Dear Mr Sahoo, probably is cost. Platinum is a precious metal more expensive than gold. However, I didn't know that graphite was used as conductivity sensor just as a transducer in voltametric, amperometric or potentiometric sensor. Glucose strips use carbon black. This last material has higher electrochemical activity than graphite, but lower electrical conductivity (See the article: McCreery, R.L. Advanced carbon electrode Materials for Molecular Electrochemistry). I hope that this helps you.  

Dear Mr. Sahoo, probably is cost. Platinum is a precious metal more expensive than gold. An advantage may be economy, because platinum devices are very much robbed. Technical advantages, I don't know. I didn't know of this use for graphite (conductivy electrode). Generally, graphite electrodes are used as a transducer in voltametric, amperometric or potentiometric sensors. Another option is carbon black, which is used as transducer in glucose strip. An excellent review about this subject is McCreery R.L., Advanced Carbon Electrode Materials for Molecular Electrochemistry, Chem. Review 2008, 108, 2646-2687. I hope that this paper help you.

Cost may not be a factor. We have developed a pulsating sensor based conductivity meter which works purely in digital domain. We explored this technique for high resolution conductivity measurements besides deploying in many physico chemical techniques. In all cases we used platinum wire (0.5 mm or 1 mm dia.). The quantity needed for such application is much less. I feel there may be some technical advantage of graphite electrode. The main purpose of raising such question to refresh my knowledge which may help to use in my work. Thanks.

Dear Mr. Sahoo, Could you indicate a manufacturer about this conductivity electrode based on graphite? I would also like to know about this subject, because I have used graphite for manufacturing of electrochemical sensors. I apologize for duplicate answer, but I didn't see the answers up to send the same response. Best regards.

graphite is easier to manifacature in different cases than platinium. such as COOH activation by acids thus scientists can form an active residues easier way, because platinium is hard and rigit material, carbon is easier to clean, less edge effect.

Sorry, I do not understand the question. Is graphite the sensor itself? In this case what is the physical/chemical property which varies? The conductivity? Or is graphite used as an element (electrode for exemple) of a sensor? In this case please give more details.

@Jean-Georges Gasser -" I feel there may be some technical advantage of graphite electrode."

Graphite is inexpensive inert conductive material, suitable for measuring electrode in many applications. Even the core of many pencils can be used as graphite electrode.

If it is in oxygen free atmosphere and the medium does not dissolve carbon (iron dissolves carbon) probably graphite is first choice. Graphite is brittle. 

If water based solutions are measured, then Pt-Pt electrode will be better choice, because of the high quality finish of the deposited platinum over the main platinum sheet (much higher surface area compared to polished platinum sheet) and the well defined geometry. Platinum is catalyst in for some reactions.

Do not know if platinum can be electrodeposited, but graphite can not be. Copper from copper electrodes can be deposited.

Platinum can be magnetron sputtered on glass/quartz substrate and the resulting film is with good properties. Never seen someone preparing and using graphite layer in laboratory to use it as electrode. Graphite as protective coating of quartz tubes/ampoules is although common.