155 Appendix D
Pump/Airflow Measurements
EVM Series User Manual
Pump/Airflow Measurements
1. How is the flow rate
controlled?
There is a differential pressure sensor on the PC board that is used to
measure the pressure drop across the orifice above. The reason is to maintain
the correct pressure drop across the orifice.
2. Will the pump always
regulate?
The pump tries to maintain 1.67 L/min flow rate. When the flow rate is not
maintained, the message “Pump unable to regulate” will appear on the
screen’s display.
Solution: (1) the gravimetric cassette may need to be replaced, (2) detach any
external devices (such as a cyclone).
3. How often do we need to
calibrate the pump?
TSI recommends an annual factory calibration. If the user has an accurate flow
meter, such as a bubble-flow meter, the user may perform more periodic pump
calibrations.
4. How do we calibrate the
pump?
An accurate flow meter (such as a primary standard calibrator) and tubing is
required to perform this calibration. The primary standard calibrator tubing is
inserted in the air flow outlet (located at the back of the housing). Navigate to
the CALIBRATION\FLOW RT screen. Press the CAL quick key and then the
START quick key. Adjust the flow rate (using the up and down arrow keys) to
1.67 L/min and then confirm by pressing the SAVE quick key. It should be
noted that in order for the impactors to work properly the flow rate must be
adjusted to 1.67 L/min.
5. Can we adjust the flow
rate?
The flow rate can be adjusted (see the "How do we calibrate the pump?"
question above). It should be noted that in order for the impactors to work
properly the flow rate MUST be adjusted to 1.67 L/min.
6. How can we verify the
constant flow?
Using an accurate flow meter (or primary standard), calibrate before your
run/logging and verify after to ensure a constant flow rate. NOTE: The primary
standard calibrator tubing is inserted in the air flow outlet (located at the back
of the monitor).
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