GB560641A - Improvements in or relating to electrical means for the detection of gas in liquids - Google Patents

Abstract

560,641. Determining physical qualities of materials; capacitance measurements; condensers. NAPIER & SON, Ltd., D., and CLARKE, M. E. Oct. 7, 1942, No. 14072. [Class 37] Apparatus for detecting gas in liquids, particularly for detecting the amount of air contained in lubricating oil, consists of a condenser comprising a series of plates in a chamber through which the liquid is caused to flow, the plates which are spaced apart lying parallel to each other and to the direction of flow, a meter which will indicate variations in the capacitance of the condenser, and means whereby an alternating current is passed through the condenser and meter. The oil under test is arranged to flow constantly through a sampling condenser shown in Fig. 5. The condenser plates M are mounted in a rectangular casting L provided with tubular members K, K1 which are connected to inlet and outlet pipes for the oil. The plates M are mounted on two bases, one insulated and alive and the other earthed to the casing. Connection to the plates is made by a terminal N, while N1 is a pressure tapping point for measuring the pressure of the oil. The plates may be constructed of aluminium or aluminium alloy and may be anodised. The measuring circuit is shown in Fig. 4. A dynatron oscillator D5 has an oscillatory circuit D6 in its anode circuit and feeds the grid of a valve E4, the output of which passes through resistances G2, G3. Automatic volume control is applied by means of a copper oxide rectifier K supplied from a potentiometer S1. As the output increases the rectified portion becomes more negative and increases the negative bias, which reduces the amplification and hence the output.. A delay is provided by biassing the rectifier positive to a value slightly below the output voltage required. This prevents rectification occurring until the output voltage exceeds the value of this positive bias and any excess of voltage is rectified and passed on as negative bias to the controlled valve. The oil sampling condenser is arranged in a bridge circuit of which the resistances G2, G3 form two arms, the fourth arm being a variable condenser H. In the diagonal of the bridge is a rectifier J and D.C. instrument A2. The condenser H is adjusted to balance the bridge when the sampling condenser is in air, giving zero deflection. A standard condenser C4, filled with de-aerated oil, is then substituted and the high-frequency voltage applied to the bridge is adjusted by means of the potentiometer S1 until full scale deflection is obtained. A condenser C3 in parallel with the condenser C4 serves for temperature correction. Connection to the condenser constituting the aeration element is either at the terminals C2a, C2b, or C2c.