Digital pH Meter with 4-20MA Output

Digital pH meter with 4-20 MA analog output, Digital pH Meter with 4-20MA Output

What is pH value:
The pH indicates the Hydrogen ion concentration of any given solution. The pH value of a solution signifies the power of hydrogen. To understand the theory of pH, it is important to know about the dissociation property of water. The pH scale has been derived from the dissociation of water. The water dissociates into its H+ and OH- components. The concentration of H+ ion found in pure water 7pH This H+ ion concentration is neither acidic nor alkaline and hence called as neutral.

When the H+ ion concentration is more than 7.0 pH, the solution is acidic; when the H+ ion is less than 7.0 pH, then the solution is alkaline. Low pH indicates high H+ ion concentration; High pH indicates low H+ concentration. Hence the pH scale is inversely related to the concentration of H+ in any given solution, and directly related to OH– ion concentration.

pH = -Log10 [H+] | Digital pH Meter with 4-20MA Output

The pH scale is in the range from 1 to 14. When there is a change of pH by unit 1 (for ex. pH changes from 4 to 5), it indicates the change in hydrogen ion concentration by 10 times. When there is change of pH by 2 units it indicates that the change in hydrogen ion concentration by 100 times. Due to this relationship, the pH scale is called as logarithmic.

pH Value Scale for pH meter.
While we test many experiments, it is important to check the pH of any given chemical solution. while the pH is checked by pH or litmus paper. The change in litmus paper color indicates the change in pH, it is called as visual method. For precise noting of pH, an instrument is used and it is called a pH meter. The pH meter works on potentiometric principle.
As the acidic solution has a more positive charge (H+ ion) than the alkaline solution, and the acidic solution has greater potential to produce current than the alkaline solution. The pH meter works measures the potential difference (voltage) of test solution and standard or known solution and calculates the pH. Hence, it works like a Voltmeter. To complete the circuit, two electrodes are connected in order to complete the circuit. The complete circuit allows the movement of electric current.

Working Principle of pH meter:

Digital pH Meter with 4-20MA Output, The working of pH meter based on the Nernst equation. Nernst equation derives the relation between the electric voltage with ion concentration. The Nernst equation derived for H+ ion concentration is the basis of pH meter. The working principle of pH meter is potentiometry. The pH meter consists of glass (also called an indicator electrode) and a reference electrode. The glass electrode consists of a glass membrane, which is sensitive to hydrogen ion concentration of test sample solution. And the glass electrode potential varies from sample to sample. The reference electrode is standard and has constant potential. The reference electrode does not respond to the test sample solution. The pH meter measures and compares the potential difference between both glass and reference electrodes.

Using the Nernst equation, the potential difference used to measure the hydrogen ion concentration indicating the pH of given solution. Due to the potential difference between two electrodes, the electron flows and generates current. This generated current measured by a voltmeter. The relationship between the potential difference generated current and pH has been derived. The potential difference of 1 pH is 59.16mV at 25° C and hence when there is a difference of one pH unit, there will be a change in voltage by 59.16mV. This relationship employed in measuring the pH.

Digital pH Meter with 4-20MA Output

Construction of pH meter:
pH sensor or probe of modern pH meter combined type, in which test and reference electrodes placed into a glass tube-like structure. The combined electrode consist of following parts-

design and Construction of pH meter Probe

1. Glass bulb: The sensor that senses the H+ ion concentration made from a special type of glass and membrane. The glass bulb consists of 0.1M HCL Solution.
2. Internal electrode: This electrode made by silver chloride.
3. Internal solution: The silver chloride electrode, dipped in a buffer solution of 0.1 mol/L KCL of pH 4 to pH 7.
4. Reference Electrode: It also the silver chloride electrode used for reference.

5.Junction: It made from a ceramic junction also called a diaphragm that allows the contact of sample solution and reference electrolyte. It should not disturb the electric connection between both electrodes.
6. Filling hole: This used for refilling the electrolyte if required.
7. Electrode body: Electrode body Made from non-conductive glass, plastic material and may coated by epoxy to prevent glass bulbs.

Digital pH Meter with 4-20MA Output

when acidic solution is rich in H+ ion concentration. When the pH probe dipped in an acidic solution, the H+ ion moves close to the glass membrane of the sensitive glass bulb (external side of the bulb). Hence Similar reaction occurs inside the bulb, Which filled with buffer solution of neutral pH 7. This neutral buffer solution has a constant number of Hydrogen ions. The H+ ions present inside the bulb also move close to the glass membrane (internal side of the bulb). Hence, this causes the difference in the concentration of hydrogen ion or degree of hydrogen ion activity across the membrane causing a difference in the potential (voltage). When the hydrogen ion concentration inside the glass bulb is less than the outside solution (test solution), then the given solution acidic and hence the pH is lower than 7.

When the Hydrogen ions concentration across the membrane similar then it called as neutral pH and the pH is equal to 7. while If the concentration of hydrogen ion of inside the bulb than outside solution then the given solution alkaline and the pH is more than 7. Hence pH meter measures the potential difference at both the electrodes and calculates the pH as per the Nernst equation.

pH Meter

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