Category Archives: Sensor

An Instrument for Measuring Air Velocity, Pressure and Temperature in Electronics Enclosures

For engineer-level thermal management studies, the iQ-200 instrument from Advanced Thermal Solutions, Inc, ATS, can simultaneously measure air velocity, air pressure and the temperature of components and surrounding air at multiple locations inside electronic systems. This enables users to obtain full and accurate profiles of components, heat sinks, PCBs and other electronics hardware to enable more effective thermal management.

Developed by Advanced Thermal Solutions, Inc., ATS, the iQ-200 system simultaneously captures data from up to 12 J-type thermocouples, 16 air/velocity sensors, and four pressure sensors.

The thermocouples provide surface area temperature measurements on heat spreaders, component packages, housing hardware, and elsewhere to track heat flow or detect hot spots. Temperature data is tracked from -40 to 750°C. The sensors (available separately) measure both air temperature and velocity at multiple points allowing a detailed analysis of airflow.

Candlestick Sensor from ATS

Thin, low profile ATS candlestick sensors can be easily positioned throughout a system under test and measure airflow from -10 to +6°C. Air velocity is measured from natural convection up to 6 m/s (1200 ft/min). The iQ-200 can be factory modified to measure airflow to 50 m/s (10,000 ft/min) and air temperature up to 85°C. Four differential transducers capture pressure drop data along circuit cards, assemblies and orifice plates. Standard pressure measurement capabilities range from 0- 1,034 Pa (0 – 0.15 psi).

The ATS iQ-200 system comes preloaded with user-friendly iSTAGE application software which effectively manages incoming data from the various sensor devices, and allows rich graphic presentation on monitors and captured on videos or documents. The iQ-200 connects via USB to any conventional PC for convenient data management, storage and sharing.

More information on the iQ-200 system from ATS can be found on Qats.com (http://www.qats.com/products/Temperature-and-Velocity-Measurement/Instruments/iQ-200/2632.aspx), or by calling 781-769-2800.

New Electronics Cooling Webinars are Open for Second Quarter of 2012

Each month during the second quarter of 2012, ATS will present a technical webinar covering different topics within the dynamic world of electronics cooling. Each of these one-hour, online tutorials will include detailed visuals, definitions, instructions, case studies and references. One or more ATS PhD-level thermal engineers will be presenting live. Viewers will be able to key in questions during and after the presentation.

Each Q2 webinar is planned for a Thursday afternoon (ET) late in the month. These are the second quarter topics for the ATS webinars:

April 26, 2012 at 2:00 p.m. ET

How to Perform and Understand Air Velocity Measurement within Electronics Systems

Participants will learn about the importance of measuring air velocity in a system, the instruments necessary for obtaining useful measurements and where these velocities should be recorded.

May 24, 2012 at 2:00 p.m. ET

CFD as a Tool to Perform Heat Sink and System Modeling

Computational Fluid Dynamics (CFD) tools have become indispensable simulation tools, enabling design engineers to confront electronics cooling challenges on demand. Some tips and tricks are invaluable in performing these analyses. Among them: the simplest methods of preparing a CFD model; the best techniques for meshing; and how to model a systems components, such as fans and perforated plates. Attendees will learn about common and not-so-common issues in CFD, and how to overcome them.

June 28, 2012 at 2:00 p.m. ET

Heat Sink Selection Made Easy

As heat dissipation needs for electronic devices rapidly grow, choosing the right heat sink the first time is essential. With so many application requirements and heat sink options, this can be a daunting task. In this webinar, attendees will learn about the importance of system airflow and its impact on heat sink design; attachment methods; and how to solve thermal design challenges.

Seats at each of these webinars are free, but limited. Registration is available online at http://www.qats.com, or by calling 1-781-949-2522.

Sensors for Temperature Measurement and Their Application (part 3 of 3)

Today we conclude our three part series, “Sensors for Temperature Measurement and Their Application”. We’ll be talking about the last three sensor types: Infrared or Radiation, Fluorescent Detector and Liquid Crystal. To catch up on the series, you can click to Part 1 of our series or click over to Part 2 of our series.

4. Infrared Thermography

Infrared thermography works on the basis of the IR waves emitted from a heated surface. The infrared system captures the waves, and based on internal calibration converts them into temperature. The following are required for IR-based measurements:

  • Infrared imaging system — The market offers a broad range, but a worthy system starts at around $30-70k. For IR microscopy (down to 5mm only-lower limit of IR wave-length), the system starts at $180k.
  • Signal processing equipment.
  • Knowledge of emissivity if the test specimen must be coated with a known emissivity material.
  • Calibration.

