Teledyne 202 Manuel D’Utilisation

 

Page 16 of 24

 

 

This section contains a functional description of Hastings flow controllers.  Detailed schematics and 

parts lists can be obtained by contacting Hastings using the contact information found at the end of this 

document.  In this section and other sections throughout this manual, when a power supply is mentioned, 
it is assumed that the customer has a Hastings Power Supply.  These sections are not applicable if another 

type of power supply is used. 

The Hastings flow controller consists 

of a sensor, electronic circuitry, a shunt 

and a valve.  The sensor measures the 
flow rate from 0 to 10 sccm of the gas to 
be metered.  The shunt divides the flow 

such that the flow through the sensor is a 
precise percentage of the flow through 

the shunt.  The flow through the sensor 
and the shunt is always laminar.  The 

circuit board amplifies the sensor output 
and uses this output to control the valve 

position.  The valve is an automatic 
metering solenoid type; its height off the 

seat is controlled by the voltage in its 
coil.  All of these components working 

together result in a fast, stable flow 
controller. 

The Hastings HFM-200/HFC-202 series operates on a unique thermal electric principle whereby a 

metallic capillary tube is heated uniformly by a resistance winding attached to the midpoint of the 

capillary (see Figure 3.1).  Thermocouples TC-1 and TC-2 are welded at equal distances from the 
midpoint and develop equal outputs at zero flow.   

When flow occurs through the 

tubing, heat is transferred from 
the tube to the gas on the inlet 

side, and from the gas back to 
the tube on the outlet side 

creating an asymmetrical 
temperature distribution (see 

Figure 3.2).  The thermocouples 
sense this decrease and increase 

in the capillary tube temperature 
and produce a millivolt output 

signal proportional to that 
change.   

For a constant power input, 

the differential thermocouple 
output is a function of the mass 

flow rate and the heat capacity 
of the gas.  Since the heat 

capacity of many gases is 

Figure 3.1 

Figure 3.2