SOP for Calibration of Conductivity TDS Meter
1.0 OBJECTIVE
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.
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3.0 RESPONSIBILITY
3.1 Doing: Technical Assistant
3.2 Checking: Executive /Manager
4.0 ACCOUNTABILITY
Head of the department
5.0 PROCEDURE
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.
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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 measured value of the cell constant will be displayed as (x.xx CEL.C) for a short time, where x.xx is a measured value of cell constant.
5.12 Thereafter the display will ask ‘PUT SOLU’.
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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”.
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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.
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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.
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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 an unknown sample.
5.34 Conductivity & TDS limit of std. KCl solution at 25°C is below.
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5.35 If the value is out of limit then follow the SOP.
5.36 Check the electronic circuits once in a month with a standard resistor (1 MΩ)
5.37 Check the resistor accuracy with multimeter once in a month. If the register is 1 MΩ, potency, the multimeter will show 1 MΩ + 5%.
5.38 Clean the instrument with the dry clean cloth.
5.39 If the conductivity cell and temperature probe are connected with the instrument, disconnect it and connect –1 MΩ (i.e. 1 µS) resistor.
5.40 Switch ‘ON’ the instrument.
5.41 After about 3 seconds, if the instrument has been calibrated previously, the 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 times and the 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.
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5.45 After few second, display will show the value of the resistor in µs if the resistor potency 1 MΩ, the 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.
6.0 ABBREVIATIONS
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 = parts per trillion