Spot Cooling with Vortex Tubes – a Viable Option

RTD’s v. Thermocouples, which is best?

RTDs v. Thermocouples

The question is often asked, “what is the best temperature sensor for my temperature testing or environmental testing application?”

The answers can vary a lot but the two main leaders of the pack are RTDs (Resistance Temperature Detector) followed by Thermocouples.

If you are looking for the short answer of which is best, it is RTD’s but here is a little more to the story

The primary reasons RTD are best:

Better long-term stability, more linear response, More gain- that is more signal change for a given temperature change, also they have easier to manage lead wire connections.

So why would someone choose a Thermocouple over an RTD?

Arguments in favor of Thermocouples:

The number one reason – Thermocouples are cheaper.  Market demands often dictate cheaper.

Thermocouples generally hold up better in environments of severe vibration or thermal shock.

They typically are better for point sensing instead of sensing a larger area or air temperature.

Stepping back a little: There are more tradeoffs, but those are the main considerations. To be fair, there are other viable temperature sensors for many applications but just a short history lesson first. German Physicist Thomas Johann Seebeck first discovered in 1821 that any junction of dissimilar metals will produce an electric potential related to temperature.  Thus the name for a device that senses temperature by the coupling of two metals.  The result was the first electronic temperature sensing device and it could be designed to work without any external power source. A couple of issues about how this sensor works are: 1) The carefully controlled types of metals in the sensor used have to be continued all the way to the instrument that is measuring the temperature. 2) The instrument itself requires an additional thermocouple to be used as a fixed reference.  Since the temperature of the fixed reference usually changes, often an additional RTD or bandgap sensor is used to compensate for the thermocouple calibration.

In 1871 Sir William Siemens discovered the Resistance Temperature Detector or RTD.  He found that Platinum wire and other materials have a well-defined relationship between temperature and the electrical resistance of the material.  The relationship between temperature and ohms is much more linear and easier to work with than the relationship between volts and temperature with thermocouples.

Thermistors are simply a specific type of RTD, often made with a polymer or cheaper materials than Platinum.  They typically have a narrower temperature range and have less long-term accuracy. Also as a side note, Thermistors most often but not always have a Negative Temperature Coefficient (NTC), meaning that they have less resistance as temperatures get higher.  This feature makes them handy for several special compensation applications, for example canceling out other factors that increase with temperature.

The Bandgap (transistor) Temperature Sensor is one other significant, modern temperature sensor.  This device makes use of the known effect that the forward Base to Emitter voltage of any transistor is directly and predictably affected by temperature.  These devices although rarely used in applications such as temperature chambers are popular because they are inexpensive and can be easily integrated into other silicon circuits making internal component temperature sensing very simple and affordable.  Their usability is primarily limited to the range of -40C to +200C.

RTDs are widely accepted as the preferred temperature sensor for long-term repeatability.  It is my position that they will continue to prevail as “the best quality sensor” however I do hear some interesting reports that there have been recent improvements to the technology of making and reading thermocouples.  I think the jury is still out but I would be interested to hear what experiences others have had with a so-called new generation of thermocouples and available accompanying 24-bit A/D sensing circuits.

As a final note, there are several distinctions between types of thermocouples and likewise different types of RTDs.  The thermocouple type must match the type the instrument is configured to read.  In the same manner, the RTD must match the curve (Typically DIN curve) the controller is configured for.  Additionally, the RTD has a base resistance value that must match controller configuration (typically 100 ohms at 0C)

If you want to know more, just ask.

TotalTemp Technologies offers a selection of 100 and 500 ohm RTDs and thermocouples for thermal platforms and other applications.

Our experienced team can provide assistance with your temperature sensing, hot/cold plate controlling, and thermal testing needs.

Thermal Testing with Convection and Conduction… together at last!

A Marriage Made in Heaven?

[Who could know, but now we do]

The Hybrid Benchtop Chamber – True Thermal Testing Bliss

Combines Thermal Conduction and Convection
in one incredibly fast and efficient design

A heartfelt Congratulation is in order for the happy and successful union of two distinct thermal testing methods that are finally sharing the same dance floor together – as the first true Hybrid.  To better understand the specific benefits from both sides of this collaboration of two testing methods, please review the following white paper:

Conduction vs. Convection for Thermal Testing

Typical Environmental Test Equipment used for Thermal Convection and Thermal Conduction

Thermal testing by convection is usually achieved with the use of a Temperature Chamber.  For versatility, standard chambers are very popular and meet the needs of a lot of testing purposes.  Chambers provide performance regardless of the shape of the device under test, are typically slower transitioning and settling, and require more lab space.

