01 Sensors Concept Overview
SENSORS | CONCEPT OVERVIEW
The topic of SENSORS can be referenced on page 124 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
CONCEPT INTRO:
MEASUREMENTATION is the process of experimentally obtaining one or more quantity values that can reasonably be attributed to a physical parameter influencing a solution, body, or system. An INSTRUMENT is a device that provides an output reading or signal used to measure a physical quantity or parameter by having specialized materials or equipment to capture the desired characteristics of a physical parameter. Measurements are made by instruments and either directly reading the scale and output of an instrument, or using the change in one or more physical parameters and developing relationships to measure the magnitude of a physical property. A SENSOR is a device that detects and measures the conversion of energy based on physical parameters or processes, and converts the real world information into an electrical signal. Sensor are usually used with the purpose to sense or detect some characteristic of its environment. Sensors are commonly use measure variables such as flow rate, temperature, pressure elevation, and the pH of a solution.
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A sensor that is used on a regular basis is the thermostat in our homes. As the temperature changes, the thermostat detects the change and sends an electronic signal to the air conditioning unit that the air temperature needs to be heated or cooled. A TRANSDUCER is an electronic device that utilizes sensors to convert mechanical energy in one form to another energy form, typically in the form of an electronic signal. Transducers are typically used to convert a physical parameter such as temperature, pressure, flow, light intensity, etc. into an electrical signal. A speaker changes electrical energy from an amplifier into mechanical energy or sound waves. The electrical energy in the amp causes the speaker cone to move in and out creating air waves that our ears perceive as sound. A microphone is the reverse of a speaker. It is a transducer that converts acoustic energy in the form of sound waves from a human voice and turns it into electrical energy or electrical impulses. The formula for SENSITIVITY is not provided in the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We must memorize this formula and understand its application independent of the NCEES Supplied Reference Handbook. The SENSITIVITY is defined as the ratio of the change in output to the corresponding change in input under static or steady state conditions. Sensitivity can be thought of as the measure of the change in instrument output that occurs when the quantity being measured change by a given amount.
ππππ ππ‘ππ£ππ‘π¦ =
πΆβππππ ππ πΌπππ’π‘ πΆβππππ ππ ππ’π‘ππ’π‘
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The TRANSDUCER SENSITIVITY is the ratio of change in electrical signal magnitude to change in magnitude of the physical parameter being measured. Transducer sensitivity will have different units depends on the instrument being used and the parameter being measured. For example, a platinum resistance thermometer gives a change in resistance to correspond with a change of temperature, and would have its sensitivity defined in units of πΊ/Β°πΆ. PIZEOELECTRIC TRANSDUCERS: The topic of PIEZOELECTRIC TRANSDUCER can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. PIEZOELECTRICITY is defined as the electrical forces or electrostatic stresses applied to a material that resulted in the appearance of an electrical charge on the surfaces of the material. A common application of piezoelectricity is a printer electronically communicating with an ink cartridge on how to apply ink a specified pattern or format on a piece of paper. Each droplet of ink is electrostatically charged to appear on the surface of the paper is a defined pattern and position. PIEZOELECTRIC TRANSDUCERS are comprised of a special ceramic that converts the electrical energy to mechanical energy, or electrical voltage to mechanical force, and vice versa. When an electric field is applied to the material, it will change dimension. Conversely, when a mechanical force is applied to the material, an electric field is produced. Piezoelectric transducers can have multiple layers and many different geometries.
