Potentiometric Sensor Applications

Thursday, November 16th, 2017 - Passive Transducers, Resistive Transducers

Potentiometric Sensor Applications

Potentiometric sensors are broadly used to measure position, displacement, level, motion, pressure, airflow, and many other physical parameters. They are also integrated into other sensors to monitor chemicals, gases, or biocells. The major advantages of potentiometers are simplicity, low cost, adaptability to many applications, and high output signal level (thus, eliminating the need for signal amplification and conditioning required by many other sensors). Their disadvantages include high hysteresis due to sliding friction, sensitivity to vibration, and finite lifetime associated with wiping elements. Some application examples of potentiometric sensors are described as follows.

1. Potentiometric Pressure Sensors

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FIGURE 1. (a) A rotary potentiometric pressure sensor; (Courtesy of SFIM SAGEM, France.) (b) a linear potentiometric pressure sensor.

Figure 1a shows a rotary potentiometric pressure sensor developed by SFIM SAGEM, France. When the pressure of an input liquid or gas expands the diaphragm, the wiper connected to the diaphragm will sweep across the potentiometer. The movement of the wiper indicates the magnitude of the pressure. Figure 1b is a linear potentiometric pressure sensor. When the wiper arm moves up or down due to a pressure change, the resistance varies, causing the output voltage to change. A similar design can also be used to measure water level, motion, or displacement.

2. Potentiometric Airflow Sensor

A potentiometric airflow sensor used in Toyota vehicles

FIGURE 2. A potentiometric airflow sensor used in Toyota vehicles. (Courtesy of Toyota Corporation, Japan.)

Figure 2 shows a potentiometric airflow meter used in Toyota vehicles. It converts the air flow volume to a vane opening angle that is measured by a potentiometer. The sensor’s output voltage is then sent to the vehicle’s electronic control unit (ECU) to determine the volume of air that is getting into the engine.

3. Potentiometric Gas Sensor

A typical potentiometric gas sensor is shown in Figure 3. It consists of a measuring (working) electrode, a gas selective membrane, and a reference electrode-together forming a sandwich with the membrane in the middle.

A potentiometric gas sensor

Figure 3. A potentiometric gas sensor

The gas selective membrane binds the gas of interest. The bounded gas then reacts with the analyte on each side of the membrane, causing a change in conductivity of the membrane. This change is indicated by an output voltage change between the two electrodes. By convention, the measuring electrode is considered as the cathode in potentiometric sensors. Table 1 shows several typical membranes for gas detection.

Typical membranes for gas detection

Table 1. Several typical membranes for gas detection

4. Potentiometric Biosensor

Figure 3a is a potentiometric biosensor. It consists of a measuring electrode (Ag-AgCl lectrode) and a reference electrode. Both electrodes are placed on a person’s skin but at different locations to measure electrical signals generated by the flexion and extension of muscles. Each electrode acts as a transducer that converts ion flow in the body into electron flow (current) in the conductive electrode (see Figure 3b).

A potentiometric biosensor (a) and its Ag/AgCl electrodes (b)

Figure 3. A potentiometric biosensor (a) and its Ag/AgCl electrodes (b)

This transduction takes place at the electrode-electrolyte interface where an oxidation or reduction reaction occurs (determining the direction of current flow). The biopotential between the two electrodes is proportional to the size of muscle and the amount of flexion or extension.

I hope this information about “Potentiometric Sensor Applications” is useful.