Each week we receive several phone calls and emails from individuals asking a variety of questions related to particle counter monitoring systems. Many people looking for particle counter monitoring systems for their cleanroom procedures seem overwhelmed by all of the variables involved in particle counting to meet ISO Cleanroom Standards. You have chosen your particle counter and now you need to determine the best monitoring system for your particular application. Hopefully the questions from our customers listed below are some of the same questions you need to have answered.
What is a Facility Monitoring System?
Facility Monitoring Systems (FMS) are used to allow all of your particle counters, manifolds, sensors, samples and other assessment equipment to communicate with each other within a central monitoring system. This process allows you to collect and analyze the particle data. This allows you to correlate the particle counts with actions like a filter failure or an open door. Facility Monitoring Systems are typically used in cleanrooms and associated areas. Although a FMS cannot be used to classify an area, they perform a monitoring function to provide evidence that an area’s environmental conditions have been maintained within the required specifications. The FDA and other regulatory agencies accept that if you’re using a Facility Monitoring System, the period of reclassification can be extended (ISO 14644-2).
How do I determine how many particle counters or monitoring locations I need?
How can I collect particles in one area and count them in another area?
How can I avoid particle dropout?
Does size matter?
What is the difference between Real Time particle monitoring and Sequential particle monitoring?
Sequential Particle Monitoring is also referred to as Pneumatically Multiplexed Particle Counting or a Manifold Monitoring System. This system involves using a single particle counter to monitor multiple points. This can be accomplished by adding a Sequential Manifold Sampler that connects the particle counter to different sampling tubes. Each individual tube is sampled in sequential order; when a tube is sampled, the manifold moves to the next tube to be sampled.
During this tube change, the particle counter stops counting particles until the change is complete, then it delays to allow any air from the prior sample to be purged. A blower continuously pulls air through all the sample tubes, avoiding any "air hammering" that may free particles in the sample tubing from the start and stop of the air flow. The frequency of each sample is determined by the number of monitoring points. In a typical application, each location is sampled for 60 seconds then purged for 10 seconds as the sampling arm moves to the next location.
What things should I consider when determining what type of monitoring system to use?
What are the advantages of Real Time particle monitoring?
What are the advantages of Sequential (Manifold) particle monitoring?
If you have additional questions about particle counter monitoring systems not covered here, please feel free to call and speak to the experts at particlecounters.org
Archive for Facility Monitoring
Monitoring for any type of contamination is essential to contamination control. Monitoring, specifically, for airborne molecular contamination (AMC) is important in industries where AMC can directly impact the product or processes. Implementing a multipoint AMC sampling system allows users to reap the benefits of online monitoring, while lowering the cost per sample point.
AMC is chemical contamination in the form of vapors or aerosols. These chemicals may be organic or inorganic in nature and can include acids, bases, polymer additives, organometallic compounds and dopants. AMC can cause many adverse effects, from corrosion on metal surfaces on the water to haze on wafers and optics to voltage shifts.
The main sources of AMC are building and cleanroom construction materials, general environment, process chemicals and operation personnel. Only continuous monitoring can ensure that facilities are performing properly and alert personnel when incidents occur. With multipoint online monitoring, incidents can be responded to almost instantly, instead of days or weeks after contamination. The most common chemicals to be monitored include ammonia, NMP, total amines, total acids and total sulfur, H2S, HF and HCL.
Implementing an online AMC monitoring system involves a number of distinct steps. These steps include determining the process to monitor, the chemicals to monitor and level at which monitoring will take place. In addition, itâ€™s necessary to identify the instrumentation that will be most appropriate for the application. When evaluating different analyzers, the following factors should be considered:
- Target chemical: Some analyzers can evaluate multiple types of chemicals, while others are restricted to one. Generally, a detection limit of 1 ppb or less requires the use of an analyzer that targets a single chemical.
- Detection limits: The detection limit of the instrument should be, at most, half of what the maximum allowable limit is for the chemical being monitored. This will provide enough headroom to ensure the analyzer is delivering accurate data.
- Dynamic range: Minimum and maximum concentration levels that the analyzer can track determine its dynamic range. Itâ€™s advisable to use an analyzer with as large a dynamic range as possible so that the actual peak of any major events can be determined.
- Response time: This is the time that it takes to adjust from one fixed concentration level to another. Normally, an analyzerâ€™s response time is listed as a percentage of the change in chemical concentration that the analyzer can display within a fixed amount of time.
