Tag Archives: thermal analysis

How To Place the ATS Candlestick Sensor For Thermal Analysis

Posted on June 30, 2011 by | Leave a comment

ATS’s Candlestick Sensor is our best selling sensor to collect air temperature and air velocity in thermal analysis. Like all of our thermal engineering instruments, ATS developed our Candlestick sensor out of necessity: we were simply breaking too many standard sensors and needed a more robust and accurate sensor. And the Candlestick Sensor was born!

Many of our customers often ask how our thermal engineers place the Candlestick Sensor in a wind tunnel in order to analyze a heat sink or other device. In this one minute video, Greg shows you just how we do it.

Leave a comment

Posted in heat sink design, Thermal Analysis, thermal engineering, Thermal Research

Tagged , , ,

Why Temperature is Critical in Thermal Management

Posted on May 18, 2011 by | 9 comments

Last week in this series on How to Select a Heat Sink for an OEM Project, we talked about why thermal management is a challenge to design for. This week we want to talk about why temperature is critical in Thermal Management.

The fact that temperature is critical in thermal management would seem self-evident, but, as with many things in thermal management, there’s more here than meets the eyes.

Power dissipation from electronics is on the rise, and so is its consequence on temperature. As a result, accurate temperature measurement is playing a larger role in the successful launch of new products.

Figure 1 shows a typical flow chart for a products design cycle [1]. Thermal engineering is required in three distinct areas: Concept, Prototype, and Verification.

The Role of Thermal Management in the Product Design Cycle

At the Concept level, thermal analysis is performed to ascertain the design feasibility and move the product to the Prototype stage. Here, the product is assembled and temperature measurements are taken to ensure the design meets the intended specs while there is a level of system functionality. If the design passes this stage, the product is fabricated. Then, the fully-functional system is checked for adherence to its intended design features while it is stressed at elevated temperatures. This is part of the Verification stage.

At all three stages, accurate knowledge of temperature is needed to ensure the system meets expected performance levels. An engineer designing an MRI system certainly wouldn’t want to include non-existing, extra features in the digital image as a result of excess temperature. Nor, by analogy, would someone transferring funds in a bank transaction want their electronics to place extra zeros in the transfer amount because of temperature overshoots in the system.

Equally important is the expected life of an electronics system. Every company wants to ensure that its products will successfully function in their intended environment. And every company wants their products to be first on the market. To support these goals, a fair amount of reliability calculations must be performed.

Continue reading →

9 Comments

Posted in heat sink, How to Select a Heat Sink, Thermal Analysis

Tagged , ,

What is electronics thermal management?

Posted on January 6, 2011 by | Leave a comment

We talk a lot here on the ATS Thermal Management blog about thermal management. And there’s a good reason for that of course! That’s what we are fanatical about. Keeping electronics cool so they operate at their best design point.

But, after you peel back boiling points, forced thermal spreaders, heat sinks, liquid cooling, thermal interface material, and more you are left with one critical, salient point about what is electronics thermal management.

To ensure that the device junction temperature (Tj) stays below a set limit.

What is a junction? The Hottest Spot on a Chip

this photo shows the semiconductor junction temperature hot spot

When semiconductor designers make a chip, especially a complex ASIC or something like an Intel server processor, these chips are effectively systems. Packed with circuits, and often in very dense packages, certain parts of the chip have sections that operate with greater frequency than other parts.  The result, those “spots” or “junctions” are very hot.  And so, cooling that junction is the key to all this Thermal Management. That’s our goal.

In fact, the first step in really getting the right solution to your projects thermal challenge is to determine it’s junction temperature. Here’s some handy helps to get you there….

How to calculate a semiconductor junction temperature part 1

How to calculate a semiconductor junction temperature part 2

Once you’ve calculated your junction temperature, you can then have a much better chance of choosing the right heat sink.

Of course, if you ever need help with this ATS is here. You can email us at [email protected] or give us a call at 781-769-2800 We’re always happy to help with your thermal management projects.

Leave a comment

Posted in thermal management, Thermal Science

Tagged , ,

Managing to the Junction Temperature for Thermal Management of Telecom and Datacom Equipment

Posted on November 3, 2010 by | 16 comments

Kontron has just released their first Cavium OCTEON® II AdvancedMC packet processor module, the AM2411. Kontron’s module features the Cavium Networks Octeon II CPU. It’s an incredibly powerful network processor and Kontron has really taken advantage of it to create an industry thumping feature set. This kind of product will serve telecomm companies very well in creating 4G networks using either LTE or WiMAX. The board designers clearly made the product durable as it has passed testing for Telcordia GR-1089, GR-63, IEC 60950-1, EN/CSA/ UL 60950-1. And this quote from their datasheet really tells it all regarding the 4211’s design point, quality: “This board is designed to meet NEBS Level 3, Earthquake Zone 4”

Board quality and specifications are not going to be a question with this product!

