Bimba PCS - Manual (Page 6)

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SPAN (Full Scale Position)
When the PFC rod is fully extended or the PTF shaft is rotated fully clockwise
(CW), it will reach a mechanical stop, due to either a mechanical limit in the
application or the actuator’s end of stroke or rotation. The PCS’ Span adjustment
allows you to adjust the position of the cylinder at 10 VDC control voltage input.
Adjustment range is from the fully extended mechanical limit to approximately
50% of the full actuator stroke or rotation. Refer to the installation section for a
description of the adjustment procedure.
The Zero and Span adjustments can be combined for a total adjustment
window of only 50% of total actuator travel, i.e., if the Zero Adjustment is
adjusted out to 50% of actuator travel, then the Span Adjustment cannot
be adjusted lower than 100%. The effective travel of the actuator in this
case would be between 50 and 100%.
Special Note for PTF’s with less than 180 degrees of Travel
:
Due to the 50% window limitation, the minimum effective electrical
rotation for PTF’s is 180 degrees of rotation. This is explained further in
the PTF application example on Page 21.
MAIN CONTROL (Command or Input Signal)
The Main Control command signal is a variable analog signal, either 0-10 VDC or
4-20 mA depending on the position of jumper JO2 (see the illustration on page 11
for instructions on setting jumpers). The command signal, proportional to the
displacement of the actuator, can be supplied by a PLC analog output card or any
other low noise signal source. The low end of the range affects the zero position
of the actuator and the high end of the range affects the full scale position of the
actuator.
The command signal can be translated into actuator displacement with the
following formula:
CS = (d * R / t ) + Z
where:
CS
= the command signal required to achieve a desired position
d = the displacement the desired position is from the zero position
R = the full range of the command signal
t = full scale travel of the actuator (Note: for PTF rotary actuators
with total rotation less than 180º, always make t = 180)
Z = the command signal for the zero position
Example
1: A system uses a 0-10 volt command signal, “R” is 10 and “z” is 0. If
a position of 2 inches is desired from a 7 inch stroke cylinder, the required
Command signal (CS) is ( 2 * 10 / 7 ) + 0 or 2.857 volts.
Example
2: A system uses a 4-20 mA command signal, “R” is 16 and “z” is 4. If
a 30º position is desired from a 90º rotary actuator, the required Command signal
(CS) is (30 * 16 / 180) + 4 or 6.67 mA.