Temperature Chamber

Thermal testing by conduction is most commonly done on a Thermal Platform.  Platforms control temperature by conductive heat transfer and thus are inherently faster however are restricted to devices that have a flat conductive surface or can be fixtured to work on a platform.  Platforms provide fast-cycling time, require little laboratory real estate, and offer very good accessibility to test objects.

Thermal Platform (Coldplate)

Hybrid Benchtop Test Equipment Solves Many Problems

* Improves thermal uniformity gradients

* Increases throughput with faster cycle times

* Small footprint with easy access benchtop operation

* The fully-featured Synergy Nano Temperature Controller is capable of controlling platform temperature and air temperature independently or together

* Controller offers DUT and other data logging, remote access, cloud capability, and many networking functions

Click here: Hybrid Benchtop Chamber Flyer Datasheet

Hybrid Benchtop Chamber Test Equipment

Shown with Lid up revealing the Thermal Platform floor of the Chamber

Thermal testing is an important part of electronic manufacturing for reliability and design verification.

There are a variety of products for thermal testing and now TotalTemp is presenting a completely new and unique contender.

Temperature chambers, thermal platforms, air forcing units, and liquid baths have been around for a while and work well with many types of testing requirements.   But the Hybrid Benchtop Chamber Test Equipment provides many of the best features of Temperature Chambers and Thermal Platforms together to maximize performance and control and shows new promise of filling the need for faster, superior thermal testing.

Hybrid Benchtop Chamber Has Performance Results

As shown in the data chart above, in the basic operation mode, The Hybrid Benchtop Chamber demonstrates a significant improvement in thermal test performance.  The floor of the chamber is a completely functioning Hot/Cold Plate and operates independently or in conjunction with the chamber.

Because the controller is capable of advanced temperature control algorithms, it can allow even better performance by monitoring DUT temperature and allowing air and platform temperatures to be carefully controlled while verifying that required DUT temperatures are achieved.

The standard model currently available is called the HBC49-N with a thermal platform size of 6.5” D x 7.5” W, the chamber interior dimensions are  8.5” W x 7.5” D, Height is 4.5” to 6.5” at the rear.  The system can be cooled with liquid nitrogen (L-N2) or liquid carbon dioxide (L-CO2) and is rated for a temperature range of -100°C to +150°C.

TotalTemp Technologies is the manufacturer of the Hybrid Benchtop Chamber.  TotalTemp is a manufacturer of temperature cycling and conditioning equipment.  They are located in San Diego, CA.

Evaluating Thermal Imaging for Temperature Test

Initial FIndings

We acquired a FLIR ONE for Android from sources online, they are about $250 in most places. So the question is Toy or valuable tool. My opinion is Both! Not to deny the fun factor, (it is important to enjoy your job, right?) I say very much more on the useful tool side.  In the 90’s we paid more than that just to bring our products to a facility that allowed us to do some brief tests with less conclusive results. Laboratory grade thermal imagers still have a comma in the price tag and go upward from there.  This unit is primarily marketed as an uncalibrated tool but I found that the Flir One gives some very useful relative readings for testing and evaluating purposes.  As for absolute temperature readings, there is still a little something to be desired. The unit’s instructions are a little vague regarding measurement accuracies but the on-screen spot reading is quite useful.  The FLIR One unit offers better image quality and measures tenths where other units such as the Seek Compact thermal imager show readings with less precision.

Emissivity is an important factor in thermal imaging. Per the Wikipedia link here, emissivity is the effectiveness of a surface in transmitting energy as thermal radiation.  A cat would have very low emissivity whereas a black anodized aluminum surface would have nearly 1.0 emissivity. Professional grade and Non-imaging handheld thermometers all struggle some with emissivity. This unit has four different emissivity settings.

Useful Findings

For our Thermal Platform Business as you might expect it is useful in demonstrating the advantages of the thermal platforms and our Hybrid Benchtop Chamber over other environmental test equipment or thermal testing gear.

