Posted on Mar 19, 2013

If the tube is level with respect to gravity, the bubble resides in the tube`s center and the electrode resistances to common are identical. As the tube shifts away from level, the resistances increase and decrease proportionally. Transducers of this type must be excited with an ac waveform to avoid damage to the partially conductive liquid inside the tube. The level transducer is configured with a pair of 2-KO resistors to form a bridge. The required ac bridge excitation is developed at ClA, configured as a multivibrator. Cl biases Ql, which switches the LT1009`s 2.5-V potential through the 100-~

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The bridge differential output ac signal is converted to a current by Al, operating as a Howland current pump. This-current, whose polarity reverses as bridge drive polarity switches, is rectified by the diode bridge. Thus, the 0.03ILF capacitor receives unipolar charge. A2, running at a differential gain of 2, senses the voltage across the capacitor and presents its single-ended output to ClB. When the voltage across the 0.03-~

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