Abstract: A vibration type liquid density meter comprising a base, a connector having a mass substantially smaller than said base, two hollow cylindrical elongated pipes each having two ends, one end of each pipe connected to the base, and the other end of each pipe connected to the connector with the pipes disposed substantially parallel to each other and a piezoelectric element attached to the connector for driving the pipes into self excited oscillation at their natural frequency. The liquid to be measured is supplied through the base, pipes and connector and the density of the liquid is measured by the frequency of oscillation with corrections for temperature.

Abstract: A data communication system comprising a master station and n number of substations, each substation comprising a receiving photocoupler and a transmission photocoupler, and wherein a particular substation may be connected into a transmission line leading to the master station by connecting the receiving photocoupler in series in parallel circuit to the transmission line and wherein data transmission from the master station to the substation is accomplished by means of a current supplied forward with respect to the receiving photocoupler of the substation, and data transmission from the substation to the master station is done by means of a current supplied reverse with respect to the transmission photocoupler of the substation.

Abstract: A variable resistance circuit comprising a field effect transistor, a plurality of amplifiers and a feedback circuit for one of the amplifiers with the equivalent resistance value derived from a circuit comprising the field effect transistor electrodes and a reference resistor being controlled by a digital signal or a pulse-width signal supplied to the feedback circuit.

Abstract: A recorder comprising a flat bed disposed toward the upper portion of a recorder case and equipped with a built-in chart feed wheel, and a chart storage area located below the flat bed and within the recorder case. The flat bed is made movable in the chart feed direction and, as the flat bed is moved the feed wheel is moved therewith and an opening is formed in the recorder case to allow the storage area to be exposed and the chart material stored therein to be readily accessible.

Abstract: A multi-range, self-balancing instrument using a Zener diode circuit and a phase compensating circuit is disclosed. The Zener diode circuit is capable of generating a white noise, which is effectively applied to the self-balancing system whereby the dead zone is maintained constant irrespective of the range. The phase compensating circuit, comprising a non-inverting input amplifier, is capable of compensating for the phase lag of the self-balancing instrument by adjusting the amplification factor of the amplifier without affecting the stability of the servo amplifier system.