VICI Selectors (multiposition) Standard electric - Manual (Page 5)


Controlling the Actuator with a Computer
The first step in interfacing the Valco multiposition electric actuator to a
computer or data system is to consult the user’s manual of the control
device to determine what kind of outputs are available, and how many
there are. There may be relays, open collector transistors, logic level
signal outputs, or an RS-232 connector. (These are not cleanly delineated
categories; for instance, BCD logic will involve one of the others.)
The second step is to determine how the valve is to be moved. The
simplest implementation is for the control device to duplicate the STEP
and HOME commands of the manual controller. The other option is to
access the positions randomly via BCD-encoded logic level signals. In
this mode, the actuator passes through each intermediate position, stopping
when it reaches the encoded position. In either case, as the valve sequences
through each position it is possible that sample may flow briefly as each
position is made.
STEP and HOME Commands
Look at Drawing 21464, page 18, to determine the functions of the different
wires in the interface cable. All of the inputs are held at five volts, called a
“logic high”. When they contact ground, the voltage drop signals the logic
circuits in the actuator to direct the motor to the appropriate point.
Locate the violet wire for HOME, the grey wire for STEP, and the white wire
for GROUND. After stripping a small amount of insulation from each of the
wires, touch the grey wire to the white wire and observe that the actuator
advances one position. Touching the violet wire to the white wire causes
the actuator to rotate all the way around to Position 1, or HOME. (If the
actuator is already in Position 1, nothing happens.) The contact must be
maintained for at least 0.2 seconds to be recognized as valid.
These steps demonstrate the goal; that is, getting the control device to
emulate the action of touching the two wires together. Nothing else, such
as applying a voltage to one of the wires, is involved. For relays or open
collector transistors, which are essentially switches, connect the three wires
to the proper terminals as indicated by the manual for the control device.
(
Figures 2 and 3)
NOTE: A poor quality relay may cause the unit to step multiple times, due
to the relay’s excessive contact bounce. If contact bounce lasts longer than
50 ms, the actuator will see this as repeated STEP commands.
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