This calculator converts pH values to corresponding voltage levels for pH sensors. pH sensors typically output a voltage signal that is proportional to the pH level of the solution, which can be used for monitoring acidity or alkalinity.

Calculator Inputs

pH Value (pH)

• The pH value of the solution. pH is a measure of the hydrogen ion concentration in a solution. It typically ranges from 0 (very acidic) to 14 (very alkaline), with 7 being neutral.

Temperature (T)

• The temperature of the solution in degrees Celsius (optional for temperature compensation). Temperature affects the sensitivity of pH sensors, so compensation can provide more accurate results.

Calculator Output

• Voltage (V): The voltage output corresponding to the pH value. The voltage output can be measured by the pH sensor and is typically proportional to the difference between the solution’s pH and neutral pH (7).

How do you convert pH to voltage?

Formula for pH to Voltage Conversion 

For a standard pH sensor at 25°C, the relationship between pH and voltage is given by the Nernst equation:

Where:

• R = Universal gas constant (8.314 J/(mol·K))
• T = Temperature in Kelvin (K) = Temperature in Celsius + 273.15
• F = Faraday’s constant (96485 C/mol)

This equation adjusts for temperature changes, ensuring that the voltage output is accurate at varying temperatures. The factor RT/F​ changes depending on the temperature, affecting the voltage output.

At the standard temperature of 25°C (298.15 K), the equation simplifies to:

This simplified formula makes it easy to calculate the voltage output for any given pH value when the temperature is 25°C.

Click here for pH transmitter calibration with standard solutions

Example Calculation

Let calculate the voltage output for a pH value of 4 at 25°C.

Start with the simplified formula for 25°C:

V=(7−pH)×0.05916V 

Substitute the pH value of 4 into the equation:

V=(7−4)×0.05916V

Perform the calculation:

V=3×0.05916=0.17748 V

Result: For a pH value of 4, the voltage output from the sensor at 25°C would be approximately 0.177 V (177.48 mV).

Click on the link for How to troubleshoot pH transmitter issues?

Temperature Compensation

If the temperature of the solution is different from 25°C, you can adjust the formula accordingly by using the full equation with temperature compensation:

V = 2.3×(7−pH)×RT/F​

For example, if the temperature is 50°C, convert it to Kelvin:

T = 50+273.15=323.15 K

Then substitute the values of R and F along with the temperature to get a more accurate voltage reading.

Click here for How to do pH electrode calibration?

FAQ related to pH to Voltage Conversion

How is pH related to voltage?

pH is directly related to voltage in pH sensors because the sensor generates a voltage that is proportional to the hydrogen ion concentration in the solution. 

A higher concentration of hydrogen ions (lower pH) will result in a higher voltage, while a lower concentration (higher pH) results in a lower voltage. 

The relationship follows the Nernst equation, with a voltage change of approximately 59.16 mV for every unit change in pH at 25°C.

Click on the link for How to do Preventive maintenance of pH transmitter?

How many mV is pH 7?

At pH 7 (neutral), the voltage output from a standard pH sensor is 0 mV. This is because pH 7 is the neutral point in the Nernst equation, and the voltage is proportional to the difference between the pH of the solution and neutral pH. A pH of 7 represents no difference, resulting in 0 mV output.

Here you can refer more Online Instrumentation Calculators Collections