CONTROLS TECHNICAL CONTENT

Applying PID to Temperature Variances in Vacuum Furnaces

 

Source: Solar Manufacturing

 

Controlling process temperature with accuracy and without extensive operator involvement is a crucial task in the heat treat shop and calls for the use of a temperature controller, which compares the actual temperature to the desired control temperature, also known as the setpoint, and provides an output to a control element. This comparative process relies upon an algorithm, the most commonly used and accepted in the furnace industry being the PID, or Proportional-Integral-Derivative, control.

“This popular controller is used because of its robust performance in a wide range of operating conditions and simplicity of function once understood by the processing operator,” writes Real J. Fradette, a Senior Technical Consultant with Solar Atmospheres, Inc, and the author of “Understanding PID Temperature Control as Applied to Vacuum Furnace Performance” (with William R. Jones, CEO, Solar Atmospheres, Inc, contributing).

The PID algorithm consists of three basic components, Proportional, Integral, and Derivative which are varied to get optimal response. If we were to observe the temperature of the furnace during a heating cycle it would be rare to find the temperature reading to be exactly at set point temperature. The temperature would vary above and below the set point most of the time. What we are concerned about is the rate and amount of variation. This is where PID is applied. ~ Fradette

In this week’s Technical Tuesday, we direct our readers to Fradette’s article at Solar Manufacturing’s website where he and Jones cover the following on PID temperature controllers:

  • Definitions, e.g., Closed Loop System; Proportional (GAIN); Integral (RESET); and Derivative (RATE)
  • Actual operation of a PID temperature controller, including understanding PID dimensions and values; and general rules for manually adjusting PID
  • The art of tuning, a manual
  • Autotuning
  • Tweaking the furnace PID controller
  • and other factors

 

Read more: “Understanding PID Temperature Control as Applied to Vacuum Furnace Performance”

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Jason Schulze on Understanding AMS 2750E — Standard SAT Description

Dan Bender, Understanding the Short Circuit Current RatingJason Schulze, Conrad Kacsik Instruments, Inc.


This is the second in a series of articles by AMS 2750 expert, Jason Schulze. Don't miss the Q&A section at the bottom of this article and please submit your AMS 2750 questions for Jason to Doug@HeatTreatToday.com.


Introduction

Considering the abundant number of Nadcap heat treat audits performed in a single year, the area receiving the most findings is pyrometry, and within this group, system accuracy testing (SAT) is the third most common finding.

The SAT process has been refined through each revision of AMS2750 (C through E). We’ve seen SAT thermocouple requirements, for example, gradually incorporated into the tables but not within the body of the specification. Also, we’ve seen the definition of a SAT incorporated into revision D within the definitions section; however, with revision E it was added to the body of the specification.

AMS2750E presents three optional methods for performance of SATs that must be implemented; the Standard (or Regular) SAT, the Alternate SAT, and the SAT Waiver. Within this article, we will focus on the Standard SAT process.

Standard SAT Description – AMS 2750E

AMS2750E has defined the Standard SAT as:

An on-site comparison of the instrument/leadwire/sensor readings or values, with the readings or values of a calibrated test instrument/leadwire/sensor to determine if the measured temperature deviations are within applicable requirements. Performed to assure the accuracy of the furnace control and recorder system in each control zone.

Put simply, an SAT is a comparison of two systems: the furnace system (whether control, monitoring, or load) against a test system. It’s important to recognize that the comparison is being made against two systems and not against an instrument or thermocouple alone. Each system is made up of three variables:

  1. the instrument
  2. the lead wire
  3. the sensor

 

image-1

SAT Procedure

There is no general SAT procedure that can be applied for every supplier. Each supplier has their own needs as well as their own mechanical arrangement of thermocouples within their furnace system. The key to conformity is to ensure that, once a method for performing an SAT on a furnace is established, it is documented (i.e., in detail, including photos, if necessary) and repeated each time an SAT is performed. Some requirements to incorporate into your system are:

1) The tip-to-tip distance between the furnace system thermocouple and the test system thermocouple cannot exceed 3 inches.

2) The test thermocouple shall be in the same position/depth as the initial test.

3) The furnace is cycled and maintained at a temperature normally used during production.

4) Each system that makes up the applicable instrumentation type must be tested.

SAT Difference

Many findings arise from suppliers calculating the SAT Difference incorrectly. AMS 2750E states the following as a way to calculate the SAT Difference.

