FP-25 for in-field PM air sampler calibration
Alicat’s FP-25 flow devices can be used to calibrate any low-volume particulate air sampler on your deck. The devices are NIST-traceable and designed for in-field flow calibration.
At their core, the FP-25 is a multivariate mass flow meter which simultaneously displays flow rate, pressure, and temperature. It uses uses multiple pressure sensors to capture both ambient barometric pressure and the internal pressure of the flow stream, resulting in a device which is accurate in any weather conditions.
Operating principle: How the FP-25 works
The core principle of the FP-25’s flow measurement is laminar differential pressure technology. This technology relies on knowing the viscosity of a gas in order to calculate its volumetric and mass flow rates.
However, the the actual viscosity of a gas varies with changes in temperature and relative humidity, making flow rates difficult to determine in outdoor environments with frequently changing atmospheric conditions.
To account for environmental conditions, the FP-25 uses live readings of flow stream temperature, relative humidity, and pressure to continuously update the viscosity value of the gas being measured. Using this method, the FP-25 can accurately provide flow readings at temperatures as high as as high as 60°C, in environments with up to 95% relative humidity.
Constant pressure & temperature measurements
The FP-25 contains two pressure sensors, to capture both the external barometric pressure and the internal flow stream pressure. The barometric pressure sensor, which monitors ambient atmospheric pressure, is housed in the instrument casing above the display. A sensor package, housed in the stainless steel flow body where it is in direct contact with the flow stream, monitors the internal flow stream pressure. It captures both the differential pressure between the inlet and outlet of the stream and the absolute pressure of the stream.
The FP-25 similarly uses two temperature sensors. One is mounted directly in the flow stream, while the other is at the tip of the external temperature probe.
Together, the raw data from these pressure and temperature sensors, together with a humidity sensor, calculates both actual (volumetric) and standardized (mass) flow readings each millisecond.
Calculating actual volumetric flow using the external temperature probe
FP-25 devices require a reference to a set of standard temperature and pressure conditions (STP). As a default, the FP-25 matches the standard set by the United States Environmental Protection Agency: STP conditions of 25 °C and 1 atm for standardized (mass) flow readings. However, you can request your FP-25 to ship with a different STP or change the STP conditions in-field.
The FP-25 uses the external temperature probe to reference the standardized flow readings against the ambient temperature, and the barometer to reference internal to ambient pressure. It then displays the actual volumetric flow rate, which reflects the volume of air that passes into the air sampler (at the local barometric pressure and probe temperature) per unit time.
When the FP-25 is in Standard Mode, actual volumetric flow always appears at the bottom left of the screen. Whenever the FP-25 is displaying volumetric flow referenced to the temperature reading of the external probe, the word “Probe” will flash on the right side of the display, alternating with the relative humidity value.
Technology that works for you
Alicat’s FP-25 flow device was developed by working closely with air monitor technicians across various jurisdiction. The result is a robust, durable, highly accurate, and easy-to-use air sampler calibration device. The FP-25 comes in a kit complete with all the equipment required to fully calibrate any EPA-approved air monitor.