The Calibrate Temperature Sensors In The Process Industry
Numerous processes have certain temperature requirements. It is critical that this temperature is achieved and maintained throughout the process. Thus, temperature sensors must be located in the processes and instrumentation.
Usually, they are embedded on valves, turbines, motors, bearings, etc. They can be a part of smart devices like flow meters, level transmitters and pressure transmitters. They can also be stand-alone devices such as thermometers, temperature indicators, recorders and controllers.
Importance of calibrating temperature devices within a facility
When you calibrate temperature devices, it ensures that the devices measure accurate temperatures at all times. This helps in making sure that the quality control of the entire process and the end product is maintained throughout. When the temperature is accurate, you can be sure that the process runs at the right temperature, ingredients are included in their correct dosages and that the end product adheres to the specifications.
In industries such as pharmaceutical, food and beverages, and nuclear sites, the importance of having the right temperature is highly crucial. You must have a dedicated calibration team or personnel who can implement robust calibration practices, and who can identify and handle process issues within the plant. Quality systems such as iso recommend periodic calibration of all temperature sensors within the facility.
Types of temperature calibrators
There are numerous ways in which you can calibrate temperature devices, however, the four primary calibration methods include:
Intrinsic standards or fixed-point cells
Intrinsic standards offer the most accurate form of temperature calibrators, such as melting point of metals such as zinc, aluminum, or indium, and the triple point of water. These methods are intrinsic and occur naturally. However, they are expensive standards and are mostly limited to calibration labs or in plants with a department specializing in high-end metrology. Additionally, multiple standards are required to cover the entire range of typical temperature calibrations.
Liquid bath calibrators
These calibrators incorporate a liquid (oil in most cases), a stirring mechanism and a heating/cooling element. Liquid baths usually have uniform specifications throughout, due to the constant stirring and the liquid being circulated through the bath. Moreover, they are ideal for calibrating odd-shaped or extremely small sensors due to the uniformity of the liquid. A few negatives of liquid bath calibrators are that they cannot be transported to different locations with ease and are stationary, they are difficult to maintain, they get quite messy, and they take longer to reach the desired temperature. The oil/liquid in the bath must be drained and refilled periodically. It is critical to dispose of the liquid carefully.
These calibrators consist of a heating ‘block’, an internal sensor, and control mechanism to reach and maintain the desired temperature range. They do incorporate a heating/cooling element, however, no liquids are used in the process. They are portable due to their structure and are less messy. One of their biggest advantages is that they reach the desired temperature much faster as compared to traditional baths but are less accurate and less stable than them. Technological developments are improving the performance of dry-blocks in terms of accuracy and stability.
Electronic calibrators have the ability to simulate the sensors under test (sut) and provide readout results on the sensor’s performance. The one drawback of electronic calibrators is that the integrity of the sensor is not tested since there is no temperature source to subject the sensor to. On a positive note, they cost a lot less than traditional liquid baths or dry-block calibrators, and are quite portable.
All temperature sensors must be calibrated periodically to ensure that the processes run smoothly, product specifications are met and that measurements are always accurate. This ensures that the quality of end product always stays high.