GF Signet pH Meter Calibration Procedure-Dry Calibration

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pH and ORP Meter back panel
pH and ORP Meter back panel

If you are exposed to a company that is using a water on one of its main process, then   surely you encounter this kind of meter, the pH/ORP meter.  Just like a conductivity meter, a pH meter or ORP meter also has a probe that is soaked in the water (or some other liquid) to monitor its pH or ORP.

Calibrating pH meters can be accomplished in 2 methods (the most accurate), 1st method is Wet calibration where  the pH probe is soaked in a liquid solution usually in the range of 4, 7 and 10 pH, then comparing the result, and the 2nd method is a dry calibration which is a simulation of electrical signal specifically a mV signal with a corresponding pH value.

Dry Calibration Means there are no liquid solution involve in the process of calibration. The most familiar term is electrical simulation, where a mV signal with a corresponding pH or ORP value is used.  And this is the method that I will present here in addition to the  calibration set up and adjustment. I have included the ORP  meter verification since the 2 are related.

I will use a Fluke 754 process calibrator to simulate and calibrate a GF Signet pH/ORP meter. GF Signet pH/ORP meter is also a  controller and a transmitter because it can be connected to a PLC using a 4-20 mA signal.

What is a pH?

A pH (potential hydrogen)  is a scale or range (from 0 to 14) use to describe how high or low the acidity or basicity  of a certain aqueous solution like water used in pharmaceuticals or food industry. A lower pH value (approaching zero) means  very acidic while a high value (approaching 14) means very basic or alkaline. 7 which is in the middle is the neutral value.

pH to mV conversion

pH to mV conversion
pH to mV conversion

 

You can read more about pH in this link.. WIKIPEDIA

 

What is ORP

ORP stands for Oxidation Reduction Potential which is measured in millivolts. ORP meter measures how much electrons an atom, molecules or an ion loses or gain. A higher positive reading indicates  a more oxidizing  while a lower negative reading indicates a more anti oxidizing.

Read here for more info about ORP…Fundamentals of ORP

 

How to calibrate pH meter using Fluke 754 as the reference standard.

Equipment/Reference  standards

Fluke 754 process calibrator

Connecting leads

 

Requirements:

  • Warm-up time ( Unit Under Calibration): At least 1 hour for proper stabilization
  • Temperature: 23 +/- 5 deg C
  • Humidity: 50 +/- 30%
  • Perform 3 trials for each points or range
  • Measurement Data Sheet (MDS)- for data recording

pH/ORP Meter Calibration Setup

pH and ORP Meter back panel
pH/ORP Calibration set up using Fluke 754 connecting probes. Just remove and replace the wires on port 13 and 14 (Blue and Brown) with the probe of the Fluke 754 which is in the mV source function. These are the location of the pH sensor probe used by the pH meter.

Procedure for Calibration pH Meter 

GF Signet pH meter with analog and digital display
GF Signet pH meter with analog and digital display
  1. Check the pH meter for any visual defects that can affect its accuracy. Discontinue calibration if any defect is noted.
  2. Observe proper stabilization time of at least 1 hour.
  3. Prepare the measurement data sheet (MDS) and record all necessary details or information (Brand, Model, serial #, etc).
  4. Determine the test point to be calibrated (we will choose 4, 7, and 10 pH).
  5. Connect the Fluke 754 as shown on the calibration set up above
  6. Set Fluke 754 to voltage source.
  7. Based on the table presented above, simulate the desired voltage with equivalent pH value.
    • 4 pH = +177
    • 7 pH = 0
    • 10 pH = -177
  8. Wait for the display to stabilize and record to it on your MDS
    Fluke 754 used to simulate a mV signal to the pH/ORP meter
    Fluke 754 used to simulate a mV signal to the pH/ORP meter.
  9. Check readings if within the accuracy defined by the manufacturer, in this brand of GF Signet, accuracy = +/- 03 pH and 2 mV for ORP. If the readings are already within limits update the corresponding record, do labeling and sealing and issue to owner, otherwise, do necessary repair or adjustment. ( see adjustment procedure below)
  10. End of Verification

 

ORP Meter calibration procedure

GF Signet ORP meter with analog and digital display
GF Signet ORP meter with analog and digital display

The  set up and calibration procedure  is almost the same with the pH meter, the only difference is the range of simulated input. The ORP meter have a range of -1000 to +2000 mV.

Below are the calibration points that we can use:

  • -1000 mV
  • -500 mV
  • 0 mV
  • +500 mV
  • +1000 mV

GF Signet Adjustment procedure

During the verification process where the result are not within their tolerable range. We can adjust the meter by performing below procedure. This is applicable to both ORP and pH settings.


pH/ORP adjustment procedure

Check the video below on how to adjust. It is presented using a buffer solution but the procedure for accessing the EASY CAL is the same.

For the complete details of adjustment procedure including the use of pH buffer solution, you may check the GF Signet pH/ORP meter  manufacturer’s manual.

Conclusion

I have shared to you the basics regarding what is a pH and ORP meter. I also presented on how to set up and calibrate a pH/ORP meter using a dry calibration method also known as electrical simulation method. In this method, we used the mV source function of Fluke 754 to simulate the required signal used by the GF Signet pH/ORP meter.

This method provides a fast and accurate result, but the disadvantage is that we are only performing the calibration only on the meter itself, the probe is not included. But for accuracy verification of the meter, this is a good method to follow.

Looking for a pH meter to use? Check this link  ph meter.

Do you need a complete set of buffer solution which is NIST traceable? visit below link.
Biopharm Buffer Calibration Solution Kit 3-Pack of 500 ml each pH 4, 7 and 10 Calibration Standards Color coded NIST Traceable For All pH meters
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2 Responses

  1. Mezghiche Abdelkrim
    | Reply

    Well presented ! Thank you Dear, i found this technic very useful, my question regarding other kind of mesurment like Conductivity, Total carbon.
    thank you

    • edsponce
      | Reply

      Thank you. Appreciate you liked my post and that it helped you in any way. I will consider your concern in my future post.

      Thanks and regards,
      Edwin

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