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A simple piezoelectric transducer generates a voltage that is proportional to the change in its ceramicβs volume, or will change volume proportional to the applied voltage. Dimensional changes are usually very small, and can be predominantly in one direction. PRESSURE SENSORS: The topic of PRESSURE SENSORS can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A PRESSURE SENSOR is a sensor that detects pressure in the form of mechanical or kinetic energy and responds with an electrical signal. Pressure sensors are also called pressure transducers, pressure transmitters, pressure senders, pressure indicators, piezometers, and manometers. The formula for PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. PRESSURE, (π), is defined as the force per unit area normal to the force:
π=
πΉ π΄
Pressure is measured as GAGE PRESSURE, the difference between ABSOLUTE and the ATMOSPHERIC. Gage pressure is either positive or negative (vacuum). The
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AMBIENT PRESSURE is pressure at which the vapor pressure is equal to the surrounding pressure. This is the pressure at which a liquid boils. RELATIVE PRESSURE is measured with respect to ambient pressure. ABSOLUTE PRESSURE is measure with respect to vacuum at zero pressure.
DIFFERENTIAL PRESURE is
measured relative to another pressurized container or system. The formula for ABSOLUTE PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We use the following formula to relate absolute pressure, atmospheric pressure, and gage pressure. π:;< = π:=> + π@:@A Where: π:;< = Absolute Pressure π:=> = Atmospheric Pressure π@:@A = Gage Pressure (positive or negative)
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The table for PRESSURE RELATIVE MEASUREMENT TYPES can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. Pressure Relative Measurement Types Absolute
Relative to 0 Pa, the pressure in a vacuum
Gage
Relative to local atmospheric pressure Relative to either absolute vacuum (0 Pa) or local
Vacuum
Comparison
atmospheric pressure
Differential
Relative to another pressurized container
Sealed
Relative to sea level pressure
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PH SENSORS: The pH value of a substance is directly related to the ratio of the hydrogen ion [H+] and the hydroxyl ion [OH-] concentrations. If the H+ concentration is greater than OH-, the material is acidic; i.e., the pH value is less than 7. If the OH- concentration is greater than H+, the material is basic, with a pH value greater than 7. If equal amounts of H+ and OH- ions are present, the material is neutral, with a pH of 7. Since the relationship between hydrogen ions and hydroxyl ions in a given solution is constant for a given set of conditions, either one can be determined by knowing the other. Thus, pH is a measurement of both acidity and alkalinity, even though by definition it is a selective measurement of hydrogen ion activity. Since pH is a logarithmic function, a change of one pH unit represents a ten-fold change in hydrogen ion concentration. The topic of ACIDS, BASES, AND PH can be referenced under the topic of CHEMISTRY on page 54 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. It is important to remember that a solution with a ππ» < 7 is considered ACIDIC, and a solution with a ππ» > 7 is considered BASIC. The formula to calculate the pH of a solution based on the hydrogen ion concentration is expressed as:
ππ» = logIJ
1 π»L
Where: β’ [π» L } is the molar concentration of hydrogen ions, in gram moles per liter.
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The topic of PH SENSORS can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A PH SENSOR is a pH meter consisting of a special measuring probe made up of two electrodes that connect to an electronic meter that measure the electrical potential difference between the electrodes and displays the pH reading. One of the electrodes is a reference electrode and assumed to act a pH of 7, while the other electrode measures the hydrogen-ion concentration difference and measures the electro-potential difference between a neutral solution and the concentration in the solution being analyzed. The formula for the RELATIONSHIP GOVERNING A PH SENSOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The voltage output reading for a pH sensor is directly proportional to the pH of the solution. Therefore, at a pH of 7 (neutral) the output would be 0, and then produce a negative reading for an acidic reading (pH < 7) and a positive reading for a basic reading (pH > 7). πΈAP = πΈ J β π(ππ»: β ππ»S )
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Where: β’ πΈAP is the electrode potential β’ πΈ J is the zero potential β’ π is the slope (ππ πππ ππ» π’πππ‘) and represents the sensitivity of the pH sensor β’ ππ»: is the pH value of the measured solution β’ ππ»S is the pH value of the internal buffer. CHEMICAL SENSORS: The topic of CHEMICAL SENSORS can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A CHEMICAL SENSOR is a sensor that produces an electrical signal in response to a chemical reagent. A chemical sensor operates by converted the energy of a chemical reaction into heat using a transducer, and generates an electrical signal based on the amount of thermal energy in the environment. For example, a smoke detector uses an optical sensor such as a photo resistor. Smoke is allowed to flow between the source and sensor of the smoke detector, and sampled to determine the light intensity, velocity, phase, or other measurable property. Then based on the reference of the light intensity, it will transmit a signal that there is smoke in the air. Another commonly used chemical sensor is a POTENTIOMETRIC SENSOR, which operates on the principles that electric potential develops at the surface of a solid material is immersed in solution containing ions that exchange at the surface.
