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Basics of Temperature Control

Basics of Temperature Control

For accurate control of the process temperature without constant operator involvement, industrial thermal processes rely upon a controller. The controller gets its inputs from a contact temperature sensor such as a thermocoupleRTD or from a non-contact temperature sensor like an infrared temperature sensor. The controller transmits an electrical signal (current or voltage) to a power switch device which can be a simple relay, a solid state relay or a SCR (Silicone Controlled Rectifier).


Remember: The temperature controller is just one part of the entire control system, so it must be selected accordingly.


The  two basic types of temperature controllers are:


On / Off control These units turn the power on and off when the set point is crossed. This type of controller is adequate when the process temperature is not very critical and/or larger masses need to be heated (like immersion tanks). Thermostatic controls are on/off controllers.


Microprocessor control (PID control) This is a generic term for a control feedback mechanism widely used in thermal control systems. A PID controller attempts to correct the error between a measured process temperature and a desired set point by calculating and then outputting a corrective action that can adjust the process accordingly. PID is shorthand for Proportional, Integral, and Derivative calculations.


On / Off Controls and Thermostats


Thermostats or ON/Off controls are relatively simple and economic switches widely used for switching power for electric heaters. These controls are found in most residential HVAC systems.  The output will be on or off when the process temperature crosses the set point. This constant crossing of the set point means the temperature is constantly cycling around this set point. This constant cycling around the set point will also reduce heater life because full heat is applied whether the process temperature is 5 degrees or 100 degrees below set point. ON/Off controls increase thermal fatigue and oxidation rate on heating elements by causing wide temperature swings of the internal heating element (Imagine a light bulb turned on and off constantly).


To minimize stress for the heaters and avoid damage to the contactors by rapid cycling, a so called “hysteresis loop” can be added to the on/off control. To maximize heater performance, use a solid state relay (SSR). Such a solid state zero-cross contactor can cost as little as $100 and will save you money in the future. Another option is a silicone controller rectifier (SCR) (single phase or 3-phase).


A thermostat can be built from a mercury switch (a glass tube with a small amount of Mercury), a bimetallic strip (lamination of two different metals together) or other temperature sensing devices. Sometimes they also have a heat anticipator, which shuts down the power to the heater before the heat actually reaches the set temperature.


On / Off controls can be used for:


  • high temperature alarms
  • applications where maintaining accurate process temperature is not necessary
  • applications where the mass of the system is so great that temperature changes slowly


PID (Proportional-Integral-Derivative) Microprocessor Temperature Control


This very popular type of controls provides a proportional temperature control combined with integral and derivative temperature control. Proportioning the heat means less power to the heater is supplied if the heat is closer to the set point. This is achieved by the derivative and integral operating modes. The controllers come with set parameters which may be adjusted to your application.


PID controllers can be a very simple set point and auto-tune (adjusts the parameters to match the heating application) or very complicated with temperature and duration programs (ramp and soak) or multiple inputs and outputs.


General Considerations


Select PID Controller panel size.  Most popular sizes:

  • 1/32 DIN (48 x 24 mm)
  • 1/16 DIN (48 x 48 mm)
  • 1/4 DIN (96 x 96 mm)


Determine what Inputs will feed the PID controller.


The signal input (T/C, RTD or voltage) on most standard controllers may need to be selected at the time of ordering.


Decide which control operation is required for the PID control.


Most PID controllers come standard with two main control functions.


    • on-off control (you still can set the hysteresis or “deadband”)
    • PID control (Proportional, Integral, Derivative). For various applications, the PID controller can be used as P control only, PI control (no offset=higher overshoot), PD control (steady state in shortest time) or PID controller. PID control is essentially a compromise between the advantages of PI and PD control (“fuzzy-logic” controllers is just another marketing term for this type of controllers.).
    • Programmable ramp and soak
    • Communications requirements


Ensure you have enough outputs from the PID controller.


If only required for heating (as opposed to heating and cooling), one output is sufficient. Outputs can be a relay, SSR, SCR, pulsed voltage, linear voltage, or linear current.


To further protect equipment, a high temperature alarm output may be employed. This is an independent monitor that shuts down operations when a set temperature is exceeded.


Programming the PID controller.


Order and names of parameters vary among control manufacturers, but the parameter names are usually very similar. Programming tools are useful if sets of saved parameters need to be downloaded through an interface (RS 485, RS 232) into different controls or for integrating several controllers into a higher control.

The Amazing Properties of Aerogels

The Amazing Properties of Aerogels

Imagine holding a gauzy blue block of the lightest solid material on Earth. To the naked eye, it looks like a self-contained cube of gaseous fog. To the touch, it feels like dry Jell-O. You apply a flame to this ethereal substance and, much to your surprise, your hand remains cool and comfortable. The mystery material you hold in your hand could only be an aerogel.


