Responses of Temperature-Sensing-Element Analogs
G. A. Coon · Transactions of the American Society of Mechanical Engineers · 1957
Abstract From the standpoint of stability, temperature-sensing elements used in control systems should not contribute much phase lag at the frequency where the open-loop phase lag is 180 deg. For those cases where the temperature-sensing element does not contribute appreciable (less than 30 deg) phase lag around 180 deg, it would be advantageous to have a low-frequency approximation which works for complicated thermal systems. This paper presents such an approximation and establishes its validity for the electrical analogs of many sensing elements. In addition, it shows how the approximation is related to the thermal lag measured during a ramp input and the 63 per cent response time. These results, which are obtained in terms of transfer functions, can be applied to other systems having the same analogs.