Examples here show a Thermal Platform heating up with locations of heaters evident and then a few seconds later stabilized at a hot temperature.

Thermal Platform heating to the temperature

In this case, further adjustment of the camera’s emissivity settings allowed more accurate absolute readings.

The thermal imager is also very useful in finding gradients during thermal tests and hot spots due to internal device heating or “convection shadows” which frequently happen with standard temperature test chambers.

Sensitive Relative Readings

Here is a surprising little demonstration.  Having a foot on the carpet for just 20 seconds, the heat transmitted through a thick boot sole and sock shows up as 2-3 tenths of a degree temperature gradients several seconds after the foot was moved.  More specific thermal test examples to follow but you can see how this tool would be useful to evaluate thermal stresses in electronic and power control systems.

Here are what I feel to be the takeaway points:

• Quick easy and low-cost demonstration of temperatures differentials.
• Accurate absolute temperature readings are more challenging.
• Paying attention to the unit under test emissivity helps achieve more accurate results.

Is Thermal Testing a Necessary Evil? – Made Better Here

Automation makes it easier

I am thinking a certain number of test engineers feel that thermal testing is more of a necessary evil than a joyful endeavor. Well, we are here to make things fall as much as possible onto the side of the joyful endeavor.

How does that play out in the real world? My thoughts include several aspects of thermal testing that can make it feel more like a joyful endeavor.

1) Knowing that you are working toward a goal of making tested, and reliable hardware can make it feel like valued work.  People don’t enjoy making junk.

2) Not following an arbitrary script but doing real verification, tracking results with the ability to easily analyze and not a lot of manual parsing of data also makes it more enjoyable and improve quality.

3) When done correctly automating a process will produce easier, more consistent good results.

4) Traceability – Providing a detailed written report without spending hours toiling over numbers easily proves that the job was done correctly.  Thermal testing is all about verification, Right?

5) Saving money is generally a good thing, hopefully, more profits, eventually more for the people who do the work too.

The Synergy Nano temperature controller helps to achieve the above goals with automation plus precise temperature control. Just one instrument is required to produce printed results whereas in many cases these results might require several expensive pieces of equipment and hands-on data manipulation.  The Synergy Nano has easy-to-use interfaces that can provide communication over Ethernet, serial, GPIB front panel, and other means. Logging several DUT temperature points is easy. Ramp and dwell profiles can be loaded by a user or by computer then stored/transferred as needed. Remote monitoring in real-time via a web server is easy as well. FTP data transfer or front panel graphing and thumb drive capture add flexibility. Logging of setpoints, numerous data options, even PID information or system, and DUT temperatures complete the picture.

A real big-time saver and the main point of this conversation is quickly producing documented results. Synergy Nano’s ability to print PDFs of test results and send that plot directly to a network printer or email in real-time without a PC adds real value.

Several of the below-detailed automation features also expedite the process of making accurate test results happen quickly.

Here are several useful links to some of the application notes/videos with additional information about automating your thermal testing with the Synergy Nano:

Network Plotting and Printing

Email notifications

Logging

Thermocouple data acquisition/logging with UUT modules

Synergy Server for automating data collection among several test stations

Synergy Controller Cloud Storage

Using Synergy’s FTP server

FTP Server Demo VIDEO

Web Server function

Web touch Web Server demo VIDEO

Manual data graphing Demo VIDEO

 Part 1 of Temperature Profile wizard

Part 2 of Temperature Profile wizard

If you are interested in more information on how to make your thermal testing better faster, more efficient, and maybe even more fun too,  then…

The Bigger Picture of Cryogenic Cooling Costs

First thoughts on cooling

Many people initially think of refrigeration compressors for cooling when product testing. Compressors work great for home refrigerators and sometimes they work the best for temperature chambers or thermal platforms as well. There are caveats but the main conditions where mechanical refrigeration systems work best are as follows:

• Where the temperature is held steady for long periods of time.
• Where cooling rate or getting to temperature quickly is not important.
• When the lowest temperature range required is above -35C.

The hourly cost of consumption for cryogenic cooling using expendable refrigerants like Liquid Nitrogen or L-CO2 is indeed higher but in the big picture, often the total cost of running mechanical refrigeration is greater.  Several factors can contribute to the cost advantage of using Liquid Nitrogen.