Aerogels, like many great human innovations, were first created as the result of a bet. In 1931, a chemical engineer by the name of Samuel Stephens Kistler made a friendly wager with a fellow scientist to see who could replace the liquid component of a gel with a gas without causing the structure of the gel to collapse. Kistler first succeeded in creating aerogels by employing supercritical drying processes to remove the liquid component of silica gel.


The end result was truly remarkable. Kistler’s aerogel was a gel in name only. In fact, its structure was composed of 98% air, and only 2% solid silica. Later, Kistler was able to produce similar results by using other substances such as alumina and tin dioxide as substitutes for the silica.


So what can we do with aerogels?


We can create lightweight jackets that insulate so well that they have to be vented in order to keep a person from overheating in freezing temperatures. We can purify water by using aerogels to absorb heavy metals. We can use them as a controlled dosage drug delivery system. We can even capture the dust from the tail of a comet in their pores.


NASA was the chief patron of aerogel technology for much of the twentieth century, but in recent years aerogel applications have spread to a number of other earthbound industries.


The world’s tallest skyscraper, the Burj Khalifa in Dubai, employs aerogels to insulate the mammoth structure. The US Navy has been experimenting with aerogels to produce next generation wetsuits for its divers. Carbon aerogels have even been used as an electrode material in supercapacitors.


We can’t wait to see what the future has in store for aerogel technologies. Over the course of their 80 year history, they’ve evolved from scientific curiosities to versatile industrial materials with a myriad of practical applications.


Want to learn more about the latest advances in thermal technology? Stay tuned for more updates from HTS Amptek!

Tennessee Laboratory Unveils Next Gen Insulation

Tennessee Laboratory Unveils Next Gen Insulation

Thermal insulation technology has been in development since, well, the dawn of human civilization. In the earliest days of R&D, our cave dwelling ancestors used whatever they had on hand –furs, earth, wool, etc. – to keep their homes and bodies warm. Later, the Romans discovered the remarkable insulating properties of cork and asbestos. During the industrial age, waste slag from furnaces was used extensively in building and industrial applications.


Today, researches are still searching for the next great breakthrough in insulation. According to a recent press release, the scientists at the Oak Ridge National Laboratory outside of Knoxville, Tennessee believe they’ve found it. We’re still waiting to learn more about the new material, but here’s what we know so far.


Oak Ridge’s next generation insulation consists of foam insulation panels designed for use primarily in building applications. Preliminary estimates suggest that the foam panels could reduce heating and cooling loads in buildings by as much as 38 to 50 percent. The material has a projected R-Value of about 25, roughly equivalent to that of molded expanded polystyrene.


While the new material would be slightly more expensive than current insulation materials – roughly 30 cents per square foot more – it has the potential to save home and business owners a bundle on their utility bills.


Oak Ridge undertook the project in support of the Department of Energy’s initiative to cut energy consumption in buildings in half by 2030. Oak Ridge still has work to do to optimize the materials for widespread practical application, but before too long we’re likely to see the mysterious foam boards in construction projects all over the country.


At HTS Amptek, we know that effective insulation matters a great deal to your business. Likewise, we strive to always employ the latest insulation technology in our manufacturing process in order to produce the very best results for our clients. Want to learn more about the insulating products available at HTS Amptek? Give us a call today for more information.

The High Performance Insulation Market is Booming

The High Performance Insulation Market is Booming

According to a recent report from research firm Markets and Markets, the worldwide high performance insulation market is projected to balloon into a $6 billion industry by 2020. Currently, North American consumers comprise the epicenter of market growth, accounting for over half of the global market.


Next-generation insulating materials such as aerogels, ceramic fiber, and glass bubble insulators which were once relegated to space programs and experimental laboratory applications are now being employed in other well-established industries, driving the demand for these materials to unexpected heights.


According to the report, the oil industry is the currently the foremost consumer of high performance insulation materials. The fastest growth rates in the next five years are expected to come from construction and automotive industries. Automotive companies, in particular, stand to benefit from the improved acoustic performance and lightweight properties of these new insulating materials.


Aerogels are projected to see the highest increase in consumption. By virtue of their remarkable insulating capabilities, relatively low cost of production, and the abundant availability of their constituent raw materials, aerogels stand out as the most promising new high performance insulation materials. Meanwhile, the oil & gas is continuing to drive the demand for gas bubble insulation products.


At HTS Amptek, we employ the latest, most efficient insulating materials available whenever possible in the design and manufacture of our products. We carry a diverse line of reliable, durable heating and insulation products designed to accommodate a variety of applications. Give us a call today to learn more.