Do You Have a Thermocouple or an RTD? They are similar, but what are the exact differences between them? In this video, Thermal Corporation engineer, Kyle Otte, explains the differences between thermocouples and RTDs.
In this video, one of our engineers, Kyle Otte, explains the different types of junctions available on thermocouples:
grounded
ungrounded
exposed
He also describes each of their uses and purposes for thermocouples. For more information on the different types of thermocouple junctions, view this blog post.
In 2014, a customer called about an octagonal extrusion die. This octagonal extrusion die had three zones. The customer wanted to know how he could monitor the temperature of each face of the octagon for all three zones at once.
How to Monitor All Three Zones
Each face of the octagon would require a thermocouple. We recommended a
Our resellers, along with our other valued customers, are one of the major parts of Thermal Corporation and what help keeps our company going. We, at Thermal Corporation, are always looking to reach out to new resellers for our products. Our goal for this post? To grab your attention — if you are a part of an industrial heating sales company who is interested in buying and reselling Thermal Corporation products, then this post is for you!
What We Sell
As you may already know (or not), Thermal Corporation designs, manufactures, and sells industrial heating products. The types of industrial heaters we manufacture can be standard, or designed to exact customer specifications. Our products are used mainly for the plastics industry, but can also be used for other industrial applications such as food processing. These products include:
Our delivery time is second to none! Ask about our express line of heaters that ship on the same day with no extra cost! Limitations do apply. We also specialize in custom and unique heaters. We can provide these heaters with short lead times.
How to Become a Reseller
So, are you an industrial heating sales company looking for new product categories to offer or who wants more of a variety of brands to sell? Then, contact Thermal Corporation today and chat with us about becoming one of our resellers! Don’t forget about the discount you can receive if you decide to resell Thermal Corporation products. Resellers have the opportunity to get the largest available discount from Thermal Corporation. Discounts are based on annual sales of Thermal Corporation products.
Thermal Corporation is looking to reach out to new possible resellers right now! Need more specific information on our products? Check out the products page on our website at www.thermalcorporation.com/products.
Interested in chatting with us and getting more information about doing business with Thermal Corporation? Contact Ushma today by email at ushma.s@thermalcorp.com or by phone at 256-837-1122 x127.
Written by Shelby Reece Edited by TC Marketing Team Date Published: 03.04.2019 Last Updated: 09.04.2019
A customer called in about having problems with their thermocouple readings. The customer was attempting to measure the surface temperature of a barrel two separate ways, using two different types of thermocouples. The first measurement was done with a Fluke handheld surface probe thermocouple. It read 646°F. The second measurement was taken using a J-type thermocouple probe with an attached bayonet adapter. This time it measured 450°F. After changing out the J-type thermocouple several times and getting about the same readings each time, the customer gave us a call.
The customer believed that, based on the way the plastic was reacting to the heat, the Fluke thermocouple was giving him the correct reading. The first step I took in this case was drawing out how and where the readings were being made. I came up with the following diagram:
Why Are the Thermocouple Readings Different?
Both thermocouples, the Fluke and the J-type, were reading correctly. So, why are the readings different? The reason is that the Fluke surface probe thermocouple, as shown in the above diagram, is reading the true temperature of the surface. The J-type thermocouple is NOT a surface probe thermocouple, therefore, it is not reading the actual surface temperature. The probe tip is 450°F whereas the surface itself is 646°F. This particular probe had a drill-shaped tip, designed to fit a hole that has been drilled into a barrel, not a flat surface (see image below).
How Is This Happening?
The heat being transferred from the barrel through a point is a very small amount of heat. This small amount of heat is being removed by conduction to the back of the probe and through the wire. This pulls the temperature down at the junction, giving a true reading of 450°F.
The Solution to the J-Type Thermocouple Reading Issue
Drill a shallow hole into the barrel and insert the J thermocouple down into the hole. It will now read the correct surface temperature of the barrel.
Have a Question About a Heating Application?
Contact the Thermal Corporation engineers for assistance! We will work with you on any heating application struggle you may be encountering. Contact us today at engineering@thermalcorp.com or by phone at (800) 633-2962 x152.
Written by Jim Dixon and Shelby Reece Edited by Kyle Otte Date Published: 09.09.2019 Last Updated: 09.09.2019
In this video, Thermal Corporation Engineer, Kyle Otte, explains how to identify different types of thermocouples by…
plug or jack
lead
color code chart
He also explains a case study in which the customer did not know which type of thermocouple he had.
Looking at the chart, Kyle is able to show you how to determine your type of thermocouple.
To see the color code chart that Kyle mentions in the video, click here.
View all of our Thermocouple & RTD Configurations. We manufacture all of our products in-house right here in the USA! Great quality. Competitive pricing. The Fastest Shipping in the Industry!
There are three different types of junctions for thermocouples: exposed, grounded, and ungrounded. Each of these serves a different purpose and has different characteristics. Let’s look at each type of junction and where they should be utilized.
What Are Thermocouple Junctions and Why Are They Important?
Briefly, a thermocouple works utilizing the Seebeck Effect. The Seebeck Effect is the conversion of thermal energy into a voltage potential at the junction of different types of metals. If a continuous circuit is made using dissimilar metals joined at two junction points, and the two junction points are at different temperatures a small voltage will flow through the wire. By measuring this small voltage (usually tens of millionths of a volt), we can determine the temperature at the place where the two dissimilar metals are joined (the junction). The thermocouple junction is, therefore, extremely important because this is the point where we are actually measuring temperature.
