How to

How to do Preventive maintenance of pH transmitter?

How to do Preventive maintenance of pH transmitter?1
  • Preventive maintenance of pH transmitters is crucial for ensuring accurate and reliable measurement of pH levels in various industrial processes.
  • By implementing regular maintenance procedures, such as calibration checks, sensor cleaning, and verification of signal integrity, potential issues can be detected and addressed proactively. 
  • This helps to prevent measurement inaccuracies, equipment failures, and costly downtime. 
  • Additionally, preventive maintenance enhances the lifespan of pH transmitters, reduces the risk of process disruptions, and ensures consistent product quality. 
  • By prioritizing preventive maintenance, industries can optimize their pH monitoring systems and minimize the likelihood of unexpected problems, resulting in improved operational efficiency and customer satisfaction.

Safety

  • Ask the panel operator to configure the MOS (maintenance override switch) for the controllers’ manual mode (pH conductivity transmitter control loop) and ESD loop, respectively. 
  • Both of these parameters must be simultaneously configured before starting any PM activity on the pH transmitter.
  • Locate the pH transmitter for which you want to do PM maintenance.
  • Before PM the pH transmitter, you might need to drain the pH  as well as the system’s sample impulse tubes.
  • Depressurize the system using suitable techniques (such as by closing the main sample inlet isolation valve of pH transmitter).
  • Utilizing an instrument loop diagram to search for any adjacent junction boxes or Marshalling Cabinets close to the control room can help you find the power supply source for isolation and turn off the pH transmitter’s power.
  • This method may need to be modified depending on the pH transmitter’s equipment and process location.
  • Always follow the manufacturer’s instructions and regional safety standards while utilizing a pH transmitter or other piece of process equipment.  this may include wearing additional PPE, using specific tools or equipment, or following specific safety protocols.
  • Be aware of any hazardous materials or chemicals present in the vicinity of the pH transmitter. Follow proper handling, storage, and disposal procedures to prevent exposure or environmental damage.
  • Wear appropriate PPE, such as safety glasses, gloves, and protective clothing, as specified by the company’s safety guidelines. Consider the specific risks involved in the maintenance tasks being performed.
  • Be sure to abide by lockout/tagout procedures to prevent accidental starts. Keep the pH transmitter out of the process for preventative maintenance.
  • Review process documentation related to the pH transmitter, such as piping and instrumentation diagrams (P&IDs), standard operating procedures (SOPs), and safety data sheets (SDSs) for any hazardous materials that may be present.
  • Coordinate with other plant staff members, such as operators or maintenance technicians, who may be impacted by the maintenance work. Make sure they are informed of the work being done and any necessary safety measures for PM on pH transmitter.
  • You might need to seek permission from the plant’s safety department for PM on pH transmitter depending on the type of maintenance work.
How to do Preventive maintenance of pH transmitter?2

Inspection of sampling system

  • Check for leaks in all connections in the pH transmitter sampling system. The pH probe, sample line, and any valves or fittings are all included. Look for any indications of deterioration or damage.
  • Clean the sample system to remove any debris or buildup that may be interfering with the accuracy of the pH transmitter readings. This may require the use of specialized cleaning solutions or tools.
  • Examine the pH transmitter sampling probe for signs of wear or damage. This includes the pH probe tip, which can wear or become damaged over time, affecting the accuracy of the pH values.
  • Examine the pH transmitter sample line for signs of wear or damage. Check for kinks, bends, or other impediments that may be interfering with the flow of the pH transmitter sample.
  • Check the sample’s pressure and flow rate to ensure they are within the recommended range. This could involve measuring the flow rate with a flow meter or other specialized equipment.

Inspection of pH transmitter

  • Remove any dust, dirt, or other material that may be impacting the pH transmitter’s operation. This could involve cleaning the pH transmitter’s exterior with a gentle cloth or brush.
  • Inspect the pH transmitter’s wiring to ensure that all connections are tight and secure. Examine the wire for evidence of corrosion or damage.
  • Check the pH transmitter’s power source to check that it is operating within the recommended voltage range. This could involve measuring the supply voltage with a multimeter.
  • Check the pH transmitter’s grounding to ensure it is correctly grounded. This may entail measuring the resistance to ground with a multimeter.
  •  Inspect the pH transmitter housing for evidence of wear or damage. Examine the pH transmitter for any fractures or other damage that could be compromising its operation.
  • Verify the parameter using an instrument data sheet or the pH transmitter’s commissioning report.
  • Check for pH transmitter firmware upgrades and make sure it is running the most recent software.
  •  Verify function of the pH transmitter using standard buffer solution. Please refer the the below link for the calibration of pH transmitter

