopted because ion-selective probes, which is used to measure pH, respond to activity. Ideally, electrode potential, E, follows the Nernst equation, which, for the hydrogen atom can be expressed as follows:
(where E is measured potential, E0 is the standard electrode potential, R is the gas constant, T is the temperature in kelvin, F is the Faraday Constant. For H+ number of electrons transferred is one)
For example, it is necessary to control the pH of an aquarium as some species of fish can only live within a set pH range. Other fields where controlling the pH is important include hydroponics, fermentation processes like beer and wine production, environmental monitoring of soils, sewage treatment tanks, monitoring of solution and buffers in chemistry laboratories. It is quite hard to find good and cheap pH sensors. So we have decided to build a cheap and simple pH sensor with easily accessible materials. We will be build it so it can fit in a box with a small display making it portable. Building a small and cheap pH sensor will benefit many people by making pH sensor a widely available product.
B. GOALS/EXPECTED OUTCOMES/HYPOTHESES /ENGINEERING GOAL
- To perform research and develop a pH sensor that is both reliable and affordable.
- Find ways to improve the functionality to make it a much more usable product.
- Integration of various sensors to provide consumers with a one stop solution to all their measurement needs.
- Must be affordable.
- Must fit in a box the size of a typical scientific calculator.
- Must be portable.
- Must be able to run on both wall circuit and 2 x 9V rectangular battery.
- Must be reliable
- Build a digital pH meter that you can use instead of an expensive industrial ph meter or benchtop ph meter for a fraction of the cost.
- Instead of using a pH probe, one can simply use a widely available litmus paper to test for the approximate value of pH.
- This method, however, is not accurate and is not suited for use in industries that require precise values, not vague guesses. Such example would be in the aquatic industry, in which the pH would affect the business itself (a fish farm would be a good example for this, as some fish are adapted to live in certain pH values)
- Another solution would to be to use the conductivity of the medium to find the pH.
- This is not used as it is overly complicated. However, for people that need to know pH without having to go through the hassle of calibrating the sensor, they can use this method for its versatility. It is called the inferred pH, calculated from the cation conductivity and normal conductivity.
E. EQUIPMENT REQUIRED
- TL082 pH probe
- Arduino with codes
- Seven beakers of water
- Sulphuric acid to make water acidic
- Baking soda(sodium bicarbonate) to make alkaline
F. METHOD AND PROCEDURES
- Purchase the materials needed for conducting the experiment from Sim Lim Square. Compile a part list to ensure the correct equipment is bought.
- Conduct a quality check to ensure that all equipment purchased is not defective. If equipment is defective , exchange it immediately.
- Assemble all the parts together carefully under the guidance of an article related to our project.
- ZHONGZHI COPY THE STEPS FROM THE WEBPAGE
- ZHONGZHI COPY THE STEPS FROM THE WEBPAGE
- ZHONGZHI COPY THE STEPS FROM THE WEBPAGE
- Once we finished the creation of the pH meter, we would install in the code that acts like the “brain” of the meter, enabling all the parts to work together.
- Prepare seven beakers of water, using sulphuric acid and sodium bicarbonate to change the pH of the different beakers, but leave one beaker unchanged and label it as “Control”. Label the others according to their respective pH.
- Then, we would proceed on to test the our pH meter on the beakers of water.
- Then, we would proceed on to test the reliability of our readings to ensure that our pH meter is accurate. We accomplish this by testing our results against the results of other commercially available pH meters.
- Repeat step 7 and 8 three times, then average and plot the data on a graph to prevent random errors.
- If we manage to achieve a percentage error of less than 10%, we would then proceed on to improve on its functionality by making it portable.
- If we did not manage to achieve a percentage error below 10%, we would work on calibrating the sensor until we have achieve our goal.
- Once we have ensure that everything is working properly, we would then proceed on to make it portable.
- We would try to fit it into a compact package (that includes shrinking the size down to as small as possible)
- We would need to find a portable power source ( for example 2x9V rectangular battery). The Arduino is a relative low power device (9V to 12V) and can be powered with a commercially available batteries. (which is convenient)
- Remember to document the project and include in videos and pictures
G. Risk and Safety
1. List/identify the hazardous chemicals, activities, or devices that will be used.
-There is a risk of electrocution from mishandling of wires and electricity.
-The acids and alkalis that will be used are corrosive and can harm skin greatly if mishandled.
2. Identify and assess the risks involved.
-Care must always be taken when handling tools.
-Follow lab rules strictly to prevent injury from incorrect usage of machinery.
3. Describe the safety precautions and procedures that will be used to reduce the risks.
-Use gloves and proper lab materials when holding the test tubes of acids and alkalis.
-Clean hands thoroughly so we do not contaminate any of the liquids.
-Keep water away from Arduino sets and the voltmeter to prevent electrocution.
H. Data Analysis
We will be comparing our pH meter to a store-bought sensor. We will test our meter against the store-bought meter on jars of water that have different acidity as explained under Procedures. We will be using Arduino to help us extract and plot the data on a graph. We will then plot the data from our pH sensor against that of the store-bought sensor. If our data is correct, the line graph that is plotted should have a gradient very close to one.
This is the target accuracy of our developed pH sensor compared to the commercial sensor. If data from our sensor closely matches that of commercial sensor, sensor is properly calibrated.
1. Benoit, A. (2013, July 09). pH, Conductivity and TDS. Retrieved from http://environmentalet.hypermart.net/env1221/phcondtds.htm
2. Covington, A. K.; Bates, R. G.; Durst, R. A. (1985). Pure Appl. Chem. 57 (3): 531–542. http://www.iupac.org/publications/pac/1985/pdf/5703x0531.pdf
2. Covey, J. (2007, November 01). Inferring pH from conductivity and cation conductivity. Retrieved from http://www.power-eng.com/articles/print/volume-111/issue-11/features/inferring-ph-from-conductivity-and-cation-conductivity.html
3. Crispa, H. (2006, September 07). Creation of a DIY conductivity meter. Retrieved from http://www.reefcentral.com/forums/showthread.php?t=931044
^ Nørby, Jens (2000). "The Origin and the Meaning of the Little p in pH". Trends in the Biochemical Sciences 25 (1): 36–37.
4. Pratical, M. (2011, August 11). DIY EC Probe. Retrieved from http://www.youtube.com/watch?v=0NPtmHdbW3k
5. Reithmayer, K. (2013, July 10). pH Calibration. Retrieved from http://www.globalw.com/support/calibration.html
6. Sorensen, S. P. L., Enzymstudien. II, Über die Messung und die Bedeutung der Wasserstoffionenkonzentration bei enzymatischen Prozessen, Biochem. Zeitschr., 1909, vol. 21, pp. 131–304.