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?
This can be calculated by determining the square root of the square meters of the room you’re monitoring.  An example would be a room that is 25 square meters.  Square root (25) (square meters) = 5M² or 5 monitoring points.  Always round up.

How can I collect particles in one area and count them in another area?
This can be done by using a tube or duct.  You should remember that 2 things happen when a sample medium is conducted from the sampling area to the particle counter by tubing: 1) you will experience some loss of pressure; 2) some particles will adhere to the tubing.

How can I avoid particle dropout?
The rule of thumb for this is "the shorter the sampling tube, the more accurate the reading".  Ideally, if you’re using .1 CFM, don’t allow the sampling tube to be longer than 2 feet.  With 1 CFM, you can go up to 10 feet, but it is better to keep it between 3-4 feet.

Does size matter?
Particle size, yes, depending on your particular application, particle size range may be important because they may cause specific types of damage during your process.

What is the difference between Real Time particle monitoring and Sequential particle monitoring?
Using Real Time particle monitoring involves placing a single cleanroom particle counter or particle sensor at a specific location in your cleanroom.  The sensor is committed to monitor particles only at a designated location, where every event is detected and counted.  There are no gaps in the particle counting data and particles are monitored in particles per cubic foot or per cubic meter.  The Real Time system is well suited for use at critical locations where sensitive processes can be adequately monitored.  You can use a stand alone particle counter that is a dedicated counter with a built-in vacuum pump.  Another option is a remote particle counter.  This instrument has no display; a process vacuum is provided for sampling or you can use a separate pump dedicated to particle counting.

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.

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:

• notification or alarming of yield-destroying particle levels
• feedback to staff when procedures are not being followed
• feedback after shut down/evacuation procedures to determine if the area is in specification

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 “air hammering” 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 cleanroom—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.

If you have additional questions or feedback on this topic, please click on the comments button below or call us at 1-800-531-4889