How to

How to troubleshoot pH transmitter issues?

How to troubleshoot pH transmitter issues? 1

  The table below provides detailed guidelines for doing thorough troubleshooting of the pH transmitter.

What can interfere with the accuracy of pH measurements?

Drifting/Erratic Readings

Possible causeSolutions
Contaminant on the sensing glassRegularly clean your electrodes. There are a variety of application-specific cleansing solutions. 
Clogged junctionUtilize cleaning solutions that are application appropriate depending on the type of sample that is clogging the electrode.
Sample with low conductivityUtilize an electrode with a high junction flow rate or add potassium chloride (KCl) of high purity to enhance conductivity.  Stable readings in low conductivity materials are made possible by the sensor’s triple ceramic connection. 
The electrode is not adequately hydrated.Use the recommended storage solution and soak for at least one hour. 
Interference caused by electrical noise 
The high impedance measuring circuit may be affected by noise from rectifiers, motors, pumps, or ballasts. Consider location of the transmitter installed.

Inaccurate Readings

How to troubleshoot pH transmitter issues? 2

Possible causeSolutions
Tissue wiping of a pH electrodeThe loss of the hydration layer from the electrode bulb or the scratching of the electrode surface can all result from wiping or rubbing an electrode. Make sure to use a lint-free paper towel to remove any moisture that needs to be removed from the electrode bulb. 
Incorrect calibration To avoid cross-contamination, make sure the pH electrode is thoroughly washed with distilled water (DI) in between calibration buffers and that it is in thermal equilibrium with the buffer. Make sure to use brand-new buffer for each calibration. 
calibrating and measuring at various temperaturesUse a transmitter  with automatic temperature compensation mode, calibrate it, and then take your measurements there. Keep in mind that the buffer pH will change depending on the temperature. On buffer bottles, these variations are mentioned. 

pH Readings after Freezing

Possible causeSolutions

Faulty electrode 
When inserted into various buffers or samples, the pH meter will show the same reading. This suggests that the sensor glass has a break or crack in it. Replace the electrode with new one.
How to troubleshoot pH transmitter issues?3

In a powered-off state, a pH analyzer and not getting ON

Possible causeSolutions
In the field, check the pH analyzer’s cable connection. Each connection needs to be tight and securely lugged. 
Next, verify the supply voltage.Check the connections in the junction box and marshalling cabinet
  if voltage is not obtained. Inspect the connection for looseness. If the cable is loose, tighten it properly. If the cable is not lugged properly, lug it properly. 
Additionally, inspect the fuse in the marshalling cabinet. Replace the fuse if it has been blown. 
In the marshaling cabinet, check the barrier. Replacing the barrier is necessary if it has faults.
Faulty cable If everything indicated above is determined to be in order, we can also inspect the cable’s overall health.

pH Value mismatch in the Field and PLC/DCS

Possible causeSolutions
Check the range in the field analyzer and on the system side if the value in the pH analyzer does not match the value in the PLC/DCS. The pH scale runs from 0 to 14. Depending on which is incorrect, change the field’s range or the PLCDCS.

pH value does not match the results of the laboratory tests

Possible causeSolutions
Verify that the sample is not present in the sampling line.Check the sampling system’s isolation valve if no sample is discovered. If the isolation valve is closed. it should be opened.  
Also possible is choking the tube.Release the tubing’s choke.
Verify the sample flow rate. Set the appropriate flow rate in accordance with the pH analyzer’s datasheet’s flow rate recommendations.
Air bubble present in the sampling lineThe sample that goes into the pH analyzer needs to be free of air bubbles.Give the correct tubing to expel the air bubble from the sample system if there is any air bubble present.
The sensor became faulty.The pH sensor should be taken out and examined for physical damage. Replace the pH sensor if it is broken or weakened in any way.
A leak in the tubes is a possibility.To obtain an accurate pH reading, attend to the leaks.
pH sensor’s internal RTD is workingPut the temperature measurement in automatic mode if it is currently in manual mode.
In the field or in the PLC/DCS, any force is present. If force is being used, it should be removed after being reported to all management involved in the process and the Instrumentation department. As an alternative, if the bypass method is used, remove the force after filling out the necessary documents for interlock restoration.
Check the pH analyzer’s calibration.Replace the pH sensor or pH transmitter or calibrate the pH analyzer transmitter if there are calibration problems with the pH analyzer during calibration.
Wrong configurationVerify all settings according to the pH analyzer’s datasheet, including the pH range, mA range, and device address if applicable.

