Abstract: A liquid bulk density monitoring apparatus which is particularly suitable for monitoring suspended sediment levels has a plummet suspended from one end of a balance beam and submerged in a vessel containing a liquid to be monitored. A sensor detects tilting of the beam from a reference or balance position as a result of variation in the sample bulk density, and produces an output to an output device for recording density variations. The apparatus is designed to compensate automatically for any changes in temperature, for example by making the plummet of a material having a coefficient of thermal expansion substantially the same as that of the liquid being monitored.

Abstract: A purge gas pressure monitoring system has a piezometer tube running from a pressure measuring instrument into a medium to be monitored. A temperature detector device extends the length of the piezometer tube. Outputs from the pressure measuring instrument and the temperature detector device are coupled to a central processing device or microcomputer for monitoring the outputs and using the outputs along with stored data to calculate a corrected pressure signal which is corrected for errors including errors arising as a result of variations of the average temperature along the piezometer line from a reference value.

Abstract: A temperature compensating device is provided for a purge gas pressure monitoring system in which a piezometer line has an outlet end for submerging in a medium to be monitored and an opposite end for connection to a suitable pressure responsive instrument, with a purge gas supply connected to the line so as to supply purge gas as bubbles from the outlet end of the tube. A temperature detector device runs the length of the piezometer line to produce an output signal proportional to an average of the temperature along the length of the line. This may be a resistance temperature detector in the form of a U-shaped conductive wire with opposite legs of the U wound spirally in opposite directions along the length of the line with the connected end of the U being located at the outlet end of the tube. This provides a variable resistance which varies as a function of the average temperature, and which can be connected to conditioning circuitry for producing a desired temperature dependent output.

Abstract: A base assembly for a beam balance instrument includes a box-like, open bottom base of lightweight sheet metal having an elongated slot in its upper wall, and a reinforcing strip or bar inlaid into the slot for rigidly supporting parts of the balance. The reinforcing strip is thicker and bulkier than the remainder of the base, and the fulcrum which pivotally supports the beam above the base is rigidly fastened on the strip, as is the sensor for detecting tilting of the beam in response to an applied force, and the bellows if the balance instrument is of the type used in measuring pressure variations.

Abstract: A method and apparatus for monitoring liquid levels using pressure responsive instruments is described, in which an arrangement for compensating for the effects of errors including gas weights errors is provided. The required compensation factor for a particular installation is first calculated theoretically, and then used in order to raise the output signal of the instrument electronically by the calculated factor. In one arrangement, the output signal is amplified by the desired factor. Alternatively, the excitation voltage of the instrument itself, or of a potentiometer used to interface the instrument to electronic data acquisition devices, is varied in order to raise its output voltage by the desired compensation factor.

Abstract: A balance beam has a fulcrum, at least one bellows (connected to a source of pressure or vacuum) acting on the beam and a connection to the armature of a differential transformer at one end. A poise is mounted for movement along the beam by rollers riding on shoulders formed on the beam. A carriage having a connection to the poise at the elevation of the axes of the rollers moves the poise and is, in turn, driven by a screw turned by a servomotor controlled by the differential transformer. Provision is made for minimizing temperature error both longitudinally and transversely of the beam. The fulcrum and bellows may be moved to different locations relative to the beam, using spaced drilled holes in the beam and the base plate. Various readouts may be connected to the screw, and recorders and control devices may also be driven by the screw.

Abstract: A circuit for a servo-amplifier saves power when the position servo has reached balance. The servo input is a high frequency differential transformer having its armature positioned by mechanical means driven by a servo motor controlled through amplifier circuitry. The power to the amplifier is turned off in the vicinity of the servo null point.

Abstract: A balance beam has a fulcrum, at least one bellows (connected to the source of pressure or vacuum) acting on the beam at a point along its length and a connection to the armature of a differential transformer at one end. A poise is mounted for movement along the beam by rollers riding on shoulders formed on the beam in a unique arrangement. A carriage having a connection to the poise at the elevation of the axes of the rollers moves the poise and is, in turn, driven by an expansible belt, chain or cable extending around two sprockets, one of which is driven by a servo-motor controlled by a circuit including the differential transformer. Careful provision is made for temperature compensation both longitudinally and transversely of the beam yet the drive elements are elastic. The bellows may be moved to different locations relative to the beam by use of pre-drilled holes in the beam and base plate. Two bellows, on opposite sides of the fulcrum, may be used to gauge pressure differences.