The difference calculated between the reading of the furnace sensor system being tested (sensor, lead wire, and instrument) and the corrected reading of the test sensor system (after test sensor and test instrument correction factors are applied) shall be recorded as the system accuracy test difference. Applicable correction factors shall be applied algebraically.

I’ve highlighted the word “corrected” as it applies to the test instrument systems because this seems to be a source of frequent findings. The furnace system does not get corrected, the test system does get corrected.

 

image-2

As an example, let’s consider a vacuum furnace which has had an SAT performed. The vacuum furnace is designated a Class 3 (±15°F) Type D furnace. Let’s assume no additional furnace thermocouples are employed and we are performing an SAT on the control and recording systems. The readings obtained are below in the picture.

image-3

 

*The example above is not an SAT Certification. It’s an example of how to calculate the SAT Difference in a given situation.
*The example above is not an SAT Certification. It’s an example of how to calculate the SAT Difference in a given situation.

Conclusion

SATs can be difficult depending on the equipment and processes suppliers have. As always, it’s important to receive comprehensive training regarding the specific requirements of System Accuracy Testing as they apply to your facility. There are many particular aspects of SATs that may not have been accounted for in this article. If you have specific questions, please email them to doug@heattreattoday.com, and I will answer them in an upcoming article.

Submit Your Questions

Please feel free to submit your questions, and I will answer appropriately in future articles.

Out next topic will focus on the requirements and execution of an Alternate SAT per AMS2750E, the requirements of AC7102/8 and the Pyrometry Guide.   

 


 

Q/A with Jason Schulz

Q: When calculating the SAT Difference, should I include the correction factors of the furnace sensor?

A: No, the correction factor from the furnace sensor is not to be included in the SAT Difference calculation.

Q: How do I account for an internal (pre-programmed) TUS offset within the controller when calculating the SAT Difference?

A: Internal or electronic TUS offset must be algebraically removed when calculating the SAT Difference.  Below is an example that includes an electronic TUS offset of -2°F.

 

sat-qa

Q: I operate a furnace with 2 load sensors. One of them is used to signal the start and end of each soak cycle, the other is reference only. Do I have to perform an SAT on the load thermocouple I use as a reference only thermocouple?

A: Any thermocouple that is not used as product acceptance may be deemed reference only and is not subject to the SAT requirements of AMS2750E. Nadcap requires that the reference only thermocouples be accounted for in internal procedures.

Q: When performing my bi-weekly SAT, I get a difference of +2.6°F on one test and two weeks later I get a difference of -3°F; this constitutes a spread (within two weeks) of 5.6°F. Would this be cause for SAT failure?

A: According to AMS2750E and Nadcap, no, this would not constitute a failed SAT, though is something to be cautious of. This type of shift in SAT results does reflect some sort of change or degradation of the system being tested. A well-established tack, in this case, is to plot SAT results as part of an SPC (statistical process control) program which will govern future replacement of system thermocouples and/or leadwire (in the case when large difference is SAT results over a pre-determined amount). A documented SPC system for SAT results would also satisfy the requirements of AC7102/8(NA) page 2, paragraph 3.12.

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Should You Replace Your Aging Heat Treat Technology?

Consideration #1:  Sometimes, Hardware and Technology Forces You to Change Your Software.

Nothing is more frustrating than having to change your software systems because of unexpected developments that have occurred in the underlying and supporting technology.  For example, think about the enormous amount of software applications that ran fine on Windows XP, but now need to be replaced, or undergo a complete remake, because Windows XP is not supported by Microsoft anymore and has now become a risk to the continuity of your business.

Is your heat treat department running an outdated system, a customized software application, or a conglomerate of pieced-together, homegrown apps still limping along? If so, now is the time to look at making that much needed transition and move to a more flexible environment, preferably one that remains on the cutting edge of technology advancements with continuous monthly updates and new software releases.

Consideration #2: Benefits of Using Browser-based Software

A browser-based application is any application that uses a website application as the “front end”, or interface.  A browser-based application can be run in the cloud (SaaS), OR it could be run on your own internal (intranet) server(s). Users access the application from any computer (or mobile device if the software can handle it) connected to the Internet using a modern standard browser, instead of using an application that must be installed on each individual local computer or device.  As an example, Microsoft Word is a common word-processing application.  Google Docs is also a word-processing application, but all the functions are performed using any web browser instead of using software that has been installed directly onto their computer.

