of An A-c. System of Remote Indication and Its Application to the Measurement of Fluid Pressure and Flow.L-HOWARD D. WARSttAWfl A moving-vane indicator in circuit with a two-coil transmitter forms a system of remote indication relatively free from errors due to variations in ambient temperature, supplyvoltage, and supply frequency. The transmitter is simple and should withstand severe vibration and extreme temperatures. The electrical elements of the transmitter are completely isolated from the mechanical components so that measurements in the presence of corrosive or explosive fluids may be made with safety. Applications are presented in which the transmitter measures oil pressure in the crankcase of a gasoline engine and the flowmeter measures fuel flow. This system of remote indication has been developed for use in aircraft, but its potentialities for industrial applications will become evident. The experimental models were designed to operate from 400-cycle aircraft power sources; larger components would be required for 60-cycle operation.
The transmitter contains a movable core within a set of coils which are connected so that their magnetic fields are in opposition. The core is displaced by a force derived from the fluid under measurement, and its position is established when the fluid force is balanced againstthe opposing force of a coil spring. Three conductors serve to transmit two electrical signals from the transmitter to the indicator.
The indicator contains a vane of highly permeable magnetic material located within a set of crossed coils. The transmitter voltages are applied to the indicator coils through a bridge circuit, and their resultant magnetic field positions the vane which is fastened to the pointer shaft. The indicator contains resistors for sensitivity and end-scale adjustments, and suitable assemblies for damping and pointer zero return.
One application of this system is to the electrical remote indication of aircraft engine oil pressure. There is a need for an aircraft remote-reading oil-pressure gage with a transmitting element suitable for direct mounting on the aircraft engine. The coagulation, at low temperatures, of the engine oil in the line from the crankcase to the transmitter of any of the remoteindicating oil-pressure gages in present use makes these gages inoperative during a part of the engine warm-up period. The lack of oil pressure indication at this time frequently leads to serious engine damage which would not otherwise occur. The device herein described is capable of offering a satisfactory solution to this problem.
Models of both transmitter and indicator for measuring oil pressure are shown in Fig. 1. Figure 2 shows the same transmitter partly disassembled.
Another application of this system is to the remote indication of fluid rate-of-flow through tubing such as the fuel supply line of an aircraft engine. One model of the flowmeter transmitter is shown in Figs. 3,4.
Electromagnetically, the operation of the flowmeter transmitter is identical to that of the pressure transmitter. The difference lies in the hydraulic system used to derive the force necessary to displace the core. In this application, the magnetic core is tubular, and is designed to supportfirmly an orifice plate that restricts the flow of fluid. The restriction sets up x Paper published in Instruments, Vol. 22, p. 402 (1949).