Sterilization of medical equipment is one of the most important treatment 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. Although there are many methods of sterilization, one of the most widely used methods in medical service centers, hospitals, and dental clinics is hydrogen peroxide, because this method is effective, safe, and inexpensive. Let's understand two sterilization technologies using hydrogen peroxide, and how to select the correct pressure sensor suitable for sterilization equipment based on the technical parameters and operating characteristics of the sensor.
main content
One. Hydrogen peroxide sterilization process · Process pressure (vacuum pressure gauge) · Liquid level pressure in the tank (gauge pressure sensor)
two. Select the correct pressure sensor·pressure range·accuracy·long-term stability·pressure connector·electrical output·medium compatibility·overpressure·installation direction·institutional certification.
Hydrogen peroxide sterilization process
1. Vacuum pressure gauge for measuring process pressure of sterilizer
There are two different sterilization processes for sterilization using hydrogen peroxide. Each requires different measuring equipment to ensure proper operation. The first type of sterilization process is plasma sterilization using a capacitive vacuum pressure gauge to measure the process pressure during the sterilization cycle. Insert the medical equipment into the sterilizer compartment. Medical equipment includes scalpels and cardiac catheters, dental equipment (such as periodontal cleaning machines and dental extraction forceps), and other equipment with grooves and grooves in which microorganisms can grow. The cabin is then sealed and evacuated to form a vacuum. The hydrogen peroxide sterilizer in the pre-packaged box is injected into the cabin. After the sterilizer vaporizes, it interacts with the surface of the medical/dental equipment, which causes the pressure to increase; then the pressure will drop again and generate plasma. The free radicals of hydrogen peroxide interact with microorganisms and kill them. The hydrogen peroxide will then decompose, leaving only water vapor and oxygen. Medical equipment can be used or stored immediately after sterilization.
In order to ensure the effective execution of the sterilization process, a specific base pressure is required in the sterilizer compartment when the plasma is excited. To this end, a capacitive vacuum pressure gauge is installed on the sterilizer to monitor and/or control the cabin pressure and ensure that the appropriate pressure is maintained at all stages of the sterilization process. When choosing a vacuum pressure timer suitable for your application, please cooperate with a supplier that can provide a range of such products: with a full-scale pressure range from 10 to 1000 Torr, and a reading accuracy of +/-0.5% (if possible, choose +/-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 for measuring the liquid level in the tank
The second sterilization process uses vaporized hydrogen peroxide. These hydrogen peroxides are stored in the liquid tank before being converted into steam in the sterilization chamber. When in use, the liquid sterilant in the storage tank is sprayed to the system to kill the microorganisms on the equipment. This application uses a gauge pressure sensor to measure the pressure exerted by the liquid in the sterilant tank (the gauge pressure sensor itself) to indicate the level of hydrogen peroxide.
The working principle of the sterilization process: the pressure sensor is installed at the bottom of the sterilant storage tank. The weight of the sterilant will cause pressure on the sensor. The cable on the back of the sensor contains a ventilation tube, which allows the sensor to measure the pressure relative to the local atmospheric pressure (gauge pressure measurement). As the sterilant is consumed, the weight (pressure) decreases, and the output signal sent by the sensor to the redundant monitoring system also 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 that the storage tank has been drained.
Because gauge pressure sensors are referenced to atmospheric pressure, they “breathe” through the vent tube (in some cases the vent tube passes through the vent of the cable). In order to ensure normal operation and prevent liquid from entering the sensor, the ventilation pipe must be properly connected to a dry location, such as a control cabinet or junction box that is ventilated with the atmosphere. A desiccant cartridge can be installed on the connector surface of the ventilation cable for additional protection.
Choose the right pressure sensor
1. Pressure range
Before choosing a sensor, specific technical parameters and operating characteristics must be considered, one of which is the pressure range. For example, if the application requires 10 Torr, a 20 Torr sensor can achieve the best accuracy. Conversely, buying a 1000 Torr sensor will waste most of the measurement range. Do not specify an overly high sensor operating range "just for safety". The manufacturer gives safety overload limits for the sensor, and this information should be sufficient. If you specify a sensor range that is too high, the signal amplitude of the sensor will be reduced, and the zero point error will increase by a percentage with the measurement range.
