DESCRIPTION AND OPERATION
HSS MODULE CIRCUITRY
2 - 10
I-E96-322A
®
Digital I/O
If the HSS module loses communication with the MFP module,
the manual control circuitry enables the operator to manually
change actuator position. The HSS module provides two
24 VDC isolated digital inputs as raise/lower commands from
a manual station (pushbuttons, contacts, etc.). These inputs
connect to the microprocessor. The microprocessor increments
or decrements a position demand to the servo valve when the
operator activates the contacts. Figure
shows a schematic
of a typical isolated digital input circuit.
Trip bias is the third digital input. The trip bias input signal is
sent to the position error circuit (see Figure
). Activating the
trip bias input drives the actuator to the zero percent position
(fully closed) for shutdown. Hard manual is an isolated output
that provides a connection for an external indicator (LED) or
alarm. The indicator notifies the operator that the module is in
the hard manual mode.
Figure 2-5. Typical Digital Input Circuit
TP25410A
+
HSS DIGITAL INPUT
0.1 µF
2.2 K
PUSHBUTTON
OR
CONTACTS
3 AMP
+24 VDC
SYSTEM POWERED
24 VDC FROM
TERMINATION UNIT
2.2 K
Ω
Ω
-