Frequently Asked Questions
Below are some common questions searchers ask when looking for probes and sensors.
1. What is it used for?
A pH sensor is a part of a measuring device that tests the pH value of a liquid or solution. The pH scale measures the acidity or alkalinity of a solution. The pH scale ranges from 0 to 14, with 0 being the most acidic and 14 being the most alkaline. A pH sensor is used to measure the acidity or alkalinity of a solution so that the solution can be adjusted to the correct pH level.
For example, owners or managers of swimming pools need to record the pH levels through active monitoring to maintain the water quality so it’s safe to use.
2. How does the pH sensor work?
The sensor consists of a glass electrode and a reference electrode, which are connected to a pH meter that measures the voltage between them. The glass electrode is sensitive to the hydrogen ion concentration of the solution, while the reference electrode is not. When the two electrodes are placed in a solution, the meter measures the voltage between them.
3. What are the different types of sensors?
There are seven different types of sensors, ranging in cost and accuracy.
- The combination sensor – The combination sensor uses two electrodes, a reference electrode and a measurement electrode. The combination sensor produces an electrical signal from the differences between the two electrodes, which is converted into a pH value.
- The differential sensor – The differential sensor uses three electrodes in its measurement system. Using a third metal grounding sensor can reduce background noise caused by pollution.
- Consumer Grade sensor – This pencil-like sensor is often used for detecting neutral and mild temperature solutions, such as household water, spas and pools.
- Lab grade sensor – The next level above consumer-grade, set up to measure more intense pH levels and temperatures in areas such as wastewater and drinking water. Different materials are used in the combination electrode setup.
- Micro sensor – These are available in consumer and laboratory grades and are designed to be screwed into small closed circuits for continuous monitoring.
- Spear tip sensor – Using a sharp glass point to penetrate food and soil to achieve accurate pH readings.
- Industrial sensor – Follows the same setup as a combination sensor. However, it uses robust materials and more substantial external housing—ideal for screwing into piping for continual monitoring.
4. How accurate are the sensors?
The accuracy and the cost of the sensor are directly linked. Accuracy generally ranges from +/- 0.1pH to +/-0.001 pH. If you are in the quality assurance and research field, you may need to purchase a sensor that is accurate to +/-0.001; if it’s for a school laboratory, then an accuracy of +/- 0.1 pH may suffice.
5. What is the range of a sensor?
The sensor follows the pH value spectrum calculated using the potentiometric measurement principle. The pH sensor’s range is 0-14, with 0 being the most acidic and 14 being the most basic.
6. What is the sensor’s resolution?
The resolution refers to the intervals over which the reading is taken. If the pH sensor’s resolution is 0.1 pH, the measurement of pH values is taken in increments of 0.1 pH.
7. What is the pH sensor’s response time?
A sensor does not show the pH value instantaneously, and it is common to wait at least 30 secs before you get a reading. However, if the electrode and the solution differ by 10 degrees, you will need to wait longer. Also, if the sensor has been stored in distilled water or left to dry out, the response time will be considerably slower.
8. How is the pH sensor calibrated?
The pH sensor is calibrated by measuring the sensor’s voltage output in response to a known pH buffer solution. The pH sensor is placed in the known pH solution, and the voltage output is measured. The voltage output is then compared to the known pH of the solution. The pH sensor is then adjusted to match the voltage output to the known pH of the solution.
9. How often does the pH sensor need to be replaced?
If a probe/sensor has been correctly maintained, you should look to replace it every 18 months to 2 years. However, for those in the aquatic sectors, they will replace the sensors every nine months as they can not risk the effectiveness of their pH probes.
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