Gas Sensors Sampling. TSI Quest Quest Environmental Monitor EVM Series, EVM-7

4 Gas Sensors Sampling

Particulates and Cut-Point

Particulates and Cut-Point

In consideration of how the size of particulates affect the human body, it is important to select a particulate size cut-point. Essentially, the particle size selector on the EVM is a top-mounted rotary impactor. Based on your setting, it will filter out all particulates at or above the selected size. The instrument has four settings which include 2.5 μm, 4 μm, 10 μm, or none (100 μm). (This is explained in

more detail in Chapter 4 .)

Collecting/Sensing the Particulates

Once the impactor setting is selected, the EVM collects (or measures) real-time aerosol/dust concentration using a 90º optical light scattering photometer to determine the total mass concentration

(in units of mg / m 3 ) of particulate matter. Additionally, gravimetric sampling, a more accurate method, is also used to determine the mass of particulates.

Gravimetric Sampling

Gravimetric sampling is a type of filtering process in which the particulates are collected and filtered into the gravimetric cassette after the dust passes through the optical engine of the

EVM. A user supplied sealed gravimetric cassette can be used in place of the cassette provided by TSI. The sealed cassette can be sent to a laboratory for analysis. This testing is typically used to measure personal exposure to inhalable dust concentrations.

Pump

The pump is used in the particulate sampling process as a source of air movement so the particulates are aspirated (or suctioned out) and collected for measurement. The flow rate is 1.67 Liter per minute.

The pump is typically calibrated before each gravimetric sampling.

Gas Sensors Sampling

The EVM uses a unique smart sensor technology includes automatic sensor recognition and measures up to three gases simultaneously: a selection of optional nine toxic gases, Carbon Dioxide, combustible gases, and VOCs.

EVM Series User Manual

5 Gas Sensors Sampling

Gas Sensors and Path

Gas Sensors and Path

TSI’s unique smart sensor technology includes automatic sensor recognition, calibration levels, temperature compensation information and other valuable data that travels with the sensor from one unit to another.

The following diagram illustrates the gas sensor path for Toxic, CO

2

, and PID sensors. It also identifies the temperature sensor for additional analysis/measurements.

Air inlet cover

(1) AIR INLET COVER

The path begins with the air pulling through the air inlet cover.

(2) GAS SENSOR CHAMBERS

The air continues through the gas sensor bar passing the Toxic, PID, and

CO

2

sensor chambers.

(3) Fan

It is continuously ventilated by the fan.

( NOTE : When the pump is off, the fan can be heard near the louvers on the back cover.)

(4) Temperature sensor

Measures the ambient air temperature.

❶

❷

❹

Temperature sensor

Gas sensor(s) path

❸

Fan

Very quiet!

Figure 1-3: Gas sensor path illustration

EVM Series User Manual