Abstract: An apparatus and method employing a liquid level detection conductance probe mounted in a container to sense resistive differences between the probe and container depending upon the presence or absence of liquid therebetween. A sensing circuit senses probe signal variations and stores a probe signal. A comparator compares the stored probe signal to current probe signals and switches means connected to the comparator depending upon the presence or absence of liquid between the probe and container. The sensing circuit has sufficient sensitivity to differentiate between liquid between the probe and container and foam or scale deposits therebetween.

Abstract: A probe which mounts in a liquid container has a conductance electrode containing a temperature sensor. A conductance control circuit is coupled to the probe to control an output relay in accordance with predetermined impedance conditions at the probe, and a temperature limit control circuit also controls the output relay in accordance with predetermined temperature conditions at the probe.

Abstract: A solid state circuit for sequencing a valve mechanism from its normal operating position through a sequence of cycles to blow down various different lines of the network to which the valve mechanism is connected. The circuit may be set to initiate its sequence at one of a number of time periods such as once a day or once a week. Once initiated, the circuit operates a motor drive for the valve mechanism continuing for a timed interval followed by a delay or dwell at each blow down position. A signal is provided to indicate that the circuit is about to enter a blow down sequence followed by the sequence itself. Various alarms and safeguards are provided for the sequence.

Abstract: Liquid level control system in which there is a basic resistive level sensing electrode or probe extending into a vessel or tank containing liquid. In addition there is a conductive guard ring or shield insulated from both the probe and from the conductive member or portion of the body of the vessel. The guard ring electrode acts as a current source to counteract electrical leakage across the surfaces between the probe and vessel body to minimize the effects of leakage and maintain the liquid level sensing control operative under most leakage conditions by balancing the leakage currents. In the event the leakage becomes excessive, a control is activated to signal the excessive leakage condition in a suitable manner.

Abstract: A fiber optics level sensor (FOLS) or flow sensor (FOFS) system for use in hazardous environments, process control, and industrial and environmental control applications. The system includes a pair of fiber optic bundles arranged between a remote sensor and a control module. The remote sensor detects the position of a movable vane--which is mechanically coupled to a float in the sensed environment--by means of a transmission gap between confronting ends of the pair of fiber optic bundles. The control module includes a light output device driven by an oscillator which thereby generates pulses of light which are optically coupled to the end of one of the bundles. The end of the other bundle is coupled to a photodetector which generates electrical pulses in response to the returning light pulses. The electrical pulses are amplified and then gated through a sampling circuit which is internally synchronized by means of and in resonse to the oscillator.

Abstract: A system for monitoring the liquid level in containers such as boilers and tanks. An electrode inserted into the container completes a path through the liquid when the liquid is at or above a predetermined level. When the liquid falls below the level, the path is opened. If the open path persists uninterruptedly for a timed period, an output device such as a relay is energized (or deenergized, if desired) to signal the low fluid level. The circuit path is powered at a low AC level from an AC source which also powers the output device. The low level AC in the circuit path to the liquid minimizes electrolytic and other problems within the container. The low level AC periodically resets a timing device within a direct current monitoring circuit before the expiration of the timed period, as long as the circuit path through the liquid remains closed. The output device is an optical coupling device isolating the output device from the timing device and from the low level AC path.