How Data Logging is Used in Sterilization Applications

Introduction

A data logger is a leading-edge data acquisition device that automatically monitors and records environmental parameters. Data loggers use a microprocessor, an internal memory for data storage, and an internal or external sensor to assemble data. They monitor temperature, humidity, carbon dioxide, pH, pressure, voltage, current, and many other conditions, thus making them useful for many applications. They are an ideal way to capture data without human intervention continuously.

Data loggers have multiple applications spanning the industry spectrum, including agriculture, chemicals, civil engineering, food, medicine, mining, solar energy, and more.  They appear frequently in the medical sector in laboratories and healthcare, sterilization processes and environmental controls; in vaccines, organ and medical equipment transportation; and for medical storage in freezer and culture rooms. Data loggers are required for a variety of reasons in the medical sector, frequently to ensure compliance with industry-specific regulations and quality and environmental control procedures. In this Tech Spotlight, we will discuss the utilization of data loggers for sterilization applications, along with characteristics of data loggers for steam sterilization systems, designs, and mention a few examples of how a data logger validates a deliberated process.

Medical Application Overview: Autoclaves and Sterilization

The process of sterilization eliminates, removes, kills, or deactivates all forms of life, in particular, microorganisms. Medical devices in proximity to sterile body tissues or fluids are considered critical items. These items must be sterile during use, as any microbial contamination may lead to disease transmission. Such devices include surgical instruments, biopsy forceps, and implanted medical devices. Medical devices are sterilized in several ways, including the use of moist heat (steam), dry heat, radiation, high pressure, vaporized hydrogen peroxide, and other sterilization techniques.

Steam sterilization, among all sterilization procedures, is the most prescribed due to its reliability. A steam sterilizer is popularly known as an "autoclave" and is typically used in healthcare or industrial applications. An autoclave is a steel vessel (Figure 1) that uses pressurized steam to kill harmful microorganisms on items placed inside a pressure vessel. The objects are heated to an appropriate sterilization temperature for a designated time. The moisture in the steam efficiently transfers heat to the items to destroy the bacterial spores' protein structure.

Figure 1. Block Diagram of Autoclave Sterilization System

Four factors are critical to ensure a successful autoclave-enabled steam sterilization: time, temperature, pressure, and steam quality. Commonly recommended temperatures for steam sterilization are 250° F (121° C) or 270°F (132°C). Exposure periods for steam sterilization vary with size, shape, weight, density, and material composition of the device being sterilized, among other factors. Sterilization autoclaves find widespread use in microbiology, medicine, podiatry, body piercing, veterinary medicine, funerary practice, dentistry, and prosthetic fabrication.

Data Logging in Sterilization Applications

We will now discuss the significance of data loggers in sterilization applications and why they are crucial for medical instruments.

Data loggers have a significant role in monitoring autoclave validation and the sterilization process. Validation involves regular measurement and monitor of temperature and pressure within the autoclave chamber, to ensure that sterilization transpires as designed. Irregular validation of sterilization cycles risks sterilization failure, invalidation of scientific results, and even lawsuits if pathogens infect patients. The electronic data logger shields the device from such fiascos as it is active, accurate, and reliable compared to periodic manual readings.

A data logger is placed within the autoclave chamber and then subjected to a sterilization cycle. It simultaneously monitors temperature, pressure, and time. There is also the possibility of connection to a computer and transference of data via the interface. The sterilization process, based on measurements received with the help of a data logger, is either approved to be valid or otherwise.  If you operate a small tabletop style autoclave, you may need just one or two data loggers to verify that the chamber of your autoclave attains sufficient sterilization temperatures. For freestanding autoclaves, especially large ones, a set of six or more data loggers should be used to map the autoclave chamber confines.

Data loggers are occasionally used during a regular check of autoclaves.  This action guarantees security and safety, improves quality, and ensures adherence to regulations and requirements. Advanced data loggers for autoclaves can be configured to check against a set tolerance of temperature and pressure, to determine if an alarm state exists.