Web applications are easier to upgrade and do not require to be completely re-installed if you replace your computer system.  They still need to be kept up-to-date in order to cater to any new internet web browser technologies and information security threats.  With browser-based applications, users access the system via a uniform environment—the web browser; however, the user interaction with the application needs to be thoroughly tested on different web browsers so the system will function properly using any of the popular modern browsers.

Unlike traditional applications, web systems are accessible anytime, anywhere, via a computer or handheld device that has an Internet connection, putting the end user in charge of where and when they access the application.  Someone on vacation can quickly log into the system from anywhere in the world to see what is happening back at the shop.

Using Internet technologies based on industry-wide standards, it’s possible to achieve a far greater level of interoperability between applications than with isolated desktop systems. For example, it is much easier to integrate two browser-based systems than it is to get two proprietary systems to talk to each other. Browser-based architecture makes it possible to rapidly integrate enterprise systems, improving workflow and other business processes. Installation and maintenance becomes less complicated. Once a new version or upgrade is installed on the host server, all users can access it immediately. There is no need to upgrade each device with the new version of the application.

Speaking of data security and confidentiality of business-sensitive information, browser-based applications are typically deployed on dedicated servers, which are monitored and maintained by experienced server administrators. This is far more effective than monitoring many client computers or handheld devices, as is the case with new desktop applications that requires each device to be ‘touched’ every time there is a software change or new upgrade release.

Consideration #3: Most Businesses Know They Need to Update Their System

Various surveys and studies that have been done, and found that the majority of organizations polled know they need to, or should, update their enterprise software systems.  However, they have no plans to do so in the near future, mainly because of cost. This reason is conveniently used a lot, but it just doesn’t add up to be a legitimate reason.  Many businesses have no problem spending millions of dollars on new equipment, but don’t want to spend a few thousand dollars on new software that will get them the information they desperately need to make better decisions in the management of the business, and to help their employees be more efficient with fewer errors.  They are swimming in data, but starving for the information they need, usually because the data is held in disjointed silos across the enterprise…and it isn’t consolidated for better business metrics and knowledge-based reporting.

The problem with not wanting to spend money on software is that it will eventually lead to higher costs, both now and down the road, because the current system(s) require work-arounds, duplication of effort, data redundancy, etc.  There is also the possibility of decreased revenue and business income because the competition is better prepared, and has more to offer their customers. Budgets are important, but they shouldn’t be the only consideration when evaluating the need to modernize your software systems. These considerations should play a large part in the decision-making process.

Nothing Stays the Same:  One thing about technology is that it is always changing.  Your business is always changing too, and your software needs to keep up with your business…not be a hindrance to it. It is essential for nearly all organizations to stay in competition, but aged software applications can be as dangerous as not having an application at all. Not only do older systems not have the functionality that newer systems do, they become a competitive disadvantage and are a detrimental hindrance to achieving the goals/objectives of the business.

Winning Is About Staying in the Fight: “If it ain’t broke, don’t fix it.” This common phrase is used in reference to many things, even software applications. However, consider this: how detrimental can a ‘not-broke’ system be that is not efficient and causes additional time and effort from the workforce to do their day-to-day jobs?  Although modernizing your existing software application system might seem costly, if it is inefficient, you need to answer the question: How much is the existing system costing me?

It is costing you. Inefficiencies are expensive. That is the reason so many manufacturing organizations are working to become lean organizations. That is the reason that technology exists—to improve inefficiencies. Don’t be fooled. Just because the system was the most efficient thing on the market 10 to 15 years ago doesn’t guarantee that it’s the most efficient solution for your organization today. Take the time to study how much efficiency a new system could create before making the decision to modernize. If you still think modernization is too expensive, add the cost of that inefficiency to your operating budget and look again.

Agedness = Feebleness:  One last consideration when determining whether modernizing your software is the right option for the business, is the security of that system. You want your business data and confidential customer information to be secure and readily accessible at the same time. Just as the human body becomes feeble over time, so does the security of your application systems.

In an age when security is paramount to survival, your software applications could actually be putting your organization at risk. There have been multiple companies that have had their corporate servers hacked, sensitive data was breached, and in some cases they lost many months of valuable company data, not to mention the public humiliation, loss of customers’ trust, legal ramifications, and very expensive recovery efforts.  There’s a new data breach or malicious hack identified in the news almost weekly.

