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SOP for Calibration of Conductivity TDS Meter

Standard operating procedure to evaluate the performance of conductivity TDS meter.


       To calibrate the equipment for reliable & accurate results.

2.0  SCOPE

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


3.1  Doing        : Technical Assistant
3.2  Checking  : Executive /Manager


       Head of the department


       Frequency :- A) For conductivity 1) Daily (With KC1 solution)
                                                              2) Monthly (With 1 MΩ resistor)
                             B) For TDS               1) Daily (With KC1 solution)
5.1  Connect a conductivity cell of 0.1K & temp. probe to the cell socket if not connected.
5.2  Operate the instrument as per SOP.
5.3  Press the ‘CAL’ key.
5.4  Display will show Std Y n, asking whether standardization is to be done yes (y) or not (n).
5.5  Then again press the ‘CAL’ key.
5.6  Display will show ‘put std’.
5.7  Stroke the ‘PUT STD’ key until 0.01 M KCL solution indicated by the LED lamp.
5.8  Immerse both probes in the 0.01 M KCL std solution.
5.9  Press ‘CAL’ key.
5.10  The unit starts calibrating itself against the standard solution, the display in between blinks with ‘CAL’.
5.11  After 20 second the measure value of the cell constant will be displayed as (x.xx CEL.C) for a  short time, where x.xx is measured value of cell constant.
5.12  There after the display will ask ‘PUT SOLU’.
5.13  In case when the display shows ‘str data’ & cell constant with concentration of previously calibrating solution, press ‘CAL’ key. Or in case display shows, conductivity value or TDS value, press “ABORT NO” key. Then press ‘CAL’ key.
5.14  Carry out TEMPCO correction as per SOP.
5.15  Press ‘COND’ key.
5.16  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.
5.17  Simultaneously check the TDS of std KC1 solution.
5.18  Press “ABORT No” key. The display will show “PUT SOLU”.
5.19  Then press “TDS-F TEMPCO” key. The display will show (x.xt x.xxt). Where xxt. is temp correlation factor & x.xx is TDS factor.
5.20  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.
5.21  Enter temp. correction factor & TDS factor as per SOP.
5.22  Then press “TDS” key, the display will show busy. After a while it will show the actual temp. and TDS value in PPM/PPT.
5.23  Remove conductivity cell & temp probe from the std 0.01 M KCl solution.
5.24  Rinse it with purified water.
5.25  Press ‘ABORT NO’ key, the display will show put solu.
5.26  Immerse both cell & temp probe in 0.001 M KC1 std solution.
5.27  Then again press ‘CAL’ key the display will show put std.
5.28  Stroke the ‘PUT-STD’ key unit 0.001 M KCl solution indicated by the LED lamp.
5.29  Press ‘CAL’ key.
5.30  Follow the step 5.10 to 5.22.
5.31  Rinse it with purified water.
5.32  Keep the cell immersed in purified water in between and after the measurement.
5.33  This instrument is now ready to measure the conductivity & TDS of unknown sample.
5.34  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
0.01M KCl
1.41 ms/cm + 0.01
747.5 ppm + 5
or 0.7474 ppt + 0.005
0.001 M KCl
0.146 ms/cm + 0.005
74.46 ppm + 2.5 or 0.0745ppt + 0.0025

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

Related: Conductivity of Purified Water (Apparatus and Procedure) in Pharmaceutical


6.1  M= Molar
6.2  °C = Degree centigrade
6.3  ms/cm = militiamen’s per centimetre
6.4  us/cm = micro simians per centimetre
6.5  % = Percentage
6.6  Mr = mega ohms
6.7  ppm = part per million
6.8  ppt = part per trillion

Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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