
81-6 Environmental
81.2.2 Measurements of Flow
81.2.2.1 Linear Resistance PTM
e
standard LRPTM contains the following elements (Figure 81.4a and b):
1. A xed resistive load
2. A dierential pressure sensor
3. Electronic instrumentation for processing and displaying the output of the pressure sensors
e relationship between ow rate and pressure dierence should be linear within the range of useful
ow rates; the maximum ow value, determined by the onset of turbulence, and the linearity range are
given by the manufacturer’s specications.
It is good practice to calibrate the PTM periodically, by connecting it in series with a bell spiromet ...