Fluctuations in the value of the PH analyzer

Possible causeSolutions
Sample line leakagesExamine the sample tube for leaks. The pH analyzer’s reading can vary as a result of tube leakage. 
Damping set at low valueIf the variations are extremely large, increase the pH analyzer’s damping factor.

Electrode Impedance Alarms – High

Possible causeSolutions
There is a problem with the cable connecting the measurement sensors.Either correctly terminate, or replace.
Measurement sensor badReplace measurement sensor

Electrode Impedance Alarms – low

Possible causeSolutions
Measurement sensor with a crackReplace measurement sensor
Cable that is either wet or defective in some other wayReplace cable
Sensor contaminatedRecalibrate after cleaning, then soaking in pH buffer. If it’s malfunctioning, replace it

Reference Impedance (RZ) Alarms – High

Possible causeSolutions
Dirty reference sensor
Keep your sensors clean
Depletion of the reference sensorReplace the sensor or refill it.
cable with damage or an open circuit Test cableIf it’s not good, replace it.
Contaminated sensorSensor should be replaced or refilled.
How to troubleshoot pH transmitter issues? 4

Reference Impedance (RZ) Alarms – low

Possible causeSolutions
Wet/shorted cable Keep the connectors and cords for electrodes dry. Damage to the insulation from infiltration can result in a partial short circuit and inaccurate measurements. 
When cables break, this frequently occurs. 

Slope Issues – low

Possible causeSolutions
Sensor is outdated, Verify the date on the serial number and replace it if necessary.
Contaminated sensorConsider cleaning, pH buffer soaking, and then recalibrating the sensors.Replace the measurement sensor if the value remains low.
Dirty sensor After cleaning, recalibrate
Broken sensorLow impedance is expected. The measuring sensor should be changed.
Shorted or wet cables Check cable; if defective, replace.

Slope Issues – High

Possible causeSolutions
Incorrect calibrationUtilize the right buffer solutions to calibrate the sensor.
Contaminated sensorConsider cleaning, pH buffer soaking, and then recalibrating the sensor. The measurement sensor should be changed if the reading is still high.

Which of the most common cause of error in pH measurement?

Common Problems and Remedies with pH transmitter

How to troubleshoot pH transmitter issues?5
Possible causeSolutions
cable preparation gone wrongUtilize a cable that is the right length.Cutting a longer connection could lead to mistakes. A cable has a unique layer of graphite for screening that prevents inside radiation or disruptions. This layer is extremely difficult to remove. Due to a significant decrease in isolation resistance between the cable’s core and screen, measurement errors and instability are frequently present in shortened cables. This isolation resistance for a glass electrode cable must be greater than 1,000 times the resistance across the glass membrane.
Noisy readings. The reference electrode is the weakest link in the measurement loop because it is exposed to the process through the junction and is very sensitive to interference from stray voltages in the liquid. When determining pH, it is important to consider the voltage potential of the process liquids in many applications. Because of this, the technician must ground the liquids at the location of the pH measurement. This is typically done by utilizing metal fittings or plastic fittings with a grounding (solution ground) electrode of the appropriate metal.
Inaccuracy in the measurementA probe’s reading can shift up or down over time. The electrode will drift as the asymmetry potential (mV offset) increases, forcing more frequent calibration. Depletion of KCl in the reference electrolyte is a typical cause. The most common cause of this is using a gel-filled reference electrode in the incorrect process solution, like high-purity water. The reference potential becomes unstable when the concentrated reference electrolyte (KCl) and the low conductivity (mineral-free) process solution come together at the reference junction because the process solution leaches salt from the reference electrolyte. 
Sluggish reaction timeSlow performance reflects coating or junction clogging, which may be brought on by a thin film on the glass sensor that is undetectable to the naked eye.

Useful links for maintenance of pH transmitter

The following link will take you to information about how to do preventive maintenance on a pH transmitter.

Please follow the link below to calibrate your pH transmitter using standard solutions.

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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