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The table for EXAMPLES OF COMMON CHEMICAL SENSORS can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
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CONCEPT EXAMPLE: A solution is measured using a pH sensor with a sensitivity of 0.02 mV per pH unit, an electrode potential of 0.0704 mV, and zero electrode potential of 0.05 mV. If the solution is known to have a pH of 7.98, what is the pH value of the internal buffest closest too: A. 7 B. 9 C. 11 D. 13
SOLUTION: The formula for the RELATIONSHIP GOVERNING A PH SENSOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The voltage output reading for a pH sensor is directly proportional to the pH of the solution. Therefore, at a pH of 7 (neutral) the output would be 0, and then produce a negative reading for an acidic reading (pH < 7) and a positive reading for a basic reading (pH > 7). πΈAP = πΈ J β π(ππ»: β ππ»S )
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Where: β’ πΈAP is the electrode potential β’ πΈ J is the zero potential β’ π is the slope (ππ πππ ππ» π’πππ‘) β’ ππ»: is the pH value of the measured solution β’ ππ»S is the pH value of the internal buffer. Plugging in the given values in the problem statement, we can re-write the formula for the relationship governing a pH sensor as: (0.0704 ππ) = (0.05 ππ) β (0.02)(7.98 β ππ»S ) Solving for the pH value of the internal buffer, we find: ππ»S = 9
Therefore, the correct answer choice is B. π
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The topic of SENSORS can be referenced on page 124 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
CONCEPT INTRO:
MEASUREMENTATION is the process of experimentally obtaining one or more quantity values that can reasonably be attributed to a physical parameter influencing a solution, body, or system. An INSTRUMENT is a device that provides an output reading or signal used to measure a physical quantity or parameter by having specialized materials or equipment to capture the desired characteristics of a physical parameter. Measurements are made by instruments and either directly reading the scale and output of an instrument, or using the change in one or more physical parameters and developing relationships to measure the magnitude of a physical property. A SENSOR is a device that detects and measures the conversion of energy based on physical parameters or processes, and converts the real world information into an electrical signal. Sensor are usually used with the purpose to sense or detect some characteristic of its environment. Sensors are commonly use measure variables such as flow rate, temperature, pressure elevation, and the pH of a solution.
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A sensor that is used on a regular basis is the thermostat in our homes. As the temperature changes, the thermostat detects the change and sends an electronic signal to the air conditioning unit that the air temperature needs to be heated or cooled. A TRANSDUCER is an electronic device that utilizes sensors to convert mechanical energy in one form to another energy form, typically in the form of an electronic signal. Transducers are typically used to convert a physical parameter such as temperature, pressure, flow, light intensity, etc. into an electrical signal. A speaker changes electrical energy from an amplifier into mechanical energy or sound waves. The electrical energy in the amp causes the speaker cone to move in and out creating air waves that our ears perceive as sound. A microphone is the reverse of a speaker. It is a transducer that converts acoustic energy in the form of sound waves from a human voice and turns it into electrical energy or electrical impulses. The formula for SENSITIVITY is not provided in the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We must memorize this formula and understand its application independent of the NCEES Supplied Reference Handbook. The SENSITIVITY is defined as the ratio of the change in output to the corresponding change in input under static or steady state conditions. Sensitivity can be thought of as the measure of the change in instrument output that occurs when the quantity being measured change by a given amount.