Exposed Thermocouple Junctions
As depicted in the picture to the left, exposed junctions consist of two bare wires that are joined outside of a protective metal probe. Exposed junctions are used to measure the temperature of a gas. Because there is no protective cover, the junction is very fragile. No moisture, or liquid or solid contaminants should be present in the gas. Exposed junctions, however, do provide a faster response time because thermal energy does not have to travel through a metal sheath and/or compacted insulation to impart energy to the junction.
Grounded Thermocouple Junctions
Grounded junctions are the most common type of junction. In this application, the junction is connected directly to the probe tip usually via soldering or welding. This provides a relatively fast response time as heat only has to travel through a metal sheath or probe and weld, all of which have a high thermal conductivity. This also provides durable protection for the junction inside the probe tip.
Ungrounded Thermocouple Junctions
Ungrounded junctions are used to protect sensitive electronics from small feedback voltages. Ungrounded junctions are similar to grounded junctions in that they are inside of a protective probe. However, they are not welded or soldered to the probe tip; instead, they are surrounded by an insulator, usually magnesium oxide. Ungrounded junctions provide a slower response time because heat must travel through the probe tip and then through the magnesium oxide (which has a lower thermal conductivity than a metal) before reaching the junction.
So, Why Have an Ungrounded Junction-type Thermocouple?
One reason for an ungrounded junction-type thermocouple is if there is a small voltage difference between grounding points. For example, an electronically-sensitive control panel is grounded at 0V. This instrumentation is connected to a temperature sensor that is on a machine which has a small voltage leak through the ground circuit and thus is grounded at 1V. There exists the possibility that a small current could travel through the sensor back to the control panel and have an unwanted effect on the electronic equipment.
Main Points
Each junction is useful for different types of applications.
Exposed junctions have no protective cover and are very fragile.
Grounded junctions are the most common junction type and have a fast response time due to the highly thermal conductive material.
Ungrounded junctions are surrounded by an insulator and provide a slower response time, but are useful for protecting sensitive electronics from small feedback voltages.
Written by Kyle Otte Edited by Shelby Reece Date Published: 02.01.2019 Last Updated: 09.04.2019
These tips will apply to both thermocouples and RTDs
#1 Avoid Tip Deformation
The actual sensing part of a temperature sensor is very close to the tip of the probe, so keeping the tip protected is extremely important. This is especially important when it comes to Resistance Temperature Detectors (RTDs). RTDs consist of a very small platinum resistor that is very fragile. Any hammering or mechanical force on the tip of an RTD can ruin the sensor. Thermocouple junctions can also be broken or become unreliable if they are deformed or disturbed. (Learn more on thermocouple junctions in our video on Youtube about the Different Types of Thermocouple Junctions.)
Make sure that the probe fits securely into the bore that it is meant to go in. Temperature sensors should not have to be forced into place. If the sensors are not easy to install there is most likely some contamination (plastic overrun) in the bore hole that needs to be removed.
Be careful with the temperature sensors when changing dies or servicing your machine. We see a lot of bent temperature sensors that no longer work correctly after being removed and reinstalled in a different die, because they were treated roughly during the transition.
#2 Avoid Contamination of Leads
While temperature sensors are not as prone to contamination as our other heating products, such as mica band heaters and cartridge heaters, it can still happen. Often what we see is plastic that has been melted and somehow made its way onto the temperature sensor leads. Depending on the type of lead wire insulation, and the type of plastic, the plastic can create a “short” between the leads. This is really a secondary junction. This causes problems in thermocouples and RTDs. It is very important to not allow the leads to be contaminated.
#3 Avoid Over Temperature
Published literature states that a J-type thermocouple is accurate up to 1382°F. However, keep in mind that this is the maximum temperature rating for the thermocouple junction. The insulation surrounding the thermocouple wire will not be rated to this high of a temperature. Often times what we see is that the fiberglass insulation around the thermocouple wire has got hot and burned through. This leads to a bare thermocouple wire that makes contact with the metal of a machine. This creates a secondary junction which then gives a bogus temperature reading and causes the machine to have problems.
This same phenomenon can happen when using an RTD. In that case, the resistance that the controller sees changes drastically, thus giving a false temperature reading.
If possible, run the thermocouple wire leads in open air where the temperature is much lower than the process temperature.
#4 Take Care with Lead Routing
A high percentage of the temperature sensors that we see fail have done so because the leads have been damaged in some way. Machines have sliding or moving parts, and can easily pinch or nick leads if care is not taken when routing the leads.
A stainless steel hose will help with deflecting mechanical force, but can still be crushed.
A stainless steel over braid can help with mechanical wear, or rubbing, but again it is best to avoid this scenario, if possible.
Teflon leads will be moisture resistant, but it is always better if temperature sensors can be kept dry. Thermocouple wire will rust if exposed to a high-moisture environment and, over time, will fail.
Written by Kyle Otte Edited by Shelby Reece Date Published: 02.20.2020 Last Updated: 02.20.2020
Learn ways to extend the life of your thermocouples and resistance temperature detectors (RTDs). Taking these tips, presented by Kyle Otte of the Thermal Corporation Engineering team, into consideration can lengthen the lifespan of a thermocouple and RTD.
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