What is going to be a consideration is what this product is like in a chassis full of other boards operating at peak performance. There is no question Kontron has done a great job designing their board, but, their board now becomes a component in an integrated system. Such an integration of Commercial Off the Shelf Components (COTS)is almost always a challenge across a number of technical areas.

Trenton Technologies wrote a bit on this in their blog back in July of 2010 with their post, “Can You Really Simplify Integration of Industrial Computer Systems?” In that post they noted that 6 key factors to decided if a COTS solution could be used in an application, those six points are:

  1. System location requirements
  2. Projected service life of the system
  3. Number of option cards needed in the computer
  4. System expansion requirements
  5. System power and fail-over requirements
  6. System O/S and application software solution requirements

But the one piece they missed was the overall system thermal load. So let’s talk about that a bit. First, the key target temperature to keep in mind is the junction temperature. The junction temperature is the temperature of the silicon die within the package of the device when the device is powered. The junction temperature can also be referred to as the operating temperature. The goal of thermal management is to manage the heat to the junction temperature.

What is semiconductor junction temperature and how do you manage to it

A successful thermal design requires that the junction temperatures of all critical devices in a system be sufficiently below their critical level in the worst-case ambient temperature. Otherwise, higher temperatures may result in data transmission bit errors and/or a decrease in a system’s life expectancy. Thermal coupling and non-uniform PCB layout make this determination a complicated process.

The list of thermal parameters that a complete system has to manage to help reduce the junction temperature on a device are pretty long:

  1. Thermal coupling within the system and surrounding equipment
  2. System standardization (e.g., the ATCA Standard)
  3. Constrained space
  4. EMI/EMC requirements for high frequency devices, boards and packaging
  5. Acoustic noise/li>
  6. Limited air flow
  7. Rigid performance standards (e.g., 72 hours operation at 55oC)
  8. Non-uniform power distribution and congested PCBs
  9. Service Level Agreement(e.g., system operational within 4 hours of failure)

The following table shows the approach, domain, anticipated results, and the needed tools to successfully obtain the junction temperature of a device in the system.

Solution Order Package Level Expected Results Requirements and Tools
First System System flow distribution and boundary conditions for the card racks, T, V, and Pressure Measurement or
Second’ Card Rack (chassis) Boundary conditions for the PCB, and thermal coupling between the board and the rack Measurement or Simulation (CFD) and solid modeling (temperature gradient in the solid)
Third Board (PCB) Boundary conditions for the component on heat transfer and fluid flow Measurement of fluid flow distribution and board properties and board level solid modeling
Fourth Component (device or module) Boundary conditions for the Die (Tj) and its cooling solution Fluid flow and temperature measurement equipment; Heat sink; Interface materials and their properties;Solid modeling;Package material properties

Once the junction temperature is obtained by using two independent methods, it must be ensured that there is at least a 10% margin of safety in the design. Therefore, the following equation must be satisfied.

Junction temperature formula

Where

Tj, calculated = junction temperature as the result of above calculation.
Tj, spec = critical junction temperature specified by the manufacturer.
Ta, reference = reference ambient or approach air temperature.

With a properly determined junction temperature in hand, a cooling method can be selected for maintaining the desired performance. Depending on the data obtained from the table, we can choose from these options:

  • Natural convection
  • Forced convection (air-mover)
  • Active air cooling (not very common)
  • Jet impingement (air or liquid)
  • Advanced systems (liquid or refrigeration)

Although cooling by air is the most common and preferred system, liquid cooling has been used in unique circumstances. Regardless of the method selected, every cooling decision should consider the following parameters:

  • Cooling capacity – does it satisfy the junction temperature requirements?
  • Size – does it comply with the packaging requirements?
  • Regulatory requirements – does it meet the system and site implementation requirements (e.g., NEBS) ?
  • Reliability – does it meet the expected life requirements?
  • Budget – does it comply with the cost constraints imposed on the system?
  • Market availability – is it readily available? Can supply-chain requirements be met?

Obtaining a successful cooling solution is made possible by combining methodical thermal analysis (as delineated in our table) with the results from at least two independent approaches, and taking into account the above system parameters.

