Rate-controlled shrinkage of ZnO varistors

Shrinkage of ZnO varistors has been controlled during the firing process at a constant rate using a feed back loop to control the heating rate. This was accomplished by developing software which calculates the shrinkage from a signal coming from a displacement transducer, then it compares the current shrinkage rate with a previously set limit and upon this comparison the software gives some commands to the furnace controller to change the heating rate. A linear-linear relationship has been established between the current shrinkage rate and the heating rate. This relation has proved to be satisfactory for controlling the shrinkage.