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Tips for Extending the Life of Temperature Sensors

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Home > Blog Archive > Category: Industrial Heating Technology > Tips for Extending the Life of Temperature Sensors

photo of a Thermal Corporation Thermocouple

Extending the Life of Temperature Sensors

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.

photo of a Thermal Corporation RTD

#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

different thermocouple types

How to Identify Different Thermocouple Types

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Home > Blog Archive > Category: Thermal Corp Vlog > How to Identify Different Thermocouple Types

How to Identify Different Thermocouple Types

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!

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Written by Kyle Otte
Filmed and Edited by Shelby Reece
Date Published: 10.07.2019
Last Updated: 10.07.2019

bayonet adapter on heater

Case Study #004: Problems with J-Type Thermocouple Reading

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Home > Blog Archive > Category: Case Studies > Case Study #004: Problems with J-Type Thermocouple Reading

Case Study #004

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:

diagram showing how the thermocouple reading was being made

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).

diagram showing the tip of the j-type thermocouple probe touching the flat surface of the barrel

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

photo showing a Thermal Corporation RTD and a Thermal Corporation thermocouple

How Do You Tell a Thermocouple From an RTD?

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Home > Blog Archive > Category: Industrial Heating Technology > How Do You Tell a Thermocouple From an RTD?

photo of a thermocouple and rtd with labels

Some thermocouples look very similar to an RTD. There are, however, usually some small differences. You usually can’t just replace a thermocouple with an RTD without making some changes, such as, reprogramming the controller for a different type of temperature sensor.

The Clues to Tell the Difference

There can be several clues as to whether you have a thermocouple or an RTD (Resistance Temperature Detector). For example, if the temperature sensor has three leads, the sensor is an RTD. Thermocouples only have two leads. On the RTD with three leads, almost always two of the leads will have one color and the third lead will have another color.

For a two wire RTD, usually both leads will be of the same color. For a thermocouple, the two leads will always be of different colors.

(Click here to view our thermocouple color codes/conductor combinations and characteristics chart!)

The “Gold Standard” Difference

The “gold standard” for determining whether a sensor is a thermocouple or is an RTD is to measure the resistance using a Volt Ohm Meter. If the sensor has two lead wires, measure the resistance between the two leads. If the sensor is a thermocouple, you are just measuring the resistance of that length of wire. You would probably measure a few ohms. If you are measuring an RTD, you are measuring the resistance of the wires plus the resistance of the RTD element. For the plastics industries, this RTD element is almost always 100 ohm at 0 0C. At room temperature, this element will read more like 105 to 110 ohms. Thus, if we are measuring an RTD, the ohm meter will read a few ohm more than 105 to 110 ohms, certainly much greater than just a few ohms like the thermocouple would.

If the sensor has three leads, it will be an RTD. There will be three combinations where the resistance can be measured. Two of the leads go to one side of the RTD and the third lead goes to the other side of the RTD element. Thus, two of the reading will read 105 to 110 ohms and the third will read just a few ohms.

If there is a plug on the sensor, a white plug will be an RTD, a black plug will be Type J thermocouple and a yellow plug will be Type K thermocouple.

Looking to order a thermocouple or an RTD? Click here to go to our thermocouple & RTD configurations page.

Written by Jim Dixon
Edited by Shelby Reece
Date Published: 10.23.2017
Last Updated: 09.06.2019