Teledyne MODEL T703 ユーザーズマニュアル

stays at least 2:1 the gas flow rate is unaffected by any fluctuations, surges, or changes in downstream pressure 
because such variations only travel at the speed of sound themselves and are therefore cancelled out by the 
sonic shockwave at the downstream exit of the critical flow orifice.   

The actual flow rate of gas through the orifice (volume of gas per unit of time), depends on the size and shape of 
the aperture in the orifice.  The larger the hole, the more gas molecules, moving at the speed of sound, pass 
through the orifice.   

 

 

There are two pressure sensors in the T703.  See Figure 3-5 for the location of the Pressure/Flow PCA. 

A 100 psig pressure sensor on this PCA is used to monitor the downstream regulator pressure.  This value is 
displayed on the front panel as a test measurement called REG PRESSURE. 

A second pressure located on the rear PCA measures the pressure of gas in the photometer’s absorption tube.  
This sensor is a 0-15 psia (absolute pressure) range sensor.  This data is used by the CPU when calculating the 
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 concentration inside the absorption tube.  This value is displayed on the front panel as a test measurement 

called PHOTO SPRESS.  Note that this value is converted to units of Inches of Mercury (IN-HG-A) when 
displayed on the front panel. 

 

 

07223B DCN6378