Figures 5a and 5b show a typical IR image of heat-emitting surfaces:

IR Image of PCB Board In Forced Convection Air Flow5a shows and IR image of a PCB in forced convection air flow[3]

PCB Board IR Image in natural convection air flow5b shows and IR image of a PCB in forced natural convection air flow[3]

 

The following points are noteworthy when using an IR camera for temperature measurement:

  • Application accuracy is a function of emissivity.
  • The measurement situation must duplicate the actual environment, as far as air velocity, temperature and air flow distribution are concerned.
  • The IR camera is sensitive to reflected radiation.
  • Carbon dioxide and water vapor absorb significant energy and may cause significant error.
  • In an electronics application, surfaces typically have different emissivities thus, one must make the emissivity uniform before measurement of known emissivity (black paint or powder).
  • In most IR equipment, the temperature readout is the average over an area. Therefore, temperature peaks may be ignored as the result of integration. To remedy the situation, better IR optics must be used to reduce the area where integration occurs.

5. Optical Probes

Optical sensors are light-emitting devices that illuminate the test body with source radiation, and can detect reflected radiation, or simulated radiation such as fluorescence. Although not broadly used, optical probes are used at the die or component level. Figure 6 shows one such a probe.

Optical probe for temperature measurementFigure 6. Optical Probe For Surface Temperature Measurement The Probe Either Touches The Surface Or Captures The Reflected light From A Fluorescent Treated Surface.

6. Liquid Crystal Thermography

LC thermography works on the basis of visible light reflected from a surface treated with the LC material. The system captures the reflected wavelengths, and based on internal calibration, converts them into temperatures. Liquid crystals (LCs) are cholesteric materials. When applied to a heated surface they realign and reflect light at a different wavelength. The reflected light shows the standard colors seen in a rainbow. Figure 7 shows the application of LCs on an IC.

Liquid crystal color display on a semiconductorFigure 7. Color display of liquid crystal applied on an IC. Blue reveals the circuit’s hottest point, and black shows that the temperature is outside the range of the crystal material [3].

The following are salient features of LC material:

  • Liquid crystals are organic compounds that can be poured like a liquid, yet reflect light like a crystal.
  • Changes in LC optical properties can be produced by externally applied fields (e.g., electrical, magnetic, and thermal).
  • Cholesteric liquid crystals progressively exhibit all colors of the visible spectrum when heated over their event temperature range.
  • Width and placement of the event temperature range can be controlled by selecting and mixing the appropriate liquid crystals.
  • Liquid crystals are commercially available with event temperatures ranging from below 0oC to 160oC, with spans ranging from 1 to 50oC.

An LC thermography system such as the one shown in Figure 8 can provide a very effective temperature-mapping system.

thermVIEW LCD Instrument from Q ATS

Figure 8: The thermVIEW System for Macro and Microscopic (down to 1um) Surface Temperature Measurement[4]

Figure 9 shows a typical result of LC thermography at die level:

Temperature distribution across a memory chip
Figure 9. Temperature distribution across a memory chip (5 x 5 mm) at Tambient = 25oC, as shown using Liquid Crystal Thermography [3].

Like any other system for temperature measurement, LC thermography offers distinct advantages and disadvantages. One salient advantage of LC thermography is that its not dependent on surface emissivity. A second is that at micron and submicron levels, though not a trivial task, LC thermography allows easier and less costly temperature measurements while enabling 1µm or smaller spatial resolution. One disadvantage of LC thermography is that it is not a pick-up-and-measure system like IR. One must apply the calibrated liquid crystal material to a surface in order to perform the measurement. But, this is similar to the IR system, in that you need to make the surface emissivity uniform if the measured surface has multi-emissivity (e.g., a die or PCB).

In this article, we reviewed six different probes/techniques for temperature measurement. It would be a missed opportunity not to include a word on calibration. Irrespective of the types of measurement and sensors one uses, calibration is of utmost importance. Pay special attention to the calibration process and ensure that the sensors are properly calibrated. Further, one needs to ensure that the chosen sensor is suitable for the type of measurement. As Prof. Frank White states in his Viscous Flow book, Bad data is worse than no data at all [5].

To catch up on the series or read from the start, you can click to Part 1 of our series or click over to Part 2 of our series.

References

  1. Klinger, D., Nakada, Y., Menendez, M., AT&T Reliability Manual, Van Nostrand Reinhold, 1990.
  2. Azar, K., Thermal Measurement in Electronics Cooling, CRC Press, 1997.
  3. Advanced Thermal Solutions, Inc., Tutorial Series, Principles of Temperature Measurement.
  4. thermVIEW System, product of Advanced Thermal Solutions, Inc.
  5. White, F., Viscous Fluid Flow, McGraw-Hill, 3rd Ed., 2005.

