
Technical Description | Teledyne API Ultrafine Particle Monitor - Model 651 |
Changes in optical alignment, laser power, operating temperatures, flow rates, presence of water, or optical cleanliness can all reduce pulse amplitude, therefore the pulse amplitude indicates the “health” of the WCPC. A
Flow System
Refer to Figure
The Model 651 relies on an external vacuum supply to maintain constant flows through three critical orifices. These independent flows can be verified by toggling into the different flow modes.
Orifice | Description |
0.12 L/min aerosol | Carries the aerosol to be sampled. This is not |
sample flow mode | |
3.0 L/min auxiliary | Provides a higher flow rate for use with sampling |
flow mode | systems. |
| Note: 2.4 L/min auxiliary flow is removed to |
| leave a transport flow of 0.6 L/min. |
0.6 L/min transport | Reduces particle losses. |
flow mode | Note: 0.48 L/min transport flow is removed to |
| leave a sample flow of 0.12 L/min. |
The flow rate through the sensor is always 0.12 L/min, independent of the inlet flow rate setting. Problems with the aerosol flow can be detected by monitoring the pressure drop across the nozzle and verifying that the critical orifice pressure is maintained.
Critical Flow
To achieve the 0.12 L/min sample flow through the sensor, an orifice is used (operated at the critical pressure ratio) to provide a critical flow. Critical flow is very stable and is a constant volumetric flow, ensuring accurate concentration measurements despite varied inlet pressure.
56 | 07506C DCN6727 |