Patent GB-966884-A (GB)
Title: Pressure-sensitive transducer
Inventor: KEALY WELLESLEY ASHE
IPC: G21C17/10
Filed: 1961-03-06
Abstract: 966,884. Pressure gauges. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Feb. 23, 1962 [March 6, 1961], No. 8164/61. Heading G1L. [Also in Divisions G6 and H4] The pressure of a fluid (carbon dioxide) in thermal relationship with a nuclear fuel element is deduced from a measurement of the resonant frequency of an oscillating diaphragm loaded by the fluid and the temperature of the fuel element is then derived from such measurement. The diaphragm 39 (Fig. 1), which forms part of a transducer capsule 23 mounted in the lower end fitting 21 of a nuclear fuel element, carries a soft iron armature 41 coacting with a soft iron core 29 energized by a winding 31. The capsule communicates via a capillary tube 25 with a carbon dioxide filled bulb 27 supported by one of the element locating fins 12b and to balance the pressure on each side of the diaphragm the latter is provided with an aperture 42. In practice, a number (six in the embodiment disclosed) of fuel elements are stacked in vertical order the lower end fitting 21 of one element resting in the upper end fitting 19 of the next (lower) element. The windings 31 of each capsule are connected in series and to enable selective measurement of the resonant frequencies of the different diaphragms to be effected the latter are made to differ for a given temperature by altering the masses of the armatures 41. The series connection is automatically brought about when the elements are stacked by means of three (only one shown) insulated contact studs 33 in the lower end fitting connected (in parallel) to one end of the winding 31 the other end of which is connected to an insulated contact plate 37 in the upper end fitting 19 via a lead 35 supported by the other locating fin 12c. The electrical circuit terminals then comprise the upper contact plate 37 of the top-most element and the studs 33 of the lowest element (earth) connection to which is made via the structure of the reactor. By adjustment of the masses of the armatures 41 the different diaphragms are made to resonate over bands of 300 c.p.s. between 2.2 kc./s. and 5.0 kc./s. each band being separated by a 200 c.p.s. guard band and to measure the actual resonant frequency an oscillator 43 (Fig. 3) is set in turn to the lowermost frequency of each band by a selector switch 45 and for each setting the frequency is swept over the band by means of a control 46 calibrated in temperature whilst resonance is indicated by a meter 47 responsive to the power supplied to the windings 31 and which rises to a peak at the resonant frequency. A measure of this is derived in a circuit 44 comprising a resistor in series with the energizing circuits of the windings the voltage across which is amplified and supplied to meter 47. Known data logging techniques may be employed for automatic measurement. The Provisional Specification refers to alternative arrangements for measuring the temperature of a nuclear fuel element comprising (1) By measuring the change produced in the resonant frequency of a coil by the movement of a metal core carried by a part of a sealed capsule which moves when its internal pressure changes with temperature. (2) From the resonant frequency of an acoustic resonator e.g. a Helmholtz resonator, excited either by an electrically driven diaphragm or by the noise in the reactor. (3) By varying the resonant frequency of an acoustic resonator by a temperature sensitive bi-metallic strip. (4) By employing a number of acoustic resonators of different resonant frequency energized by an acoustic signal of varying frequency so that identification of a particular resonator and hence a particular fuel element may be effected. (5) By employing a resonator in the form of a whistle excited by the flow of reactor coolant and detecting the whistle frequency by means of a microphone.