Characteristics of 9 mm metallic triple-beam tuning fork resonant sensor

Abstract

Abstract. This paper describes the design and testing of the first miniaturised metallic triplebeam tuning fork resonant sensors for use in force, pressure and torque measurement applications. The new devices with 9mm length vibrating tines have resulted in over a 40% in size when compared to previously tested resonators. The four fold increase in operating frequency to 26 kHz, with Q factors in air up to 4000, provides additional benefits for resolution, accuracy, range and overload capability. Measurement repeatability of at least 0.02% of span levels for torque transducers employing the sensors are quoted. Results of characterisation over the temperature range -30 o C to +90 o C are given. IntroductionResonant sensors have been used in a wide range of sensing applications, such as load, pressure, torque and fluid flow characteristics [1]. The key element of these sensors is the resonator, an oscillating structure, which is designed such that its resonance frequency is a function of the measurand. The most common sensing mechanism is for the resonator to be stressed as a force sensor. The applied stress effectively increases the stiffness of the resonator structure, which results in an increase in the resonator's natural frequency. The resonator provides a virtual digital frequency output, which is less susceptible to electrical noise and independent of the level and degradation of transmitted signals, offering good long-term stability. The frequency output is also compatible with digital interfacing and no analogue-to-digital conversion is required, therefore maintaining inherent high accuracy and low cost. The first successful metallic triple-beam tuning fork (TBTF) resonant sensor with thick-film drive/pickup elements [2, 3, 5] has a resonating 'tine' element length of 15.5mm and an overall sensor length of 23.5mm, a thickness of 0.25mm and beam widths of 1mm, 2mm and 1 mm. The gap between the beams was 0.5mm. However, this device is too large for current force/torque and pressure sensing applications. The challenge has been to reduce the sensor dimensional footprint and if possible enhance sensor performance.

A3.1 - Use of Metallic Resonant Sensor in Torque Measurement Transfer Standard

“…The first phase of the miniaturisation process was achieved by simply reducing the overall length by 50% from 40mm (T15, 15.5mm tine) to 20mm (T9, 9mm tine) [2]. The latest version of the sensor T6 has reduced the size by 70% from the original, as shown in figure 2.…”

“…Resonator operation and characteristics of the three miniaturized metallic TBTF resonant sensors (* Results previously published[2])…”