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Problem with measuring potentiodynamic anodic polarization

I use e.g., & G PAR potentiostat/galvanostat 273A for potentiodynamic anodic polarization measurement.I use ceramic coated magnesium alloy as working electrode, platinum sheet as counter electrode and saturated Ag/AgCl(KCl)The electrolyte is o.5 molar NaCl solution .I am facing a problem which is like this: potential becomes very low (-10V vs Ag/AgCl and current is about 2 nA. The expected OCP is around -1.5 V. Current does not increase with increase in potential even up to -700 mV. Sometimes potentiostat shows error with potential and sometimes with current.I suspected that error may be with reference electrode. I checked the potential difference with another saturated silver/silver chloride electrode, the difference is 2-3 mV, that is the reference electrode is in sound condition. I think there is problem with potentiostat. How can I check the performance of the potentiostat?

Santosh Sah
student - Japan
September 5, 2009