GB1422613A - Apparatus for use in monitoring the level of the free surface of an electrically-conductive liquid - Google Patents

Abstract

1422613 Measuring liquid level electrically INTERATOM INTERNATIONALE ATOMREAKTORBAU GmbH 1 March 1973 [3 March 1972] 10097/73 Heading G1N In the measurement of the level of an electrically conductive liquid (liquid metal) using an elongate transformer dipping into the liquid a temperature compensating circuit is connected to the secondary. The transformer, Fig. 1 (not shown) comprises monofilar primary and secondary windings wound in respective helical grooves formed in an elongated core so that respective turns of the primary and secondary windings alternate along the core with each turn of the secondary winding spaced apart along the core from two adjacent turns of the primary winding by equal respective distances. Temperature compensating circuit: The output of the secondary winding when the probe is dipped into the liquid is dependent not only on the level but also the liquid temperature. To compensate for this the output of the secondary winding L E , R E (primary winding L S R S being energized from circuit II) is fed via capacitor CE to a filtering and rectifier circuit and a liquid level dependent voltage UpV varying inversely with the liquid level is derived from potentiometer P v . This voltage is combined with an auxiliary voltage from potentiometer P v which is selected so that the combined voltage is zero when the probe is at a low temperature and does not extend into the liquid, the combined voltage in operation then being applied to one input of amplifier V2. The temperature of the liquid is monitored by its effect on the resistance of the winding R E , L E and to this end a constant current is applied to the secondary through RKS and choke D1 and the voltage drop developed across 100, 90 is applied to the inputs of amplifier V 1. Thus amplifier V 1 provides an output which is proportional to the potential and hence temperature. The output of V1 is fed via R LK to the input of amplifier V2 and also to an input U LK(x) of a multiplier to a second input of which is fed the partially temperature compensated signal from the output of amplifier V2. The multiplier provides at output UK a further compensation voltage, produced by multiplying the two inputs together, which is fed to an input of amplifier V 3 to which is also fed the partially temperature compensated signal from amplifier V 2 . The output of amplifier V3 provides the temperature compensated level signal. In order to balance out the effects of the supply lead resistances Rz a constant current is supplied to one set of leads and a supplementary pair of leads are provided to apply the resulting voltage drop across the coil to the amplifier whose output is connected to 110, Fig. 3 (not shown).