Temperature Measurement


Primary concerns for measuring temperature with thermocouples

February 2025 Temperature Measurement

Temperature values are one of the most common elements measured in any data acquisition system. Temperature measurements are often required in production test systems, energy management systems, environmental monitoring, aviation systems and more. These temperature values are measured with sensors such as resistance temperature detectors (RTDs), thermistors or thermocouples.

Each of these temperature sensors includes unique measurement characteristics that must be considered when selecting sensors for a data acquisition system. Characteristics such as measurement range, accuracy and the electronic circuitry required to measure are all important considerations. The physical packaging style of the sensor may also be a consideration. For example, will a thermocouple with twisted wires be acceptable, or does the application require a screw-in metal probe? These characteristics all need to be considered.

When specifying temperature sensors for any system, the first consideration is the temperature measurement range. Each of these sensors contains different measurement ranges. Thermistors offer a small measurement range, typically from sub-zero to a few hundred degrees Celsius. Thermocouples offer a much wider measurement range from sub-zero to over 2000 degrees Celsius.

Sensor accuracy is another important consideration when specifying sensors for a data acquisition system. Each of these sensors offers different accuracy specifications from tenths of one degree up to multiple degrees. Thermistors have the best overall accuracy specifications, close to one tenth of one degree Celsius. RTD accuracy specifications are slightly higher than thermistors at a few tenths of one degree Celsius. Thermocouple accuracy on the other hand is generally within a couple of degrees Celsius.

Sensor accuracy can be impacted by electrical noise. Electrical noise can be generated from sources around and along the sensor, such as pumps switching on and off or generators running. While thermocouple measurements are not affected by the length of their wires, they are susceptible to picking up electrical noise. RTD sensors are less immune to electrical noise, but are susceptible along the length of their wires, commonly referred to as lead resistance. Thermistors with a negative temperature coefficient have a high sensor resistance and are often immune to both electrical noise and lead resistance.

The electronic circuitry used to measure each of these sensors has different requirements. Each data acquisition hardware manufacturer designs its own unique circuits and implements them within its products. Typically, each circuit will contain circuitry to measure millivolt DC signals from the sensor. Thermocouples output a very small millivolt DC signal. Additionally, the thermocouple measurement circuitry will include an electronic cold-junction-compensation reference, as found within all DGH thermocouple measurement products.

Thermistors and RTD’s are resistive devices and do not output millivolt signals. The circuitry required to measure these sensors must include a small electronic current source. The current source signal is passed through the resistive sensor to develop a millivolt signal. That signal is then measured and converted to a temperature value.

The amount of current passing through the sensor can be an important consideration. Some current source values can be as high as one milliamp. This current value should be designed and specified to be as low as possible to prevent internal self-heating of the temperature sensor, as self-heating can lead to accuracy errors within the system. DGH, RTD and thermistor products use a much lower current value to prevent sensor overheating.

Finally, the cost of temperature sensors can be a budget concern. Sensor accuracy requirements will usually lead to increased sensor costs. RTD sensors tend to carry a higher pricetag , while thermocouples and thermistors less costly. Sensor packaging styles can also impact the sensor pricing.

While there may be concern for additional sensor parameters in each application, this article attempts to address the primary concerns for measuring temperature with thermocouples, RTDs and thermistors. Additional information about each temperature sensor, its intended applications and DGH measurement solutions is available upon request from Vepac Electronics.


Credit(s)



Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

New HMI panel PC series
Vepac Electronics SCADA/HMI
Industrial computing giant, AAEON has released its OMNI-ADN series, a four-model collection of modular HMI panel PCs, with display sizes ranging from 26 to 55 cm.

Read more...
Power over Ethernet (PoE) injector for seamless deployment
Vepac Electronics Fieldbus & Industrial Networking
The Edimax GP-203IT from Vepac Electronics is a Power over Ethernet injector that not only delivers a cost-effective solution for power distribution, but also enables seamless deployment on the existing LAN infrastructure.

Read more...
Portable appliance tester
Vepac Electronics Electrical Power & Protection
The new appliance tester from Vepac is the ideal tool for testing the safety of electrical appliances in accordance with DGUV regulation 3 and BetrSichV. It enables the precise measurement of protective conductor or touch current using the equivalent leakage current method.

Read more...
Cost-effective industrial PoE injector
Vepac Electronics Fieldbus & Industrial Networking
The Edimax IGP-203IT from Vepac Electronics is an industrial PoE injector that not only delivers a cost-effective solution for power distribution, but also allows seamless deployment on an existing LAN infrastructure.

Read more...
Non-contact infrared thermometer
Temperature Measurement
AMETEK LAND has developed a new non-contact infrared thermometer for precise measurement and control during deposition processes in optical fibre manufacturing.

Read more...
Power over Ethernet splitter without electric cabling
Vepac Electronics Fieldbus & Industrial Networking
The GP-101ST Gigabit PoE (Power over Ethernet) Splitter from Vepac Electronics delivers both data and electrical power to non-PoE Fast Ethernet or Gigabit Ethernet-enabled products such as network cameras and wireless access points, using an Ethernet cable, without the need for power outlets and electrical cabling.

Read more...
High-precision fill quantity control in food supplement production
Temperature Measurement
Vital Products was looking for a precise and efficient solution to check the weight and ensure the completeness of its products. Minebea Intec, a specialist in industrial weighing and inspection technologies, was able to provide a solution.

Read more...
DIN rail UPS series: DC reliability and availability in the smallest of spaces
Vepac Electronics Electrical Power & Protection
The power supplies with UPS function in the DCH series from Vepac Electronics are among the most compact of their kind and impress with their outstanding overload ability.

Read more...
The critical role of temperature measurement in flame hardening
Instrotech Temperature Measurement
Flame hardening is a heat treatment process widely used on parts made from mild steels, alloy steels, medium carbon steels and cast iron. Accurate temperature measurement is not just important, but critical for the success of flame hardening.

Read more...
Noncontact infrared temperature control in aluminium rolling process
Instrotech Temperature Measurement
The aluminium rolling process is critical to the aluminium manufacturing industry, where precise temperature measurement is essential for ensuring high-quality product output and protecting equipment. The Optris long-wavelength camera can accurately measure strip temperatures in cold rolling and coiling applications.

Read more...









While every effort has been made to ensure the accuracy of the information contained herein, the publisher and its agents cannot be held responsible for any errors contained, or any loss incurred as a result. Articles published do not necessarily reflect the views of the publishers. The editor reserves the right to alter or cut copy. Articles submitted are deemed to have been cleared for publication. Advertisements and company contact details are published as provided by the advertiser. Technews Publishing (Pty) Ltd cannot be held responsible for the accuracy or veracity of supplied material.




© Technews Publishing (Pty) Ltd | All Rights Reserved