• The initial cost of cryogenically cooled equipment is generally much less due to the far lower complexity.
• Productive thruput is generally greater due to the cooling speed of LN2 and often even reduces real estate square footage requirements dedicated to testing.
• Simpler system design of LN2 systems directly relates to less money to maintain.

Within limits, speed generally = productivity. Ramping to temperature with mechanical refrigeration can be time-consuming.  The faster cooling times of expendable cryogenic coolants represent a large percentage of the ongoing savings using LN2 or CO2. More batches per day can be accomplished by reducing the requirement for yet more costly test stations, the space to keep them, and the energy to power them.  If your testing routine requires more temperature cycling pulldowns to cold temperatures or your devices are active/massive loads, the savings can be greater with Liquid Nitrogen cooling.  LN2’s superior ability to remove heat gives it the capacity to get cooling jobs done in favorable time frames.

While the efficiency of scale is to be gained with larger temperature test systems, benchtop systems with smaller batches can make sense too.  I am reminded of the theory of optimum carpooling partners which says If you carpool with one person, you cut your driving in half, you would have to carpool with everybody to eliminate the other half of the driving…  Not to mention the delays that would inevitably happen.  As I digress, the point is that a lot of time can be spent waiting to get many devices ready to undergo tests, thus holding up testing progress.

Cascade refrigeration systems used to cool to temperatures below -40C have had made strides towards improved reliability in recent years but are far more complex than single-stage systems, more expensive to buy, operate and maintain.  Another story here: When I worked at another thermal test equipment company, I remember being more than a little surprised when a contractor had performed warranty repair work on a refrigeration system at their shop. They had an amazingly large line item on the bill for “Electricity used by the unit while in the shop”.  Just how legitimate the charge was can’t be said but there is a significant cost that often is not seen or figured into ownership of refrigeration systems.

Actual costs of course will vary; load, profile other factors play into the decision.

We sell systems with mechanical refrigeration and systems with expendable cryogenic cooling so we don’t have too much agenda beyond helping you find the system that best suits your application.

Small Hybrid Benchtop Chamber            Mechanically Chilled Hybrid concept

Several aspects of the overall cost of operation/ownership of mechanical refrigeration systems v. expendable cryogenic liquids are covered here, if you have any questions about general possibilities or your specific application, contact our engineers who are available to help you find the test equipment you require.

Thanks for reading and thinking about your thermal testing requirements.

Thermal Imaging Reveals Environmental Test Performance

The Smartphone-based (FLIR-ONE in this case) infrared imager is really useful for displaying very small relative temperature gradients. The Hybrid Benchtop chamber brings to your lab bench performance in the form of convenience, automation, and also thermal performance capabilities that are easily seen with these relatively inexpensive imaging tools.

On the left- at 5 minutes in the hybrid benchtop chamber set to 75°C, a thermal image of a computer hard drive as a Device Under Test (DUT) shows very good thermal uniformity.  On the right, the same part on just a thermal platform alone still gets the base of the part to temperature very quickly but shows larger gradients to the surface of this higher profile part given a similar timeframe.

Using just a chamber alone can achieve the same uniformity for this part however due to the limitations of heat transfer by convection, the time required to achieve good uniformity is much longer.  Often twice as long.

The Hybrid benchtop chamber gets parts to temperature faster like a thermal platform while minimizing thermal gradients of the parts like a chamber. The Hybrid design helps the thermal platform along with its many other advantages work effectively with higher profile parts.

Thermal platforms alone are often an optimum solution for a lower profile and active heat-producing parts.

Without the thermal imager in hand, temperatures are easily and automatically measured by the Synergy Nano Temperature controller at several points on the DUT thus confirming the speed and uniformity of the Hybrid Benchtop Chamber. Advanced temperature control algorithms (cascade PID loop) provide good benefits to speed up the process as well.

The Synergy Nano temperature controller controls a profile and logs any thermal testing results to local storage. At the completion of the test, the controller delivers the test results automatically.  It can use email to deliver charts and logs in PDF format directly to a network printer without a PC. This makes the whole process more efficient.

Temperatures can be measured at several points on the DUT to confirm speed and uniformity. Advanced temperature control algorithms (cascade PID loop) can improve the performance as well.

Thermal Test Engineers are becoming accustomed to a new level of thermal test performance with TotalTemp Technologies products.