With that said, can you really afford to ignore that your older application systems and databases might be less secure than a new system?

Consideration #4: The Secluded Silo Syndrome

Many companies have purchased various software products over the years to meet some type of business or operational need. These purchases inevitably resulted in creating silos in different parts of the organization where it is hard to keep information (some/much of it duplicated) synchronized. Old software and old technology also means that newly hired employees have no experience in that technology and require extensive training just to use the technology to carry out their duties. Also, reporting is simply so much work that the business doesn’t get the information they want when they need it.

Some businesses have considered whether to spend money to develop something like a business intelligence layer over the top of the existing systems, or whether to spend their dollars to upgrade to a modern software system where all the data is stored in one place.  Past Chairman and CEO of General Electric, Jack Welch, once said that “If the rate of change on the outside exceeds the rate of change on the inside, the end is near.”

A key consideration that is faced by companies who find themselves in this position, is whether their existing software systems can effectively scale up to accommodate the planned growth of the business, or will the limitations of these old systems hinder their growth? Given the rate of change in business today, there will come a point at which the existing collection of systems just can’t accommodate the organization’s needs.

For example, can those applications support new governmental regulations, or any necessary certification/accreditation requirements? With natural attrition, there is a growing gap between new and existing employees. Does a viable business really want to invest in training new employees on obsolete applications?  Usually, this is a negative…therefore, the question becomes not “Should we change?”, but “When should we change?”

Everyone understands that there is a cost of replacing outdated systems and software tools, and this is usually the main reason that management gives to delay any upgrades.  But, remember this; you’re also paying a daily price by continuing to rely on those clunkers, and possibly putting the business at undue risk.

Consideration #5: Acknowledge the Objections

Because old software or hardware is still in use, senior management personnel often see no need to replace it.  They think, “If it ain’t broke, don’t fix it.” There are many phrases that management teams have used over the years when defending the continuing use of old software and continuing to delay what they know in their heart really needs to be done, based on the feedback (and sometimes complaints) they are getting from their ‘down in the trenches folks’.  Some of these include:

  • The old system works fine.
  • We’ve always done it that way.
  • New technology costs lots of money.
  • New software will require a big investment in training time as well as money.
  • New software may require some customizations.
  • We’re busy; we don’t have time for this.
  • We’re slow; we don’t have the money for this (please ignore the new Escalade in the parking lot).

Everyone understands that management is simply trying to limit spending in any way it can. However, think about this; if you never swapped out your old equipment, and upgraded to better, faster, more efficient, cost cutting machines, think about the problems you’d still be trying to solve!  The use of software is a very critical component of your business; so, it’s really not a question of if you should switch to better, faster, more efficient software, but when.

Consideration #6: Dangers of the Do-nothing Approach

For the sake of argument, let’s say that your company decides to change nothing, and continues to use the old software or hardware forever. Take a moment to think about what would happen…

At some point in time, your software will not work on newer machines and modern operating systems and browsers, because they are constantly changing.  Here’s something on a more personal note for you to consider; if you oversee your company’s technology investment you need to understand that when the old computer equipment and/or old software systems fail, and the business is ‘dead in the water’ without it, management is going to blame you.  So, why wait for it to fail when you can be proactive, rather than reactive; start planning now and mitigate the risk.  Assistance is available to help you develop a strategy for reporting on the risk of the situation, and help senior management begin to study the possibility of replacing old technology based on effective risk management techniques.

At some point — and you never know when — some sort of system update or service pack may cause your old software to simply stop working.  Also, we have heard from other companies that their customers started complaining because they couldn’t get them the right data that they needed in a timely fashion in order to continue to do business with them. Why risk losing a good customer?  Even if time stands still at your company, it’s still moving right along for your customers (and your competitors).

Summing Up

The challenge now falls upon us, as business owners, to estimate the financial risk that each of our companies are taking when we choose to work with outdated computers, peripherals, operating systems, and the software we use to collect the day-to-day data that we need to run the business and stay competitive. By explaining the cost of doing nothing to the rest of your management team, you may be able to persuade them to start doing something instead.

 

Author
Ron Beltz
Director of Sales – Strategic Accounts
THROUGHPUT I BLUESTREAK

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