SU916995A1 - Float-type inductive level indicator - Google Patents

Description

(54) FLOAT INDUCTIVE LEVEL

The invention relates to instrumentation, namely, devices for the control of liquid level in process vessels. The liquid level indicator in the vessels is known, which contains a steel ball float moving in accordance with the level change relative to two inductive coils differentially connected to the AC bridge, and to increase the sensitivity, the coil along the axis of which moves the float is variable in height number of SI turns. The disadvantage of this liquid level gauge is a relatively low sensitivity, resulting in significant errors at meter control ranges. The closest to the proposed technical essence is an inductive float level gage. It contains a linear displacement transducer with a float sensitive element and fixedly fixed X-shaped magnetoprostherases on which windings are placed, and a measuring transducer t21. A disadvantage of the known device is low accuracy with large measuring ranges, which is determined by the distance between the X-shaped cores. The purpose of the invention is to improve accuracy. This goal is achieved by the fact that the float induction level gauge contains a linear displacement transducer with a float sensitive element and fixed magnetic conductors on which the excitation windings are interconnected according to each other and connected to the excitation source, and the measuring windings interconnected a counter-series and connected to the measuring trans | To the applicant, an additional excitation source was introduced with a different frequency, two outputs, the voltages of which are shifted by 90 relative to each other, and the linear displacement transducer is made in the form of a smooth ferromine rod covered by a float with a short-circuited coil, on different sides of the rod are fixed - shape the magnetic cores so that each extreme rod of one magnet of the wire is located opposite the groove of the opposite magnetic core, and ya middle cores. Additional windings are interconnected They are interconnected in series within each row and connected to the outputs of a supplementary excitation source. I FIG. 1 shows the construction of a linear displacement transducer in FIG. 2 - sensor element - a short-circuited metal tied coil, mounted on a float glass; in FIG. 3 shows the operation of the converter portion in FIG. 4 shows the characteristics of the current section of the converter in FIG. 5 is a block diagram of an inductive float level gage. The level gauge contains an inductive linear displacement transducer (Fig. 1) with a movable short-circuited coil 1 freely moving along a smooth rod 2, 2jf7 of curved magnetic cores .3 arranged in a checkerboard order on either side of the rod 2 (along p magnetic conductors on each side ) and forming between the cores and the core 2 air gaps, through which the coil 1 passes freely. On the middle cores of each magnetic core Odate according to the included excitation windings 4 connected to the source Uyj and n and the extreme ones include the included measuring windings 5 (Fig. 3). In addition, additional windings 6 and 7, connected in opposite, are mounted on the middle cores of each H-shaped magnetic core, and additional windings 6 are connected to the voltage source Ug ,, phase-shifted by 90 relative to the voltage Ugj supplied to the additional windings 7. Packages W-ribbed plates are bonded to each other by non-magnetic metal corners 8. The fluid level perceiving element is a float 9 made in the form of a two-shift cup 10 (Fig. 2) of a non-conducting, abrasion resistant material a bowl (for example, polyethylene terephthalate), to which top 1 is attached, which is made of a light and highly conductive material (for example, aluminum). The EMF in each nearby secondary windings located on opposite sides of a smooth rod must coincide in phase, and since the EMF of the secondary windings of one magnetic core is antiphased, then the EMF in the nearby secondary windings of neighboring magnetic cores must be out of phase. This is realized, in particular, by the consonant connection of all primary windings (so that the flows through the coil caused by MDS demarcated by a smooth rod coincide along the direction) and the counter connection of all secondary windings. Since the magnetic flux of an individual excitation winding almost completely closes within the bundle of L-shaped plates (the W-shaped links are fastened together by a nonmagnetic rod or a corner), in the absence of a coil near the packet, the resulting EMF of the secondary windings located on the outer cores of such a packet equals zero. For the section in the zone of which coil 1 (Fig. 3), the dependence of the output voltage on the coil movement for a separate W-shaped link is linear only at small displacements of the coil relative to the geometric axis of the packet, and then has a non-linear character Fig. 4). However, the summation of the EMF in the fused secondary windings of opposite packets gives a linear resulting characteristic of the sensor (solid lines in FIG. 4). The linear displacement transducer 11 (FIG. 5) is connected by its measuring windings to the measuring transducer 12, which provides a sequential interrogation of the measuring windings, counting the number of magnetic cores immersed in a liquid, and measuring the resulting voltage across

