This apparatus measures the weight of fuel in a plurality of tanks on an aircraft. In each tank, there are provided a plurality of capacitors connected so that their impedance varies linearly as an analog function of the volume of the fuel in the tank. A compensating capacitor, totally submerged in the fuel, provides another analog indication that varies with the density of the fuel. These analog indications are transmitted to a master indicator, where they serve as inputs to an analog-to-digital converter. The converter's digital output is the weight of fuel in the tank. The master indicators for the several tanks are connected to a totalizer indicator which sums the readings of the master indicators and provides an indication of the total fuel in all the tanks. The totalizer also has a gross weight indicator in which a tare weight reading may be manually set. The tare weight is combined with the total fuel weight reading to give a reading of the total weight of the aircraft. Each master indicator is connected through a digital transmission system to a repeater indicator located in a fuel loading panel on the aircraft wing. This digital transmission system is similar to that connecting each master indicator to the totalizer and comprises two control lines and a data line. The two control lines respectively carry synchronizing pulses and numerical order identification pulses. The data line carries trains of pulses representing the full weight being displayed by the master indicator.

A method and apparatus for obtaining an accurate measure of the frequency of an applied signal by generating a pair of independent frequency signals wherein one of the independent frequency signals has a frequency value which is indicative of the operating temperature of the counter. The counter has two modes of operation: a calibration mode and a measurement mode. In the calibration mode, an accurate signal having a preselected frequency value is applied to the counter. The frequency of this signal is measured with reference to the other of the pair of independent frequency signals and this measured value is then algebraically combined with a prestored value that is equivalent to the preselected frequency of the applied signals. The combined value represents the necessary normalized correction factor for any measured frequency when the counter is at the corresponding temperature. The value of the one of the independent frequency signals in this mode serves as a pointer to the memory location where this correction factor is to be stored. This procedure is then repeated several times as the temperature environment of the counter varies. In the measurement mode an unknown signal is applied to the counter, its frequency value is measured against the other of the independent frequency signals, the value of the one of the independent frequency signals is utilized as a pointer to the necessary correction factor at the then operating temperature of the counter, the measured frequency value is corrected algebraically with this correction factor, and the final result outputted for further use by the user.

To measure the recurrence frequency or cadence of the output of a pulse source, a programmer periodically opens a gate for a predetermined measuring interval during which the pulses are fed to a counter whose reading is to be registered in a numerical indicator. The counter, reset by the programmer after each measuring interval, loads the indicator through a buffer register which stores its reading until an updating pulse from the programmer makes the register receptive to a new count. In one embodiment, such updating is inhibited as long as the stored contents of the register differ by only a unit step from the current count. In another embodiment, the pulse cadence of the source is stepped down by a frequency divider inserted between that source and the counter; prior to each measuring cycle, the divider may be automatically preset by the programmer to an initial position, different from its counter-stepping zero position, depending upon the final position reached in the preceding cycle in order to minimize the possibility of digital errors. A further embodiment includes a timing circuit which determines the period between the end of a preceding measuring interval and the immediately following pulse in order to shift the end of the next measuring interval to a time position approximately midway between two pulses, a delay circuit letting the start of such interval occur a fraction of a pulse cycle after reception of a pulse from the source.

A resist film coating apparatus comprises a resist receiving plate secured to a rotatable support plate carrying a wafer so as to be disposed along the outer periphery of the wafer, an interference type film thickness meter for measuring the thickness of a resist film spun out to the resist receiving plate, and modifying means for changing the revolution number of the support plate on the basis of a result of measurement by the film thickness meter such that a desired resist film thickness can be obtained.

A control is provided for a wire coating line which includes means for driving wire along a path at controllable speed while coating it with plastic extruded at a controlled rate and temperature, and cooling means are located at a controllable distance from the coating means to solidify the plastic. The controllable factors affect both the capacitance and diameter of the wire produced. The control allows the line to be run in accord with stored digital values for the matters to be controlled. Closed loop control is provided because the relevant factors of line operation are measured, the analogue measurements converted to digital values and compared with the stored values to produce a control signal which has the effect of reducing the differences between a desired and measured line condition as represented by the digital values compared. Closed loop control is also provided for control of the line to produce desired capacitance or diameter values in the coated wire. Whichever of capacitance or diameter is used as the basis for line control is measured and provided as a digital value to the control. This digital value is compared to a stored digital value representative of the desired capacitance or diameter. The results of the comparison is used to update the stored digital value for an operating condition of the line so that the parameter is altered to provide an operating condition which brings the capacitance or diameter closer to the desired value.