Rotational vibratory viscometer transducer and circuit

Abstract

A torsional mode rotational vibratory viscometer having an elastic hollow metal sheath extending below a support plate and secured to the plate by a weld. A rigid rod is disposed within the sheath and welded to the lower end of the sheath. An immersible tip is also secured to the lower end of the sheath. The free upper end of the rod extends above the support plate. A crossbar with ends of magnetically permeable material is secured to the free end of the rod and is caused to oscillate by a magnetic drive coil adjacent one end of the crossbar. Prior to mounting of the crossbar, the assembly is subjected to a specific heat treating schedule. A magnetic detector coil adjacent the other end of the crossbar detects the angular oscillation of the rod. Circuitry connected to the coils maintains the amplitude of oscillation of the rod constant. When the tip is immersed in a fluid, the power supplied to the drive coil is determined by the circuit and is a measure of the viscosity-density product of the fluid. The circuitry includes a sample-and-hold circuit having a clipping level which varies with the detector coil signal level, and a variable exponent amplifier to accurately correct for deviation of the drive coil current-power relationship from a square function.