59

windings. The measuring transducer includes a step switch 13 connected to the windings of the converter P. by its outputs. The stepping switch is started from the low-frequency pulse generator 14 through an AND 15 circuit, which has a signal from the 1I to another input

through the inverter 16. At the same time, the signal from the output of the coincidence circuit is fed to the input counter 17, which is intended to count the number of magnetic cores immersed in the liquid. At the same time, the resulting voltage at the output of the measuring windings is monitored by a voltmeter 18.

The gauge works as follows.

The control pulses from the low-frequency (5-10 Hz) pulse generator 14 (Fig. 5) through the circuit 15 enter the control winding of the step switch 13 and the pulse counter 17. The step switch 13 alternately connects (starting with the first pair of measuring windings of the transducer 11 linear shifts to the input of the inverter 16. The output voltage of the pairs of measuring windings located on the outer cores of the W-shaped magnetic conductors is zero, if the coil is out of the zone of this magnetic circuit, and, on the contrary, the voltage will be nonzero if the magnetic circuit is in the zone.

if the coil is in the zone of the K-th U-shaped magnetic circuit, then the pulse counter 14 will go to. pulses, because after the arrival of the k-th pulse, the voltage from the sensor output will not go only to voltmeter 18, but to the input of the inverter 16, which will remove the voltage from the output of the inverter 16, i.e. From one of the inputs of the circuit, And 15, and stop the step switch 13. To supply additional windings of the linear displacement converter, an additional excitation source 19 was introduced at a frequency different from the supply voltage frequency of the main excitation source (not shown in Fig. 5) and having two outputs with voltage Ug and Ugj. shifted in phase relative to each other by 90.

The voltage Ug feeds the additional counter-included windings, located, for example, to the left of smooth 9956

which rod and Ug located to the right of the rod. The dimensions of the cores and grooves of the magnetic cores of the magnetic cores are chosen so that each extreme core is located opposite to the width equal to the width of the groove of the opposite magnetic core (Fig. 2). Thus, additional windings create a weak distribution in space, an unambiguously varying field (the flow of each core of the U-shaped magnetic circuit lags or advances in phase the flow of the previous or next opposite magnetic circuit, i.e., the running field. A weak running field will be Porosity imposes a small electromagnetic force acting on the coil, shifting it from the equilibrium position to an insignificant distance, which will allow to unambiguously determine its location. the coil rises above the liquid level and as the voltage increases, this means that the coil is in the magnetic circuit section corresponding to the upstream part of the characteristic, if the voltage drops the coil is in the descending part of the characteristic.

If the step switch does not stop anywhere during the preliminary survey (turn in the center of one of the middle cores), then it is necessary to move the turn by an additional field and determine the level of the liquid by the pulse counter reading.

Headings and interferences from the additional field, which differ in frequency from the main field, are easily eliminated by the corresponding filters, which are placed at the input of the voltmeter.

Thus, the height of the controlled level is determined by the number of pulses arriving at the step switch and the readings of the voltmeter 18, which ensures uninterrupted level measurement over the entire measurement range, high measurement accuracy when the level changes within a single magnetic circuit and eliminates ambiguity.

Claims (2)

1. USSR author's certificate number 224833, cl. G 01 F 23/10, 1967. 2. Authors certificate of the USSR 1 201697, cl. G 01 F 23/10, 1964 (prototype), ig.5