“Sterilization of medical equipment is one of the most important processes in medical treatment. It can kill all living microorganisms on medical and dental equipment, including bacteria, spores, viruses and fungi, so as to ensure the safety and repeated use of these equipment. While there are several methods of sterilization, one of the most widely used in health care centers, hospitals, and dental offices is hydrogen peroxide because it is effective, safe, and inexpensive. Let us learn about two sterilization techniques using hydrogen peroxide and how to choose the right pressure sensor for sterilization equipment based on the sensor’s technical parameters and operating characteristics.
Sterilization of medical equipment is one of the most important processes in medical treatment. It can kill all living microorganisms on medical and dental equipment, including bacteria, spores, viruses and fungi, so as to ensure the safety and repeated use of these equipment. While there are several methods of sterilization, one of the most widely used in health care centers, hospitals, and dental offices is hydrogen peroxide because it is effective, safe, and inexpensive. Let us learn about two sterilization techniques using hydrogen peroxide and how to choose the right pressure sensor for sterilization equipment based on the sensor’s technical parameters and operating characteristics.
one. Hydrogen peroxide sterilization process: process pressure (vacuum pressure gauge), liquid level pressure in the tank (gauge pressure sensor);
two. Choose the right pressure sensor: pressure range, accuracy, long-term stability, pressure fittings, electrical output, media compatibility, overpressure, mounting orientation, agency approvals.
Hydrogen Peroxide Sterilization Process
1.Vacuum Manometer for Measuring Sterilizer Process Pressure
There are two different sterilization processes for sterilization using hydrogen peroxide. Each requires different measurement equipment to ensure proper operation. The first type of sterilization process is plasma sterilization using a capacitive vacuum manometer to measure the process pressure during the sterilization cycle. Insert the medical device into the sterilizer chamber. Medical equipment includes scalpels and cardiac catheters, dental equipment such as periodontal cleaners and extraction forceps, and other equipment with grooves and grooves in which microorganisms can grow. The chamber is then sealed and evacuated to create a vacuum. The hydrogen peroxide sterilant in the pre-packaged box is injected into the chamber, the sterilant vaporizes and interacts with the surface of the medical/dental device, which causes the pressure to rise; the pressure then drops again and a plasma is generated. The free radicals of hydrogen peroxide interact with microorganisms and kill them. The hydrogen peroxide then decomposes, leaving only water vapor and oxygen. Medical equipment can be used or stored immediately after sterilization.
To ensure an efficient sterilization process, a certain base pressure is required in the sterilizer chamber when energizing the plasma. To this end, capacitive vacuum pressure gauges are installed on the sterilizer to monitor and/or control the chamber pressure and ensure that the proper pressure is maintained during all stages of the sterilization process. When choosing a vacuum manometer for your application, work with a supplier who offers a range of these: with different full scale pressure ranges from 10 to 1000 Torr, +/- 0.5% of reading accuracy (if possible, Then select +/- 0.25% of reading accuracy option), and the temperature coefficient can be ignored in the temperature compensation range of 0 ℃ to 50 ℃.
2.Gauge pressure sensor to measure the liquid level in the tank
The second type of sterilization process uses vaporized hydrogen peroxide, which is stored in a liquid state in a storage tank before being turned into steam in the sterilization chamber. When in use, the liquid sterilant in the tank is sprayed into the system to kill microorganisms on the equipment. This application uses a gauge pressure sensor that measures the pressure exerted on it (the gauge pressure sensor itself) by the liquid in the sterilant tank to indicate the level of hydrogen peroxide.
How this sterilization process works: The pressure sensor is installed at the bottom of the sterilant tank. The weight of the sterilant causes pressure on the sensor. The cable on the back of the sensor contains a vent tube that enables the sensor to measure pressure relative to the local atmospheric pressure (gauge measurement). As the sterilant is consumed, the weight (pressure) decreases and the output signal sent by the sensor to the redundant monitoring system decreases accordingly. The sensor can then warn the sterilization technician that the tank level is too low. When the sensor register value is 0PSIG, it means the tank has been drained.
Since gauge pressure sensors are referenced to atmospheric pressure, they “breathe” through a vent tube (in some cases the vent tube goes through the cable’s vent). To ensure proper operation and prevent liquid from entering the sensor, the ventilation duct must be properly routed to a dry location such as a control cabinet or junction box vented to the atmosphere. A desiccant cartridge can be installed on the connector surface of the ventilation cable for additional protection.
