Traceable Thermometers and Hygrometers – Things You Must Know

Accuracy and reliability are paramount when it comes to temperature and humidity measurements. This is especially true for laboratories, warehouses, food processing and storage, and healthcare industries, where slight deviation from the standard can have severe consequences. Today, there are different devices to measure temperature and humidity levels in industrial processes, wherein thermometers and hygrometers are widely used. These instruments through accurate values help maintain optimal conditions, quality, efficiency, and safety standards in sensitive environments. The National Institute of Standards and Technology (NIST), a non-regulatory agency of the United States Department of Commerce provides traceable standards for these meters, which is also known as NIST traceability. Would you like to know more about thermometers and hygrometers in terms of their working, uses, and more? If yes, read this post till the end.

Thermometers and Hygrometers – Definition, Benefits, and Working Explained

This section explains the fundamental aspects of these thermometers. So, let’s take a look at it.

Traceable Thermometers: Traceable thermometers are authenticated to NIST standards and serve as a reference point for other thermometers to establish traceability. These thermometers are designed to measure the temperature of a given environment object, air, or a surface. These meters offer many benefits, making them indispensable devices in various fields. For instance, in homes and medical facilities, thermometers provide accurate temperature measurements for health monitoring, helping detect conditions like fever and hypothermia. However, industrial thermometers are designed differently, and used for temperature measurements in various industrial settings to ensure safe operation of machinery and equipment, and prevent overheating and potential damage. Thermometers operate based on the predictable and measurable change in the physical properties in response to temperature variations. Most thermometers operate by exploiting the thermal expansion property. This means substances expand when heated and contract when cooled. For instance, in mercury-in-glass thermometers, mercury expands with the temperature rise and moves along a calibrated scale to indicate the temperature. Digital thermometers use sensors such as thermistors, which change their electrical resistance with temperature changes, while infrared thermometers detect the infrared radiation emitted by objects, which correlates with their temperature, allowing for non-contact temperature measurement.
Traceable Hygrometers: These instruments have the certificate of traceability from NIST and measure the humidity or the amount of moisture in the air. They play a crucial role in maintaining optimal indoor humidity, which reduces respiratory issues and allergies and prevents mold growth in homes and buildings. Hygrometers also maintain specific humidity levels for processes in pharmaceuticals, food production, and electronics manufacturing, ensuring quality and safety. The working principle of hygrometers involves detecting changes in moisture levels through various methods. Mechanical hygrometers use materials like synthetic fibers that expand and contract with humidity changes, while electronic hygrometers utilize sensors, such as capacitive or resistive elements, to convert humidity-induced changes in electrical properties into digital readings.

Types of Thermometers and Hygrometers

Thermometers and hygrometers are categorized into different types, providing different methods for measuring accurate temperature and humidity levels. Here are a few common types.

Thermometers

Liquid-in-glass Thermometers: They use mercury or alcohol in a glass tube to measure temperature. Mercury thermometers are more accurate and designed for higher temperature ranges, while alcohol thermometers are safer, used for lower temperatures, and are less toxic.
Thermocouples: They consist of two different metal wires joined at one end. The temperature levels are measured by producing a voltage proportional to the temperature difference between the joined end and the other ends of the wires. This makes them suitable for a wide range of temperatures.
Resistance Temperature Detectors (RTDs): RTDs measure temperature by correlating the resistance of a metal, typically platinum, with temperature. They are known for their high accuracy, stability, and repeatability over a broad temperature range.

Hygrometers

Capacitance-based Hygrometers: These hygrometers can measure humidity levels by detecting changes in the capacitance of a sensor. The sensor contains a hygroscopic dielectric material between two plates. Thus, as humidity changes, the material absorbs or releases moisture, altering the capacitance.
Psychrometers: They use two thermometers to measure humidity, one with a wet bulb and one with a dry bulb. The difference in temperature between the wet and dry bulbs allows the calculation of the relative humidity based on the rate of evaporation from the wet bulb.
Impedance-based Hygrometers: These devices measure humidity by detecting changes in the electrical impedance of a hygroscopic material. As the material absorbs or releases moisture, its impedance changes, which is then used to determine the humidity level.

How to Select Thermometers and Hygrometers?

Selecting NIST-certified traceable thermometers and hygrometers is crucial for ensuring accurate and reliable measurements. Here's a detailed explanation of the key pointers to consider while making a decision.

Measurement Range: Determining the specific temperature and humidity range relevant to your application environment is important. Choose either of these that covers your expected minimum and maximum temperature and humidity levels. Most thermometers can span from 50°C to +150°C, but specialized thermometers can measure temperatures well below or above this range. Hygrometers typically measure relative humidity (RH) from 0% to 100%, but the accuracy and reliability can vary across the range.
Required Accuracy: The accuracy level for thermometers and hygrometers varies depending on the application requirement. For food storage, pharmaceutical, or other applications, look for thermometers with accuracy within ±0.5°C at least. For less critical applications, an accuracy of ±1°C to ±2°C might be sufficient. For environments, such as museums, archives, or industrial processes, select hygrometers with an accuracy of ±2% RH, while for general monitoring purposes, a hygrometer with an accuracy of ±3% to ±5% RH may be acceptable.
Data Logging Capabilities: This is another important differentiating aspect for thermometers and hygrometers. Devices with data logging capabilities can record temperature and humidity readings over time. Depending on the logging frequency, select the devices that can store massive data. The sampling rate, or how frequently the device records data, is another crucial factor.
Interface Option: In addition to the above pointers, choosing the right interface is significant. The method of accessing logged data through interfaces, such as USBs and wireless or cloud-based platforms, influences data retrieval and integration with other systems. While choosing the right interface, consider the data management systems and environment in which the device will operate.

Maintaining Traceability of Thermometers and Hygrometers

Maintaining the traceability of these meters helps ensure the reliability and accuracy of measurement across industries. Here are some essential practices for maintaining traceability:

Performing periodic calibration as per the manufacturer’s recommendations and industry standards is essential to uphold traceability. This involves comparing an instrument's measurements with standard values to detect and correct any deviations. This ensures the instrument consistently produces accurate results, which is vital for quality control, safety, and regulatory compliance.
Implement calibration services from leading providers accredited by recognized bodies, including the International Organization for Standardization (ISO) or the National Institute of Standards and Technology (NIST). This ensures that the calibration process meets high-quality standards.
Record all calibration activities, including certificates of calibration. These records are required for audits and quality assurance.
Store thermometers and hygrometers in clean, dry, and controlled environments to prevent damage and degradation. Avoid exposing them to extreme temperatures, humidity, or mechanical shocks.
Conduct periodic checks between scheduled calibrations to verify the accuracy of thermometers and hygrometers. Also, the environmental conditions where these meters are used should be monitored.
It's not just about the instruments; immediate corrective actions and staff education on the importance of calibration and traceability are equally vital. This collective effort ensures the reliability and accuracy of measurements, contributing to quality control and regulatory compliance.

Ready to ensure the traceability of your thermometers and hygrometers? Consider consulting a reliable industry player like Triplett. With several years of market presence and a wide range of traceable instruments, they can help you maintain the reliability and accuracy of your measurements. Contact their team of experts today to learn more about their traceable thermometers and hygrometers.