Abstract: A system for maintaining back-pressure in chemical laboratory testing apparatus includes a modified flow control valve governed by a special control system which includes an input/output controller. That controller includes a microprocessor and memory into which a program developed specifically for the modified valve has been placed. A pre-pressure valve is also used upstream of the instrument in which the pressure is to be maintained for effecting quicker control of the pressure. The input/output controller, in conjunction with the servo-amplifier, integrates out the error between the desired set-point pressure and actual pressure thereby enabling maintenance of pressure within one pound.

Abstract: An electromagnetically actuatable probe is inserted in a vessel containing a body of liquid and in which high pressure, high temperature, corrosive, or other hostile conditions exist. Pulses are transmitted to the probe within a predetermined range of frequencies which include the normal resonant frequency of the probe. Return signals are generated by the probe between the times the transmitted pulses are sent. These return pulses are processed to produce signals which are a function of the level of the liquid that are then employed to control the discharge of the liquid or used by another utilization circuit.