System 350 A350P Electronic Proportional Plus Integral Temperature Control Product/Technical Bulletin
3
Minimum Output Adjustment
The minimum output adjustment sets the minimum
voltage or milliampere output provided by the A350P
control. It can be adjusted from 0 to 60% (0 to 6 VDC
or 0 to 12 mA) of the output range.
Example:
A controlled device responding to a 4-20 mA output
would require the minimum output to be adjusted to
20% or 4 mA. (See Figure 3.) The minimum output
adjustment may also be used to set valves or dampers
to minimum positions.
Deviation Above Setpoint (F°)
Output
(mA)
0
2 4 6 8 10 12 14 16 18 20
0
4
10
20
50%
20%
0%
Throttling Range
Figure 3: Output vs. Deviation from
Setpoint for: Minimum Output = 0, 20, and
50%, Throttling Range = 20°F (DA)
Make the adjustment at the minimum output
potentiometer marked as MIN OUTPUT.
(See Figure 2.) For each 10% increase in output, the
next
bar on the LED indicator will light (only one bar is
lit at any time).
Note:
Before setting the minimum output
potentiometer, verify that the control reads
zero output (that is, no LEDs are lit).
Throttling Range (Proportional Band)
The throttling range is the range over which a control
is active. Throttling range for the A350P control can be
adjusted from 2 to 30F° (1 to 17C°). Make the
adjustment at the throttling range potentiometer
marked THROT RANGE (see Figure 2).
Integration Function
Proportional-only controls cannot hold a process at the
exact setpoint. A proportional offset is always present
because the control output is 0% at setpoint. Any load
on the system will cause the control point to be offset
from the setpoint. The greater the load on the system,
the further the control point will be offset from the
setpoint. (This is commonly referred to as proportional
offset, and under maximum load this error will
approach the throttling range.)
Some proportional-only controls are designed with
their setpoint located midway through the proportional
band to help compensate for this offset. This results in
a plus/minus error from the setpoint rather than a
single-ended error. Refer to Figure 4.
