A new method for on-line monitoring of brake fluid condition using an enclosed reference probe

The double-ended excitation self-balancing bridge excitation method is a capacitance measurement method with rather a high measurement accuracy currently. However, the reference impedance of the electric bridge limits the traditional self-balancing excitation measurement method, making it difficult to achieve high accuracy and a wide range of capacitance sensor measurements. In the proposed paper, frequency adjustment method is introduced to enable impedance matching between the measured capacitance and the reference resistance. The measurement range is broadened as well as maintaining the accuracy of the capacitance measurement. The measurement circuit is composed of a reference resistor, a bridge in series with the measured capacitance and an operational amplifier follower circuit. First, we roughly measure the input impedance of the operational amplifier and the capacitive reactance of the capacitance under test using a two-step excitation method. Then, the best excitation frequency is calculated to match the reference resistor according to the capacitive reactance under test, and the input impedance of the operational amplifier is re-estimated with the best frequency. Finally, we complete the accurate measurement of the capacitive reactance under test through the use of dual excitation. The experimental results demonstrate the method's high accuracy measurement within the range of 1.6pF to 16nF, with the reference resistance set at 1MΩ and the excitation frequency adjusted between 10-100kHz. Additionally, dual excitation stability testing verifies relative standard deviations in the range of 0.01% to 0.12%. Experiments on filter capsule sensing detection show that the proposed frequency adjustment measurement method can perform highly sensitive capacitive sensing measurements under the influence of parasitic effects.

Section: Introductionmentioning

confidence: 99%

Dual excitation self-balancing capacitance measurement method based on frequency adjustment

Wang,

Yang,

Cai

et al. 2024

“…Capacitive sensors are widely used for the measurement of many physical and chemical quantities [1], such as liquid level [2,3], humidity [4,5], pressure [6], carbon dioxide [7], position and displacement [8], among others. These sensors are generally modelled with a lossless capacitance C x that is modulated by the measurand, but some of them show a loss term that is usually modelled by a parasitic conductance G x in parallel with C x [1], as shown in figure 1.…”

Section: Introductionmentioning

confidence: 99%

A microcontroller-based interface circuit for lossy capacitive sensors

Reverter¹,

Casas

2010

This paper introduces and analyses a low-cost microcontroller-based interface circuit for lossy capacitive sensors, i.e. sensors whose parasitic conductance (Gx) is not negligible. Such a circuit relies on a previous circuit also proposed by the authors, in which the sensor is directly connected to a microcontroller without using either a signal conditioner or an analogue-to-digital converter in the signal path. The novel circuit uses the same hardware, but it performs an additional measurement and executes a new calibration technique. As a result, the sensitivity of the circuit to Gx decreases significantly (a factor higher than ten), but not completely due to the input capacitances of the port pins of the microcontroller. Experimental results show a relative error in the capacitance measurement below 1% for Gx < 200 nS, which is quite remarkable considering the simplicity of the circuit proposed. The measurement of a commercial capacitive humidity sensor subjected to condensation (in order to have a significant value of Gx) shows the effectiveness of the circuit.

“…Thus monitoring the lubricating oil level in a compressor is very important to ensure safe and reliable operation. However, it is difficult to employ most conventional level sensors [2][3][4][5][6][7][8][9][10][11][12][13] in a compressor because the sensor should measure oil levels under harsh conditions, such as electrical noise, mechanical vibration, turbulent flow and limited space inside the compressor. Optical sensors do not perform well when films of viscous liquid such as lubricant form on their surfaces [2,3].…”

Section: Introductionmentioning

confidence: 99%

“…Optical sensors do not perform well when films of viscous liquid such as lubricant form on their surfaces [2,3]. Electrical sensors are highly sensitive to environmental noise and contaminants [4,5]. Particularly, the residue of viscous oil left on the sensor surface after it has been exposed to gas is a critical source of sensing error.…”

Section: Introductionmentioning

confidence: 99%

Development of a micro liquid-level sensor for harsh environments using a periodic heating technique

Hong¹,

Chang²,

Kim³

2010

This paper describes the development and testing of a novel micro thermal sensor for point sensing of lubrication oil level in industrial compressors. The results reported in this work can be applied to various harsh environments that feature high temperature/pressure, limited space and flow/vibration. The sensor employs an ac (alternating current) thermal technique with a single heating/sensing element. As the sensing scheme is based on the so-called three-omega method, the sensing signal is noise-resistant and hardly affected by flow in the liquid being measured. Experiments with DI water, ethanol and ethylene glycol confirm that the sensor performance is satisfactory under atmospheric pressure. Also, to mimic harsh conditions as in an industrial compressor, tests are performed in a pressure vessel containing R410A gas and polyvinylether lubrication oil under high temperatures and pressures. The results indicate that the sensitivity and response time of the developed sensor are appropriate for practical usage in harsh environments. As the sensor can be easily mass-produced at low cost using photolithography, it has strong potential for industrial applications.