Pressure-responsive apparatus having hysteresis to prevent hunting

摘要

A snap-action diaphragm having an electrically conducting central portion is electrically insulated inside a case to separate it into two parts each of which is ported to a fluid, and is biased by an electrically conducting spring towards one port which serves as an electrical contact to form a switch with the diaphragm when connected to an external circuit. The snap-action characteristic of the diaphragm between two stable states when coacting with the biasing force of the spring provides a hysteresis force that can be predetermined to avoid hunting of the switch in response to anticipated alterations in pressure difference across the diaphragm. In another embodiment, the diaphragm also acts to open or shut a valve to control fluid flow, again with the benefit of hysteresis to prevent hunting during operation.