Calibrating temperature measuring devices and instruments is essential in various applications, including:
- Industrial processing
- Scientific research
- Manufacturing
- Environmental monitoring
What is a Temperature Calibrator?
The primary purpose of a temperature calibrator is to ensure that temperature measurement devices provide reliable and accurate readings. Over time, temperature instruments may drift or experience deviations from their original calibration, leading to incorrect temperature measurements. Calibrating these devices with a temperature calibrator helps maintain their accuracy and traceability to recognized standards.
Temperature calibrators come in a wide range of forms and designs, including portable handheld devices and benchtop units. They provide a controlled temperature source and may incorporate additional features, such as signal generation, data logging capabilities, and display options.
Types of Temperature Sensors
Five types of devices commonly found in manufacturing are:
- Bimetal or spring-type thermometers. Widely used despite their slow response and lack of accuracy as they are inexpensive and easily adjusted.
- Thermocouples. The most widely used industrial sensor, consisting of two dissimilar metal wires joined at one end, these produce a voltage proportional to temperature.
- Resistance-temperature detectors (RTD’s). Typically wound from platinum wire, these are expensive but give rapid response and good measurement accuracy.
- Thermistors. These semiconductor-based devices measure temperature over a limited range and are often used in medical applications.
- Infrared (IR) radiation detectors. These non-contact sensors measure surface temperature and fall into one of two types: IR pyrometers and thermal imaging cameras. Use of both is growing rapidly as many more products come on to the market.
Temperature Calibrator Types
Temperature calibrators can be broadly categorized into two types: those that offer simulation and those that produce a physical heat.Simulation Calibrators
Function Simulation calibrators emulate temperature values electronically without physically generating heat - meaning there is no actual heat source. They generate a signal that mimics the output of a temperature sensor at various temperature points.Operation
Simulation calibrators are typically programmable and allow users to set desired temperature values. They use built-in algorithms to generate accurate signals corresponding to those temperatures.
Use
Simulation calibrators are commonly used to calibrate temperature measurement devices, such as thermocouples, RTDs (Resistance Temperature Detectors), and temperature transmitters. They simulate the temperature range and response characteristics of these devices for calibration purposes.
Advantages
Simulation calibrators offer precise and repeatable temperature simulations. They are versatile, allowing calibration across a wide temperature range. They are also non-contact, eliminating the need for physical contact with the device being calibrated.
Limitations
Simulation calibrators cannot access the thermal response and accuracy of the device under calibration in real-world conditions. They do not account for environmental factors that may affect temperature readings.
Heat-Producing Calibrators
Function Heat-producing calibrators generate physical heat as a heat source to establish specific temperature values. They typically use heating elements, such as resistive coils, to produce heat.Operation
These calibrators can heat up to desired temperature points and maintain them within a specific range. They rely on direct thermal transfer to the device being calibrated.
Use
Heat-producing calibrators are commonly employed to calibrate temperature sensors, thermometers, and other temperature measurement devices that require physical exposure to heat.
Advantages
Heat-producing calibrators enable the assessment of the device’s thermal response and accuracy under real heat conditions. They provide a more comprehensive calibration experience, considering both environmental and thermal factors.
Limitations
Heat-producing calibrators may have limitations in terms of temperature range, heating speed, and stability. They require direct contact, which may introduce measurement errors due to thermal gradients or thermal mass effects.
The choice between simulation calibrators and heat-producing calibrators depends on a wide range of factors, including the specific temperature calibration requirements, the type of temperature device being calibrated, and the desired level of accuracy and realism needed. Simulation calibrators are useful when electrical signal simulation is sufficient, while heat-producing calibrators are preferred for calibrations that require direct thermal exposure and assessment.
Calibrating Temperature Measurement Devices
- The temperature at which ice melts
- The boiling point of water
Dry block temperature calibrators overcome this problem and provide a quick and accurate means of calibrating thermistor, thermocouple, and RTD probes. A calibrator like Omega’s Hot Point® Dry Block Probe Calibrator is used to heat a thermocouple to a chosen temperature and the reading on the indicator compared with that on the calibrator. Next, an Ice Point® Reference Cell such as the OMEGA TRCIII is used to provide the 0 oC comparison temperature. Again, the indicated reading is compared with that on the calibrator. Corrections can be determined form these two measurements.
Infrared Blackbody Calibrators are used for calibrating non-contact temperature measurement equipment – such as infrared thermometers, thermal cameras, and pyrometers. These use a surface of “perfect” emissivity (between 0.95 and 0.98) that is heated to a known temperature and compared with the reading from the device.
(Note, that while accuracy depends on the quality of the temperature measurement within the Blackbody Calibrator, and may only be with 1%, repeatability should be very high).
Product Quality and Documentation
In many industries, simply controlling temperature is insufficient – documentation is essential. Having documentation, such as a calibration certificate, is important for several reasons:Traceability and Compliance
A calibration certificate provides traceability – establishing a documented chain of measurement from the device being calibrated to a recognized standard. It ensures compliance with quality standards, regulations, and a wide range of industry-specific requirements.
Quality Assurance
Calibration certificates serve as evidence that the temperature measurement device has undergone a reliable and documented calibration process. They support quality assurance efforts in that they assure the user that the device’s accuracy has been verified and adjusted, ensuring it reliability in providing accurate temperature measurements.
Calibration History and Trend Analysis
Maintaining calibration certificates allows for the creation of a historical record of the device’s calibration results over time. This record helps identify trends, patterns, and potential issues with the device’s performance. By comparing current and previous calibration data, one can assess the device’s stability, identify any deviations or drift, and make informed decisions about maintenance, repair, or replacement.
Audits and Inspections
In regulated industries or environments with quality management systems, audits and inspections may be conducted by regulatory bodies or external auditors. Calibration certificates serve as crucial documentation during such audits, demonstrating compliance, adherence to standards, and the proper maintenance of calibration records. The availability of calibration certificates helps facilitate smooth audits and ensures regulatory compliance.
Confidence in Data and Decision-Making
Accurate temperature measurements are vital for critical processes, product quality, safety, and decision-making. Calibration certificates provide assurance that the temperature measurement device is reliable and accurate. This documentation enhances confidence in the measured data, enabling informed decision-making based on trustworthy temperature readings.
Calibrate In-House or Use a Calibration Lab?
For most organizations the determining factors on whether to calibrate in-house or to use a calibration lab are the volume of calibration work to be performed and the availability of in-house resources. If gauge calibration is already performed, adding temperature sensors to the list of equipment requires only investment in a dry block probe or blackbody calibrator. However, some external calibration is always needed to ensure NIST traceability.The Importance of Using an AS17025 Accredited Lab
Just as ISO9000 provides a Quality Management framework for manufacturing companies, AS17025 (the US interpretation of ISO 17025) does the same for calibration laboratories. Defined procedures document the methods used for the calibration work undertaken, ensuring methods are robust and provide an appropriate level of NIST traceability and that they meet national standards. Significant emphasis is placed on communicating results to customers, and this includes information on measurement uncertainty. A lab not meeting the requirements of ISO 17025 may perform satisfactory calibration work with appropriate levels of traceability. However, formal accreditation means a customer can be confident that appropriate procedures will be followed and so is spared the expense of verifying this for themselves.
Product Info
What is a Calibrator and why is it an important device? Introduction to Instrument Calibration
Technical Learning
