On-off Temperature Controller with PD Action

Abstract

On-off temperature controller described here is a modification of the controller whose electric contact is actuated by thermal expansion difference of a metal pipe and a quartz bar set in the pipe. If a part of the quartz bar is replaced by a metal pipe, the response of the inner pipe lags behind that of the outer pipe. Therefore, the expansion difference makes a proportional plus derivative action toward the ambient temperature.
In this controller, derivative action can be adjusted by changing the ratio of quartz length and inner pipe length, but in this case, proportional gain also changes as the ratio of lengths does. In order to adjust the derivative action without changing the gain, thermal resistance between outer and inner pipes is changed by inserting metal pipes of various lengths into the gap. Result of experiments shows a fairly good coincidence with theoretical calculation and accordingly, it seems to be applicable to designing.