Calibration of the pH transmitter using standard buffer solutions

Inspection of pH electrode

How to do Preventive maintenance of pH transmitter3
  • Inspect the electrode for any physical damage, cracks, or signs of wear. Check the condition of the glass membrane, reference junction, and connector. Ensure that the electrode is intact and free from any visible defects.
  • Look for any buildup, fouling, or coating on the electrode surface. Contaminants can affect the accuracy and response time of the pH measurement. Clean the electrode if necessary, following the manufacturer’s recommendations and using appropriate cleaning solutions.
  • For refillable electrodes, check the electrolyte level. Ensure that the electrolyte is at the appropriate level as specified by the manufacturer. Refill or replace the electrolyte if needed.
  • If the pH electrode has a separate reference electrode, examine it for any signs of contamination or damage. Ensure that the reference junction is clean and free from clogs.
  • Inspect the electrode cable and connector for any damage, fraying, or loose connections. Ensure that the cable insulation is intact and the connector is securely attached to the pH transmitter.
  • Consider the age of the electrode and its expected lifespan. Electrodes have a limited lifespan and may need to be replaced periodically, even if no visible issues are present. Follow the manufacturer’s guidelines for electrode replacement.
  • Perform a calibration check using certified pH buffer solutions to verify the electrode’s accuracy. Compare the measured values to the expected values and make adjustments if necessary.
  • Check that the temperature correction is working correctly. This may involve employing a temperature sensor to measure the temperature of the solution being monitored and ensuring that the pH transmitter compensates for changes in temperature.
How to do Preventive maintenance of pH transmitter4
  • Inspect the cable connection between the measuring pH electrode and the pH transmitter for stability and damage. Examine the cable connection for evidence of corrosion or wear.

How do you maintain a pH electrode?

Cleaning of pH electrode

Cleaning should be done as follows if the electrode is coated or dirty:

  • Take the sensor out of the process.
  • Use a tissue or soft, clean, lint-free cloth to clean the glass bulb. Proceed to next Step if this doesn’t get rid of the dirt or coatings. (Detergents remove grease and oil; acids dissolve scale.)
  • The glass bulb should be cleaned with a powerful detergent solution and then rinsed in clear water. Move on to the following step if this is unable to clean the glass bulb.
  • The glass bulb should be cleaned with a 5% hydrochloric acid solution that has been diluted.
  • The cleaning effect of the sensor can be improved by soaking it in the acid solution overnight.
  • The next examination will be conducted with a solution that contains acid and should be handled carefully. adhere to the acid manufacturer’s instructions.
  • Put on the appropriate safety gear. Keep the solution away from your skin and clothing. Rinse with fresh water very away if skin contact occurs.
  • Due to the accumulation of reference junction potential following an acid soak, inaccurate pH measurements may be obtained. In the event that cleaning does not restore sensor operation, the sensor should be replaced.
  •  The mV output chart given by the manufacturer should be used to verify the pH sensor’s mV output. Below is an example mv vs pH chart taken from the electrode datasheet.
How to do Preventive maintenance of pH transmitter 4
  • The temperature-sensitive temperature compensator element can be tested using an ohmmeter (multimeter).
  • As temperature rises, resistance rises as well. At 25 °C (77 °F), the 3K element will register 3000 ohms +1%, while a Pt-100 will read 110 ohms. 
  • For a 3K and Pt-100 element, resistance varies with temperature and may be calculated using below table.
How to do Preventive maintenance of pH transmitter? 5

Inspection of junction boxes

  • Conduct a visual examination of the junction box exterior. Look for any signs of damage, corrosion, or moisture ingress. Check for loose or disconnected cables, wires, or connectors.
  • Verify the integrity of the junction box seals or gaskets. Ensure they are intact and free from cracks or deterioration. Proper sealing prevents moisture, dust, or other contaminants from entering the box.
  •  Inspect the cable connections within the junction box. Ensure that all connections are secure, properly tightened, and free from corrosion. Check for any exposed wires or loose connections that could affect the signal integrity.
  • Check the strain relief mechanism for the cables entering the junction box. Ensure that it is properly installed and provides adequate support to prevent strain on the cables, protecting them from damage.
  • Open the junction box and inspect the interior. Look for any debris, moisture, or contaminants that may have entered. Clean the interior if necessary using appropriate cleaning methods and materials, ensuring not to disturb any sensitive components.
  • Examine the terminal blocks or connectors within the junction box. Ensure they are clean, properly tightened, and free from corrosion. Check for any signs of overheating or discoloration that may indicate a potential issue.
  • Confirm that the junction box is properly grounded. Check the grounding connection for tightness and integrity. A reliable ground connection helps protect against electrical hazards and reduces the risk of signal interference.

Environmental conditions 

  • The accuracy of the measurement could be impacted by the environment surrounding the pH transmitter’s temperature and humidity conditions. 
  • Maintenance professionals advise placing the pH transmitter in a steady location away from heat and moisture sources. 
  • They must also regularly examine the ambient conditions to ensure that they remain within the pH transmitter’s allowed range.

Documentation

  • It is essential to maintain accurate records of all maintenance chores, calibration dates, and any issues with or repairs performed to the pH analyzing system in order to troubleshoot and spot trends in the functioning of the pH transmitter. 
  • The maintenance team for the pH analyzer should record this information in a logbook or database so that it may be used for analysis and reporting.

Completion of PM maintenance

  • After performing any maintenance procedures, you should always calibrate the pH sensor.
  • Following completion of the pH analyzing system PM, clean the tools and equipment, store it securely, and make a note of the details from the PM checklist for future reference.
  • Check that the PM’s workspace has been kept neatly organized for the pH analyzing system.
  • De-isolate the equipment and resume the sample supply system after conducting a PM on the pH measurement system. 
  • Verify the pH sample flow rate  and should not have any bubbles.
  • Restore the bypassed or disabled signal of the pH analysis equipment to its original level.
  • Make sure the  pH analysis system is in good working order before utilizing it.

Preventive maintenance checklist 

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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