Sensor Care

Maintenance Free

Turtle Tough pH and ORP sensors are a completely sealed assembly and are sealed for life, making them maintenance free. This provides extreme process resistance as well as a totally maintenance free sensor which greatly increases sensor life and reduces labour costs. A Turtle Tough pH, ORP or ISE sensor does not contain any O-rings, washers, gaskets, or serviceable components or assemblies. It does not require refreshing or refilling of electrolyte. Maintenance free however does not mean it doesn’t have to be cleaned. Regular cleaning with either a strong acid, alkaline or surfactant cleaner (depending on your application) needs to be performed on a regular basis to keep the elements free of contamination and blockage. Even if the sensor does not show sign of contamination, it should be regularly cleaned with the appropriate solution to remove microscopic contamination. Regular cleaning will prolong the life of your sensor and ensure hassle free operation.
**Please note Dissolved Oxygen sensors are an exception to this rule. They do have serviceable components that need to be periodically replaced.

Storage

The standard shelf life for all Turtle Tough pH and ORP sensors is one year from the date of shipment. Sensors stored longer than this period may still be functional but are no longer under warranty. Sensors should be stored in a cool, dry location with the sensor tip (sensing element) oriented toward the ground. All sensors come standard with a conditioning solution in the cap. This conditioning solution is 50% pH 4 buffer and 50% saturated potassium chloride (mixed by volume). The sensor cap should be kept tightly affixed to the sensor body and sealed with common PVC tape when the sensor is not in use. Sensors that are to be returned for shelf life warranty claim must have the original sensor cap and conditioning solution intact to be eligible for warranty replacement.

Cleaning and Calibration Frequency

The most common question we are asked is how often must you clean and calibrate a Turtle Tough sensor. While this question is virtually impossible to answer, a Turtle Tough sensor will have up to 10 times the stability of mainstream sensors. Most of our customers are able to extend calibration intervals by 2 to 5 times, whilst still maintaining their required accuracy and performance.

How often a sensor requires cleaning and calibration depends upon:

  • The process conditions and how quickly the major constituents are poisoning the sensor
  • The desired accuracy for the measurement to maintain acceptable process control
  • The amount of fouling or process build-up that will eventually affect sensor performance
  • How well the sensor is cleaned and maintained at the specified interval (ie using the correct chemicals to decontaminate the sensor)

Turtle Tough sensors are specifically designed to improve these maintenance requirements by incorporating the following:

  • Turtle Tough sensors have very tough measurement elements that are slow to deteriorate and therefore drift is minimised.
  • Turtle Tough sensors utilised open geometry designs and low fouling materials to reduce build-up and extend cleaning intervals
  • Turtle Tough sensors have very resilient materials of construction to withstand harsh cleaning regimes. Strong acids, alkaline, organic solvents and abrasive mechanical cleaning can be deployed to efficiently and effectively clean sensors returning them to optimum operating condition.

General Guideline

Drift (pH units)TOUGH APPLICATION
(ie: intensive chemical process)
MODERATE
(ie wastewater)
EASY
(ie clean water)

0.1

3x per week

1x per week

1x per 2 weeks

0.3

1x per week

1x per 2 weeks

1x per 2 months

0.5

1x per 2 weeks

1x per 4 weeks

1x per 6 months

** please note this is a general guideline only and should not be relied upon for accurate process control.

 

How do I determine the calibration frequency?

It is important to note that you can never rely on our guideline as the basis for your calibration requirement. Every chemical process is unique and the accuracy required can only be determined by your site requirements and expert process control personnel. Each user will need establish a drift profile on their own application before deciding on an appropriate calibration interval. Cleaning and calibration intervals can vary significantly across individual applications. To determine the drift characteristics you will need to periodically test the sensor against a known buffer or accurate grab sample to determine the rate of drift (ie the difference between the displayed value and the standardised solution). Test frequently at the half life of your expected calibration frequency to determine how far the sensor has deviated from the standard solution. Once the sensor reaches the threshold of your accuracy requirement, that is a good indicator for establishing your calibration regime.

IMPORTANT: It is recommended that a sensor is properly cleaned each time it is removed for calibration. Even if it does not appear dirty, you should following the cleaning process to remove microscopic contamination that will affect the performance of the sensor.

Cleaning

Cleaning requirements will vary depending on the application for which the sensor is used. The following should always be observed when cleaning:

Never scratch or aggressively scrub the pH or ORP (sensing) elements. These are delicate glass electrochemical electrodes. They can be easily broken by mechanical force.

The reference junction is a solid state material and can be cleaned with aggressive chemicals. See list below of recommended cleaning solutions. This solid state reference can also be cleaned effectively by using a sharp razor edged tool. GREAT CARE SHOULD BE TAKEN NOT TO SCRATCH THE pH GLASS OR ORP ELEMENT DURING CLEANING OF THE REFERENCE JUNCTION.

Common approved cleaning solutions include:
5-15% Hydrochloric Acid – (For Alkaline deposits)
5-15% Sodium Hydroxide – (For Organic Contaminants)
Surfactant (NON-IONIC SOAPS SUCH AS MICRO-90)

Please contact your local Turtle Tough representative if you plan to use any other cleaning agent

Avoiding Thermal Shock

For high temperature applications where process liquid exceeds 70°C you will prolong the life of the sensor by avoiding thermal shock. Thermal shock occurs when you rapidly change the temperature of the sensor from hot to cold or vice versa. This rapid expansion/contraction of sensor components can damage internal elements and cause micro-cracking that will accelerate the rate of deterioration. In extreme cases it will crack the sensing element causing a total failure. To avoid this sensor should be heated or cooled slowly during removal/insertion and cleaning and calibration processes. Consult your Turtle Tough representative for techniques to avoid thermal shock.

Conditioning for Calibration

After the sensor has been cleaned, it must be thoroughly rinsed with deionized water to remove any residual cleaning reagents. The sensor can then be soaked in pH 4 buffer to recondition the pH and reference elements. Some sensors will also require conditioning in saturated potassium chloride if the reference junction has been depleted of the ions in the solid state conductive polymer (typical Reference Junction Sensing Element for clean water applications). Condition the sensor in saturated potassium chloride and/or pH 4 buffer for whatever period of time is required to achieve optimal calibration results.