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TUNING THE ER1200
Span Pot Rotation Effect
Signal (mA)
Figure 5: Span Adjustment
Typically, Gain and Stability adjustments are
not needed. However, the following general
guidelines can be followed to fine tune your
system:
Rotating the gain pot clockwise increases the
system gain and decreases the system
response time. Too little gain will result in slow
response and inaccurate signal tracking. Too
much gain will result in system instability, fast
vibration, or in the feedback signal
overshooting the setpoint signal when a large
step change in setpoint is initiated.
Rotating the stability pot clockwise will
decrease the reset time and quicken the
addition of gain into the system. This can
again result in setpoint overshoot. Rotating
the pot counter-clockwise will increase the
reset time and dampen the control response
to a step change in setpoint.
The stability adjustment does not interact with
any of the other adjustments, however, if the
gain or deadband pots are turned at this point,
the zero and span will need to be readjusted
per the procedure outlined above.
Form # 1925
Rev. 4/06
TESCOM
Reaction To Step Change In Setpoint
Under Damped
Critically
Damped
Over Damped
0
Figure 6: System Response
If the system is experiencing a slow oscillation,
decrease the gain by rotating the pot counter-
clockwise until the oscillation stops. If the
oscillation is rapid, increase the reset action by
rotating the stability pot clockwise until the
oscillation stops. These settings will be the
maximum gain and minimum reset time that
can be used with the system as it is configured.
If the feedback signal severely overshoots the
setpoint signal when a change in setpoint is
made, turn the stability pot counter-clockwise
alternately with the gain pot (also counter-
clockwise), until the overshoot is eliminated.
For very precise tuning of the control, a dual
channel storage oscilloscope is recommended
so that the user can see the effect of gain and
integral adjustment on the response of the
system. One channel of the scope is used to
monitor the setpoint voltage and the other
channel to monitor the feedback voltage. The
gain and integral adjustments have the
greatest effect on the system response to a
step change in setpoint signal. The control
can be tuned in this fashion for millisecond
response to step changes in setpoint from 0 to
100%. Remember, after adjusting the gain
pot, the control will need to have its zero and
span readjusted.
7
Continued
Time
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