Select the appropriate pressure sensor
Certain technical parameters and operating characteristics must be considered before selecting a sensor, one of which is the pressure range. For example, if the application requires 10 Torr, a 20 Torr sensor will achieve the best accuracy. Conversely, buying a 1000 Torr sensor would waste most of the measurement range. Do not specify too high a sensor operating range “just for safety”. The manufacturer gives the sensor safe overload limit, this information should be sufficient. Specifying a sensor range that is too high reduces the signal amplitude of the sensor and the zero error increases as a percentage of the measurement range.
Available standard ranges for vacuum manometers are 10, 20, 100, 200 and 1000 Torr. Some medical applications occasionally require unique non-standard pressure ranges such as 147 Torr. In this case, the designer should contact the sensor supplier’s application engineering technician. Suppliers may be able to provide custom products to meet the required pressure range with greater accuracy. The same applies to system engineers and sterilization technicians designing new equipment. The supplier’s engineering staff can discuss upcoming projects together, provide phone support, answer questions, and be able to recommend the best sensor for the application, saving significant time and money.
Accuracy is of course one of the most important considerations when choosing a vacuum pressure gauge or gauge pressure sensor. In both cases, the higher the accuracy, the better the process control. This is especially important in the hydrogen peroxide plasma sterilization process, where pressure at all stages of the sterilization process must be precisely controlled to work effectively. Confirming the accuracy of a vacuum pressure gauge or gauge pressure sensor is actually a measure of their error. To complicate matters further, each instrument calculates accuracy differently.
Take a gauge pressure sensor as an example. They are usually expressed as a percentage of full scale error from the expected output value. for example. The full-scale output of a sensor is 10 volts. The sensor’s output range is 0 to 10 volts direct current (VDC). An accurate reading of 10% of the output should be 1 volt, but due to error, the sensor bias is assumed to be 1 millivolt. If you calculate the accuracy as a percentage of full scale (as the name suggests), divide the 1 millivolt error by the full scale output and multiply by 100, and you end up with a full scale error of +/- 0.01%.
Vacuum manometers, on the other hand, typically use a percent reading error. In the same case as the previous example, the 1 millivolt error is divided by 1 volt (which is the reading at that point) and multiplied by 100, resulting in a +/- 0.1% reading error. The same 1 mv, expressed using a different error calculation method, the percentage value of the reading error is 10 times the full-scale error!
For vacuum manometers, seek a rated accuracy of +/- 0.5% of reading. For gauge pressure sensors, seek a rated accuracy of +/- 0.20% of full scale. Keep in mind that these accuracies are specified at room temperature. So if the sensor is installed in an environment outside the typical room temperature range, the change in ambient temperature will cause the output of the sensor to change. The temperature error published by the sensor manufacturer is a function of temperature, so the sterilizer technician can calculate this error and determine the true accuracy of the pressure reading.
3.long term stability
Long-term stability is another very important consideration. Long-term stability is a measure of how much the output signal drifts over time under stable operating conditions. Drift is caused by pressure cycling, extreme temperatures, environmental changes, vibration, shock and aging. Long-term stability is usually expressed as a percentage of full scale over 12 months. For capacitance vacuum manometers, seek +/- 0.5% full scale/year (+/- 1.0% full scale/year when operating temperature is 80°C and full scale pressure range is less than 100 Torr). For gauge pressure sensors, the expected stability is 0.5% of full scale/year. The long-term stability and accuracy of the hermetically sealed hygienic gauge pressure sensor is guaranteed due to the use of a capacitive sensing element, as well as a signal conditioning IC integrated circuit.
All sensors drift over time, regardless of build quality. The key question that a sterilization technician needs to know is: “How accurate does the sensor need to be for my application?” A sterilization technician measuring the tank level of a sterilizer may not be concerned with tiny sensor drift over time, Especially when using redundant systems. As a result, technicians only need to adjust the sensor every two years instead of every year. Conversely, vacuum gauges that control pressure require more frequent calibration. Fortunately, drift can be adjusted in the field by adjusting the zero potentiometer or by calibration, depending on the needs of the application. For gauge pressure sensors, the load on the diaphragm must first be removed. The potentiometer screw on the back of the sensor can be turned to return the setpoint at 0 PSI to 0 volts. To set the measurement range based on full scale, it is recommended to return the sensor to the original factory or send it to an accredited calibration facility. Retesting depends on the severity of the situation.
Therefore, it is strongly recommended that system engineers and sterilization technicians consider the possibility of requalification in the overall design to ensure that the sensor can be serviced and can be removed safely and easily. However, resetting a vacuum gauge is much more difficult. First, it must be removed from the sterilization chamber. It is then connected to a pump capable of reducing the pressure below the minimum resolution of the sensor. Then manually adjust the zero potentiometer to obtain the desired 0 volt setting at 0 PSI pressure. Additionally, in severe cases, it is recommended that the vacuum gauge be returned to the manufacturer or an accredited calibration facility.