Thomas Glatzl

Concept of a thermal flow sensor integration on circuit board level

A concept of a flow sensor optimized for the use in HVAC (Heating Ventilating Air Conditioning) systems is presented. The fabrication of the transducer is based on PCB (Printed Circuit Board) technology to keep costs low and allow for easy handling and replacement. The complete sensor device consists of a quantizer, a conversion circuitry, and a network link. Through interaction with the streaming fluid, the transducer generates an electrically measurable signal which allows determination of the total flow of the fluid. The measurement principle is based on a modification of the calorimetric principle. Hence, miniaturized heat sources and nearby temperature detectors have to be implemented. The behavior and performance of the sensor concept has been studied by means of finite element simulations. The quasistatic and transient simulations reveal the temperature allocation inside the sensor and the surrounding fluid and therefore allow a further optimization of the sensor for different applications.

Towards distributed enthalpy measurement in large-scale air conditioning systems

Air conditioning systems are among the major energy consumers in buildings. Energy-efficient operation of AC systems is an important step towards better energy management in building automation, but requires efficient monitoring of the energy or enthalpy flows within the AC installation, which is currently still difficult because of the lack of appropriate equipment. This paper introduces a distributed data acquisition system for large-scale AC systems based on low-cost flow sensors implemented by means of standard printed circuit board technology and interconnected via a wireless sensor network. A critical issue for the system installation is the placement of the sensors in the air ducts to obtain representative measurements of the air flow. To this end, extensive aerodynamical simulations are carried out to analyze the flow distributions in typical building blocks for air ducts, particularly with respect to turbulences. The simulation results are compared with experimental data from the literature and are shown to be reliable.

Characterization and optimization of a thermal flow sensor on circuit board level

The characterization and optimization of a low-cost thermal flow sensor optimized for the use in heating ventilating and air conditioning (HVAC) systems is presented. The fabrication of the transducer is exclusively based on printed circuit board technology to keep costs low and allow for easy handling and replacement. The measurement principle utilizes a calorimetric principle with thermoresistive heat transfer. The thermistors form a Wheatstone bridge while the heating element is supplied with a constant current. The AC bridge output voltage is a function of the flow offering adequate sensitivity and a suitable measurement range for HVAC systems. The main experiments focus on flow measurements with a Lock-In amplifier technique to evaluate the measurement range and sensitivity. Based on prior results for time constants, output voltage, sensitivity, etc., the sensor design has been optimized.

Thermal flow sensors based on printed circuit board technology

Measurement of air flows is an important task in many process monitoring systems. In applications like control of ventilation and air conditioning systems, robustness, ease of use, and cost are important issues calling for simple and effective sensor design. This paper investigates the use of commercial-off-the-shelf printed circuit board technologies for the fabrication of calorimetric flow sensors. Such sensors are known to be sensitive when being implemented using thin-film technology. The paper reviews the operation principle of thermal flow sensors and their performance in micromachined silicon technology for comparison. Subsequently, a similar design is introduced where heating and temperature sensing elements are made from standard copper traces on a flexible PCB substrate. Simulation studies demonstrate the basic viability of this approach, even if it might entail some performance penalties. First experimental data of sensor prototypes show that the repeatability of the PCB manufacturing processes is basically sufficient for using copper traces as sensors, but leaves also room for future improvement in both technology and sensor design.

Towards low-cost printed flow sensors

Air conditioning systems need permanent monitoring of the mass and energy flows in the air ducts to assess their proper operation and detect and correct changes that may occur over time. This is a prerequisite for energy efficiency and demanded by recent legislation like the Energy Performance of Buildings Directive issued by the European Union. Such distributed monitoring systems require low-cost and robust flow sensors that need not be extremely precise, but should give a good indication of the flow distribution within the air conditioning system. In this paper we present a technology feasibility study to implement flow sensors based on thick-film thermopiles printed by silk screen printing on a plastic carrier film. Finite element simulation studies prove the viability of the sensor concept, and first samples of the printed Ag-Ni thermopiles demonstrate the feasibility of the production technology.