If you are in need of sensors for thermal measurement, click now to ATS’ sensor family. To learn more about ATS ‘ thermVIEW liquid crystal thermal analysis system, click to thermVIEW System. You can also email or call us with your questions on temperature measurement and one of our engineers will be happy to help you. Email us at ats-hq@qats.com or call us at 781-769-2800.

Sensors for Temperature Measurement and Their Application (part 2 of 3)

In part 1 of our 3 part series, “Sensors for Temperature Measurement and their Application”, we introduced various kinds of sensors and discussed the linear and exponential relationships that temperature has in the operation of the electronic components.In part 2 we’ll cover three specific sensor types: the resistor thermometer, thermocouple and diode transistor. In part 3 of our 3 part series we’ll finish up and discuss infrared or radiation, flu0rescent detector, and liquid crystal.

1. Resistance Thermometer

With these sensors, the resistance of the sensing element changes with temperature. The sensors come in two primary forms: thermistors (lightly doped semiconductors) and metal resistors. Equations 3 and 4 represent the relationships between resistance and temperature for these two sensors, respectively:

equation for the relationship between resistance and temperatureFigure 1 shows a surface-mounted RTD (resistance temperature detector) that can be installed onto a surface for temperature measurement:

Surface mounted RTDFigure 1: Surface mounted RTD (photo courtesy of RDF Corporation)

The following must be considered when using these types of sensors:

  1. The sensor (resistor) must be in intimate contact with the test specimen solder or careful epoxy is recommended.
  2. The sensor must be placed in an isothermal region constant temperature over the sensor.
  3. The resistor power dissipation (if in voltage mode) must be minimized to not impact the problem.
  4. This sensor is suitable for part-level measurement as it can be embedded directly on the die.

2. Thermocouples (TC)

These sensors are far and away the most commonly used devices in the field. Wide flexibility and broad availability enable their use for a variety of temperature measurements. TCs work on the principle that bringing together two wires of different elements or alloys produces a voltage as a result of temperature. Equation 5 provides the governing principle for TCs:

Thermocouple governing principlesTable 2 shows some of the typical TC types that are used in electronics thermal measurement.

Thermocouple types and their respective voltage outputsTable 2: Thermocouple Types and Their Respective Voltage Outputs [2]

Of the TC types shown above, E, J, K and T are the most commonly used. Many thermocouple meters on the market can use all of these sensors interchangeably. That’s because the voltage output of these TCs is in the same range; hence, the internal electronics can be designed to accommodate each of them.

There are some unique features about each sensor type that one needs to know. For example:

  • E-type: Though accurate, has a limited range.
  • J-type: Should not be used in a humid environment, since the iron component of the TC will oxidize, resulting in erroneous output.
  • K-type: Though widely used, the voltage output can be negatively impacted if the wire kinks.
  • T-type: Can be an effective heat transfer medium, because of its copper component, either as a fin or a conductor.

It is also important to note that thermocouples measure temperature at the point where the two wires are connected. The smaller the junction, the more precise the temperature that is read. A large TC junction will result in the temperature being averaged over its entire area. Multiple junctions, as shown in Figure 2, will have the same impact. In Figure 2, the multi-junction created as a result of twisting the wires prior to spot-welding the ends (the TC below), creates a significantly larger junction. Whether measuring surface or fluid temperatures, the number reported by this TC will report an average temperature over a 2-3mm junction length.

Thermocouple errors can be attributed to the following areas:

  • Poor junction connection
  • Galvanic action
  • Thermal shunting
  • Electrical noise
  • Installation problem due to tester

 Single and Multi-Joint ThermocouplesFigure 2: Single and Multi-junction Thermocouple Sensors [3]

Of the errors listed above, electrical noise is uniquely problematic, especially in todays high frequency equipment. A TC can be used in a 4-wire format to resolve the electronic noise that may affect the reported temperature. Using a 4-wire thermocouple, as shown in Figure 3, we can measure temperature and electrical noise.

Let us consider a J-type thermocouple formed of Iron and Constantan. All four wires are spot-welded together to form the TC junction. The temperature can be read across any of the Iron and Constantan combinations, and the electronic noise can be read across either the two Irons or the two Constantans. Because two similar metals cannot create the Seebeck effect (convert thermal differentials to electric voltage), whatever signal is measured on these wires is the electronic noise in the measurement domain.