ππππ ππ‘ππ£ππ‘π¦ =
πΆβππππ ππ πΌπππ’π‘ πΆβππππ ππ ππ’π‘ππ’π‘
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The TRANSDUCER SENSITIVITY is the ratio of change in electrical signal magnitude to change in magnitude of the physical parameter being measured. Transducer sensitivity will have different units depends on the instrument being used and the parameter being measured. For example, a platinum resistance thermometer gives a change in resistance to correspond with a change of temperature, and would have its sensitivity defined in units of πΊ/Β°πΆ. PIZEOELECTRIC TRANSDUCERS: The topic of PIEZOELECTRIC TRANSDUCER can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. PIEZOELECTRICITY is defined as the electrical forces or electrostatic stresses applied to a material that resulted in the appearance of an electrical charge on the surfaces of the material. A common application of piezoelectricity is a printer electronically communicating with an ink cartridge on how to apply ink a specified pattern or format on a piece of paper. Each droplet of ink is electrostatically charged to appear on the surface of the paper is a defined pattern and position. PIEZOELECTRIC TRANSDUCERS are comprised of a special ceramic that converts the electrical energy to mechanical energy, or electrical voltage to mechanical force, and vice versa. When an electric field is applied to the material, it will change dimension. Conversely, when a mechanical force is applied to the material, an electric field is produced. Piezoelectric transducers can have multiple layers and many different geometries.
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A simple piezoelectric transducer generates a voltage that is proportional to the change in its ceramicβs volume, or will change volume proportional to the applied voltage. Dimensional changes are usually very small, and can be predominantly in one direction. PRESSURE SENSORS: The topic of PRESSURE SENSORS can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A PRESSURE SENSOR is a sensor that detects pressure in the form of mechanical or kinetic energy and responds with an electrical signal. Pressure sensors are also called pressure transducers, pressure transmitters, pressure senders, pressure indicators, piezometers, and manometers. The formula for PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. PRESSURE, (π), is defined as the force per unit area normal to the force:
π=
πΉ π΄
Pressure is measured as GAGE PRESSURE, the difference between ABSOLUTE and the ATMOSPHERIC. Gage pressure is either positive or negative (vacuum). The
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AMBIENT PRESSURE is pressure at which the vapor pressure is equal to the surrounding pressure. This is the pressure at which a liquid boils. RELATIVE PRESSURE is measured with respect to ambient pressure. ABSOLUTE PRESSURE is measure with respect to vacuum at zero pressure.
DIFFERENTIAL PRESURE is
measured relative to another pressurized container or system. The formula for ABSOLUTE PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We use the following formula to relate absolute pressure, atmospheric pressure, and gage pressure. π:;< = π:=> + π@:@A Where: π:;< = Absolute Pressure π:=> = Atmospheric Pressure π@:@A = Gage Pressure (positive or negative)
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The table for PRESSURE RELATIVE MEASUREMENT TYPES can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. Pressure Relative Measurement Types Absolute
Relative to 0 Pa, the pressure in a vacuum
Gage
Relative to local atmospheric pressure Relative to either absolute vacuum (0 Pa) or local
Vacuum
Comparison
atmospheric pressure
Differential
Relative to another pressurized container
Sealed
Relative to sea level pressure
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PH SENSORS: The pH value of a substance is directly related to the ratio of the hydrogen ion [H+] and the hydroxyl ion [OH-] concentrations. If the H+ concentration is greater than OH-, the material is acidic; i.e., the pH value is less than 7. If the OH- concentration is greater than H+, the material is basic, with a pH value greater than 7. If equal amounts of H+ and OH- ions are present, the material is neutral, with a pH of 7. Since the relationship between hydrogen ions and hydroxyl ions in a given solution is constant for a given set of conditions, either one can be determined by knowing the other. Thus, pH is a measurement of both acidity and alkalinity, even though by definition it is a selective measurement of hydrogen ion activity. Since pH is a logarithmic function, a change of one pH unit represents a ten-fold change in hydrogen ion concentration. The topic of ACIDS, BASES, AND PH can be referenced under the topic of CHEMISTRY on page 54 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. It is important to remember that a solution with a ππ» < 7 is considered ACIDIC, and a solution with a ππ» > 7 is considered BASIC. The formula to calculate the pH of a solution based on the hydrogen ion concentration is expressed as:
ππ» = logIJ
1 π»L
Where: β’ [π» L } is the molar concentration of hydrogen ions, in gram moles per liter.