High Pressure and Temperature Data Loggers

Autoclave validation is done using temperature and pressure data loggers. These data loggers are robust and solid devices made of stainless steel, as they function under extreme conditions, i.e., high temperatures and pressures. Most data logging devices are compact, battery-powered, and effortlessly portable. Keep these factors in mind when you pick a data logger for sterilization applications:

• Temperature range: The range on the logger must be 140°C minimum and must withstand that temperature for more extended periods.
• Pressure range: Since autoclave sterilization cycles may reach 15psi above atmospheric pressure, a minimum 35psi is recommended. Submersible data loggers can accurately measure pressure.
• Size: A small size is recommended to leave more room in the autoclave.
• External probe: Data logger models include those with internal sensors and those with an external probes, such as a thermocouple or RTD input. The external probe allows the recorder to remain in one environment while the sensor is placed somewhere different, thus enhancing accuracy.
• Number of Inputs: Data Loggers are available in both single and multi-channel designs. Single, dual, and 32 channel data loggers are popular designs.
• Speed/Memory: The recording duration depends on the data logger's memory capacity and the desired sample rate. Data logging systems are available with sampling rates as high as 200 kHz; conversely, some can be set to sample once in 24 hours.

Data loggers accumulate data independently of a computer. There are several methods to retrieve measurement results from a data logging system. For a simple USB data logger, you pick it from the instrument and plug it into a PC. Data logging software comes with the data logger to streamline the download process and assist with formatting for Excel Charts or other packages. Some loggers can be used on an Ethernet network to send data back to a central PC, while others use wireless communication to send measurements. These approaches eliminate the need to take out the logger to recover the data. A few data loggers provide an option for real-time screen display.

Omega's High Temperature and Pressure Data Loggers

Omega Engineering offers a range of temperature and humidity loggers for sterilization applications. The following listed are examples of popular temperature and humidity data loggers:

High-Temperature Data Logger

The OM-CP-HITEMP140-FR from Omega Engineering is a rugged, high precision, high-temperature data logger with an ultra-fast response time to record temperature during rapidly changing thermal processes. This high-temperature data logger features a 50 L x 1.59 mm diameter probe and can record up to 4 Hz, which is 4x faster than other data loggers in this class. The device can be placed in environments up to 140°C (284°F), and the probe can measure from -200 to 260°C (-328 to 500°F). It is also available with an optional thermal shield enclosure to extend the operating range of the data logger to -200 to 250°C (-328 to 482°F).

This data logger can store up to 32,700 dates and time-stamped readings and features a non-volatile solid-state memory that retains data even if the battery becomes discharged. You can use the OM-CP-HITEMP140 software to produce graphical, tabular, and summary data for analysis with automatic export of the result.                                        

Figure 2. OM-CP-HITEMP140-FR high-temperature data logger

High-Pressure Data Logger

The OM-CP-PR140 is a pressure data logger designed for use in autoclave validation and mapping. This rugged device can withstand temperatures up to 140°C (284°F) and is completely submersible. The OM-CP-PR140 is built with a precision stainless steel pressure gauge. The device has an accuracy of ±0.03 Bar (±0.435 psi), which can be achieved over a wide temperature range, from 20 to 140°C (68 to 284°F). The OM-CP-PR140 can be programmed to take readings as often as once per second (1 Hz) and has non-volatile memory that can store up to 32,700 measurements. The device has O-rings to ensure a tight seal and prevent liquid from entering the inside of the device. Simply place the OM-CP-PR140 in the docking station, connect to an available USB port on your computer, and the device can be started, stopped, or downloaded applying our user-friendly software.

High Temperature and Pressure Data Logger

Omega's OM-CP-PRTEMP140 is a high temperature and pressure data logger all in one, created specifically for use in autoclave validation, mapping studies, and pressurized processes. Made of rugged stainless steel, this dual-purpose device is less than 64 mm (2.5") in length, allowing it to fit discretely inside small spaces. The OM-CP-PRTEMP140 data logger downloads temperature and pressure data simultaneously and displays the combined results in a single graph, simplifying data collection and analysis and eliminating unnecessary steps for the user. Unlike devices using a submersible thermocouple, this data logger incorporates an RTD spanning a range from -20 to 140°C (-4 to 284°F), and pressure from 0 bar to 5 bar. The memory capacity on the OM-CP-PRTEMP140 stores up to 32,700 times and date stamped readings and will retain data even if the battery becomes discharged.

Figure 3. OM-CP-PRTEMP140 high-temperature data logger

Other Examples of Data Loggers