Using PCB technology for calorimetric water flow sensing in HVAC systems - a feasibility study

Optimal operation of heating, ventilation, and air conditioning (HVAC) systems can benefit from proper monitoring of the flows in the air ducts and water pipes. For large installations, this requires a large number of networked, Internet of Things (IoT) inspired sensors performing coordinated data acquisition. Cost-effectiveness and robustness are major issues for the design of such sensors. This paper investigates calorimetric flow sensors based on printed circuit board technology. While such sensors have been shown to be feasible for air flow measurement, the applicability for water flows has not been addressed yet because the thermal short circuit due to the high thermal conductivity of the fluid strongly influences the performance of the sensor. The sensor in this paper uses a modified calorimetric principle with thermoresistive heat transfer, where the sensing elements are implemented by simple copper leads. The sensor is scaled so as to fit across the diameter of the water pipe and thus have an averaging effect rather than a spot measurement. Finite element simulations as well as experimental results demonstrate that the flow- and temperature-induced chance of the resistance values is small, but sufficiently large to be measurable.

PCB-integrated flow sensors — How good is state of the art technology?

Printed circuit board technology is today well established and inexpensive, but achieves also remarkably high precision. This makes this technology interesting for the fabrication of sensors, especially when cost-effectiveness is a concern. However, since PCB technology is not actually optimized for this purpose, the question arises how reliable and repeatable the production processes are when it comes to producing acceptable quality. In this paper, we investigate calorimetric flow sensors for air conditioning monitoring, implemented by state of the art PCB technology. After demonstrating that such sensors can indeed work as expected, we examine the influence of process variations on the electrical parameters of the sensor. Using data from two different fabrication runs, we find that standard processes can yield sensor devices within a 10% tolerance range, which is sufficient for the target application.

Characterization of a thermopile-based calorimetric flow sensor

Calorimetric flow sensors are easy to fabricate and can be tailored in length if appropriate technologies are used. Such long devices can be favorably employed, e.g., in ventilation systems to judge the distribution of the mass flow. This paper presents a flow sensor based on Ag-Ni thermopiles printed on a flexible PET substrate. It reviews the basic sensor principle and its feedback controlled operation where the heating power is adjusted according to the flow velocity, which is imperative to achieve a reasonable dynamic range. Characterization data in a flow channel are compared to simulation results from a 3D FEM approach, demonstrating the feasibility of the sensor.

MEMS Micro-Wire Magnetic Field Detection Method at CERN

This paper reports a novel construction of a micromachined MEMS magnetometer characterized by static magnetic fields of CERNs reference dipole with a custom made capacitive read-out. The magnetic flux density is characterized via the vibration modes of the MEMS structure, which are sensed capacitively. The device consists of a single-crystal silicon clamped-free plate (cantilever) carrying a thin conductor. The cantilever and the thin film metal electrodes are separated by a small gap, forming a vibrating plate capacitor. Movements of the cantilever are read out conveniently by electronic circuits. A static magnetic field generates a force density acting on the conductor that alternates according to the frequency of the current. When the electrical current is known, the deflection amplitude of the cantilever is a measure of the component of the magnetic flux density that points perpendicular to the current. The highest vibration amplitudes are expected, in the vicinity of resonance frequencies of the micromachined structure. At ambient pressure, the prototype sensor has a measured resonance frequency of 3.8 kHz for the fundamental mode and 20 kHz for the first antisymmetric mode. In experiments, the magnetic flux of the dipole has been characterized between 0.1 and 1 T, with a relative uncertainty of 3 × 10-4.

MEMS μ-wire magnetic field detection method@CERN

This work reports a novel construction of a micromachined MEMS magnetometer detecting static magnetic fields of CERNs reference dipole with a custom made capacitive read-out. The magnetic flux density is characterized via vibration modes of the MEMS structure which are sensed capacitively. The device consists of a single-crystal silicon clamped-free plate (cantilever) carrying a thin conductor. The cantilever and thin film metal electrodes are separated by a small gap, building a vibrating plate capacitor. Movements of the cantilever are read out conveniently by electronic circuits. A static magnetic field generates a force density acting on the conductor that alternates according to the frequency of the current. By knowing the electrical current, the deflection amplitude of the cantilever is a measure of the component of the magnetic flux density that points perpendicular to the current. The highest vibration amplitudes are expected, of course, in the vicinity of resonance frequencies of the micromachined structure. At ambient pressure the prototype sensor has a measured resonance frequency of 3.8 kHz for the fundamental mode and 20 kHz for the first antisymmetric mode. In experiments, the magnetic flux of the dipole has been characterized between 0.1 and 1 T, with a relative uncertainty of 3·10-4.