APTech AP74B - Manual (Page 2)

Operation Manual Flow Switches
Manual 15000002 Rev 2 Page 2 of 4
adversely affect the reed switch operation.
4. Install the flow switch using the appropriate method described below.
a. For tube stub connections, weld connectors or other components to the tube stubs per
standard industry practice (reference SEMI standard F78).
b. For metal face seal connectors, assemble connections per standard practice described by
fitting supplier (typically 1/8 turn past fingertight).
5. Connect switch signal wires to appropriate controller as described below (see also section
C. Precautions and Applications).
a. Use brown and blue wires for normally closed contact installation
b. Use black and blue wires for normally open contact installation
6. After installation, verify the following to ensure correct operation.
a. Verify the AP74 is installed within 8 degrees of vertical with the inlet on the bottom
b. Verify the switch in the AP74B bypass line is installed within 8 degrees of vertical (the
AP74B mainline can optionally be horizontal or vertical)
7. After installation, perform a helium leak test of all face seal connections and welds per
standard industry practice (reference SEMI standard F1).
8. After installation, perform a nitrogen gas flow test to verify that the switch trips sending a
signal to the controller and resets when flow is shut off.
C. Precautions and Applications for Wiring Reed Switch
When a reed switch is to be connected to an inductive load or a load where surge current or a
rush current flows, the following contact protection circuits are required.
1. Inductive loads – when an electromagnetic relay, electromagnetic solenoid, or
electromagnetic counter, which has inductance, is installed as a load in a circuit, the
energy stored in the device will cause an inverse voltage when the reed contacts open.
The voltage sometimes reaches as high as several hundred volts and becomes a major
factor to deteriorate contacts. Many types of protection circuits can prevent this, typical
examples are shown in the figures below.
Contact protection by capacitor
and resistor (connection at the
load terminal is allowed).
Contact protection by varistor.
When the contact is open for a
long time, the varistor should be
connected at the load terminal .
Contact protection by diode.
Breakdown voltage of diode
should be larger than E volt.
Forward current of diode should
be almost equal to 5 E divided
by the coil resistance.