The Differences Between Glass and ISFET pH Sensors in Industrial pH Meters

pH measurement is an essential part in various industries like manufacturing, food processing, water treatment, and pharmaceuticals. pH meters are the most commonly used instruments to measure the pH of a solution. The pH sensor in the pH meter is responsible for providing accurate and reliable measurements. In industrial pH meters, the two main types of pH sensors are glass pH sensors and ISFET pH sensors. Both these sensors have their unique characteristics, leading to distinct differences. Here are the differences between glass and ISFET pH sensors.

What is a Glass pH Sensor?

A glass pH sensor is a traditional type of pH sensor that uses a glass bulb and a reference electrode to measure pH. The glass bulb is filled with a special solution containing an ion-sensitive membrane. The ion-sensitive membrane allows only certain ions to enter the glass bulb, while others are kept out. When the glass bulb comes into contact with a solution, the ions present in the solution enter the glass bulb causing a change in the potential. This change is detected by a reference electrode located within the pH meter, and a pH reading is displayed.

What is an ISFET pH Sensor?

An ISFET pH sensor is a relatively new type of pH sensor that uses an Ion-Sensitive Field-Effect Transistor (ISFET) to measure pH. The ISFET pH sensor is made up of a silicon chip with a metal oxide layer on top. The metal oxide layer acts as the ion-sensitive membrane, and the silicon chip acts as the reference electrode. When the metal oxide layer comes into contact with a solution, it creates a potential on the silicon chip, which is detected and measured by the pH meter.

The Differences between Glass and ISFET pH Sensors

1. Sensitivity

The glass pH sensor is more sensitive to changes in pH than ISFET pH sensors. This sensitivity is due to the ion-sensitive membrane of the glass bulb. The glass bulb's membrane is more selective than the metal oxide layer of the ISFET sensor, making it more sensitive to the ion's concentration in the solution. This sensitivity makes glass pH sensors the go-to sensor for applications requiring high accuracy.

2. Durability

ISFET pH sensors are more durable than glass pH sensors. Glass bulbs are fragile and can break easily, causing the sensor to malfunction. In contrast, an ISFET pH sensor has a robust metal oxide membrane that is not easily damaged, making it more resilient to harsh environments.

3. Maintenance

Glass pH sensors require more maintenance than ISFET pH sensors. Glass bulbs need to be cleaned and calibrated regularly, making them more labor-intensive. The metal oxide layer of ISFET pH sensors is self-cleaning, making them virtually maintenance-free.

4. Response Time

ISFET pH sensors have a faster response time than glass pH sensors. The ISFET sensor's metal oxide layer is thin, which allows for faster ion exchange and faster reading response times. In contrast, the thick glass bulb of the glass pH sensor has a slower response time, making it unsuitable for applications requiring real-time reading.

5. Interference

Glass pH sensors are more susceptible to interference from other ions present in the solution, leading to inaccurate readings. This is because the glass membrane is less selective than the metal oxide membrane of the ISFET pH sensor. This interference can be rectified by keeping the glass pH sensor calibrated regularly. ISFET pH sensors are less susceptible to interference, making them more suitable for applications where other ions may be present.

Conclusion

In conclusion, the differences between glass and ISFET pH sensors show that each sensor type has its unique characteristics. Glass pH sensors are more sensitive but require more maintenance than ISFET pH sensors. ISFET pH sensors are more durable and have faster response times but are not as accurate as glass pH sensors. Knowing the differences between these sensors helps determine which sensor type is best suited for a particular application.