Patent GB-440115-A (GB)
Title: Improvements in and relating to automatic control of variable physical characteristics
IPC: G05D23/275
Filed: 1934-06-20
Abstract: 440,115. Automatic control of temperature &c. CALLENDER, A., Winnington Hall, Northwich, Cheshire, and IMPERIAL CHEMICAL INDUSTRIES, Ltd., Millbank, London. June 20, 1934, No. 18298. [Class 38 (iv)] [See also Groups XXIX and XXXVII] The value of any variable physical characteristic is controlled by the relative movement between a member indicating the instantaneous value and the level of a liquid surface, this movement operating through a relay system on compensating means restoring the characteristic to a desired value, the compensating means being coupled to the surface level so that the latter is caused to follow closely, stepwise, the movements of the indicating member, the liquid level also tending to return to a predetermined level corresponding to the desired value by means of liquid flow through a resistant path, preferably from a separate body, the liquid the level of which is not sensibly altered thereby. In a system for automatically controlling temperature, the flow of a heating medium, e.g. steam, is controlled by a valve 2 operated by changes in the relative positions of a temperature indicator 17 and the level of liquid in a vessel 14. In order that this liquid level may be moved in accordance with the variation in the flow of heating medium a pulley 3 indicating the valve opening is connected to the vessel 14 through a cam device 10 which is shaped so that the movement of the vessel is proportional to the change in the rate of flow of heating medium past the valve, and any backlash existing between the valve and the indicator 3 is nullified by a lostmotion device A. The temperature controlled is predetermined by the level of liquid, e.g. mercury in a container 18 which is connected by a capillary tube 19 with the liquid in the vessel 14. The temperature indicator 17 preferably carries two pairs of contacts 17a, 17b and 17c, 17d. The liquid level under normal conditions lies between the shorter contacts 17a, 17c of each pair. Upon fall of temperature the contact 17a establishes current in the solenoid S1 of a relay which makes a maintaining circuit through the longer contact 17b of the same pair so that the circuit of a motor C is made at the contacts g to cause the valve 2 to open. This results in a partial correction of the temperature and in a movement of the indicator 17 upwards and of the liquid level downwards, but the motor circuit is maintained until the contact 17b leaves the liquid. The operation will then be repeated as often as required to restore normal conditions, but during the regulation the level of the liquid in the vessel 14 is being continually brought towards that of the liquid in the container 18 by flow through the capillary tube 19 at a rate proportional to the difference in liquid level. The reverse action takes place when the temperature rises, the maintaining circuit of a solenoid S2 of a relay operating contacts for reversely driving the motor being opened by the contact 17d, and the motor continuing in operation until the shorter contact 17c enters the liquid. Should a condition occur that would lead to a rise in temperature, such as a rise in steam pressure, this may be caused to produce a regulating action in advance of the temperature variation by taking the connection between the vessel 14 and the valve 2 over a pulley, the height of which is varied by a plunger subject to the steam pressure. The regulated quantity may be caused to vary according to any desired law by means appropriately changing the level of liquid in the container 18. The compensating means may be controlled otherwise than electrically, e.g. hydraulically, the relative movements of liquid level (or a float associated therewith), and the indicating member operating a pilot valve and relay system controlling a supply of high pressure liquid to a hydraulic cylinder actuating the compensating means.