Patent GB-149023-A (GB)
Title: Improvements in methods of and apparatus for the control of the flow of fluids
IPC: G05D11/13
Filed: 1919-03-05
Abstract: 149,023. White, A. E., (Cutler-Hammer Manufacturing Co.). March 5, 1919. Mixing fluids in flow.-In an electrical method for controlling the flow of a gas, the rate or flow is electrically measured in terms of a unit consisting of a certain volume of the dry gas measured at a standard temperature and pressure, or of liquid at a standard temperature, the meter serving to control the flow automatically. The supply of air or gas to a furnace may be thus controlled. As shown, a Thomas thermo - electric meter is used, in which the temperature of the air passing through the meter is raised through a constant range, and the quantity of electricity necessary for this purpose is measured by a wattmeter which may be calibrated to indicate the rate of flow. The electric heater 2, Fig. 1, is supplied with current through a rheostat 5 and the current coil 8 of a wattmeter, the voltage coil 13 of which is in shunt with the meter. The thermometer coils 3, 4, which measure the temperature before and after heating, are connected by conductors 26, 27 with two arms of a Wheatstone bridge, and by other conductors are connected in series with an adjustable resistance 20; the other arms of the bridge are connected to one terminal of a generator 25. A switch 61 and an auxiliary resistance are provided in the bridge circuit, so that current flows to the thermometer 3 either through the conductor 62, or through the auxiliary resistance, which is constructed of such material as to compensate for errors due to rise of temperature and variation of moisture. The bridge is balanced in the ordinary manner, with the switch in the cut-out position, the resistance 20 being adjusted till no current flows through the crosswires. The switch is then cut in, and the needle thereby deflected. The balance will be restored when the thermometer resistance 4 has been changed by the predetermined temperature rise so as to equal the combined auxiliary resistance and the thermometer resistance 3. Any variation from the predetermined temperature rise will thus deflect the needle, and this deflexion is used to control the rheostat 5 and consequently the current through the heater. For this purpose, the contact arm of the rheostat is rotated by a ratchet wheel 31 which is itself rotated by pawls 32 controlled by electromagnets 33 and carried by rocker arms continuously oscillated by a connecting-rod 35 from a motor 37 which drives the generator. The pawls are normally held out of mesh by gravity, and are put into engagement by the energization of the electromagnets which receive current from a circuit controlled by the needle. The needle 22, as shown in actual position in the lower portion of the bridge, has arranged abnve it two groups of contacts 38, 39 and below it contact strips 41, 42<1> on an insulated support periodically reciprocated by an electromagnet 42. The contact strips 41, 42<1> are connected each to one of the electromagnets 33 which are also connected to one terminal of the generator. The other terminal, and the contacts 38, 39 arranged in pairs, are connected to fingers of a contact drum 48. If the needle has been deflected, it will be periodically clamped between one of the lower and one of the upper contacts, causing one of the electromagnets to be energized for a longer or shorter period, and the rheostat to be correspondingly affected. Fig. 2 shows the application of the meter to the control of the air supply of a furnace. In this case, the heating and thermometric elements are disposed in the path of the air supply, and the current is supplied to the heater at a constant rate, and the shaft 31<1> in place of actuating a rheostat, actuates a valve 64 in the air supply pipe to provide a measured and constant flow of air. In a gas furnace, both the air and gas supply may be thus controlLed. The auxiliary resistances for the circuits controlling the gas and air supply, whereby the temperature differences of the thermometer resistances are regulated, may be in the form of rheostats, Fig. 5, operated from a single graduated wheel 71. Independent adjustment of the two supplies may be effected by securing one of the rheostat arms 68 adjustable on its shaft by a set screw 72. The auxiliary resistances for the two circuits may be enclosed together in one casing subject to the air temperature, the gas supply being brought to the same temperature as the air supply before passing through the meter by enclosing the supply conduit in the air supply conduit. Fig. 6 shows apparatus wherein the heaters for the gas and air supply meters are both controlled by a single rheostat 76 so that the temperature difference of each meter may be adjusted at the same time. Separate rheostats 77 render the heaters capable of independent adjustment. The supply of air to a furnace &c. by a pump or blower driven by an engine may be regulated by utilizing the shaft 31<1> to actuate a throttle valve on the steam supply pipe, or to alter the cut-off of the engine, or actuate a rheostat controlling the speed of the motor. A blower of the Sirocco type may be employed working at a regulated variable speed.