SOP for Calibration of Conductivity TDS Meter

Purpose

This procedure defines an operating procedure to evaluate the performance of the conductivity TDS meter

Scope

This procedure is to calibrate the conductivity TDS meter, installed in the Q.C. dept.

Responsibility

The technical assistant is responsible for following the procedure, while the quality assurance manager is responsible for complying with the SOP.

Material and Equipment

Conductivity TDS meter

Procedure

Frequency:

A) For conductivity

1. Daily (With KCl solution)
2. Monthly (With 1 MΩ resistor)

B) For TDS 

1. Daily (With KCl solution)

• Connect a conductivity cell of 0.1K & temp. probe to the cell socket if not connected.
• Operate the instrument as per SOP.
• Press the ‘CAL’ key.
• The display will show Std Y n, asking whether standardization is to be done yes (y) or not (n).
• Then again press the ‘CAL’ key.
• The display will show ‘put std’.
• Stroke the ‘PUT STD’ key until 0.01 M KCL solution is indicated by the LED lamp.
• Immerse both probes in the 0.01 M KCL std solution.
• Press the ‘CAL’ key.
• The unit starts calibrating itself against the standard solution, and the display in between blinks with ‘CAL’.
• After 20 seconds the measured value of the cell constant will be displayed as (x.xx CEL.C) for a short time, where x.xx is the measured value of the cell constant.
• Thereafter the display will ask ‘PUT SOLU’.
• In case when the display shows ‘str data’ & cell constant with a concentration of a previously calibrated solution, press ‘the CAL’ key. Or in case the display shows, a conductivity value or TDS value, press the “ABORT NO” key. Then press the ‘CAL’ key.
• Carry out TEMPCO correction as per SOP.
• Press the ‘COND’ key.
• The unit will display busy and after a while, it will show the temp. correlation factor (1.9 t) along with the conductivity of the standard KC1 solution at 25°C. Record the observation in the format as per Annexure.
• Simultaneously check the TDS of std KC1 solution.
• Press the “ABORT No” key. The display will show “PUT SOLU”.
• Then press the “TDS-F TEMPCO” key. The display will show (x.xt x.xxt). Where xxt. is the temp correlation factor & x.xx is the TDS factor.
• For 25°C Tempco correction is 1.9 & TDS factor 0.53 is for 0.01 m KCl std. solution & 0.51 is for 0.001 m KCl std solu.
• Enter temp. correction factor & TDS factor as per SOP.

• Then press the “TDS” key, and the display will show busy. After a while, it will show the actual temp. and TDS value in PPM/PPT.
• Remove the conductivity cell & temp probe from the std 0.01 M KCl solution.
• Rinse it with purified water.
• Press the ‘ABORT NO’ key, and the display will show put solu.
• Immerse both cell & temp probe in 0.001 M KC1 std solution.
• Then again press the ‘CAL’ key the display will show put std.

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• Stroke the ‘PUT-STD’ key unit 0.001 M KCl solution indicated by the LED lamp.
• Press the ‘CAL’ key.
• Follow the steps 6.10 to 6.22.
• Rinse it with purified water.
• Keep the cell immersed in purified water in between and after the measurement.
• This instrument is now ready to measure the conductivity & TDS of an unknown sample.
• Conductivity & TDS limit of std. KCl solution at 25°C is below.

Co-relation factor for 25°C	TDS factor of std KCl solution	Conc. Of std KCl solution	Limit of conductivity value at 25°C	Limit of TDS value at 25°C
1.9	0.53	0.01M KCl	1.41 ms/cm + 0.01	747.5 ppm + 5 or 0.7474 ppt + 0.005
1.9	0.51	0.001 M KCl	0.146 ms/cm + 0.005	74.46 ppm + 2.5 or 0.0745ppt + 0.0025

• If the value is out of limit follow the SOP.
• Check the electronic circuits once in a month with a standard resistor (1 MΩ)
• Check the resistor accuracy with a multi-meter once a month. If the register is 1 MΩ, potency, a multimeter will show 1 MΩ + 5%.
• Clean the instrument with a dry clean cloth.
• If the conductivity cell and temperature probe are connected to the instrument, disconnect it and connect –1 MΩ (i.e. 1 µS) resistor.
• Switch ‘ON’ the instrument.
• After about 3 seconds, if the instrument has been calibrated previously, the display will show ‘Str data’ and cell constant with the previous calibrating solution concentration, alternatively.
• Press the ‘CAL’ key, and the unit display will show ‘PUT Std’ then press the “put std” key seven times, and the display will show ‘res’.
• Press the ‘COND’ key display will show ‘busy’.
• Carry out ‘Tempco correction’ for 25°C as per SOP.
• After a few seconds, the display will show the value of the resistor in µs if the resistor potency is 1 MΩ, the display will show the value as a temp in °C along with 1.0 µs + 5%.
• If the value is out of limit, follow the S.O.P.

Abbreviations

M= Molar

ms/cm = militiamen’s per centimeter

us/cm = micro simians per centimeter

Mr = mega ohms

ppm = part per million

ppt = part per trillion

Revision History

Nil

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