Available standard ranges for vacuum pressure gauges are 10, 20, 100, 200, and 1000 Torr. Some medical applications occasionally have unique non-standard pressure range requirements, such as 147 Torr. In this case, the designer should contact the application engineering technician of the sensor supplier. Suppliers may be able to provide customized products to meet the required pressure range with higher accuracy. The same applies to system engineers and sterilization technicians who design new equipment. Supplier engineering and technical personnel can discuss upcoming projects together, provide phone support, answer questions, and be able to recommend the best sensor for the application, thereby saving a lot of time and cost.
2. Precision
When choosing a vacuum pressure gauge or gauge pressure sensor, accuracy is of course one of the most important considerations. In both cases, the higher the accuracy, the better the process control. This is particularly important in the hydrogen peroxide plasma sterilization process, in which the pressure in each stage of the sterilization process must be precisely controlled to work effectively. Confirm that the accuracy of the vacuum pressure gauge or gauge pressure sensor actually measures their error. Even more complicated is that each instrument has a different method of calculating accuracy.
Take the gauge pressure sensor as an example. They usually use the full-scale percentage error to indicate the deviation from the expected output value. for example. The full-scale output of a sensor is 10 volts. The output range of the sensor is 0 to 10 volts direct current (VDC). The accurate reading of the 10% output should be 1 volt, but due to the error, the sensor deviation value is assumed to be 1 millivolt. If the accuracy is calculated as a percentage of full scale (as the name suggests), divide the 1 millivolt error by the full scale output and then multiply by 100 to get +/-0.01% of full scale error.
On the other hand, vacuum pressure gauges usually use a percentage reading error. In the same situation as the previous example, the 1 millivolt error will be divided by 1 volt (this is the reading at this point) and then multiplied by 100, and finally the reading error of +/-0.1% will be obtained. The same 1 mv is expressed using different error calculation methods. The percentage of the reading error is 10 times the full-scale error!
For vacuum pressure gauges, seek a rated accuracy of +/-0.5% of reading. For gauge pressure sensors, seek rated accuracy of +/-0.20% full scale. Please keep in mind that these accuracies are all specified at room temperature. Therefore, if the sensor is installed in an environment that exceeds the typical room temperature range, changes in the ambient temperature will cause the sensor output to change. The temperature error published by the sensor manufacturer is a function of temperature change, so that the sterilizer technician can calculate the 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 the degree of drift of the output signal 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 within 12 months. For capacitance vacuum manometers, seek +/-0.5% full scale/year (when operating temperature is 80°C and full scale pressure range is less than 100 Torr, it is +/-1.0% full scale/year). For gauge pressure sensors, the expected stability is 0.5% full scale/year. The long-term stability and accuracy of the sealed hygienic gauge pressure sensor are guaranteed because of the use of capacitive sensing elements and signal conditioning IC integrated circuits.
All sensors will drift over time, regardless of manufacturing quality. The key question that sterilization technicians need to know is: "For my application, how high is the sensor accuracy?" A sterilization technician measuring the liquid level in the tank of the sterilizer may not be concerned about the small sensor drift over time. Especially when using redundant systems. Therefore, technicians only need to adjust the sensor every two years, not every year. On the contrary, vacuum pressure gauges that control pressure require more frequent calibration. Fortunately, drift can be adjusted in the field by adjusting the zero potentiometer or calibration, depending on the needs of the application. For gauge pressure sensors, the load on the diaphragm must be removed first. Turn the potentiometer screw on the back of the sensor to restore the setting 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 a certified calibration agency. The retest depends on the severity of the situation.
Therefore, it is strongly recommended that system engineers and sterilization technicians consider the possibility of re-verification in the overall design to ensure that the sensor can be repaired and can be removed safely and conveniently. However, resetting a vacuum pressure gauge is much more difficult. First, it must be removed from the sterilization chamber. It is then connected to a pump that can reduce the pressure below the minimum resolution of the sensor. Then manually adjust the zero potentiometer to get the desired 0 volt setting at 0 PSI pressure. In addition, if the situation is serious, it is recommended to return the vacuum pressure gauge to the manufacturer or a certified calibration agency.