The two primary factors effecting throughput are the values used for the Load and Sample time variables. Open time can normally be set to zero and is not an issue in most applications. The required Load and Sample time are a function of sample flow rate, test fixture volume and the characteristics of the filter media in use.
Test Cycle time is the sum of the following:
- “Load” (or “Ext Load”) time
- Load time allows for stabilization of the aerosol challenging the filter under test. Ext Load only occurs after exceeding an alarm bound or performing an Light Scattering Chamber (LSC) calibration.
- “Sample” time
- “Active” sample interval where the test results are evaluated against any enabled alarm bounds. Under most circumstances “Sample Time” is set to a value of 1 with stabilization occurring during either the “Ext Load” or “Load” time intervals. A notable exception to setting the Sample time to a value of 1 is when filter loading characteristics are to be observed and/or documented throughout the filter challenge as required by NIOSH 42CFR Part 84. Typically the sample time is set to a large interval or disabled entirely for this process.
- “Open” time
- Time that the unit must remain in a non-test state before the next test cycle may be initiated. This is also the time during which an audible alarm will sound if any enabled alarm bounds are exceeded during testing.
The most effective method for determining the correct test timing requirement is to perform the following steps.
- Disable all active alarm parameters to prevent early termination of testing due to elevated test values.
- Perform the initial Calibration with the appropriate adapters in place and at the operational test sample flow.
- Using the SETUP parameters set “Load Time” to 1 second and the “Sample Time” to a value ≥ 20 seconds or Disabled.
- The “Open” time can be any value.
- Perform a test cycle on the desired type of filter media or cartridge and record the elapsed time interval necessary to reach a stable % Penetration value. This is the time interval required for the LSC to recover from an exposure to 100% aerosol.
- Using SETUP parameters set the “Ext Load” time interval noted in Step 5 minus 1.
- Perform a second test on the desired type of filter media or cartridge and again note the elapsed time interval necessary to reach a stable % Penetration value.
- Using SETUP parameters set the “Load” time interval noted in Step 7 minus 1. Then set the “Sample” time to a value of 1.
- Document the values entered for future reference and begin testing.
In most cases stabilization will occur at a cumulative test interval of ≤ 10 seconds. (Load + Sample + Open = ≤10). The required time for removal and placement of test media or cartridges would then be added to that value to determine the total test cycle time.