Operation Manual HORIBA APDA-371
Particulate Monitor
Date:
April, 2010
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HORIBA Europe GmbH, Julius-Kronenberg-Str. 9, D-42799 Leichlingen,
: +49(0)2175-8978-0,
: +49(0)2175-8978-50
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maintains the flow within the EPA specified range of ±5% (±0.83 lpm) of the design value, and ±4% (±0.67 lpm) of
NIST traceable flow standards.
This section describes the different types of flow control and regulation schemes used in the APDA-371. The unit can
be set to any of three different flow types: Metered, Standard, or Actual (Volumetric), depending on the hardware
available and the desired reporting conditions. All APDA-371 units have a mass airflow sensor and a barometric
pressure sensor. The unit also has either a manual airflow valve on the back of the unit, or an automatic flow control
valve inside the unit. The unit is usually also equipped with an optional BX-592 or BX-596 ambient temperature sensor.
Each flow type requires a different process for auditing and calibrating the flow. To verify or set the flow type of the
APDA, go to the SETUP > CALIBRATE menu, and check the FLOW TYPE. NOTE: The concentration reporting
conditions can now be set independently of the flow type. See section 6.3.
METERED Flow Control:
Neither automatic flow control, nor flow correction for ambient conditions.
Metered flow control is used for APDA units that have a manual (hand-operated) air flow control valve on the back of
the unit. These units do not have an automatic flow controller inside, so the unit cannot automatically adjust the flow to
compensate for temperature or barometric pressure changes, or for filter loading. The unit does have a mass flow
sensor inside. The flow reading from this sensor is stored in EPA conditions, meaning that the volume of air is
calculated with the assumption that the ambient temperature is 25 degrees C, and the barometric pressure is 760mmHg
(one atmosphere), regardless of the actual temperature and pressure, even if the unit is equipped with a temperature
sensor. Due to the lack of automatic flow control, metered units must be frequently flow calibrated and audited, a
process which involves a fair amount of math and takes much longer than ACTUAL flow calibrations. Also, metered
units must have the flow rate set at a point slightly above the target rate of 16.7 LPM in order to compensate for the fact
that the flow rate will drop as the filter becomes loaded with particulate. Note: If a APDA with an automatic flow
controller is set to METERED flow control, then the flow will be controlled to EPA STD conditions.
STD (EPA Standard) Flow Control:
Automatic flow control, but usually no flow correction for ambient conditions.
STD (Standard) flow type is often selected when required by specific EPA monitoring regulations, or when no ambient
temperature sensor is available. Standard flow control may be selected on any units which have an automatic flow
controller instead of the manual valve (almost all APDA-371 units have the automatic controller anyway). The flow rate
is automatically controlled using EPA (standard) conditions, meaning that the volume of air (and thus the flow rate) is
calculated with the assumption that the ambient temperature is a standard value (default is 25 degrees C), and the
barometric pressure is 760mmHg (one atmosphere), regardless of the actual temperature and pressure.
NOTE: At low altitudes and moderate temperature, EPA Standard flow will be very close to the actual volumetric flow
rate. However, at high altitudes the difference between Standard and Actual flow will be quite significant, due to lower
barometric pressure. Carefully consider this effect when deciding on a flow type to implement.
ACTUAL (Volumetric) Flow Control:
Both automatic flow control, and flow correction for ambient conditions.
Actual (also known as volumetric) flow type is the most accurate flow control mode, and is required for all PM
2.5
monitoring. The actual flow type is also the easiest and fastest to calibrate and audit. The unit always uses actual
ambient air temperature and barometric pressure to correct the flow reading, and the flow rate is continuously and
automatically adjusted to correct for changes in ambient conditions and filter loading. The flow values will be stored and
displayed in actual volumetric conditions. To operate a APDA in actual flow mode, the unit must have a BX-596 or BX-
592 ambient temperature sensor on channel six.
5.3
Leak Check Procedure
Leak checks should be performed at least monthly and whenever the filter tape is changed. Almost all air leaks in the
APDA system occur at the nozzle where it contacts the filter tape. The APDA-371 has no way of automatically
detecting a leak at this interface, because the airflow sensor is located downstream of the filter tape. There will
normally be a very small amount of leakage at the tape, but an excessive leak lets an unknown amount of air enter the
system through the leak instead of the inlet. This will cause the total air volume calculation (and the concentration) to be
incorrect. Allowing a leak to persist may cause an unknown amount of data to be invalidated! Perform the
following steps to check for leaks:
