Calibration of Conductivity TDS Meter Guide

Step-by-step Calibration of Conductivity TDS Meter SOP for accurate QC testing with tips, procedure, and FAQs.

Calibration of Conductivity TDS Meter: Complete SOP Guide

Accurate measurement of conductivity and total dissolved solids (TDS) is essential in quality control laboratories. This guide explains the Calibration of Conductivity TDS Meter in a clear, structured SOP format to ensure reliable and consistent results.

1. Objective

The objective of this SOP is to ensure proper Calibration of Conductivity TDS Meter for obtaining accurate, precise, and reproducible results during testing.

2. Scope

This procedure applies to the calibration of conductivity and TDS meters installed in the Quality Control (QC) department.

3. Responsibility

• Execution: Technical Assistant
• Verification: Executive / Manager

4. Accountability

The Head of the Department is accountable for implementation and compliance.

5. Procedure for Calibration of Conductivity TDS Meter

5.1 Calibration Frequency

Conductivity Calibration:

• Daily: Using KCl solution
• Monthly: Using 1 MΩ resistor

TDS Calibration:

• Daily: Using KCl solution

5.2 Instrument Setup

1. Connect the conductivity cell (0.1K) and temperature probe.
2. Ensure the instrument is operated as per SOP guidelines.
3. Press the CAL key to initiate calibration.

5.3 Standard Calibration Using KCl Solution

1. Select standardization mode (Y).
2. Press CAL again until “PUT STD” appears.
3. Choose 0.01 M KCl solution using the PUT STD key.
4. Immerse probes in the standard solution.
5. Press CAL to start calibration.
6. Wait ~20 seconds for calibration completion.
7. The cell constant (x.xx CEL.C) will be displayed.

If previous calibration data appears:

• Press CAL or ABORT NO, then restart calibration.

5.4 Temperature Compensation (TEMPCO)

• Apply temperature correction as per SOP.
• Standard Tempco value at 25°C = 1.9

5.5 Conductivity Measurement

1. Press COND key.
2. The instrument displays:
   • Temperature correction factor
   • Conductivity at 25°C
3. Record observations.

5.6 TDS Calibration

1. Press TDS-F TEMPCO key.
2. Enter:
   • Tempco factor = 1.9
   • TDS factor:
     • 0.53 (for 0.01 M KCl)
     • 0.51 (for 0.001 M KCl)
3. Press TDS key to display results in PPM/PPT.

5.7 Second Calibration with 0.001 M KCl

1. Rinse probes with purified water.
2. Immerse in 0.001 M KCl solution.
3. Repeat calibration steps.
4. Rinse again after completion.

5.8 Maintenance During Calibration

• Keep probes immersed in purified water when not in use.
• Clean with purified water after each measurement.

5.9 Monthly Calibration Using 1 MΩ Resistor

1. Disconnect probes and connect 1 MΩ resistor.
2. Switch ON the instrument.
3. Press CAL → select “res” mode.
4. Press COND.
5. Apply temperature correction (25°C).
6. Verify reading:
   • Expected: 1.0 µS ± 5%
7. Cross-check resistor accuracy using a multimeter.

5.10 Acceptance Criteria

• Conductivity and TDS values must fall within standard limits.
• If results are out of range, follow corrective SOP procedures.

5.11 Final Steps

• Clean the instrument with a dry cloth.
• Store probes properly in purified water.
• Instrument is now ready for sample analysis.

6. Abbreviations

• M = Molar
• °C = Degree Celsius
• ms/cm = Millisiemens/cm
• µs/cm = Microsiemens/cm
• ppm = Parts per million
• ppt = Parts per trillion
• MΩ = Mega ohm
• % = Percentage

Frequently Asked Questions (FAQs)

1. What is the purpose of Calibration of Conductivity TDS Meter?

To ensure accurate and reliable measurement of conductivity and TDS values.

2. How often should conductivity meters be calibrated?

Daily with KCl solution and monthly using a standard resistor.

3. Why is KCl solution used for calibration?

Because it provides stable and known conductivity values for accurate calibration.

4. What is the standard Tempco value?

The standard temperature compensation factor is 1.9 at 25°C.

5. What is the TDS factor for KCl solutions?

• 0.53 for 0.01 M KCl
• 0.51 for 0.001 M KCl

6. What should be done if calibration values are out of range?

Follow the corrective SOP and check instrument performance.

7. Why is a 1 MΩ resistor used?

It verifies the electronic accuracy of the instrument monthly.

8. How should probes be maintained?

Rinse with purified water and keep immersed when not in use.

9. What happens if temperature compensation is not applied?

Results may be inaccurate due to temperature variations.

10. Can the same SOP be used for all conductivity meters?

No, always follow manufacturer-specific SOP alongside this general guideline.