Tips for Extending The Life of Temperature Sensor

Thermocouples are dependable temperature measuring devices that will provide trouble-free service and long life under the proper conditions. However, some problems may be encountered resulting from improper application or operation. While many factors contribute to thermocouple life expectancy, the following are simple guidelines that can help you get the most out of these sensors.

What is Temperature Sensor?

A temperature sensor is a device, typically, a thermocouple or resistance temperature detector, that provides temperature measurement in a readable form through an electrical signal. A thermometer is the most basic form of a temperature meter that is used to measure the degree of hotness and coolness.

A thermocouple (T/C) is made from two dissimilar metals that generate an electrical voltage in direct proportion with the change in temperature. An RTD (Resistance Temperature Detector) is a variable resistor that changes its electrical resistance in direct proportion with the change in the temperature in a precise, repeatable, and nearly linear manner.

What do temperature sensors do?

A temperature sensor is a device that is designed to measure the degree of hotness or coolness in an object. The working of a temperature meter depends upon the voltage across the diode. The temperature change is directly proportional to the diode’s resistance. The cooler the temperature, the lesser will be the resistance, and vice-versa.

The resistance across the diode is measured and converted into readable units of temperature (Fahrenheit, Celsius, Centigrade, etc.) and, displayed in numeric form over readout units. In the geotechnical monitoring field, these temperature sensors are used to measure the internal temperature of structures like bridges, dams, buildings, power plants, etc.

 Our Tips for Extending the Life of Temperature Sensors

• 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. Make sure that the probe fits securely into the bore that it is meant to go into. Temperature sensors should not have to be forced into place. If the sensors are not easy to install then you may deform the thermocouples. 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.
• Avoid Contamination of Leads
  While temperature sensors are not as prone to contamination as our other heating products, such as 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.
• Avoid Over-Temperature
  The maximum temperature rating for the thermocouple junction is 1382°F. 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. If possible, run the thermocouple wire leads in the open air where the temperature is much lower than the process temperature.
• Selection of thermocouple type
  The first rule of thermocouple use is to choose a type that matches your operational needs. For example, low temperature, high accuracy requirements, requires the use of a type “T” thermocouple. On the other hand, with high-temperature metals processing and heat treatment, a platinum metals type “S” is more appropriate.
• Periodic checks
  This may seem an obvious point to most of you but it is important that you check the condition of your thermocouple on a regular basis. Ideally, this should be done monthly. Doing so will put you on notice for signs of excessive corrosion, oxidization, general wear and tear and physical damage. If any of these conditions are excessive, you should consider replacing the part immediately.

Considerations when Selecting a Temperature Sensor for your Application

• Temperature range
  Different temperature sensors can measure different ranges and might be more accurate over a certain range. Make sure you check the range of the temperature sensor and the expected range of your application before purchasing. The range of the temperature sensor should be available on the datasheet.
• Accuracy and stability
  Your application may require a certain degree of accuracy; thermocouples have a higher variance in long-term stability compared to thermistors and RTDs, so this is something to be aware of. The temperature sensor with the highest accuracy tends to be the glass-coated NTC thermistors.
• Size and Package
  The space available within the application will have an effect on the type of temperature sensor selected. If space is limited, then a smaller device will be required. Package style is also important as this will determine how the temperature sensor is connected into the application and how the temperature will be measured.

If you would like to find out more about thermocouples and how to maximize their life expectancy, please feel free to contact us. Our team of experts, here at Dpstar has strong knowledge and experience in this area. Not only can they advise you on the best thermocouple for your needs, but they also offer useful tips and advice on its maintenance.

Dpstar Group
No 35, Jalan OP ½, Pusat Perdagangan One Puchong,
Off Jalan Puchong, 47160 Puchong,
Selangor Darul Ehsan, Malaysia.
Tel: +603-8071 6322
Email: [email protected]