Relative capacitance moisture

Figure 5. Relative capacitance of a polyimide capacitor versus moisture. (Reproduced with permission from Ref. 12. Copyright 1985 The Metallurgical Society.)...

Electrolytic type sensors Uxt thick film techniques, e.g. capacitor coated in gl bonded on to a ceramic disc mounted on a thermoelectric (Peltier effect) cooler. Control is by a platinum resistance thermometer which adjusts the temperature of the cooler to regain equilibrium after a change in capacitance due to moisture deposit. Range depends on technique. Capable of high precision. Limitations are similar to those for AIjO) sensor. Capable of being direct mounted. Relatively cheap. Suitable for on-line use. 

Moisture coefficient p describing the capacitance change with the relative change of air moisture F in % humidity P = 1/C dC/di7. 

Moisture. The effects of moisture degradation are more pronounced with resistance, dissipation factor, and capacitance than with breakdown. Functionally, the effect of moisture on the electric breakdown may be disastrous. High relative rather than absolute humidity is the causative factor. At higher temperatures the rate of moisture permeation increases. Moisture condensation on plastic surfaces, especially in the presence of ionizable or carbonizing contaminants, may be an important source of degradation. Surface flashover may occur almost instantaneously with moisture condensation, whereas volume breakdown develops after weeks or months. 

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