As the sun goes down this Halloween children will don their chosen costume and begin going door-to-door requesting candy with their best “Trick or Treat”. Everyone’s favorite part of Halloween is the candy (Treat), however, M4 Knick would like to focus on the Tricks that can help ensure you the most accurate pH measurement possible.

Sensor Selection

When looking at any pH application, the first thing to consider is the selection of the pH sensor used to make the measurement. Do not just assume that all pH sensors are the same and will perform with equal success in any application. Many pH sensors have different pH glass recipes, utilize a different material for the junction/diaphragm, and have their own unique reference systems. Of these unique characteristics, there are specific attributes that perform better in varying applications. It is crucial to your success that you use the correct sensor for the application.

Sensor Mounting

Equally as important to sensor selection is the physical installation of the pH sensor. When installing your pH sensor, you should consider the following tips to ensure accurate measurement.

Mounting Orientation

You should mount the sensor pointing downward with a minimum of a 15°angle above horizontal if at all possible. This ensures that the measurement electrolyte inside the pH bulb is contacting the entirety of the internal surface of the pH-sensitive glass.

Immersion Depth

When installing your sensor in a pipe or tank it is important to ensure that the sensor is long enough to extend through the total height of the remounting hardware and nozzle so that the sensor bulb and junction are completely submerged in the measurement fluid. This dimension is often referred to as the immersion depth. You need to verify ahead of time to ensure that the mounting is correct and sufficient to submerge the sensor.

Flow Path and Velocity

As indicated above, in order to make a proper and accurate pH measurement both the bulb and junction need to remain submerged at all times. This means that in a pipe mount configuration, you should install a sensor in an area where the flow path remains constant and always keeps the pipe full.

Velocity can have a significant impact on proper measurement as well. To ensure efficient pH measurement you should target a max velocity of 8ft/sec or less. You can calculate velocity with both the pipe diameter and the expected flow rate of the application.

Proper Cleaning

Over time, a pH sensor has the potential to accumulate a buildup of unwanted materials. This can have a direct impact on the sensor’s ability to maintain an accurate measurement. When this occurs, it is best to pull the sensor from the process and clean it. It is often that users will clean manually with a brush or other utensil to remove the dirt and debris. We recommend that you clean chemically as opposed to abrasively. Cleaning with sharp objects or abrasive material can damage or static charge on the pH-sensitive glass. It’s typical to clean the sensor by soaking in a diluted HCL solution of 3-5% for no more than 20 minutes.

Calibration Procedures

When calibrating your pH sensors it is vital to follow correct procedures and practices. Buffer quality is essential to ensure accuracy, so we recommend to use fresh buffers for each point of calibration. The temperature of the buffers and sensor should be the same, so you should allow for the two temperatures to equalize. pH sensor reading and temperature reading need the opportunity to stabilize during each step of the calibration process. This ensures that you are using an accurate pH value as the standard. Using a rinsing solution between each step of the calibration is also a good idea with the rinsing solution being fresh, low-ionic activity water such as distilled water.

Proper Storage

If at any time the process should shut down or run dry the sensor bulb and junction must remain wet. We recommend that you store sensors in the original manufacturer’s wetting cap. The liquid inside the wetting cap is a 3M KCl/l solution. It is the ideal liquid for sensor storage.  There are other acceptable storage solutions with, Buffer 7being a good alternative.  Well-hydrated sensors ensure accurate performance when reinstalled in the process.