 Four-wire thermocouple diagramFigure 3: Four-wire Thermocouple System for the Measurement of Electronic Noise and Temperature

Measuring surface temperature is always a challenging process. The following steps will help to increase the accuracy of such measurements:

  • Keep installation size as small as possible.
  • To reduce conduction errors, bring thermocouple wires away from the junction, along an isotherm for at least 20 wire diameters.
  • Locate the measuring junction as close to the surface as possible.
  • To avoid changes in convective or radiative heat transfer, design the installation so that it causes minimum disturbance to any fluid flow or the least possible change in the emissivity of the surface.
  • Reduce the thermal resistance between the measuring junction and surface to as low a value as possible.

3. Diode or Transistor

Diodes and transistors are parts whose electrical properties are a function of temperature. Diodes are broadly used for temperature measurement, either as embedded sensors in functional devices or as a thermal test chips. Figure 4 shows one such thermal test chip for device-level simulation.

Thermal test chipFigure 4. Thermal Test Chip [3]

The following depicts the general considerations for usage of semiconductor materials for temperature measurement:

  • Every semiconductor device has at least one electrical parameter that is a function of temperature.
  • Thermal test chips use the thermally sensitive parameter of semiconductor devices to measure chip junction temperature.
  • Separate heating and sensing elements are usually used to avoid for electrical switching.
  • Thermal calibration of the sensing device is necessary.
  • Thermal test chips provide an effective means of measuring chip junction temperature in an actual package configuration.
  • Use of materials is subject to availability/suitability for the intended package application.

We’ll conclude our series with part 3, addressing infrared thermography, optical probes and liquid crystal thermography

References:
1. Klinger, D., Nakada, Y., Menendez, M., AT&T Reliability Manual,
Van Nostrand Reinhold, 1990.
2. Azar, K., Thermal Measurement in Electronics Cooling, CRC Press,
1997.
3. Advanced Thermal Solutions, Inc., Tutorial Series, Principles of
Temperature Measurement.
4. thermVIEW System, product of Advanced Thermal Solutions, Inc.
5. White, F., Viscous Fluid Flow, McGraw-Hill, 3rd Ed., 2005.

If you are in need of sensors for thermal measurement, click now to ATS’ sensor family. Tired of using thermocouples that are finicky and breakable? Try ATS’ spot sensor. It’s durable and cost effective.  Learn more by clicking to ATS Spot Sensor. You can also email or call us with your questions on temperature measurement and one of our engineers will be happy to help you. Email us at ats-hq@qats.com or call us at 781-769-2800.

Sensors for Temperature Measurement and Their Application (part 1 of 3)

Today we start a three part series on on Temperature Measurement and Their Application. There is an IT axiom that says, “garbage in, garbage out” and no where is that more true than in thermal analysis. If you measure your data incorrectly, you’ll have no chance of getting the data you need to design the best thermal management solution for your application.

In todays market, it is very rare to see electronic equipment that has not undergone extensive thermal evaluation, either by measurement or simulation. Inevitably, the temperature of the device junction or case, or the enclosure, has been measured to ensure that the system will operate to its intended specifications. A quick look at the equations associated with stress in a lead wire, and with the acceleration factor used in reliability calculations, will show why temperature plays such an important role in electronics equipment [1].

equations showing the linear and exponential relationship of temperatureEquations 1 and 2 clearly demonstrate the linear and exponential relationships that temperature has in the operation of the electronic components. Concurrently, simulation tools are used extensively in todays thermal design. But, due to the complexity of the electronics packaging and composite nature of the materials used, the simulation data must be verified in order to ensure reliable data is obtained. In this article, we present different sensors and their application domains in electronics thermal management.

Table 1 shows six primary sensors used in temperature measurement:

table showing various temperature transducers for thermal analysisTable 1. Standard Temperature Transducers [2]

In part 2 of our three part series, we’ll start consider each sensor in detail, focusing on the resistor thermometer, thermocouple and diode transistor.

References:
1. Klinger, D., Nakada, Y., Menendez, M., AT&T Reliability Manual,
Van Nostrand Reinhold, 1990.
2. Azar, K., Thermal Measurement in Electronics Cooling, CRC Press,
1997.
3. Advanced Thermal Solutions, Inc., Tutorial Series, Principles of
Temperature Measurement.
4. thermVIEW System, product of Advanced Thermal Solutions, Inc.
5. White, F., Viscous Fluid Flow, McGraw-Hill, 3rd Ed., 2005.

If you are in need of sensors for thermal measurement, click now to ATS’ sensor family. Including our industry leading Candlestick Sensor.You can also email or call us with your questions on temperature measurement and one of our engineers will be happy to help you. Email us at ats-hq@qats.com or call us at 781-769-2800.