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The topic of PH SENSORS can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A PH SENSOR is a pH meter consisting of a special measuring probe made up of two electrodes that connect to an electronic meter that measure the electrical potential difference between the electrodes and displays the pH reading. One of the electrodes is a reference electrode and assumed to act a pH of 7, while the other electrode measures the hydrogen-ion concentration difference and measures the electro-potential difference between a neutral solution and the concentration in the solution being analyzed. The formula for the RELATIONSHIP GOVERNING A PH SENSOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The voltage output reading for a pH sensor is directly proportional to the pH of the solution. Therefore, at a pH of 7 (neutral) the output would be 0, and then produce a negative reading for an acidic reading (pH < 7) and a positive reading for a basic reading (pH > 7). πΈAP = πΈ J β π(ππ»: β ππ»S )
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Where: β’ πΈAP is the electrode potential β’ πΈ J is the zero potential β’ π is the slope (ππ πππ ππ» π’πππ‘) and represents the sensitivity of the pH sensor β’ ππ»: is the pH value of the measured solution β’ ππ»S is the pH value of the internal buffer. CHEMICAL SENSORS: The topic of CHEMICAL SENSORS can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A CHEMICAL SENSOR is a sensor that produces an electrical signal in response to a chemical reagent. A chemical sensor operates by converted the energy of a chemical reaction into heat using a transducer, and generates an electrical signal based on the amount of thermal energy in the environment. For example, a smoke detector uses an optical sensor such as a photo resistor. Smoke is allowed to flow between the source and sensor of the smoke detector, and sampled to determine the light intensity, velocity, phase, or other measurable property. Then based on the reference of the light intensity, it will transmit a signal that there is smoke in the air. Another commonly used chemical sensor is a POTENTIOMETRIC SENSOR, which operates on the principles that electric potential develops at the surface of a solid material is immersed in solution containing ions that exchange at the surface.
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The table for EXAMPLES OF COMMON CHEMICAL SENSORS can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
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CONCEPT EXAMPLE: A solution is measured using a pH sensor with a sensitivity of 0.02 mV per pH unit, an electrode potential of 0.0704 mV, and zero electrode potential of 0.05 mV. If the solution is known to have a pH of 7.98, what is the pH value of the internal buffest closest too: A. 7 B. 9 C. 11 D. 13
SOLUTION: The formula for the RELATIONSHIP GOVERNING A PH SENSOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The voltage output reading for a pH sensor is directly proportional to the pH of the solution. Therefore, at a pH of 7 (neutral) the output would be 0, and then produce a negative reading for an acidic reading (pH < 7) and a positive reading for a basic reading (pH > 7). πΈAP = πΈ J β π(ππ»: β ππ»S )
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Where: β’ πΈAP is the electrode potential β’ πΈ J is the zero potential β’ π is the slope (ππ πππ ππ» π’πππ‘) β’ ππ»: is the pH value of the measured solution β’ ππ»S is the pH value of the internal buffer. Plugging in the given values in the problem statement, we can re-write the formula for the relationship governing a pH sensor as: (0.0704 ππ) = (0.05 ππ) β (0.02)(7.98 β ππ»S ) Solving for the pH value of the internal buffer, we find: ππ»S = 9
Therefore, the correct answer choice is B. π
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