V. Jiménez

A conduction-convection design for liquid flow sensing

Abstract A modified hot-wire fluid-flow sensor design is described in which the convection of heat takes place at a distant point from the temperature sensor itself. The distant arrangement is also applied to the cold point of the flow meter. Thermal contact between the sensors themselves and the distant points is ensured by metal leads. This novel approach is implemented by using a low-cost packaging solution consisting of a lead frame and low-thermal-conductivity plastic epoxy encapsulation. The sensors are bipolar junction common-collector transistor arrays, the hot-point sensor being surrounded by an NiCr resistor. The system is completed by a sigma-delta thermoelectric converter which ensures the feedback loop and provides a digital readout. This device has been fabricated and tested and shows a sensing range of 0.2–91 min −1 water flow.

Pulsed Digital Oscillators for Electrostatic MEMS

This paper introduces a new actuation scheme for implementing Pulsed Digital Oscillators (PDOs) for electrostatic MEMS resonators. In this scheme, the capacitance of the device is biased with a voltage and it is periodically sampled. Short pulses of zero voltage are applied depending on the decisions taken by the oscillator loop. The paper discusses in detail the implementation of such electrostatic PDO (e-PDO) through a prototype and links the e-PDO to the conventional PDO theory. As an example, it is shown that with this actuation scheme it is possible to excite different resonances of the mechanical structure simply by changing the parameters of the feedback filter of the oscillator.

Simulation of flow sensors for home appliances

Hot-wire flow meters are currently usual as flow sensing devices. In this work, we explain the procedure used to simulate a water flow sensor for home appliances. The proposed system is composed of a thermally activated subsystem and an electronic subsystem which provides feedback and output read-out. The complete system has been fabricated, and the measurements corroborate the simulation procedure.

Low-cost thermal Σ-Δ air flow sensor

This paper describes the design and optimization of a hot-wire air flowmeter. A low-cost design of the packaging allows good thermal contact with the airflow, as well as good thermal isolation between the hot and cold points. It is a compact solution which allows easy PCB mounting and adaptation to standard-size small air pipes. The design has been optimized for low-cost applications. The sensor is read out by a thermal sigma-delta modulator. The dynamic range of this modulator has been extended by adding a constant power offset to its output. The fractal nature of the modulator response at low-clock frequencies is also experimentally shown.This paper describes the design and optimization of a hot-wire air flowmeter. A low-cost design of the packaging allows good thermal contact with the airflow, as well as good thermal isolation between the hot and cold points. It is a compact solution which allows easy PCB mounting and adaptation to standard-size small air pipes. The design has been optimized for low-cost applications. The sensor is read out by a thermal sigma-delta modulator. The dynamic range of this modulator has been extended by adding a constant power offset to its output. The fractal nature of the modulator response at low-clock frequencies is also experimentally shown.

Spherical Wind Sensor for the Atmosphere of Mars

A novel wind speed and direction sensor designed for the atmosphere of Mars is described. It is based on a spherical shell divided into four triangular sectors according to the central projection of tetrahedron onto the surface of the unit sphere. Each sector is individually controlled to be heated above the ambient temperature independently of the wind velocity and incidence angle. A convection heat rate model of four hot spherical triangles under forced wind has been built with finite element method thermal-fluidic simulations. The angular sensitivity of the tetrahedral sphere structure has been theoretically determined and compared with the tessellation of the sphere by four biangles. A 9-mm-diameter prototype has been assembled using 3-D printing of the spherical shell housing in the interior commercial platinum resistors connected to an extension of a custom design printed board. Measurements in Martian-like atmosphere demonstrate sensor responsiveness to the flow in the velocity range 1-13 m/s at 10-mBar CO2 pressure. Numerical modelization of the sensor behavior allows to devise an inverse algorithm to retrieve the wind direction data from the raw measurements of the power delivered to each spherical sector. The functionality of the inverse algorithm is also demonstrated.

Design end fabrication of a low cost water flow meter

A novel low-cost system consisting of a hot-wire water flow meter of capacity up to 9 liter/minute is presented. The flow does not come into direct contact with the silicon sensors. Thermal contact is ensured by pins in a lead frame. This system is less sensitive to the geometry and relative position of the sensor and the pipe, and simpler to pack, than previous solutions. This paper gives details of the design, fabrication and performance of the system extending our previous work reporting the basic ideas in a qualitative way (1997) and preliminary simulation results (1996).

Heat Flow Dynamics in Thermal Systems Described by Diffusive Representation

The objective of this paper is to analyze the dynamics of heat flow in thermal structures working under constant temperature operation. This analysis is made using the tools of sliding mode controllers. The theory is developed considering that the thermal system can be described using diffusive representation. The experimental corroboration has been made with a prototype of a wind sensor for Mars atmosphere being controlled by a thermal sigma-delta modulator. This sensor structure allows to analyze the time-varying case experimentally since changes in wind conditions imply changes in the corresponding thermal models. The diffusive symbols of the experimental structures have been obtained from open-loop measurements in which pseudorandom binary sequences of heat are injected in the sensor. With the proposed approach, it is possible to predict heat flux transient waveforms in systems described by any arbitrary number of poles. This allows for the first time the analysis of lumped and distributed systems without any limitation on the number of poles describing it.

Low pressure spherical thermal anemometer for space missions

A novel spherically shaped thermal anemometer for low pressure, Mars-like conditions, is described. The concept has been designed using finite element multyphysics simulations to find out the thermal conductance to the ambient for varying conditions of wind speed and direction and ambient pressure and temperature. A prototype 1cm diameter suitable to work under these environment in the range 0.25-10m/s speed has been build using 3D printing and tested inside a low pressure chamber. The protopype shown has two separated hemispheres, independently heated above the ambient temperature, providing angle sensitivity in one plane. Measurements of the heating power in both hemispheres required to keep an overheat of 30K are shown as a function of the wind direction showing good sensitivity at 0.5m/s. One improvement of this sensor is the means provided to also heat the core of the sphere where the circuit board is located thereby avoiding most of the conduction losses to the supports. The concept is scalable to other wind speed and pressure conditions and also to full 3D measurements.

Low-cost thermal /spl Sigma/-/spl Delta/ air flow sensor

This paper describes the design and optimization of a hot-wire air flowmeter. A low-cost design of the packaging allows good thermal contact with the airflow, as well as good thermal isolation between the hot and cold points. It is a compact solution which allows easy PCB mounting and adaptation to standard-size small air pipes. The design has been optimized for low-cost applications. The sensor is read out by a thermal sigma-delta modulator. The dynamic range of this modulator has been extended by adding a constant power offset to its output. The fractal nature of the modulator response at low-clock frequencies is also experimentally shown.This paper describes the design and optimization of a hot-wire air flowmeter. A low-cost design of the packaging allows good thermal contact with the airflow, as well as good thermal isolation between the hot and cold points. It is a compact solution which allows easy PCB mounting and adaptation to standard-size small air pipes. The design has been optimized for low-cost applications. The sensor is read out by a thermal sigma-delta modulator. The dynamic range of this modulator has been extended by adding a constant power offset to its output. The fractal nature of the modulator response at low-clock frequencies is also experimentally shown.