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HFM-E-200/HFC-E-202
Page 13 of 30
3.4. Shunt:
Measurement of flow rates higher than the 10 sccm full scale is achieved by dividing the flow with a
fixed ratio shunting arrangement, as is illustrated in Figure 3.3. This is accomplished by placing the
measuring capillary tube parallel with one or more dimensionally similar channels, called a laminar flow
element (LFE). Therefore, the sensor only needs to heat the gas passing through the capillary tube
resulting in low power requirements, while retaining all the mass measuring characteristics.
The HFM-E-200/HFC-E-202 series has many different shunts. The low range shunt consists of tubes
inserted into a cylindrical base. This shunt is adjustable for ranges from 0-10 sccm to 0-180 sccm (see
Figure 3.4). The medium range shunts consists of a piece of stainless steel foil welded to a solid steel
center core. The high range shunts consists of a corrugated stainless steel ribbon wound into a coil and
fused.
Figure 3.2
Figure 3.4
Figure 3.3
Figure 3.5