- Zero and span drift: The analyzerâ€™s zero and span drift are important to understand because, ultimately, they impact how frequently the instrument will need to be calibrated. For instance, if the control limit is 1 ppb and the analyzer purchased has a zero and/or span drift of 0.1 ppb per day, then, in the worst-case scenario, the analyzer must be calibrated every 10 days.
- Potential cross interferences: Most analyzers are susceptible to cross interference from other types of chemicals. The type of cross interference is based on the analyzing technology of the instrument and what steps the sensor manufacturer has taken to minimize such occurrences.
- Calibration method: It is ideal to purchase an analyzer that is easily calibrated without supplier support. Although some analyzers feature built-in calibration standards, most require external, fixed concentration gas samples for span calibration and N2 for calibrating the zero point.
- Operation cost: Analyzers generally require some type of monthly, quarterly or annual maintenance involving calibration and parts replacement. When purchasing an analyzer, itâ€™s important to request a quote that includes the cost of regular maintenance to get an accurate idea of the total cost involved.
Successful implementation of an online AMC sampling system also involves determining the type of sampling system that will be used. The sampling system is what enables sampling from multiple locations using a single analyzer. Some important factors to consider when choosing a sampling unit include the number of locations to be sampled, the sample/purge flow, data accessibility, connectivity of the analyzer to the sampling system and connectivity to the sampling system to an external data logger or monitoring system.
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|Constant monitoring is essential for ensuring the integrity of a cleanroom environment. To determine the best system for cleanroom particle monitoring, you must understand the two kinds of continuous particle monitoring systems. These systems are real-time and sequential particle monitoring.
Real-Time Particle Monitoring
With real-time particle monitoring, a single particle counter or sensor is used at a specified location. Each event is detected and counted, and there are no gaps in the particle counting data. And particles are monitored in particles per cubic foot or per cubic meter. This system is best suited at very critical or sensitive operations, where events can occur suddenly or without warning.
There are several kinds of particle counters available. One type is a stand-alone portable particle counter that comes equipped with a display and built-in carbon vane vacuum pump. The remote counter, on the other hand, has no display and should be connected to a computer, a facility monitoring system or data acquisition system. Vacuum for sampling with the remote counters are furnished via a seperate centralized carbon vane vacumm pump that serves several, or all, particle monitor sensors.
Whether a single particle counter or sensor or several sensors are used, real-time monitoring offers a number of important benefits. For example, it provides for the continuous detection of all particle events and emergency reaction to those events. It is also ideal for crucial monitoring, as well as watching equipment for failure and preventive maintenance. Real-time particle monitoring allows for immediate:
Sequential Particle Monitoring
Sequential particle monitoring is also known as Pneumatically Multiplexed Particle Counting and, more simply, manifold particle counting. This type of monitoring involves the addition of a sequential manifold sampler that connects the particle counter to multiple sample tubes. Each tube is sampled in sequence one at a time.
During the sampling process, air is constantly being pulled through the sample tubes through a blower. When the manifold switches to the next tube being sampled, the particle counter stops counting and pauses to allow any air from the previous sample to be purged. This eliminates any â€œair hammeringâ€ that may free particles in the sample tubing due to the starting and stopping of the air flow. Particles are monitored in particles per cubic foot or per cubic meter, as they are with real-time monitoring.
The frequency of each sample is based on the number of points. Each location is generally sampled for one minute and then purged for 10 seconds, as the sampling arm moves to the next location. The ordered nature of manifold particle monitoring offers a number of advantages. For example, fewer counters can be used to cover a specific area. This, in turn, translates in decreased costs, greater sensitivity per cost and easier service. Sequential particle monitoring is excellent for trending the overall performance of a cleanroom.
Real-Time vs. Sequential
Comparing real-time and sequential particle monitoring reveals distinct differences between the two systems. Real-time monitoring allows for the detection of every single event in the cleanroomâ€”regardless of how short the duration. It continuously detects everything with no loss in the data. The system uses multiple sensors, and the sensoring points can be located anywhere, as tubing distance is not a factor.
However, more sensors require more calibration and overall service. Operation and maintenance costs are also higher with real-time monitoring because of the individual counters involved.
Sequential particle monitoring, in contrast, has a lower cost for the same coverage area. Fewer sensors are used, which means less calibration and service. However, detection can be made only to events that happen over a longer span. Short events are missed and reported only when sampled. Sequential particle monitoring can only detect trends, not single events.
Cleanroom standards require that a number of factors be kept under tight control, including airborne particles. Selecting the most appropriate monitoring system can make the process of particle monitoring much easier to manage. Continuos cleanroom particle monitoring and cleanroom automation reduces process and product defects and contributes to refining quality control.
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