18
User Manual
Model PCS
Pneumatic Motion Control System
14. PRELIMINARY “SPAN” ADJUSTMENT
PFC cylinders and PTF rotary actuators greater than 180 degrees of rotation
(See below for PTF’s less than 180 degrees)
Use the Span adjustment to set the intended fully extended position to be the same as the full scale (maximum)
analog command input signal. Using the Main Control (or equivalent), command the actuator to go to the analog
command input signal full scale position. (Set the analog command input signal to 10 volts, or 20 mA depending
on the PCS Model.) Look at the LEDs and make the adjustments described in one of the appropriate following
paragraphs.
If the Green LED
is on or continuously flickering - (Span is currently set beyond the extended hard stop.)
Slowly adjust the Span potentiometer CW, until the green LED goes off. (If the Span potentiometer was adjusted
too far and the actuator moved, adjust the Span potentiometer CCW just enough to move the actuator back to
the full scale position. If adjusted too far, the Green LED will come back on). Both LEDs should be off when set
correctly. This ends the preliminary Span adjustment.
If neither LED
is on - (Span is currently set somewhere in mid-stroke.) Slowly adjust the Span potentiometer
CCW to move the actuator rod or shaft toward the full scale position. When the actuator hits the full scale
position, the green LED will continue to flicker even when the adjustment is no longer being turned. Now adjust
the Span CW just enough to turn off the green LED. Both LEDs should be off when set correctly. This ends the
Preliminary Span adjustment.
PTF rotary actuators less than 180 degrees of rotation
Using the command signal (CS) formula defined in the Main Control section of the Glossary, calculate the full
scale analog command signal setting the d parameter = full rotation of your actuator, and setting the
t
parameter
= 180 degrees.
For Example:
The calculation for a 45 degree PTF with Voltage input would be:
CS = 45 x (10/180) + 0 = 2.50 VDC Full Scale Analog Command Input Signal
And the calculation for a 45 degree PTF with a 4-20mA input would be:
CS = 45 x (16/180) + 4 = 8 mA Full Scale Analog Command Input Signal
Now set the analog command input signal to the calculated full scale command signal for your PTF rotation
(i.e., 2.50 volts for a 45 degree unit with voltage command input signal) and perform one of the following
adjustments:
If the Green LED
is on or continuously flickering - (Span is currently set beyond the extended hard stop.)
Slowly adjust the Span potentiometer CW, until the green LED goes off. (If the Span potentiometer was adjusted
too far and the actuator moved, adjust the Span potentiometer CCW just enough to move the actuator back to
the full scale position. If adjusted too far, the Green LED will come back on). Both LEDs should be off when set
correctly. This ends the preliminary Span adjustment.