16 Comments

Posted in thermal management

Tagged , ,

Thermocouples for Thermal Analysis: what they are and how they work (part 2 of 2)

Posted on October 28, 2010 by | 5 comments

In part 1, we covered the basics behind what thermocouples are and how they work. In part 2, we’ll cover how thermocouples can be made and know when to select the right thermocouple for your project.

Thermocouples can be made of any two dissimilar metal wires, and their emf voltage depends on the composition of the chosen metals. However, what makes thermocouples so popular is that the materials used to construct them are restricted and their output emf’s have been standardized. Certain materials and combinations are better than the others, and some have basically become the standard for given temperature ranges. Table 1 lists some of the available thermocouples in the U.S. market.

Thermocouple Type Material Composition Temperature Range Uncertainity Color Code
T Cu vs. Constantan -250 to 350°C Greater of 1°C or 0.75% Blue-Red
K Chromel vs. Alumel -200 to 1250°C Greater of 2.2°C or 0.75% Yellow-Red
J Iron vs Constantan 0 to 750°C Greater of 2.2°C or 0.75% White-Red
R Platinum vs. Platinum-13% Rodium 0 to 1450°C Greater of 1.5°C or 0.25% None Established
S Platinum vs. Platinum-10% Rodium 0 to 1450°C Greater of 1.5°C or 0.25% None Established
C Tungsten 5% Rhenium vs. Tungsten 26% Rhenium 0 to 2320°C Greater of 4.5 °C to 425°C, 1% to 2320°C None Established
E Chromel vs. Constantan -200 to 900°C Greater of 1.7°C or 0.5% Purple-Red

Table 1: Different types of thermocouples

Selecting the right type of thermocouple for an application depends on many factors. These include sensitivity, temperature range, corrosion resistance, linearity of output voltage, and cost. For example, types R and S are relatively expensive and are not sensitive. However, they perform well at high temperatures up to 1768°C and are resistant to a number of corrosives. Type C thermocouples are suitable for higher temperature applications, but they are relatively expensive and corrode easily in an oxidizing environment. A Type T thermocouple is inexpensive and very sensitive, but will corrode at temperatures above 400°C. Type K is very popular for general use, relatively inexpensive, reasonably corrosion-resistant, and can be used at high temperatures, up to 1372°C. K-type thermocouples also have provide relatively linear output as compared to the other types [2].

The actual magnitude of the thermocouple emf is very small, and is in the order of few millivolts. At a given temperature, Type E has the highest output emf among common types, but this voltage is still measured in millivolts. The sensitivity of thermocouples is also relatively low. For instance, the voltage change per degree Fahrenheit from 38 to 93°C is only 36 microvolts. As a result, thermocouples require accurate and sensitive measuring devices and cannot be used for temperature changes of less than about 0.1°C. Traditionally, expensive voltage balancing potentiometers were used to measure emf. Today, a high quality digital voltmeter is sufficient [3].

The National Institute of Standards and Technology (NIST) has developed standard calibration curves for determining temperature based on the measured emf voltage. These data represent the output emf of thermocouples when an ice cold junction is used, and are incorporated in the memory of most DAQ systems.  Unfortunately, the temperature-voltage relationship of thermocouples is nonlinear and curve-fitted using polynomial functions. Obviously, the higher the order of the polynomial function, the higher the accuracy of temperature reading. The polynomial function should only be used inside the temperature range of the thermocouple type and should not be extrapolated. To save computational time, a lower order polynomial fit can be used for a smaller temperature range.

Thermocouple wires come in variety of sizes. Usually, the higher the temperature, the heavier should be the wire. As the size increases, however, the time response to temperature change increases. Therefore, some compromise between response and life may be required.

Thermocouples can be connected electrically in series or in parallel. When connected in series, the combination is usually called a thermopile, (whereas there is no particular name for thermocouples connected in parallel). A wiring schematic of a thermopile combination is shown in Figure 3.

Thermocouples example diagram

Figure 3 – Series-connected thermocouples forming a thermopile

The total output from n thermocouples will be equal to sum of the individual emf’s. The main purpose of using a thermopile rather than a single thermocouple is to obtain a more sensitive element. Parallel connection of thermocouples is used for averaging.

 

References:

  1. Omega Temperature Handbook, Omega Engineering, Inc. 2nd edition.
  2. Wheeler, A. and Ganji, A., Introduction to Engineering Experimentation, Prentice Hall Inc., pp. 240-246, 1996.
  3. Beckwith, T., Marangoni, R., and Lienhard, J., Mechanical Measurements, Fifth Edition, Addison Wesley Longman, pp. 676-685, 1993.

5 Comments

Posted in Thermal Analysis

Tagged , , ,